The 12V DC Series

Part 2 - The Alternator Bible

By Bill "BillaVista" AnsellPhotography: Bill Ansell

Copyright 2011 - Bill Ansell(click any pic to enlarge)

INTRODUCTION

To many of us, the alternator is something of a mysterious device thatresides under the hood somewhere and makes electricity by means ofsome voodoo. And when it dies, we take it back as a core, and get anew one.

The thing is, the alternator is really the heart of the vehicle's electricalsystem and so knowing a bit more about it and how it works, whetheror not you ever plan to rebuild one, will really improve yourunderstanding of the vehicle's entire electrical system - and your abilityto design, build, upgrade and maintain it.

The other reason it's good to know a bit about alternators is becausethroughout the life of a vehicle, we tend to add more and moreelectrical accessories - lights, stereos, radios, compressors, winches,etc. As we do, we increase the demand on the vehicle's electricalsystem and particularly the alternator. Upgraded alternators withhigher output are often needed; and knowing a bit about how theywork will help us in making educated decisions when shopping for areplacement or upgraded alternator.

*Note: This article assumes that the reader has read and understood "The 12V DC Series Part 1 - 12V DC Basics".In this article, unless specified otherwise, all discussion of electrical current flow is done in "conventionalnotation."

Table of Contents

Operation

Basic Description

Laws of Electromagnetism

Simple Explanation

Technical Explanation

Alternator Warning Lamp

A Look Inside

Common GM Delco-Remy Alternators

Wiring

1 wire, 2 wire, 3 wire, 4

Voltage Sensing

Self-exciting (one-wire) Alternators

Non-self-exciting (multi-wire) Alternators

SI-series / 2 Terminal

CS-series / 4 Terminal

Performance

Failure Modes / Troubleshooting

Operation

The next time some long-haired, sandle-wearing, tree-hugging, peace-loving, soap-dodging, Prius driver looks over at yourtruck with it's massive array of off-road lights, pumping stereo, and 15,000 lb winch and gives you that supercilious, holier-than-thou sneer that they seem to be so expert at (it must be explained in the Prius owner's manual / book of hypocrisy) -feel free to explain to them that your rig is entirely solar powered.

I recommend using small words and speaking slowly as if conversing with a small and rather dim-witted child.

But you will be telling them the truth. You see, the fact is, EVERYTHING on this earth is solar powered. ALL our energyhas always come, and will always come, from the sun. Everything we power ultimately derives its energy from the sun -even your Big Block. You see, many millions of years ago the sun's rays shone down on the earth - making plants grow.Animals (dinosaurs) ate those plants. The plants and animals died, fell down, and over a long, long time got squished intooil. A few million years later some guy from Texas drills into the ground, extracts the oil, refines it into gasoline and you putthe gasoline in your truck and it goes Vroom Vroom. Presto! - solar powered Big Block!

All kidding aside, there is an important concept here in this entirely true, if somewhat fanciful, description of energy. And ofcourse, that concept is our old friend the law of the conservation of energy: "Energy can neither be created nor destroyed,merely converted from one form to another."

How does this relate to alternator tech? Simple - the alternator is the last conversion device in a long line that convert solarenergy into the electrical energy that powers your lights, radio, winch, etc. Solar energy becomes chemical energy storedin gasoline as described above. The vehicle's engine converts the gasoline's chemical energy into mechanical energy (theenergy of moving things). The alternator, driven by the engine via a belt, turns this mechanical energy into electrical energyto charge your battery, power your lights, etc.

Let's look at exactly how it does that.

Basic Description

An alternator is an electromechanical device that converts mechanical energy to AC (alternating current) electrical energy,converts the AC to DC by rectifying it, regulates the DC voltage output to 12 Volts, and supplies this 12V DC power tocharge the vehicle's battery and power the electrical components.

An engine-driven belt spins a magnet (called the rotor) inside a coil of wires (called the stator) which, by the laws ofelectromagnetism, induces an AC electrical current in the wires. The AC current is then rectified (turned into DC current)by a series of "electrical one-way valves" called diodes, and is output as DC current to the vehicle's electrical system.

OK, that was quite a mouthful. Let's break it down step by step.

The Laws of Electromagnetism

I don't want to teach a physics class here - not least because I'm wholly unqualified to do so - but a very basicunderstanding of two fundamental laws of electromagnetism will vastly ease our understanding of how an alternator works.The two complimentary laws are:

1. An electric current in a wire creates a magnetic field around the wire. The direction (orientation) of the magnetic fieldis dependant on the direction of the current through the wire.

2. An electric current is induced in a loop of wire when the wire is moved towards or away from a magnetic field, or amagnet is moved towards or away from the wire. The direction of the current in the wire is dependant on the directionof the movement.

Electrical current

We should have a good understanding of what an electrical current is from "The 12V DC Series Part 1 - 12V DC Basics".

Magnets & Magnetic Fields

Strictly speaking, a magnet is any material or object thatproduces a magnetic field. A magnetic field is an invisible forcethat can act on (attract or repel) other magnetic objects.

Magnets have "poles" - a north pole and a south pole.

By convention, we say that the magnetic field lines leave theNorth pole of a magnet and enter the South pole of a magnet.

At right is an illustration of a simple bar magnet, like the type weplayed with as kids. As per convention, the magnetic field, orlines of magnetic force, are illustrated as originating from theNorth (red) pole, and terminating at the South (green) pole.

Types of Magnets.

There are three basic types of magnets - permanent, air-core, and electromagnet.

Permanent Magnets

A permanent magnet gets its magnetism because of the materialfrom which it is made. Principally, magnetic materials are those inwhich the electrons mostly spin in the same direction. We needn'tget into any more detail than that. Magnetic materials includeiron, nickel, & cobalt, as well as less common elements such asneodymium (Nd) and samarium (Sm).

(You may have read spec sheets or advertisements for stereospeakers featuring "neodymium magnets.")

Pictured at left is a simple bar magnet made of iron.

Interestingly, if you take a bar magnet and break it into twopieces, each piece will again have a North pole and a Southpole.

Permanent magnets never lose their magnetism - hence the name. You may have seen spec sheets or advertisements forelectric motors, particularly in winches, that feature "permanent magnets".

Air Core Magnet

OK, this is where it starts to get more interesting (and relevant!).

It turns out, that if we wrap a piece of wire into a coil shape and pass an electrical current through it, it produces amagnetic field, just as if it were a bar magnet. Precisely why it should do this is WAY beyond the scope of this article (andmy ability to explain) so I shall ask you to simply believe it is true. Of course, you could always try it and prove it toyourself! Anyway, such a device is called an "air core" magnet because the "core" between the coils of wire is, well, air!Physicists are a clever lot, but not always terribly creative with their naming of things - which is probably a good thing!

This picture illustrates an air core magnet on the left and a barmagnet on the right.

The similarities in the magnetic fields are apparent.

Electromagnets

The trouble with air core magnets is that the magnetic field produced is very weak, and therefore not of much practical use.

In contrast, and electromagnet can be capable of generating extremely strong magnetic fields.

An electromagnet, also called an "iron core" magnet, is similar toan air core magnet, except that instead of there being a core ofair between the coils of wire, there is a core of magnetic materialsuch as iron (again, hence the descriptive but uninspired name:"iron core magnet"!).

The iron core of an electromagnet can produce magnetic fieldsmany hundred times stronger than an air core magnet.

An advantage of electromagnets is that, because they depend onthe flow of electrical current through the coil of wire (sometimescalled the "windings"), they can be turned on and off.

These properties of strength of magnetic field generated and theability to be turned on or off make the electromagnet a hugelypractical tool, as illustrated here.

Your Own Electromagnet

Many of us will have created our own electromagnet at one timeor another in a simple science experiment like the one pictured atleft.

The switch can be as simple as holding the wire onto one of thebattery terminals or not.

You can make your own and experiment by using it to pick upother small magnetic objects like paper clips or small nails.

NOTE: You must use a small resistor (as pictured), or someother resistance like a lightbulb, in the circuit, otherwise you willcreate a short circuit.

But what has all this to do with alternator tech?

Remember we said alternators work on the principles of electromagnetism?

Well, we have just discussed in some detail (and maybe even proven, if we did the experiment) the first of these, namely:

An electric current in a wire creates a circular magnetic field around the wire.

Now, the second law, which is the "converse" or "opposite" law to this one, states that:

An electric current is induced in a loop of wire when the wire is moved towards or away from a magnetic field,or a magnet is moved towards or away from the wire.

is precisely the principle by which an alternator works. In essence, if we could take our simple nail-and-wire electromagnetpictured above, replace the battery with a light bulb, and spin the nail inside the wire coil, we could generate an electriccurrent to light the light bulb.

That's essentially what an alternator does in the most basic sense.

Basic Alternator Operation - Simple Explanation

Let's take a look at how, using an exploded diagram of an alternator.

The vehicle engine's crankshaft drives a belt that in turn drives a pulley on the alternator (1). The alternator pulley (1) isfixed to the shaft of the alternator rotor (2).

The rotor (2) consists of a coil of wire (the rotor windings) wrapped around an iron core. When DC electrical current issupplied through the slip rings (3) to the rotor windings (4) a magnetic field around the rotor core is produced - the rotorbecomes an electromagnet. This DC current that turns the rotor into an electromagnet is called the "field current" supply -because it causes the generation of the magnetic field. We'll come back to how this field current controls alternator outputshortly.

Surrounding the rotor is the stator (5). The stator consists of a set of three wire coils, called the stator windings. The statoris fixed to the alternator case, and does not turn. As the names indicate - the rotor rotates while the stator is stationary.

As the rotor turns within the stator, the magnetic field of the rotor sweeps through the stator windings, producing anelectrical current in the windings. This current produced is 3-phase AC. It is AC because of the rotation of the rotor'smagnetic field through the windings - current is produced in one direction as the North pole sweeps through the winding,and in the other direction as the South pole does. The current produced is 3-phase because of the three windings (onephase produced in each winding).

This 3-phase AC power must be converted or "rectified" into single phase DC voltage to be useful. This occurs in therectifier (6). The rectifier consists of six diodes, one pair of diodes for each winding. One diode from each pair is for thenegative half of the AC cycle, and the other for the positive half of the AC cycle. Diodes have the property of allowingcurrent to flow in only one direction, while blocking current flow in the other direction. In simple terms, the diode pairs blockor "chop off" the negative halves of the AC cycles produced in the windings. As a result of this diode rectification, theoutput of the alternator is 12V DC, supplied to the output stud (7).

Meanwhile, the diode trio (8) takes alternator output and provides it to the voltage regulator (9). The voltage regulatorcompares this output with reference voltage, and based on the results supplies varied amounts of field current through the

brushes (10) and slip rings (3) to the rotor windings (4).

The more field current that is supplied to the rotor windings, the stronger the magnetic field produced. The stronger themagnetic field, the more voltage produced in the stator windings. This voltage is then sampled by the voltage regulator,and if it is up to spec, field current is maintained. If the output voltage rises too high, the voltage regulator cuts back thefield current, bringing output back into line.

In this manner, the system is a closed feedback loop that self-regulates. In practice, as engine / alternator rpm drop,alternator voltage output drops which the regulator senses and as a result increases the field current to the rotor whichbrings the output voltage back up at this lower rpm. It works in reverse as well - higher rpm means greater voltage output.If it gets too high the regulator senses it and cuts back the field voltage, bringing the output back down.

Now, if you have been following carefully, you may be left with just one question - where does the field current come fromwhen the alternator is not yet running at speed (as in when the vehicle is first started)? Before the alternator is up to speedand generating sufficient output to be "self sustaining", the field voltage is supplied by the battery via the alternator warninglamp. This initial supplying of field current to get the alternator working is known as "exciting" the alternator. We'll go intothe details of the alternator warning light and different methods of excitation a little later.

So that's the simple explanation of how an alternator works. In summary:

Field current is supplied by the battery initially (and later by the alternator output itself) through the brushes and slipring to the rotor windings, making the rotor an electromagnet.The rotor rotates in the stator, inducing AC current in the stator windings.The AC current is rectified by the rectifier to DC and provided to the output stud for use.The voltage regulator compares alternator output to reference level and adjusts the field current up or down to bringthe alternator output into spec.

Alternator Operation - Technical Explanation

For those that are interested in a little more technical explanation of what is going on in an alternator, let's go over it againbut this time with a little more technical detail.

NOTE: This section is optional - if you're not into tech details (Camo!) - feel free to skip down to the next yellowheading - namely "Alternator Warning Lamp".

Let's add some more detail to the material previously covered, on a component by component basis.

ROTOR

The rotor receives regulated voltage through a pair of brushesthat bear on slip rings, and this causes it to produce a magneticfield.

The rotor consists of a coil of wire (the rotor winding) wrappedaround an iron core and enclosed in two multi-claw pole pieces.You can clearly see the "claws" in the picture at left.

DC electrical current is supplied through a pair of brushes thatbear on slip rings. The slip rings are connected to the rotorwindings and thus a magnetic field around the rotor core isproduced - the rotor becomes an electromagnet.

The "claws" are actually specially shaped poles that create multiple magnetic poles from a single rotor. The rotor picturedabove has six alternating pairs of poles folded back from either end. With a single revolution of the rotor, the statorwindings are hit with six magnetic fields, each magnetic field having, of course, a north and a south pole just as allmagnets do.

This rotor has 8 pairs of "claws" or magnetic poles.

STATOR

The stator has three sets of windings, each of which produce ACcurrent when the rotor's magnetic field sweeps through them.

In this picture you can clearly see the terminals at the ends ofeach of the three windings.

This is known as three-phase winding.

As the rotor turns within the stator, the magnetic fields of the rotor sweep through the stator windings, producing anelectrical current in the windings. This current produced is an AC current because of the rotation of the rotor's magneticfield through the windings. Let's look at why this is so by first examining what happens in just one of the windings, beforewe consider all three together. Also note, for simplicity sake the rest of this section considers only a single magnetic field,but note that most alternator rotors actually have multiple (often 6 or 8) magnetic fields.

As the north pole of the magnetic field approaches one of the stator windings, there is little electro-magnetic couplingtaking place, and a weak current is produced, As the rotation continues, the magnetic field moves to the center of thewinding, where maximum coupling takes place, and the induced current is at its greatest. As the rotation continues to thepoint that the magnetic field is leaving that stator winding, the induced current is again small. By this time, the south pole ofthe rotor magnetic field is approaching that winding, producing a weak current in the opposite direction, and so on.

The result of this rotating magnetic field in a single winding is an alternating current (AC) that varies in voltage with therotational position (the degree of rotation) of the rotor as it spins inside the winding. The current produced alternates backand forth between +12V and -12V as the North and South poles of the magnetic field induce current first in one direction inthe winding, and then in the other direction.

If we were to make a graph and plot the AC voltage for a single winding against the rotation of the rotor in degrees, itwould look like this:

Now, we are only interested in a small part of this output - the +12V part. So, if we filter out the rest (this is the job of therectifier which we shall examine shortly), we end up with useful output that looks like the portion above the red dashed linein this pic:

As can be seen, using a single winding like this would be very inefficient. There are long periods of time in the rotation ofthe rotor where the magnetic field is not producing any output that is useful to us.

This is where the 3-phase winding comes in.

If we were to use not one, but three separate windings, and offset them all equally we triple our useful output per rotorrevolution. This is precisely how an alternator is constructed.

The three stator windings are physically spaced inside the alternator 120 degrees apart, producing three separate sets, or"phases," of output voltages. The output of each winding thus occurs 120 degrees offset from the others in terms of therotation of the rotor. If we were to plot a graph of this AC voltage for all three windings (A, B, and C) against the rotation ofthe rotor in degrees, it would look like this:

Now, using 3-phase winding, the alternator is putting out three separate voltages, one per winding - labelled A, B, and C inthe above diagram. In other words, we get triple the output for each revolution of the rotor.

One practical result of this design is that the alternator can generate useful levels of current and voltage even when therotor is spinning relatively slowly (as in idle RPM).

Incidentally - an electric motor is sort of like an alternator, but opposite. Instead of something spinning mechanically tocreate electricity, electricity is supplied to make something spin (the motor output shaft). Ever wonder what the deal is withbig electrical tools like industrial lathes - why they are all "3-phase" electrical power? The reason is the same as for thealternator, but in reverse. Running a tool's motor on 3-phase power means the output gets 3 "pushes" per revolutioninstead of just one. More efficient, more power. That's why the big industrial tools run on 3-phase power. It's a bit liketurning a merry-go-round in a kids' playground. Single phase power would be like one person turning it - giving it one pushper rotation. 3-phase power would be like 3 people spaced evenly apart (at 120° intervals) each giving it a push everyrotation. But I digress. Back to the alternator...

RECTIFIER

So, at this point the three separate stationary windings of thealternator are producing three-phase alternating current.

But we need single phase DC, so the alternator must convert the3-phase AC to DC.

To do this the alternator uses a rectifier (also known as a " full-wave bridge rectifier circuit" or a "diode bridge"). The rectifierconsists of six diodes - a negative and a positive for each statorcoil. These are called the "output diodes", not to be confused withthe "diode trio" which will be explained later.

Recall that a diode is like a one-way valve for electricity. It only allows current to flow in one direction. The diodes are wiredin such a way that they only conduct during half of the AC cycle, and stop conducting during the other half. The result isthat the 3-phase AC is "clipped" or "filtered", resulting in DC output that looks like this:

Note that this output is actually a "pulsating" or "lumpy" DC output, not a pure clean waveform. This is good enough formost automotive use, but sensitive electrical components will have or require additional filtering circuitry to "clean up" theDC for their use. This is why, for example, certain aftermarket accessories instruct you to connect them directly to thebattery, because the battery acts as a giant filter or "cushion" in the system, smoothing out the DC waveform.

VOLTAGE REGULATOR

Recall from Part 1 that the automotive electrical system can be likened to your shop air compressor system. Both are"supply and demand" systems that must be regulated for optimal performance. Take the shop air system: the compressorgenerates the power (the air pressure) required to fill the tank and power the air tools. The tank stores a reserve of airpressure - available for use when the compressor is not operating or to maintain adequate supply during peak demands.The regulator regulates the output to the required pressure (psi), ensuring max tool performance but without overpressurizing and damaging the air tools. And the pressure switch automatically turns the compressor on to maintainadequate psi when the system is in use, and turns it off to prevent a dangerous, uncontrolled rise in air pressure when thesystem is not being used.

The auto electrical system works very much the same way. The alternator generates electrical power, (the voltage or"electrical pressure)) required to recharge the battery and power the electrical devices. The battery stores a reserve ofelectrical power - available for use when the alternator is not operating (engine off) or to maintain adequate supply duringpeak demands. The voltage regulator regulates the output to the required voltage, ensuring max electrical deviceperformance but without allowing the development of high voltage that is dangerous and damaging to the electricalcomponents. The ignition switch / exciter wire initially "turns the alternator on" when the system is first started.

If the alternator was allowed to constantly produce all the power it could, system voltage would rise to a damaging level,the battery would overcharge, components would be damaged, and the alternator would soon overheat and burn out.

Conversely, if the alternator is not functioning the battery will try and supply all the electrical current, voltage will steadilydrop, and eventually the battery will become completely discharged and the car no more worky!

It is the job of the voltage regulator to balance the supply anddemand of the electrical system by regulating the alternatoroutput.

If the battery is fully charged and we have no lights or other electrical accessories operating, very little voltage need beproduced by the alternator (there will always be at least some demand due to voltage drop in the system wiring, caused bythe resistance of the wire itself - remember Ohm's law!)

However, if we have lights, electric fans, a weak or partially discharged battery, and a big stereo playing, system demandwill be high and the alternator will be required to produce much greater output to keep things in balance, charge thebattery, and prevent system degradation or malfunction caused by low voltage (e.g. dim lights). We'll look at an exampleusing some real numbers shortly.

Now, the output of any given alternator is primarily determined by the rotational speed (RPM) of the rotor and the strengthof the magnetic field produced by the rotor. In turn, the strength of the magnetic field produced by the rotor depends on theamount of current (the field current) supplied through the brushes and slip rings to the rotor windings.

It is this field current that the voltage regulator controls, or regulates, in order to control alternator output voltage across allalternator speeds (RPM).

Today, virtually all alternators used internal solid-state (also known as electronic or transistor) voltage regulators.

The regulator has two inputs and one output. The inputs are the field current supply and the control voltage input, and theoutput is the field current to the rotor. We will examine the concept of the control voltage input in some detail in the sectionon wiring. For now, it is sufficient to think of it as a wire from the battery or main electrical distribution block that provides aconstant "reading" of system voltage to the regulator.

The regulator uses this control voltage input to control the amount of field current input that is allow to pass through thebrushes and slip rings to the rotor windings. If the system voltage drops (e.g. when lights are turned on or engine rpmdecreases) the regulator senses this and allows more field current to reach the rotor, which increases the magnetic fieldstrength, which ultimately increases the voltage output of the alternator which brings the system voltage back to the correctlevel. Conversely, if the system voltage goes up (electrical devices are shut off, or engine rpm increases), the regulatorallows less field current through to the rotor windings, and the alternator output voltage is reduced, again bringing thesystem back into balance. It's a closed-loop feedback system and it works extremely quickly and reliably so that the endresult is almost entirely consistent system voltage regardless of electrical load or engine RPM.

The regulator uses transistors to control the field current. A transistor is a device used to amplify and switch electronicsignals. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. Avoltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair ofterminals. When system demand causes a voltage drop (the control voltage input is less than nominal) the regulatorsenses this and a small current is sent to a transistor which amplifies it and sends it to another transistor which acts as avalve in controlling the flow of the field current input to the rotor.

Field Current Supply

The field current supply is provided from one of two different sources, depending on the state of the alternator. When theengine is not running and the alternator is not spinning and producing electricity, the field current supply comes from thevehicle's battery, via the ignition switch and alternator warning lamp (if equipped). We'll go into more detail on the warninglamp shortly. The process of supplying battery voltage to "kick-start" or "prime" the alternator is known as "exciting" thealternator, and the wire that carries the current from the alternator warning lamp to the appropriate voltage regulatorterminal is known as the "exciter" wire. A few special alternators do not have this wire and are known as "self-exciting" -we'll cover this in more detail in the wiring section.

After the engine is started, and the alternator is generating electricity the diode trio feeds the alternator output back to thevoltage regulator to serve as the field current supply.

Theoretically, once up to speed, the alternator is self sustaining, and the car will run without a battery until it is shut off (aslong as system demand does not exceed alternator output capacity). However - you should never disconnect the batteryin a running vehicle as doing so can cause voltage surges that can damage not only the voltage regulator, but also otheron-board electrical equipment - particularly computer-controlled devices. Remember the diagram of the pulsed DC outputfrom the alternator and the fact that the battery acts as a large filter or cushion in the system.

Note that the field current is much smaller than the output current produced in the stator windings. For example, to produce70 amperes of DC, the field current required will be less than 2 amperes.

The Numbers

As mentioned in Part 1 - one thing most of us already know is that automotive electrical systems are 12 Volt DC. BUT - it isimportant to note that TWELVE volts is just a nominal voltage. Although we always refer to the related circuits andcomponents as "12 Volt", in reality a typical, fully charged automotive battery will produce 12.6 volts (with the engine off)and the alternator's voltage regulator will be set to maintain system voltage at somewhere between 14.0 - 14.6 volts, with14.2 volts normally being considered "optimal".

To understand why the voltage regulator is set to 14.2 volts, recall that one of the jobs of the alternator is to recharge thebattery, and remember that voltage is "electrical pressure" and therefore flow (current) will only occur when there is a"pressure difference" or voltage difference between two points.

As such, if the regulator were set to maintain alternator output (and therefore system voltage) at 12 volts, no voltagedifference would be present between alternator output and battery, and therefore no current would flow between alternatorand battery and as a consequence the battery would not charge until it fell below 12 volts - and by then it is alreadypartially discharged.

As it turns out, a healthy, fully charged “12volt” battery produces about 12.6 volts. Alternator output must therefore exceed12.6 volts for electrical current to continuously flow through the battery, which is what charges it. A detailed explanation ofbattery charging is beyond the scope of this article, but basically in order to charge a battery an electrical current must flowthrough it as this enables the chemical reaction required between the liquid acid and the lead plates in the battery. And itturns out that 14.2 volts is the required voltage to create the optimal current to continuously charge a 12 (12.6) voltautomotive battery.

In summary, we see that the voltage regulator is the "brains" of the alternator and indeed the entire vehicle's charging andelectrical system. It also holds quite a lot of potential for tinkering or modification, although we won't be getting into thathere. But the devout hackers and tweakers amongst you will no doubt have already realized that by modifying the voltageregulator, or even purchasing a custom-built unit, an alternator can be set up to produce almost any voltage up to about130 volts. Not only that, but modifying the rectifier can also allow the alternator to output 60HZ AC power for poweringelectric tools, welders, and all sorts. These modifications are indeed what is at the heart of special alternators that aremanufactured and marketed as 120V 60Hz power sources (i.e. standard North American household power).

ALTERNATOR WARNING LAMP

Far from being an "idiot light", the alternator warning lamp can tellus a great deal about the health of our alternator and otherelectrical components if we understand how it functions.

The alternator warning lamp is connected in series between a switched ignition source (the field current supply) and thevoltage regulator. The voltage regulator is also connected to ground.

When the ignition switch is closed (the ignition key is turned on), current flows from the battery, through the alternatorwarning lamp, through the voltage regulator to ground. As such, the alternator warning lamp glows.

In the following simplified block diagram (not a real electrical schematic), when the alternator is not running, the batteryprovides the field current supply (red arrows) and the lamp is grounded and therefore glows.

As we know, after the engine is started, and the alternator is generating electricity the diode trio feeds the alternator outputback to the regulator to serve as the field current supply. This equalizes the voltage across the alternator warning lamp(there is no longer a path to ground for the lamp), current stops flowing through the lamp, and therefore the lamp goes out.Remember from Part 1 - in order for the lamp to glow, there must be current flow through it - and in order for current to flow- there must be a voltage difference (pressure difference) across the lamp. In effect, the alternator output equalizes thepressure coming from the ignition switch and stops the current flow.

In the following simplified block diagram (not a real electrical schematic), when the alternator is running, the diode triofeeds alternator output back as the field current supply (blue arrows) which equalizes voltage across the lamp andtherefore it does not glow.

So, now we know, anytime the alternator warning lamp is on, it means there is a voltage difference across it. That meansthat either: 1) the battery voltage is higher than the alternator output, or that 2) the alternator output is higher than thebattery voltage.

In the case of (1), it probably means that the alternator is weak or failing. In the case of (2), it probably means that thebattery is weak or discharged.

How can we tell which it is?

Simple - if we apply our new knowledge of how an alternator works, we can easily determine which is the problem.

Recall that alternator output is dependant on alternator RPM. If we increase alternator speed, we increase alternatoroutput. Therefore, if we rev the engine, we increase alternator speed and output, and if as a result the light gets dimmer itmeans the alternator output was weak (it must be increased by revving the engine to try and equalize the voltage acrossthe lamp).

If, however, the lamp gets brighter when we rev the engine, it means the battery voltage is low. This is because batteryvoltage does not vary with RPM. Therefore, if an RPM increase causes an increase in lamp brightness, it can only bebecause the increasing alternator output is getting even higher than the battery voltage. With a healthy battery, this won'thappen - battery voltage will match alternator output. But if the battery is unable to take or hold a full charge, the more weincrease the alternator output the more it exceeds the weak battery voltage and the brighter the lamp will glow.

In summary, we can say that:

1. Any time the alternator warning lamp is on, there is a voltage difference between alternator output and batteryvoltage.

2. The light should come on bright when the ignition is on but the engine is not running [battery voltage ~ 12.6V /Alternator output 0V]. If it does not, or is only dim - suspect either:

Burned out lampA problem with the field current supply (low battery voltage or switch/wiring problem)A problem with the alternator ground.

3. If the light comes on when the engine is running, either the alternator is failing/has failed or the battery voltage isdropping. Try revving the engine and:

If the lamp gets brighter, suspect a bad batteryIf the lamp gets dimmer, suspect a bad alternator

Of course, these are just basic guidelines as wiring faults and bad grounds can cause all manner of electrical faults thatsometimes appear to be other things.

A Look Inside

Let's take a look now at the parts inside an actual alternator.

This particular unit is an older GM Delco-Remy CS-130 series alternator.

Front 3/4 view.

Rear 3/4 view.

Rear view.

The wiring terminals on this model are small pins inside thisplastic female plug.

Wiring terminals are connected to the voltage regulator.

Here I have removed the nut holding the pulley on the rotor andhave begun to disassemble the alternator.

Front parts.

There are many different fan and pulley designs used on Delco-Remy alternators.

The rear case houses the stator.

Rotor and associated parts.

Rotor and associated parts.

Looking inside the rear case with the stator in place.

You can see the spring-loaded brushes which bear against theslip rings on the rotor, and the bore in the back of the rear casewhere the rear bearing goes.

Note the rough (broken) condition of the brushes.

Here we can see the three stator winding outputs passingthrough a black plastic cover to the rectifier.

Close up of the three stator winding outputs

.

Stator removed from the rear case.

As it happens, the CS-130 series are some of the least desirablealternators as they were built to be throw-away units and are notreally rebuildable.

That's why the stator windings are cut in this picture instead ofhaving terminals on them.

Notice the copper wire of the stator windings goes in threes.

Looking into the rear case with the stator and black plastic coverremoved.

The "brains" of the alternator removed from the rear case.

Note that this model doesn't have a separate diode-trio, butfunctions the same as we have described; with the rectifier alsodoing the diode-trio's job.

Note the two electrical connections - one between rectifier andregulator; and one between brush holder and regulator.

Again, note that these connections are crimped and soldered andwere never intended to be serviceable.

Brush holder.

It's pretty much the same as the brush holder in any electricpower tool.

Voltage regulator.

No serviceable parts on this model.

But if you pry (break) off the cover, inside you can see thetransistors surrounded by a jelly-like goo.

The bridge rectifier unit.

Note the large aluminum heat sink and the three cut connectionsat the top (that used to be hard-wired to the stator windings).

The empty rear case.

Here's an exploded diagram of the alternator pictured above:

Common GM Delco-Remy Alternators

There are dozens of different brands of alternator out there - AC Delco, Delco-Remy, Bosch, Carrier, Champion,Mitsibushi, Prestolite, Ford, Hitachi, Motorola, Nippondenso, Thermo King, Wilson, and many others.

Obviously there's no possible way I can cover them all. One of the most common brands / types out there are the GM / ACDelco / Delco-Remy alternators used on tens of millions of GM cars and light trucks. These units are simple, rugged, goodperforming, mostly rebuildable, and available virtually anywhere and everywhere. They make good candidates forswapping into everything from hot rods to custom 4x4 buggies. They are also available in a huge variety of series andstyles in different sizes, performance ratings, and price brackets. Chances are, if you had to pick one type - this would bethe one with the greatest chance of having a model or part number to fit your needs.

As such, when confronted with limited space and time, it makes sense for us to cover these alternators.

There are two broad "series" of GM Delco-Remy alternators built since 1971. Both have internal voltage regulators (very

early alternators used external voltage regulators but they are now old, rare, and not really suitable for off-road use).

The early type, called the "SI" series, were used in GM cars and trucks from about 1971 to about 1986, and are stillavailable today through Delco-Remy, various rebuilders, and the aftermarket. The SI stands for Systems Integrated andthey are so-called because they were the first Delco-Remy alternators to be built with internal, or integrated, voltageregulators.

The later type, called the CS series, were used in GM cars and trucks from about 1986 to the present. The CS stands forCharging System (the creative names department must have been closed that day!).

The most common types in each series are as follows:

SI Alternators

Delco-Remy 10-SI Series

1971 - 1985

- First GM internal voltage regulator alternator

- Used extensively on GM cars & light trucks and otherapplications such as marine and agricultural.

- Available in outputs from 37 - 72 amps, with 40 amp, 63 amp,and 72 amp being the most common.

Typical 10-SI performance curve plotting alternator output inamps vs. alternator rpm.

Delco-Remy 12-SI Series

1983 - 1986

- The 12-SI was an update and improvement on the 10-SIdesign.

- The 12-SI has the same outside dimensions as the10-SI butwith several design improvements for better performance,including:.

Larger rectifier to handle more amps.Wider stator and rotor for improved magnetism, better lowRPM output, and improved heat dissipation.Larger cooling vents in rear case for better cooling ofinternal components.New high-volume, axial-turbo fan design for increased airflow and better cooling.

- Available in outputs from 56 - 94 amps, with 78 amp and 94amp being the most common.

If you look at the above photos of the 10-SI and the 12-SI, you will notice that the two easiest ways to visually distinguishbetween the two are 1) The style of fan installed and 2) The much larger air vents in the back of the 12-SI. The latter is thebest feature to use, as it is always possible that someone swapped fans - but in stock form the fans are clearly easy to tellapart.

The 10SI and 12SI are Delco Remy model series designations - not part numbers. Each was built in several different

output ratings, and assembled with any one of four available “clock” positions for different mounting bracketarrangements. Add to that the different types of pulleys that could be installed and the result is obviously many differentpart numbers.

The "clock position" of an alternator refers to the location of the electrical terminals with respect to the threaded mountinghole. If you view the alternator from the back, with the threaded mounting hole at the top (12 'o' clock position) then thelocation of the terminals in terms of "clock face position" is the "clock position of the alternator.

The following picture illustrates a 10-SI alternator with "12 'o' clock" clock position. If the terminals were to the right side, itwould be a "3 'o' clock" alternator. Straight down opposite the threaded hole would be 6 'o' clock, and so on.

Having the different available clock assembly positions allows for exit of the wiring from the alternator in the directionrequired for use with different mounting setups.

SI series alternators are an older design, but they make excellent candidates for use in off-road vehicles that don't havehuge electrical demands. They are cheap, plentiful, rugged, reliable, very easy to diagnose, repair, and rebuild and partsfor them are still available nationwide. Unlike some later design, virtually any individual part in an SI series alternator canbe easily replaced - they were built to be serviced - something that is not always true for later designs.

CS Alternators

First produced in the mid-1980's, Delco-Remy CS series alternators are probably the most numerable on the planet. Thefollowing are the most common:

Delco-Remy CS-121 & CS-130 Series

1986-1996

In 1986, the CS-121 and CS-130 alternators were a completedesign departure from the SI series alternators they weredesigned to replace.

Designed to produce high ampere output per pound of weight,they featured a new and different voltage regulator, differentterminals, and no diode trio.

In stock trim thay are available in the following outputs:

CS-121: 61-74 amps

CS-130: 85-105 amps

They certainly produced good output per pound, but there were a couple of design elements that make them a poorchoice. First, by packing high performance in a small case - they tend to get hot, and heat leads to breakdown andmalfunction .

This is compounded by the fact that the units were designed to be either "maintenance free" or "throw-away unitsincapable of being repaired", (depending on your outlook).

The 121 and 130 are visually nearly identical, and share the same design, but the 130 is slightly larger than the 121. Infact, the numbers 121 and 130 denote the outside diameter, in millimeters, of the stator ring.

Delco-Remy CS-130D Series

1994-2000

In the mid 1990's the CS-130D took over as the standardapplication alternator on most GM vehicles. In stock trim itoffered 100-105 amp outputs.

Don't let the name fool you, although it had "CS-130" in its name,the CS-130D was a completely different unit from the earlier CS-130.

Design improvements from the earlier CS-130 include:

More open design for better air flow - notice the manywindows in the case design.Larger bearings.Dual internal fans to increase air flow.Voltage regulator and rectifier were moved to the outside ofthe alternator, away from stator and rotor heat.

This last feature is one of the more readily identifiable features of the CS-130D alternator, as can be seen in the pictureabove. Notice how the black plastic housing that contains the regulator and rectifier sticks off the back of the rear case.

Delco-Remy CS-144 Series

1986-2006

The CS-144 series alternators are physically larger, higher-outputalternators used during the same period as the CS-130 and CS-130D. Early models were 108-124 amp and later versions 124-145 amp output.

Despite their larger size, the mounting bolt pattern is the same asfor the CS-130 and CS-130D, so if you have the room they canmake an easy swap.

The larger size of the CS-144 offers a reliability increase as theextra mass is better able to absorb and dissipate the heatgenerated when making 100 amps or more.

Wiring

OK, now we're getting down to it!

Probably the most frequently asked question with regards to alternators is: "How do I wire this alternator?"

It should be an easy question to answer, but sadly it isn't always that simple. There are thousands of different alternatorsin use and available on the market - made by American, Asian, and European companies. There are equally as manydifferent vehicle wiring systems. On top of that - there is a distinct lack of standardization in the industry with respect tothings like the name, location, and function of the different connections or terminals on alternators.

The result can be a confusing mess - or at the very least leaves us with a situation a little more complicated than "unplugthis unit and plug this one in in its place"!

Obviously, I can't possibly cover every alternator, engine, and wiring harness combination - can't even begin to scratch thesurface really. That's why we've covered so much detailed tech so far in this article - so that you can understand howthings work, and puzzle out answers and solutions for yourself - or at the very least stand a good chance of determining ifwhat you read on the internet makes sense.

1 wire, 2 wire, 3 wire, 4

There can be much confusion when discussing different types of alternators base on the designation "1 wire" or "2 wire" or"3 wire", etc. There is a simple reason for this confusion which I hope we can clear up.

From our description of how an alternator works, it should be clear that all alternators require a minimum of four "elements"to operate - 1) Field Current, 2) Voltage sensing, 3) Ground, and 4) Output.

The trouble is, there are multiple designs that use different methods of providing these four "elements", and they usedifferent numbers of wires in doing so. What complicates the matter is that: a) The number of wires does not alwayscorrelate on a 1:1 basis with the required "elements", and b) Some designs use additional wires for "optional" features andthese wires may or may not be included in the count when someone describes an alternator as "2-wire" or "3-wire" etc.

So, there are different designs with different numbers of wires, but ALL must have the four "elements" to operate - 1) FieldCurrent, 2) Voltage sensing, 3) Ground, and 4) Output.

For example, the so-called "1-wire" alternator, even though it does indeed have only a single wire connecting the outputterminal to the battery, still has the four "elements".

But, many self-exciting alternators (so-called 1-wire) can be (and often are) hooked up using two wires - the bat cable forelements (2) and (3), and an additional excitation wire for initial field current supply (i.e. they can self-excite, but they canalso use an excitation wire). So would this be a "1-wire alternator", a "2-wire alternator", or a " 1-wire hooked up with2 alternator"?

Then there are those alternators that come with a dedicated grounding terminal (as opposed to just grounding through thecase / mounting bracketry). Does this "wire" get included in the wire count?

And if that wasn't enough - what do you call an alternator that has four terminals on the voltage regulator (S F L P ), a Batterminal, and a dedicated ground terminal? Is that a 6-wire alternator? What if it's hooked up with wires going only to theBat, Ground, and L terminal? Does it "become" a 3-wire alternator now?

It gets confusing.

As such, I prefer to avoid referring to alternators by "wire number" as that is clearly not a definitive way of delineating howthe alternator operates (and therefore how it should be hooked up).

Instead, in terms of "number of wires", I will differentiate only between two groups - the self-exciting or "one wire" alternatorand then all other non-self-exciting or "multi-wire" alternators. Then I'll break down the multi-wire alternators by theterminals they have.

But first, we must briefly discuss the concept of voltage sensing in a little detail.

Voltage Sensing

Of the four "elements": we have already discussed field current in detail. Output and ground are self-explanatory. Whichleaves only voltage sensing requiring a little more explanation.

We have already discussed briefly why voltage sensing is required - recall that it is the method by which the voltageregulator senses system voltage and compares the result to its internal setting, and based on the results of thatcomparison either increases or decreases alternator output. The "internal setting" is built into the voltage regulator and isthe system voltage the regulator will try and maintain. Internal settings may differ slightly between voltage regulators but allare about 14.0 volts.

The concept is simple, but there is a nuance that is important. Because voltage is like "electrical pressure", and becausethere is some resistance in all components in a circuit - even the wires themselves - it should be fairly easy to see that itmatters where the "system voltage" is sensed.

Let's examine why with an example, using the following basic system design block diagram:

Here we have the battery, connected through a master disconnect switch to three things: 1) Winch, 2) Starter Motor, and3) Main Electrical Distribution point (labelled "300A Bus Bar" in the diagram).

This system design is practical, easy to work with, convenient, and offers good performance, especially when electrical

components are spread out throughout the vehicle (ignition,radiator fans and radios near the front, fuel pumps, cooler fans,and amplifiers near the back, etc.) It is the preferred method of electrical distribution - i.e. having a main bus bar orelectrical distribution point. This main distribution point feeds all the vehicles electrical systems as well as receivingalternator output and either passing charge to the battery or accepting current from the battery (depending on whether thealternator is running or not).

OK, with this system, let's assume the alternator's voltage regulator is "set" to 14.0 volts. If we "sense" system voltage (i.e.hook up the alternator's voltage sensing terminal) right at the alternator output , we are going to get a value equal to thealternator's output (obviously) - say 14.0 volts. Now, the voltage regulator says to itself "I'm supposed to produce an outputsufficient to maintain system voltage at 14.0 volts. I sense system voltage (at my output terminal) as 14.0 volts. EverythingOK, maintain this level of output."

Meanwhile - 12 feet away the power-hungry amplifiers are only getting 13.0 volts because of the voltage drop that occursin the wiring from the alternator to the main bus bar and on to the amps. It's even worse for components further"downstream" from the bus bar. But the alternator has no way of knowing this - because we hooked the voltage sensingwire right to the alternator output - it thinks everything is fine, it thinks system voltage is at 14.0 volts and it has no ideaabout the low voltage at the amps.

Doing this - sensing voltage at the alternator output - seriously hamstrings the system - it's like a self-fulfilling system - it'ssupposed to maintain 14.0 volts, it outputs 14.0 volts, therefore everything must be OK, right? But it completely ignoresvoltage drop in the rest of the system - and that's bad for performance (incidentally, many electrical components, whenexperiencing as little as a10% drop in voltage supply can experience a 30% drop in performance!)

Remote Voltage Sensing

This is where the concept of REMOTE voltage sensing comes into play. Instead of sensing system voltage at thealternator or close to it (which is like congratulating yourself on a great job regardless of the results!) - we sense systemvoltage where we need full voltage - in this case at the main distribution point (bus bar).

That way, when the voltage sensing circuit detects 13.0 volts at the main bus bar, it says: " I'm supposed to produce andoutput sufficient to maintain system voltage at 14.0 volts. I sense system voltage as 13.0 volts. Better increase output to15.0 volts to bring system voltage up to 14.0 volts."

Such a system would look like this (note the remote voltage sensing wire, highlighted red):

Another advantage to this remote voltage sensing, is that it allows the alternator to compensate for increased systemdemand as more accessories are turned on. That's what it's supposed to do, after all. As more and more devices areswitched on, a voltage drop will occur at the main bus bar. With remote voltage sensing, the alternator sees this dropcaused by the extra demand, and automatically increases output to compensate. To not use remote voltage sensing, or tosimply jumper the wire to the alternator output or some other nearby source would be like hiring a blind sniper - sure youmight hit the target, but only by blind luck!

Now - if you're thinking about what I've just written and looking at the diagram and thinking: "But why do I need that #10GA wire for voltage sensing? I already have that big fat #2 wire going from the alternator to the bus bar - why not justjumper that to the voltage sensing terminal?" well, all I can say is I am soooooo disappointed in you! ;-) Have you forgottenPart 1 so quickly? Remember voltage is the "electrical pressure" difference between two points and that voltage is related

to current flow and resistance. In the diagram above - as system demands draw more and more current, so the voltage atthe bus bar will drop. However, if we take our voltage sensing directly from the alternator output, we will only be readingalternator output not system voltage, despite the fact that the #2 wire connects to the bus bar - the current is flowing fromthe alternator output to the bus bar, not the other way around, and it is "losing pressure" as it goes. If we just jumper the #2wire to the voltage sensing terminal, we are reading the "pressure" at the beginning of its journey, and yet we know itdecreases as it goes. On the other hand, the advantage to the #10 voltage sensing wire is that very, very little current flowsthrough it, and this doesn't vary with system demand (i.e. when we switch more stuff on) AND it is sensing the voltage atthe END (or at least the middle) of its journey, which is what is important to us.

Also, note that connecting the remote voltage sensing terminal to the battery will only result in the alternator being a goodbattery charger - it still won't compensate for voltage drop in the system caused by wiring to the main distribution point andincreasing electrical demand as more components are powered on.

Also note that this "main distribution point" system only works properly when the “battery charging wire” connects from themain distribution point to the battery (as seen in the diagrams above). There should never be a wire connected from thealternator directly to the battery. This is because, the voltage regulator can only "sense" and "respond to" one voltage - inthis case the voltage at the main distribution point. If we also ran a heavy gauge charging wire from the alternator directlyto the battery, we risk dangerously overcharging the battery as the alternator adjusts output to maintain the maindistribution point at 14.0 volts. That's why the battery must also take its charge from the main distribution point - so thesystem is in equilibrium and we don't risk sending 16.0 volts directly to a battery because that's what the alternator isoutputting to keep the main distribution point at 14.0 volts.

Before we move on, here are some quick pics of some of the actual components used in the above type of system design(based on the system in my buggy). We'll cover these in more detail in Part 3 of the series.

Odyssey battery.

Marine main battery switch.

Marine power distribution blocks. The "main" 300A bus bar is inthe middle.

Marine fuse panel.

The marine main power switches (one for (+) and one emergencyswitch for ground) are top centre.

The main bus bar is at the lower left of the pic, the fuse panellower middle, with various other bus bars between them.

Bus bars and fuse panel.

Main power switches, top right.

OK, so now that we've covered voltage sensing, we're ready to move on to the two different alternator types (in terms ofwiring) - 1) self-exciting and 2) Non-self-exciting.

Self-exciting alternators

The so-called "one wire" alternator is actually a self-exciting alternator. This design has one advantage and manydisadvantages - which we shall cover shortly. However, let me get it out there up front - because of the manydisadvantages, I personally would not recommend anyone use a self-exciting alternator - there are just too manydrawbacks.

How it works

The short answer is, of course: "The same way every other alternator does." The real question is - how does it get the four"elements" using only a single wire? Here's how:

1) Field Current

Instead of a dedicated wire supplying field current to excite or "start" the alternator, this design is "self-exciting". It uses aspecial voltage regulator that senses alternator RPM and when it is low (as in when starting the engine) it uses the residualmagnetism in the alternator's rotor fields to supply the initial field current until the alternator comes up to speed andalternator output takes over as the field current supply.

Remember when we discussed the different types of magnets, we talked about permanent magnets and electromagnets?And we said that a permanent magnet gets its magnetism because of the material from which it is made? We then talkedabout how the rotor of an alternator, having an iron core with field windings around it, is an electromagnet. Well, becausethe rotor has an iron core, if it is initially magnetized during construction (which it is), then the core alone is a permanentmagnet, even without the windings (albeit a comparatively weak one). Therefore, if we rotate the rotor iron core permanentmagnet inside the stator windings we produce an electrical current - again, a weak current (not enough to supply thevehicle's demands) but it IS enough to excite the alternator. So what happens with the self exciting alternator is that therotor, as a permanent magnet, when turned inside the stator windings, is able to supply just enough current to the voltageregulator for the voltage regulator to supply back to the rotor windings as field current, which "turns on" the rotor as anelectromagnet, and we're off to the races.

Of course, since the initial "permanent magnet" output is weak, the rotor has to be spun fast enough to produce enoughcurrent to supply the field windings - which is why sometimes in a vehicle with a self-exciting (one-wire) alternator you haveto rev the engine initially to get the alternator working and the ALT WARN lamp to go out!

2) Voltage Sensing

Instead of a dedicated voltage-sensing wire, a self-exciting alternator uses the main battery wire for voltage sensing.We've already discussed the serious limitation this creates.

3) It grounds through the case / mounting brackets to the engine block. so there is no dedicated grounding wire. This istypical of many non-self exciting alternators too, so nothing special here.

4) It uses the main battery wire for output. Again, nothing special here, so do all non-self exciting alternators.

Advantages

The only real advantage to a self-exciting (one-wire) alternator is that it is very easy to wire - obviously. However, in myhumble opinion its many drawbacks mean it is suitable only for a diesel tractor with no electrical system whatsoever otherthan a starter motor!

Disadvantages

There are several serious disadvantages to a self-exciting (one-wire) alternator, including:

1. Inability to do remote voltage sensing - likely to result in low system voltage and poor electrical performance.2. Related to its inability to do remote voltage sensing, a powerful self-exciting alternator can cause damaging

overcharging when re-charging a battery with a low state of charge.3. No provisions for phase, relay, or external field monitoring terminals (see "Terminals" section below for details.)4. Price. Because they are much less common, self-exciting alternators command a premium price, despite their lack of

features and poorer performance.5. Availability. Self-exciting alternators are much less readily available than other alternators - which can make them a

pain to repair or replace - especially if far from home.6. Ironically, when used on low RPM motors (like those in tractors and other "equipment", the only application for which

they are really suitable), the motor may have a difficult time generating sufficient alternator RPM to get the alternatorto self-excite.

Non-self-exciting alternators

By far the better performing and more suitable group of alternators are the non-self-exciting (or multi-wire) alternators.

For GM / Delco-Remy alternators these can be broken down into two sub-groups in terms of wiring / terminals thatconveniently (for once!) correlate with the Delco-Remy series they belong to.

SI Series / 2-terminal Alternators

Terminals

The older 10-SI and 12-SI series alternators are also sometimes (somewhat inaccurately) known as either two-terminalalternators (after the 2 terminals commonly found on the voltage regulator), or three-wire alternators (after the mostcommon configuration that uses three wires - one to each of the common voltage regulator terminals plus the output wireto the Bat(+) terminal).

This is a 12-SI alternator with the so-called "2-terminal"configuration.

As you can see, there are actually three terminals, as follows:

1. The #1 terminal, the left of the pair on the voltage regulator,is the excitation or "ignition" terminal.

2. The #2 terminal, the right of the pair on the voltageregulator, is the remote voltage sensing terminal.

3. The third terminal is the alternator output terminal, labelled"Bat" on this model.

The functions of the terminals are as follows:

TerminalLabel

Delco-RemyName

Location Function Connects to: Notes

1 Ignition Left FieldCurrentSupply

SwitchedIgnition 12v+(excitor wire)

May connect alt warn lamp in series (optional).

2 RemoteSense

Right VoltageSensing

Main ElectricalDistributionPoint (Bus Bar)

The #2 terminal may be connected externally to avoltage, such as the main power distribution point, tosense the voltage to be controlled.

B or BAT OutputTerminal

Varies AlternatorOutput

Battery / MainPowerDistribution

Note: If a warning lamp is connected in series with the excitor wire (between ignition switch and Terminal #1), and aresistor is not used in parallel with the lamp, if the lamp burns out, the alternator will not excite and therefore will notwork.Note: Sometimes aftermarket housings are not marked and other times older or rebuilt cases may have markingsthat are worn off or illegible. If so, when looking at the rear of the alternator: the #1 terminal is on the left and the #2 ison the right.

So far, so good - but if we look a little closer, things get a wee bit confusing on this so-called "2-terminal" alternator

As we can see, in addition to the labels for the #1 and #2terminals, this case has three other labels - two R's and an F.

This is because the terminal labels are cast on the rear case, thecases are mass produced, and that some of the terminals areoptional (i.e. whether they are present or not depends on thevoltage regulator installed in the alternator – and one rear casemay be used in the production of several different models ofalternators with differing voltage regulators).

The result is – an alternator may have labels on the case, but no

actual corresponding terminals. Such is the situation with thisparticular alternator - the case has labels for an “R” terminal intwo different places (one by the #1 terminal and one by the BATterminal) because R terminals, when present, may be in either ofthese locations. It also has a label for an F terminal (by the #2terminal).

However, this particular alternator has neither an R nor an Fterminal. In fact, R and F terminals are fairly uncommon on thesealternators.

However, if they were present, the R and F terminals are as follows:

TerminalLabel

Delco-RemyName

Location Function Connectsto:

Notes

R Relay Either adjacent tothe #1 terminal ornear the Batterminal.

Drives externaldevice

ElectricTachometeror hourmeter, etc.

The "R" terminal is connected to thestator, and may be connected externallyto drive a tachometer, hourmeter, or otherdevice. Optional.

F ExternalFieldMonitor

Adjacent to the#2 terminal.

Used toexternallymonitor therotor’smagnetic field.

ExternalDevice(optional)

The "F" terminal is connected internally tofield positive, and may be used fordiagnostics. Optional.

Note: Voltage at the R terminal is pulsating DC and is usually half system voltage. Pulse frequency varies with alternatorRPM and alternator model. Normal maximum amp draw for R terminal is 4.0 amps.

Wiring

It should now be obvious how to wire an SI-series / 2-terminal alternator, but just to summarize:

Mandatory connections:

1) Connect the alternator output terminal (B or Bat) to the electrical system's main distribution point (bus bar, junction, etc.)Less optimal alternatives that will work include connecting it to the battery + terminal or a terminal on the starter motor thatalso connects to the battery + terminal.

2) Connect the #1 voltage regulator terminal (left spade connection) to a source of switched ignition power in one of twoways:

a) Directly from the ignition switch (or relay) to the #1 terminal; or

b) From the ignition switch (or relay) to the #1 terminal via a dash light connected in series. Note however, thatyou should also connect a 50 Ohm resistor in parallel with the light, so that if the bulb burns out, the alternatorwill still be excited.

3) Ensure there is a good ground connection between the bare alternator case, the mounting bracketry and the engineblock/heads and/or install a dedicated ground wire from the engine block to the alternator's ground terminal (if it has one).

Crucial connections:

4) Strictly speaking, the alternator will work with only the three wiring connections listed above, but I consider it crucial forgood performance that you also wire up the remote voltage sensing terminal. To do this, connect the #2 voltage regulatorterminal (right spade connection) to the vehicle electrical system's main power distribution point (bus bar, main switch, fusepanel, etc.). If the #2 remote voltage sensing terminal is not connected, the voltage regulator will revert to internal sensingof the alternator output terminal voltage - with all the limitations that brings. You will see some alternators wired with ashort jumper wire from the #2 terminal directly to the battery connection at the back of the alternator, but this is neither theproper method for remote voltage sensing nor necessary for internal sensing - do it properly or leave it out.

Optional connections:

5) If you have an alternator with an R and/or F terminal, and you have a device that can be connected to either one,connect them in the manner specified by the manufacturer of the device.

This is a diagram of such an SI-series alternator wired using terminals 1, 2, and B.

Plugs

Because these terminals use male spade connectors, in a pinch you can wire to them using standard female spadeconnectors, but be sure to insulate them well with heat-shrink tubing if you do. The problem with this method, however isthat there is no mechanical connection for security and strain-relief. The better and proper way to connect to theseterminals is to use a factory connection. These are available and known as a "regulator repair harness".

For SI alternators you can use either part number 46-1801 from WAI Global Industries, (www.waiglobal.com) picturedbelow:

or

part number C100 from Quick Start Alternators (www.alternatorparts.com), pictured below:

CS Series / 4-terminal Alternators

These days, the more common arrangement on CS series alternators is to find four terminals on the voltage regulator, plusthe alternator output terminal, and possibly a dedicated grounding terminal (for an actual total of 5 or 6 terminals). Thesealternators can be wired with anything from 2 to 6 wires, as we shall see (see why I avoid using terms like "2-wirealternator", as it actually tells us almost nothing!)

Terminals

This is a CS-130 alternator with 4 terminals at the voltageregulator (the black plastic housing labelled "Wiring Terminals" inthis pic) plus the alternator output terminal (labelled "BAT" on thismodel).

On these later-model alternators, the voltage regulator terminalsare pins rather than spade terminals.

As such, you can't just use standard electrical connectors - youneed the matching plug - see the section on plugs below.

On this model, the terminals are labelled P, L, F, and S.

Other models will also have four pins in a similar arrangement,but they may be labelled P, L, I, S.

The functions of the terminals are as follows:

TerminalLabel

Delco-RemyName

Function Connectsto:

Notes

P Phase(Relay)

Drivesexternaldevice

ElectricTachometeror hourmeter.(optional)

The "P" terminal is connected to the stator, and may beconnected externally to drive a tachometer, hourmeter, orother device. Optional.

L IndicatorLamp

WarningLamp

Alt warninglamp

F ExternalFieldMonitor

Used toexternallymonitor therotor’smagnetic field.

ExternalDevice(optional)

The "F" terminal is connected internally to field positive, andmay be used for diagnostics.

I Ignition Field CurrentSupply

SwitchedIgnition12v+(excitorwire)

Used to excite alternator, with or without a resistor betweenswitch and terminal “I”, either a) in absence of an alternatorwarning lamp in the vehicle or b) as a backup (redundant)method of exciting the alternator.

S RemoteSense

VoltageSensing

Main PowerDistributionTerminal

The "S" terminal may be connected externally to a voltage,such as the main power distribution point, to sense thevoltage to be controlled.

B or Bat OutputTerminal

AlternatorOutput

Battery /Main PowerDistribution

Notes: -

Alternator will have either an “F” terminal or an “I” terminal, but not both.

If the alternator has an “F” terminal (i.e. no "I" terminal):It must be excited by the L terminal.When exciting via the L terminal, there must be some resistance in the circuit (bulb and/or resistor) or a shortcircuit will be created.If no alternator warning lamp is desired, a 50 Ohm resistor is used.If an alternator warning lamp is used, a resistor should still be used, in parallel with the lamp. This is so that thebulb burning out does not prevent current flow and therefore alternator excitation. The resistor should beequivalent to a 3-4 watt bulb. Using Ohms law, we can use the Electrical Wheel of Doom from Part 1 tocalculate the required value of the resistor as R = V^2 / Watts. In this case R = (14v*14v) / 4W = 49 Ohms. So a50 Ohm resistor will do.

If the alternator has an “I” terminal: You can use this I terminal to excite the alternator, whether or not you are using an alternator warning lamp(i.e. whether or not anything is connected to terminal L).Terminal “I” has a built-in internal resistor to prevent a short circuit when connected to the excitor wire.Therefore, you can connect the ignition switch to terminal “I” using an excitor wire with or without a resistor inseries.If you do not have or do not wish to install an alternator warning lamp, you can excite the alternator byconnecting the ignition switch to terminal “I” using an excitor wire with or without a resistor in series.If you do have an alternator warning lamp connected to terminal “L”, you can still connect the the ignition switchto terminal “I” using an excitor wire with or without a resistor in series as a backup method of exciting thealternator. This is good practice as this type of redundancy enhances reliability.

Wiring

It should now be obvious how to wire a CS-series / 4-terminal alternator, but just to summarize:

PLFS-type

Mandatory connections:

1) Connect the alternator output terminal (B or Bat) to the electrical system's main distribution point (bus bar, junction, etc.)Less optimal alternatives that will work include connecting it to the battery + terminal or a terminal on the starter motor thatalso connects to the battery + terminal.

2) Connect the L terminal to a source of switched ignition power through an indicator lamp wired in series. Also connect a50 Ohm resistor in parallel with the indicator lamp so that if the bulb burns out, the alternator will still be excited.

3) Ensure there is a good ground connection between the bare alternator case, the mounting bracketry and the engineblock/heads and/or install a dedicated ground wire from the engine block to the alternator's ground terminal (if it has one).

Crucial connections:

4) Strictly speaking, the alternator will work with only the three wiring connections listed above, but I consider it crucial forgood performance that you also wire up the remote voltage sensing terminal. To do this, connect the S terminal to thevehicle electrical system's main power distribution point (bus bar, main switch, fuse panel, etc.). If the S remote voltagesensing terminal is not connected, the voltage regulator will revert to internal sensing of the alternator output terminalvoltage - with all the limitations that brings. You will see some alternators wired with a short jumper wire from the Sterminal directly to the battery connection at the back of the alternators, but this is neither the proper method for remotevoltage sensing nor necessary for internal sensing - do it properly or leave it out.

Optional connections:

5) If you have an external device such as a tachometer, hourmeter, or other device, it may be connected to terminal P.Connect the device in the manner specified by the manufacturer of the device.

This is a diagram of such a CS-series, PLFS alternator wired using terminals L, S, and BAT.

PLIS-type

Mandatory connections:

1) Connect the alternator output terminal (B or Bat) to the electrical system's main distribution point (bus bar, junction, etc.)Less optimal alternatives that will work include connecting it to the battery + terminal or a terminal on the starter motor thatalso connects to the battery + terminal.

2) Connect the L terminal to a source of switched ignition power through an indicator lamp wired in series. Also connect a50 Ohm resistor in parallel with the indicator lamp so that if the bulb burns out, the alternator will still be excited.

3) Connect the I terminal to a source of switched ignition power through a 50 Ohm resistor wired in series.

3) Ensure there is a good ground connection between the bare alternator case, the mounting bracketry and the engineblock/heads and/or install a dedicated ground wire from the engine block to the alternator's ground terminal (if it has one).

Crucial connections:

4) Strictly speaking, the alternator will work with only the three wiring connections listed above, but I consider it crucial forgood performance that you also wire up the remote voltage sensing terminal. To do this, connect the S terminal to thevehicle electrical system's main power distribution point (bus bar, main switch, fuse panel, etc.). If the S remote voltagesensing terminal is not connected, the voltage regulator will revert to internal sensing of the alternator output terminalvoltage - with all the limitations that brings. You will see some alternators wired with a short jumper wire from the Sterminal directly to the battery connection at the back of the alternators, but this is neither the proper method for remotevoltage sensing nor necessary for internal sensing - do it properly or leave it out.

Optional connections:

5) If you have an external device such as a tachometer, hourmeter, or other device, it may be connected to terminal P.Connect the device in the manner specified by the manufacturer of the device.

This is a diagram of such a CS-series, PLIS alternator wired using terminals L, S, I, and BAT.

Plugs

To plug the wires into a CS-series alternator you need the factory-style plug. If you can scavenge one from a donorvehicle, great. If not, they are available separately from a number of sources, such as:

For CS-121, CS-130, and CS-144 alternators you can use either part number 46-1803 from WAI Global Industries,(www.waiglobal.com) pictured below:

or

part number C120 from Quick Start Alternators (www.alternatorparts.com), pictured below:

For CS-130D alternators you can use either part number 46-1810 from WAI Global Industries, (www.waiglobal.com)pictured below:

or

part number C130D from Quick Start Alternators (www.alternatorparts.com), pictured below:

Performance

If you're with me so far, you pretty much know all you need to know in order to shop for your next replacement, factoryupgrade, or custom-built, high-output alternator.

Obviously, there are way too many variables for me to be able to tell you exactly what part number you need - but thereare a few points on alternator performance I can summarize which will be helpful for you to keep in mind when shopping;as well as a few ideas on how to go about finding that perfect alternator for your needs.

The principle factors governing alternator performance include:

The max speed at which it can be turned.The speed at which it is turned at idle / low RPM.The windings.The voltage regulator and rectifier specs / performance.The cooling ability.

Max Speed

The faster the alternator spins, the more power it will make. Therefore, one way a manufacturer can make an alternatorproduce more power is to build it in such a way that it is capable of being spun faster. Methods to do this may includestronger rotating parts like the rotor and larger / better bearings. Most alternators are advertised or sold with a performancerating that is actually the maximum possible output which of course occurs at the maximum permissible RPM. For thisreason, not all identically rated alternators are equal. In fact, in order to properly compare alternators, you really need thealternator's performance curve which is a graph of the alternator's output vs. its rpm. Such a curve would look somethinglike this:

For must users, the shape of the curve is just as important as its peak value. The curve pictured above is actually a verygood one - it shows the alternator putting out 40 amps at idle, rising quickly to almost 140 amps at 3000 alternator RPM(about 1000 engine RPM), then levelling off. It shows us that this alternator makes good idle power, quickly comes up tonear-max output, and doesn't need to be driven ludicrously fast to produce near-maximum output.

Tip: When shopping for a performance alternator, always ask to see the performance curve. Be wary if thecompany will not or cannot produce it for you.

Idle Performance

For most of us, idle performance is more important than max output rating. That's because, just like the engine'sperformance, we don't spend a lot of time at max rpm. A useful, driveable engine require low rpm torque as much as maxrpm horsepower. Similarly, the most useful alternator is one that produces good output down low - not only because wespend more time at lower rpm, but also because it's often when we're at or near idle that we consume the most electricalpower - with the air con on, the stereo pumping, and the electric fans on full to keep the engine cool. You will rarely, if ever,see idle performance listed in an alternator's description - the adds always say things like "150 amp alternator". This isanother reason that the performance curve is so important. Without it, you may buy an alternator that puts out 150 amps at8000 rpm, but that drops like a stone below that - and it would be all but useless.

The Windings

When high-output alternators are built, it is chiefly the windings that are most upgraded over stock units of the same size.And most important of those is the stator windings. The quality of the copper, the method by which it is wound, and thesheer volume of the windings all play a role. And since copper is expensive, and winding alternators time consuming, theold adage applies - you get what you pay for. Of course, another thing to be wary off is extremely high-output ratedalternators in small cases. How could they fit the required windings in there?

Tip: I would be wary of alternators advertised as having 100% or more output than the stock units whose casethey are using. In other words, a 105 amp 10-SI, a 150 amp 12-SI, and a 250 amp CS-144 are all reasonable. But a200 amp 10-SI is not!

Regulator / Rectifier

Just as when building a HO engine you also need to upgrade cooling, fuel delivery, and ignition systems for long-lastingreliable performance, so also must you upgrade alternator components other than just stuffing the world's supply of copperwindings in the case. Chief candidates include the voltage regulator and rectifier. Rectifiers especially, being that they are"valves", are subject to wear and failure if not properly rated for the pressure (voltage) and flow (current) they will besubject too. Just as using a $2 plumbing valve in a high-pressure fueling system isn't smart, so using stock components ina beefed-up alternator invites failure.

Tip: Ask the manufacturer what and how they upgrade internal components other than the windings in their HOmodels.

Heat and Cooling

Once agin, just like a motor - the more power you make the more heat is created when doing so. Failure to deal with thisextra heat leads to malfunction, failure, and an early death (along with a waste of money). This is an area whereunscrupulous companies can take shortcuts and save a few bucks - but it's a disaster waiting to happen. The goodcompanies will be pleased to explain to you what cooling modifications and upgrades they make to deal with the extra heatof producing 150, 200, or more amps. And it's a LOT of heat. Recall that the formula for Watts (a measure of heat) iscurrent squared times resistance. Therefore if you produce more current (remember it is SQUARED!) you end upproducing a lot more heat - way more heat. For example, let's say we take a 100 amp alternator and rebuild it to produce150 amps - how much more heat would it make?

For the 100 amp alternator, let's assume 0.05 Ohm resistance in the stator windings, and a 15% loss as heat. Watts = A^2* Ohms. Therefore Watts = ((100*100)*15%) * 0.05 = 75 Watts of heat.

Now, let's use the same figures, but with an output of 200 amps. Watts = A^2 * Ohms. Watts = ((200*200)*15%) * 0.05 =300 Watts of heat! How much heat is 300 watts? A lot! For example, many small electric aux. heaters for cars are in the150-300 watt range!

So - we increased our electrical output by half (50%), BUT that resulted in a heat production increase of three times or300%!

Clearly - cooling and heat-handling capacity are crucial components of a good alternator upgrade.

Cooling upgrades to look for include things like:

Improved / larger fan design.Extra internal fans on the rotor.Larger / better quality heat sinks on internal components like the rectifier.Relocation of components like the rectifier from the hot inside to the cooler outside of the case.

Also, keep in mind that the fan on the front of an alternator is a "puller" fan (for the same reason puller fans are preferredon radiators - they're more efficient and move more air than pushers). This means it draws air through the vents in theback of the alternator, pulls it through the alternator internals, and exhausts the hot air out the front.

This means, of course, that where you mount your new HO alternator is also very important. You don't want the air intakeson the back to be right beside a hot exhaust manifold, for example. You also need to make sure that the air vents remainclear and unrestricted - especially after off-road use.

Pulley Size

We have already discussed the performance curve and how alternator output relates to rpm. It is very important tounderstand that this rpm is ALTERNATOR rpm and not engine rpm. Typically (almost always, in fact) alternators are drivenby pulleys that are smaller than the crank pulley driving them. This produces an overdrive situation where the alternator isdriven faster than the engine that is driving it - much the same as an overdrive gear in a transmission or even on a bicycle.

The amount by which the difference in pulley sizes overdrives the alternator is known as the "pulley ratio" and is calculatedthe same way a gear ratio is. It is the ratio of the drive (crank) to driven (alternator) pulley sizes. The formula is:

crank pulley diameter / alternator pulley diameter = ratio.

Common alternator drive ratios are in the 3.0 range - meaning the alternator pulley is 1/3 the size of the crank pulley andtherefore the alternator is driven at 3 times the engine speed.

So, if we use a smaller pulley, we get greater alternator output per engine rpm. This is most noticeable at low engine rpmbecause alternator output tends to level off at alternator shaft rpm's above 3000 or so (depending on the unit, and inaccordance with the performance curve).

However, there is always a price to pay, and in this case we have to be careful not to use such a small pulley that at highengine rpm we exceed the alternator's maximum rpm. For example, it's no use installing a 3x overdrive pulley on analternator installed in a race car that runs all day at 7000 engine rpm - because the alternator will be spinning at 3 x 7000= 21,000 rpm!

Fortunately, race car's spend little time at idle and even when they do their electrical demands are low (no a/c, stereo,electric windows, etc.) so they can operate with high-ratio (low numerical) alternator pulleys.

If you're starting from scratch with determining pulley size, proceed as follows:

1. By calculation or measurement, determine the vehicle's total electrical load.2. Select a pulley size that will drive the alternator fast enough to generate 50% of this load at idle. You will need the

alternator's performance curve for this. For this example, let's assume we're using a 63 amp 10-SI alternator with thefollowing performance curve:

3. Proceed as follows:Determine pulley ratio as follows:

Look at the performance curve for the alternator. Enter the left side of the graph at the figure thatrepresents 50% of total electrical load, in amps.Go across until you hit the performance curve.Go down to read the required alternator rpm for 50% load.Divide required alternator rpm by engine idle rpm, the result is the required pulley ratio.

Example: Max load = 60 amps, 50% load = 30 amps.Alternator is 10-SI - 30 amps equals 2000 alternator rpmEngine idle = 800 rpm2000 alternator rpm / 800 engine rpm = pulley ratio of 2.5

Determine Pulley size as follows:Divide engine's crank pulley diameter by the pulley ratio determined above.Example: [9" / 2.5 = 3.6" (3-5/8")] generator pulley diameter.

4. Match alternator pulley bore diameter with alternator shaft diameter.5. Match alternator pulley belt width, number of grooves, and groove spacing to the engine crank pulley.

To check for alternator over-speed:

Multiply max engine rpm by the pulley ratio to determine max alternator rotor rpm. The optimum rotor speed isapproximately 6500 rpm, however, speeds up to about 12-18,000 rpm will not damage the alternator (checkalternator specifications).

To determine alternator output at engine idle:

Multiply the engine idle rpm times the pulley ratio to determine the alternator rpm, and refer to the alternatorperformance curve.

To determine maximum alternator output (max charge rate):

Multiply the normal engine operating rpm by the pulley ratio to determine the alternator rpm and refer to the alternatorperformance curve.

Of course, selecting or changing the pulley size is an exercise in compromise. Because your engine will likely run slowly attimes, and rev very high at other times, there is no “perfect” pulley drive ratio for all applications.

Improving Output at Idle Speed

In most cases, an alternator's weakest performance is at idle. In fact, normal alternator output at idle is commonly only 40-50% of rated alternator output.

Even without changing the alternator, idle performance can normally be improved by selecting a different (smaller) pulleythat multiplies engine RPM by a greater factor, thus increasing the alternator shaft rpm and therefore alternator output. Ofcourse, you must make sure you don't overspeed the alternator at high rpm, as described above.

Probably the best way to improve idle performance is by upgrading the alternator, even if you don't need a highermaximum output. Newer design and larger alternators will have better performance curves, cool better, and are able toproduce a larger percentage of their rated output over a wider range of RPM and for longer periods of time withoutsuffering damage. Once again - your best friend is the performance curve for determining what is right for your needs.

Failure Modes

So what can go wrong with an alternator? Fortunately, not very much, as they are pretty simple and rugged devices.However, they do operate in a pretty harsh environment, are subject to a lot of heat, and don't last forever. This is a list ofsome of the most common things that can go wrong.

1) Wiring

Often a problem that seems like it might be the alternator isn't the alternator at all. Fortunately, there aren't a whole lot ofwires to go wrong, but they should always be your first check. Make sure all connections are clean and tight; make surethat there are no short circuits or open circuits in the wiring (never run an alternator with the output terminal in an open-circuit condition, by the way); and make sure the wires are not crimped, pinched, frayed, tight, or otherwise in distress. Also make sure the connections between the alternator case, mounting brackets, and engine block/head are clean,corrosion free, and tight. Don't forget to check fuses, circuit breakers, and fuseable links!

2) Belt

Another major culprit is also not the alternator, but the drive belt. Make sure it is clean, not worn or frayed, free from glaze,appropriately tensioned and not slipping, jumping, or jamming, particularly at high engine rpm. Check to make sure there issufficient engagement between the belt and pulleys and modify belt routing / pulley arrangement as required.

3) Bearings

As we know, the rotor spins at very high rpm within the case, and is supported by at least two bearings - normallysealed needle bearings. Heat, time, and harsh conditions such as mud, water, and dust will eventually bring the bearingsto the end of their useful service life. This will most often show up as a grinding or squealing noise. To make sure that thenoise is in fact the alternator bearings (and not some other bearing like an idler pulley), disconnect the alternator drive beltand turn the alternator pulley by hand listening for any noise and feeling for any roughness or harshness. Also check forendplay and sideplay in the pulley. Be aware that it is also possible for the bearings to seem OK by hand, but to be noisywhen subjected to the load of the drive belt, so watch out for that. Fortunately most alternator bearings are availableseparately or in rebuild kits and they are fairly easy to R&R.

4) Windings.

The windings take a real electro-magnetic beating. Over time they can break down, short out, or open-circuit. The statorwindings are most often the culprit with bad windings. Because each of the three phases in the stator has its own separatewindings it is possible for the alternator to still operate, albeit at much reduced output, with one or even two sets of badwindings. This may be the case if it operates but output is low. Of course, if the rotor windings are bad, the alternator willnot operate.

5) The Electrical Bits Inside

The other internal parts are also subject to wear, thermal breakdown, and have a finite life.

Chief culprits include the brushes, the voltage regulator, and especially the rectifier. Over time and with use, the diodes inthe rectifier weaken and don't work as efficiently as they used to - especially when hot. Eventually they can stop workingaltogether. One possible tell-tale sign of a rectifier on the way out is an alternator that works well when cold, but whoseoutput weakens as it gets hotter and/or electrical demands increase.

Troubleshooting

Sadly, these days we live in a discard-and-replace world. Nobody fixes anything anymore. Cheap offshore manufacturinghas just made it cheaper and much more convenient to junk a suspected bad part and replace it. To be honest - this isn'talways a bad thing - the availability and reasonable price of remanufactures alternators make this a pretty valid option - IFyou are sure the alternator is bad. The possible exception may be the SI-series alternators that are very rebuild friendly.

Of course, we should probably still be able to do a little troubleshooting, as often times an electrical or charging systemproblems shows up and we are not sure whether it is the battery, alternator, starter motor, solenoids, wiring, relays, fuses,etc. etc.

Following is one approach to help narrow down whether the alternator is bad:

Eliminate the simple/obvious/unrelated

1. Check the belts and wiring.

2. Check that the battery is in good condition and has a good charge. It is damn near impossible to do any reliableelectrical troubleshooting with a bad battery installed. Check the voltage across the battery terminals with the engineoff. If voltage is:

> 12.6 – Battery is good

>11.9 & < 12.6 – Battery needs to be charged before proceeding

<11.9 – Battery is no good. You can try and bring it back to life and charge it, but especially if it has fallen belowabout 10 volts, it is probably toast.

3. Check that the source of your trouble isn't something dumb like lights or radio left on.

Check Alternator Warning Lamp Operation

1. Check each of the conditions in the following table:

Withthe

ignitionswitch:

Andthe

engine:

Thelampis:

Condition Possible Cause Corrective Action

OFF OFF OFF OK

OFF OFF ON Voltage across the lampwhen there shouldn't be.

Short between lamp wire andvoltage sense wire

OR

Bad rectifier

Unplug wiring from alternator - iflamp goes out, it is likely one ofthe positive diodes in the rectifieris shorted and the rectifier istherefore bad.

If lamp stays on, find and correctsource of voltage to lamp (short).

ON OFF ON OK

ON OFF OFF Lack of voltage acrosslamp

Open circuit condition in thelamp circuit.

Check for a blown fuse, a burnedout bulb, defective bulb socket,an open in the circuit betweenthe ignition switch / relay and thealternator (#1, L, I terminals), orshorted diode.

ON ON OFF OK

ON ON ON

Either the alternatoroutput voltage is lowerthan the battery voltage,or the battery voltage islower than the alternatoroutput voltage

If the light gets dimmer asyou rev up the engine, thenyou most likely have aproblem with the alternator. Ifit gets brighter, then thebattery is most likely bad

If battery is suspected -recharge / repair / replace asnecessary and re-test.

If alternator is suspected eitherrepair / replace alternator orproceed to voltage checks toconfirm.

Perform Voltage Checks

With engine running and all electrical accessories on, rev to 1500 engine rpm and measure voltage at alternator, mainelectrical junction, and battery. They should all be 13.8 – 14.5V.

If voltage is lower either alternator is weak, wiring is bad (too long, too small), or electrical demands exceedalternator rated output.

If voltage is higher than this, alternator operation is not being properly regulated - suspect the remote voltagesense circuit and/or the voltage regulator.

With engine running check voltage at battery - should be 13.8 – 14.5V (anything above 15.5V means battery is over-charging (dangerously!). Anything below 12.7V means the battery is not charging.

If battery is overcharging suspect the remote voltage sense circuit and/or the voltage regulator.

If battery is not charging, suspect the voltage regulator, the battery itself, or the connection between alternatorand battery. To narrow it down:

Check the battery - have it professionally load tested if necessary (didn't I already tell you to makesure the battery was good?!)

Check voltage at alternator output (BATT) terminal – if more than 0.4v greater than voltage atbattery, connection between alternator and battery is poor. If not, alternator output is low - suspectfield current supply, voltage regulator, windings, or rectifier (i.e. alternator is bad) - continue voltagechecks below.

Check field current. With ignition on / engine off, check with a voltmeter for ~12 volts at the field (exciter) wire at thealternator. (terminal 1, L, and/or I).

An alternate way to check for field current is to check and see if the rotor is an electromagnet. Hold alightweight ferrous metal object (like a hacksaw blade) close to the side of the alternator with the ignition switchon. If there is a field current present then the metal object will be magnetically attracted to the side of thealternator, not very strongly, but you can feel it.

Eliminate the voltage regulator as the problem by bypassing it. If your alternator has a "full field" capability you can use itto bypass the voltage regulator and supply full field voltage to the rotor. There are various ways of doing this depending onthe alternator. SI=series alternators have a regulator by-pass test hole in the back, on Mopar alternators you typically

jumper the field terminal (look for the green wire) to ground, on Ford alternators you normally connect the BAT and FLDterminals. In the case of an SI-series alternator, insert a screwdriver into the test hole until it touches the metal tab, thentouch the side of the screwdriver to the case, grounding the tab. If when you "full-field" the alternator output improves to"full voltage" (13.8 – 14.5 VDC is now read at the BATT terminal) the voltage regulator is faulty. If not, the alternator(windings / rectifier, etc.) are faulty.

Additional Checks for CS-series, 4-terminal Alternators

With ignition switch on and engine stopped, lamp should be on. If not, detach harness at alternator, use fused jumper toground "L" terminal lead on harness. Be very carefully to properly identify "L" terminal lead. Grounding "L" terminal shouldcause indicator lamp to light. If lamp does not light, locate open circuit between grounding lead and ignition switch. Bulbmay be bad.

With ignition switch on, engine running at moderate speed, lamp should be off. If not, stop engine, turn ignition switch backon, and detach wiring harness at alternator:

If light goes off, replace or repair alternator.

If light stays on, check for grounded "L" terminal wire in harness.

With engine running check voltage at battery - should be 13.8 – 14.5 volts (anything above 15.5VDC means battery isover-charging (dangerously!). Anything below 12.7VDC means the battery is not charging.

Detach wiring harness connector from alternator.

With ignition switch on, engine not running, connect voltmeter from ground to "L" terminal in wiringharness, and to "I" terminal, if used. Wiring harness may connect to either "L" or "I" or both.

A reading of 0V indicates open or grounded circuit between terminal and battery. Correctas required.

Re-connect harness connector to alternator, run engine at moderate speed with all electrical accessoriesturned off.

Measure voltage across battery. If above 16.0, replace or repair alternator. NOTICE: The alternatormay be O.K. on vehicles using "S" terminal if "S" terminal wiring has excessive resistance which willcause high voltage. Refer to vehicle wiring diagram. Correct wiring as needed, then re-checkvoltage.

Connect ammeter at alternator output terminal. Connect voltmeter across alternator. Turn on accessories. loadbattery with carbon pile to obtain maximum amperes output. Maintain voltage at 13.0 or above.

If within 15 amperes of rated output, alternator is O.K.

If not within 15 amperes of rated output. Check belt for slippage or replace or repair alternator.

Additional Data

The following links, documents, spec sheets, and catalogues provide an additional wealth of information about alternators.They can be very useful when trying to identify an alternator, choose an upgrade or replacement, identify specificspecifications, learn more about disassembling and repairing alternators, etc.

They are provided here for your information, learning, and convenience. VERY IMPORTANT - do not call up amanufacturer and quote prices you found here - by the time you are reading this it is highly likely that the catalogues areout of date. If you do, it ticks of the companies and they write me angry letters demanding I remove the offendingdocuments and then you loose your convenient central data source. This is no joking matter - people do it and I do getangry letters - which ticks me off too. If you need current information - like pricing - just go to the manufacturer's websiteand find the latest catalogues or online data.

PDF Documents:

Exploded Diagrams of Delco-Remy Model Alternators:

DR-10SI.pdf DR-27SI_100.pdf DR-CS121.pdfDR-12SI.pdf DR-27SI_200.pdf DR-CS121D.pdf

DR-15SI.pdf DR-29SI.pdf DR-CS130.pdf

DR-17SI.pdf DR-30SI.pdf DR-CS130D.pdfDR-20SI.pdf DR-33_34SI.pdf DR-CS144_Early.pdfDR-21SI.pdf DR-AD230.pdf DR-CS144_Late.pdfDR-22SI.pdf DR-AD237.pdf DR-25SI.pdf DR-AD244.pdf

Other Data:

Bosch Charging Systems Datasheet

Delco-Remy Alternator Identification Guide

Delco_Remy CS-144 Reassembly Instructions

Delco-Remy Diagnostic Procedures Manual

Delco-Remy Electrical Specifications & Selection Guide - Starters and Alternators

Delco-Remy Quick Reference and Cross Reference Guide - Starters & Alternators

Delco-Remy 10SI, 12SI & 15SI ALTERNATOR INSTALLATION INSTRUCTIONS

Powermaster INSTRUCTION SHEET - GM CS Series Performance Alternators

Powermaster Alternator Application Guide

Powermaster Catalog

Powermaster INSTALLATION INSTRUCTIONS - Alternators

Links:

http://parts-catalog.acdelco.com/catalog/catalog_search.php

http://www.delcoremy.com/Alternator/Literature.aspx

http://www.madelectrical.com/electrical-tech.shtml

http://www.alternatorparts.com/

http://www.alternatorparts.com/repair_manuals/10si-15si-type-116-136-repair-manual-contents.html

http://www.alternatorparts.com/CS144_alternator_repair_video.htm

http://www.powermastermotorsports.com/index.html

http://www.autoshop101.com/trainmodules/alternator/alt101.html

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