Hi-Perf Van de Graaff

7/31/2019 Hi-Perf Van de Graaff

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Fig. 1 - Van de Graaff electrostatic generator showingtheoretical charge distribution.

Motor

Brush


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HIGH PER FORMANCE

VAN DE GRAAFF GENE RATORS

Van de Gr aa ff Gener at ors a re a mu st for an y science museu m, ph ysics class room, or

experimen ter s lab. The genera tors produce high voltage electr osta tic char ges for ent ert ainin g

demonstrations of electrostatic induction, attraction and repulsion, spark discharge, capacitance,

and more.

Un like the Tesla Coil, which pr oduces a cont inuous

barr age of loud, writhing spar ks, the Van de Graa ff

Gener at or quietly builds up a d.c. cha rge on its

met al spher e, or collector, over severa l seconds. The

cha rge can then be drawn t o an electrode in the

form of a lightn ing-like spar k or us ed in a variet y of

experiments.

Since the generators collector can only hold a very

limited char ge, even at a very high voltage, th e

amount of energy the generator can deliver is small.

Except for the very large machines, Van de Graaff

Generat ors a re genera lly quite safe.

Triboelectr ic, or friction, Van de Gr aa ff Gener at ors

comm only found in class rooms an d science m use-

um s can per form quite well under good conditions.

However, when the hum idity of the surr ounding

at mospher e increa ses, th e machines perform an ce

will ra pidly degra de, or th ey will cease to work

altogether.

This manual will show design and construction

techniques for Van de Graa ff Genera tors th at will

deliver good outp ut even u nder conditions of high

hu midity, an d which will deliver sup erior perfor-

mance when conditions are favorable.

Detailed plans for a small (4' tall) Van de Graaff Generator are included, as well as design param-

eters that will allow the builder to construct a generator of virtually any size.

HISTORY

The Van de Graa ff Genera tor was invented in th e Pr inceton University labs a round 1929 by Robert

J . Van de Graa ff. He ha d used Wimshur st m achines to genera te positive ions for experiments, but

realized th at he needed far higher potentials.

Aroun d 1933, while at M.I.T., he const ru cted his gian t twin gener at or (Fig. 3-D) in a dirigible

ha ngar in Da rtsm outh , Massachussett s. Another lar ge generat or, built by Van de Graa ff in 1931, is

now housed in t he Boston Museu m of Science, wher e it is u sed for daily shows.

Fig. 2 - This science-show Van de Graaff Genera-tor can deliver a spark over 48" long. The gen-erator is 10' tall and has a 42" diameter collector.The author constructed the machine in 1988 forThe Science Place museum in Dallas, Texas.


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Supp osedly, th e first electr ical gener at or wa s a device const ru cted by Otto Von Gu ericke in th e 17th

centur y in Germa ny. His genera tor was simply a ball of sulphu r on a stick. When th e ball was

rotated a nd a han d or leather pad was brought into conta ct with it, the friction creat ed sta tic elec-

tricity.

Lat er ma chines used rota ting glass cylinders (Fig. 3-A), th en rotat ing glass disks. Man y perm ut a-

tions of th e basic friction m achine occurr ed as experim ent ers t ried to increase th e voltages a nd

cur rent s their appa ra tus could produce.

Electrosta tic devices usin g belts t o car ry char ges ma y ha ve existed pr ior t o Van de Gra affs genera -

tor, but he is th e one who deser ves credit for first developing lar ge, effective ma chines for serious

research into nuclear physics.

Van de Gra aff Genera tors a re st ill used t oday to provide ion sour ces for n uclear a ccelerat ors an d, in

some cases, to serve as th e principal accelerat or. These genera tors ar e housed in pressu rized, gas-

filled tanks to allow higher voltages than could be achieved at normal atmospheric pressure.

Fig. 3 - (A) Eighteenth century electrostatic generator consisted of a rotating glass sphere charged byfriction between a hand and the glass. (B) J ames Wimshurst invented his famous electrostatic generatoraround 1880. A crank turns two contra-rotating disks having metal sectors. (C) This large Holst generatorcould produce 30-inch discharges. (D) Robert Van de Graaff built his giant "twin" generators around 1933.The collectors were 15' in diameter; insulating columns were 24' high and 6' in diameter. They were housed

in a dirigible hangar. (FromThe Electrical Experimenter, 1915, The Burndy Library, andThe ScientificAmerican, 1934.)

BA

C D


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THEORY OF OP ERATION

Classical explanations of Van de Graaff Generator operation usually state that electrical charges

ar e deposited on a moving belt, and t hat the belt t ra nsports th e charges to a m etal Collector where

th ey ar e picked off and ar ra nge t hem selves on th e Collectors su rface (Fig.1).

The following theories elaborate a bit further and are based on the author's experience.

F r i c t io n E x c it e d Va n d e G r a a ff G e n e r a t o r s

The friction Van de Gra aff Gener at ors are th e simplest to const ru ct. They rely on a char ge being

creat ed when two dissimilar tr iboelectric mat erials ar e brought int o conta ct an d t hen separa ted; for

examp le, a ru bber belt a nd a plast ic pulley (Fig. 4-A).

At the m omen t of separ at ion, electr ons ar e rem oved from t he su rface of the pulley and deposited on

th e belt's inside sur face. This negat ive char ge at tr acts positive ions a nd repels electr ons. A row of

sha rp, condu cting points, called a bru sh, point s at th e outside sur face of th e belt at th e region of

separ at ion. The bru sh facilitat es forma tion of positive ions because it is groun ded, providing a

pat h for repelled negat ive ions (rush ing from t he vicinity of th e belt's out side sur face) to unloadth eir excess electr ons. Positive ions a re th ereby spra yed ont o th e belt's out er su rface.

The positive ions a re h ighly mobile an d probably flow thr ough the a ir an d ar oun d th e belt's surface

to neut ra lize the n egative cha rge on t he inside of th e belt. The resu lt probably resem bles a "cloud"

of loosely boun d positive ions t ra veling on an d ar ound t he belt, with t he den ser cha rge on th e out -

side belt sur face.

The belt tr avels upwar d, car rying th is positive "cloud" into the Collector. When t he belt enter s th e

Collector, a br ush inside th e Collector "sucks" electr ons from t he Collector t o neutr alize the ions. A

Fig. 4 - Theoretical charge distribution between belt and lower pulley of friction

and externally excited Van de Graaff generators.


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Collector

ConductingPulley

BrushConductingPulley

Plastic Pulley Covered

With Vinyl Tape

Brush

Brushes

Belt Belt

Conducting

Pulley

Brush

Brush

H.V. PowerSupply

BA

Fig. 5 - Recommended Brush/Pulley combinations for friction (A) and

externally-excited (B) machines.

positive cha rge t her eby builds on t he Collector's sur face. Even t hough t he volta ge on t he Collectorclimbs to many times that of the belt, the charge continues to build because the density of the

char ge is lower on th e Collector.

As the belt leaves th e Collector, it obviously car ries a lower positive char ge tha n wh en it en ter ed.

Convent iona l depictions of Van de Gra aff Gener at or cha rge distr ibution usu ally show a n egative

cha rge on t he belt as it leaves the Collector. My measur ements show that the char ge is positive

with r espect to groun d, and I 've indicat ed th is in Fig. 4.

When th e belt a pproaches t he bottom pu lley, the t riboelectric effects ar e sufficiently str ong to place

a t empora ry negat ive char ge on t he inside of th e belt, so th e cha rging process cont inues.

One pulley should be mad e of a condu cting mat erial, like alum inum . The other (friction) pulley

should be ma de of a good insula ting ma ter ial, like Plexiglas. The Collector bru sh in friction m a-

chines seems to work best wh en placed near t he center of th e pulley. I don't ha ve a theory to ex-

plain why.

Collector polarity is determined by the materials used and whether the friction pulley is at the top

or the bott om. For examp le: A comm on combina tion is a belt made of ru bber an d a pulley wra pped

with vinyl tape. If the pulley is in th e top of th e genera tor, th e Collector will be cha rged negat ively;

if it is in the bottom, it will charge positively.


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E x t e r n a l E x c it a t i o n

Exter na lly excited ma chines use a h igh volta ge power supp ly to spra y ions ont o th e belt. Becau se

tr iboelectr ic effects can hinder th e char ge tra nsfer, both pulleys should be made of conducting

material .

If th e power su pply voltage is p ositive, positive ions will be form ed by th e lower br ush es a nd

spra yed ont o th e belt (Fig. 4-B). A negat ive char ge is supplied by th e groun ded pulley. The nega-tive cha rge a tt ra cts th e positive ions, leaving a positive cha rge on th e out side sur face of the belt.

When the belt and pulley separate, positive charges migrate to the inside surface of the belt, cancel-

ling the negative charge residing there, as they do in the friction machine.

Somewhat mysteriously, performance is enhanced by the addition of a second brush placed at about

the pulley's 230 degree ma rk. Perh aps t his ar ra ngement works because th is second, or "auxiliary"

brush cau ses a denser char ge on t he belt, producing a denser cloud of ions when the belt separ at es

from t he pu lley.

As the belt ent ers th e Collector, a bru sh p icks off the positive ions, bu ilding a positive cha rge on th e

sur face of th e Collector. The au th or's experiment s have shown tha t a second bru sh, located opposite

th e first , on t he down side of th e belt, impr oves perform an ce. For some reas on, a bru sh located in

th e cent er of th e pulley gives poor perform an ce. Usu ally, perform an ce is slightly enha nced if th e

upper pulley mak es electr ical cont act with th e Collector.

FACTORS AFFE CTING PE RF ORMANCE

COLLECTORS

The t heoretical ma ximum voltage t he Collector can develop is 70,000 times it s ra dius in inches.

However, allowan ce mu st be ma de for the hole th rough which the belt tra vels. The "avera ge" ma -chine will lose ar ound 20% of its ma ximum p oten tial to this ent ra nce hole. A genera tor with a 12"

diam eter spher e would th en develop app roxima tely 336,000 volts u nder good conditions.

A smooth Collector sur face is essent ial, but p olishing to a m irror finish h elps very little (some s ay a s

little as 1% voltage increase). The most importa nt consider at ions a re th at t he Collector be clean,

ha ve no shar p protruding edges, and t hat the en tr ance hole be properly radiused.

The Collector en tr an ce hole edge ra dius sh ould be gener ous; about 8% to 10% of the Collector's

ra dius (Fig. 6). A 12" diam eter Collector, for insta nce, should ha ve an en tr an ce hole with a n edge

ra dius no smaller tha n 1/2".

Severa l differen t sha pes can be used successfully. The au th or has experiment ed with sh apes A, B,

an d C, in Fig. 6. Wheth er a sph ere or "spher oid" is used, leaka ge along th e column appea rs t o be

addit iona lly redu ced if the bottom of the Collector is slightly flat ten ed (Fig. B & D). Oth erwise, a

plain sphere is hard to beat .

The diameter of the entr an ce hole should be no larger th an ar ound one-half the diam eter of the

Collector. En tr an ce holes sma ller tha n one third t he diam eter of th e Collector will limit the belt

size too much. A wide belt a llows th e char ge to build more r apidly and redu ces th e effects of leak -

age.


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Fig. 6 - Cross sections of various Collector

shapes showing radiused support column en-

trance holes.

Fig. 7 - Removable sphere halves with attach-

ment lip rolled on lower half.

Sometimes it is desira ble that the t op of the sphere be detachable. In t his case, any lip or a tta ch-

ments should be on the inside, so the sphere retains a smooth surface (Fig. 7).

A removable hem isphere allows for a slight ly wider belt t o be used, which is good for perform an ce.

However, if portability is important, it's usually much more convenient to use a permanently as-

sembled sphere that slips easily on and off the support column.

Most Collectors a re m ade of spun alum inum hem ispheres (see Appendix for sources). If the twoha lves are to be perman ently atta ched, they

can be epoxied or welded together . The seam

mu st be san ded smooth and polished.

Inexpens ive Collectors can sometimes be

fashioned from alum inum or stainless steel

sala d bowls or somet hing similar. Lips,

ha ndles, or other protr usions will need to be

removed an d th e sur face sanded a nd polished

smooth.

Techn iques for han d-finishing alum inum or

stainless steel hemispheres, including cutting

an d radiusing the column ent ra nce hole, ar e

covered in th e const ru ction section.

BELTS

Belts can be ma de of a var iety of ma ter ials,

but I recomm end gum ru bber. Neoprene

serves very well but lacks "memory," th at is,

it tends to stretch an d not snap back as wellas gum ru bber. Latex rubber works fine, but

is mu ch m ore expensive.

I've never t ried silk or n ylon, alth ough t hey're

supposed to work fairly well. They're prob-

ably not worth t he tr ouble, as t hey tend t o

fray and have little elasticity.

The belt sh ould be a s wide as possible, as

greater width means the Collector will charge

faster . The belt/pulley combina tion mu st be

chosen car efully so th e belt fits inside th ecolumn with adequat e cleara nce.

Chemical engineer F ra nklin B. Lee, who

experiment ed with Van de Gra aff Genera-

tors, wrote that 50 square inches of belt per

second p assin g over t he pu lleys produces one

microamper e cur ren t delivered to the Collec-


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tor. This finding seems to agr ee fair ly well with my own mea sur emen ts. Maybe this is some sort of

"un iversa l consta nt " for Van d e Gra aff ma chines.

The belt should be fairly tight. A ru le of th um b for gum r ubber belts 1/8" th ick an d from one to

thr ee inches in width is tha t t he belt should be approxi-

ma tely thr ee inches shorter tha n th e distan ce between

th e pulleys. Belts up to eight inches wide should be about

six inches shorter.

I suppose elasticity could vary from manufacturer to

ma nufacturer , so you m ay want to use th e highly scien-

tific method I used to determine the proper belt length...I

went to the r ubber supply compan y, stret ched th e ma te-

rial out by hand and said, "Ok, this is about right!"

If you want to build a horizont al Van de Gr aa ff, as sh own

in F ig. 8, you'll need the belt t o be extra tight to redu ce

sagging.

The belt should be as clean as possible. You can cur l it

up an d wash it in a bucket with dish washing detergent,

then rinse well and str etch it out in a clean a rea t o dry.

Gum and latex ru bber belts will eventua lly deteriora te

from th e effects of ozone an d exposu re t o light. Expect a

heavily used gum ru bber belt to last a bout 2 1/2 years.

Latex belts m ay only last a year.

PULLEYS

Aluminum is the preferr ed ma terial for conducting pul-

leys. Plastic pulleys can be made conducting by wrapping them with aluminu m t ape, but th e tape

will event ua lly wear out a nd need t o be replaced. Use ball bear ings with t he pulleys; th ey're not

expensive, and t hey're m uch better t ha n t he cheaper sleeve types.

Pu lleys should ha ve a crown 1/8" to 1/4" to help keep t he belt cent er ed (Fig 9-A). Alth ough a crown

is best, an altern at ive for sm all genera tors is to wra p th e pulleys in t he center with several tur ns of

ta pe (Fig. 9-B). Use alu minu m t ape on th e conducting pulley, plast ic ta pe on t he friction pulley.

Non-conducting pu lleys for friction-excited m achines can be m ade from Plexiglas, n ylon, U HMW

plast ic, or an y oth er serviceable plast ic. Differen t p lastics will give differen t levels of perform an ce,

but I've found very little experiment al compa rison data . UH MW, which is similar to nylon, butcheaper an d easier to machine, works well with gum r ubber. Other experimenters h ave tried poly-

eth ylene with su ccess. Vinyl ta pe wrapp ed on th e pulley sur face work s very well with ru bber belts.

A good combin at ion for sm all friction m achin es would be: A friction pu lley ma de of Plexiglas

wrapped with vinyl tape, and a conducting pulley made of aluminum or Plexiglas wrapped with

aluminum tape.

Pulley diameter isn't critical, but it's necessary to compromise between a very small diameter,

Fig. 8 - A horizontal Van de Graaff genera-tor the author constructed for a companyinvestigating effects of static electricity on

aircraft components.


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Crown

Pulley tapered1/8" to 1/4"

Shaft

Tape

A

B

Fi g . 9 - To keep b e l t fr om wa nd e r i n g , t h e pu l leys

s hou l d have a c r own (A) o r be t a ped (B).

which would allow for a wider belt, an d a la rger dia met er, which would allow smooth er r un ning a nd

less stress on t he belt and bearings.

A "ru le of thu mb" is th at th e pulley diam eter should be about 33% to 42% of the inside diam eter of

the column.

B E L T SP E E D

The higher the belt speed, the faster the charge buildup on the Collector, and the less susceptible

the ma chine will be to cur rent leakage.

However, m ost of th e ma chines I ha ve built opera te a t a very conservat ive speed; one belt r evolution

per second for la rge m achines (10' tall) an d two revolutions per s econd for ma chines up t o five feet

ta ll. Higher speeds can sometim es cau se the belt to wan der an d pull awa y from th e pulleys. Lower

speeds ma y not supply cha rge fast en ough t o compen sat e for leak age, lowering perform an ce.

B R U S H E S

Somewhere, t her e's a per fect design for

bru shes. I've tr ied bra ss window screen, bra ss

stock cut into a series of points, "whiskers" of

copper wir e, and double bru sh es (Fig 10). All of

these appr oaches seem to work a bout the sa me.

All tha t seem s to be required is a r ow of shar p,

condu cting points placed at th e corr ect location

and distan ce from the belt. If ther e are better

designs, I ha ven't found them .

Fr om a pra ctical sta ndpoint, I like to use brassscreen or copper wire whiskers. Bra ss stock

can da ma ge the belt, and t here seems to be no

advant age to using thick or mu ltiple brush es

per location.

BRUSH P LACEMENT

Corr ect p ositioning of the br ush es is critical t o

per form an ce (Fig. 5 - A&B). Brus h locat ions

for friction machines are "standard" and well

known. However, ther e's a dear th of inform a-

tion a bout externally excited machines, and I h ad t o experiment quite a bit to arr ive at the a rr an ge-

ment in Figure 5 - B. More elabora te ar ra ngements h ave appeared in various publicat ions, but I've

ha d no particular success with t hem.

The precise alignm ent of the br ushes m ust be determined experiment ally, as belt and pulley mat eri-

als, motor speed, and oth er var iables (such a s proximity of lower pu lley to groun d) can alter th e

optimum locations. It's a good idea to leave plent y of space to experimen t with bru sh positions

when designing a generator.


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Fig. 10 - Three effective brush styles. Brass window screen iseasy to work with; brass sheet can damage the belt; copperwhiskers are very adjustable but more difficult to manage.

A simple analog microammeter can help tremendously when experimenting with brush locations.

Connect the met er between the Collector and ground and m onitor the curr ent. Maximu m current

indicat es optimu m br ush positioning. About one m icroam pere per 50 squa re inches/second of belt

tr avel should be developed. Don't u se a digita l or electr onic meter! The high voltage will ruin t he

instru ment very quickly.

The belt is sur prisingly efficient in tr an sporting its char ge, once th e correct bru sh locat ions a re

foun d. You can check th is out sim ply by ta king a cur ren t rea ding between the power supply an dthe lower bru shes an d th en between the Collector an d ground. If the system is working well, ther e

will be very little differen ce in t he t wo readings.

SUPP ORT COLUMN

PVC, Plexiglas, and fiberglass ar e excellent ma ter ials for the support column . PVC is the cheapest .

It is str ong, easily ma chined, an d comes in ma ny sizes. Plexiglas, alth ough it's expensive and

somewhat fra gile, is th e preferr ed mat erial for small to medium size machines. Plexiglas ha s

excellent electr ical pr opert ies and is clear. Plexiglas cylinders ar e usu ally sold in six foot lengths.

Fiberglass is strong and light, but it can be expensive, and it's doubtful that the correct size andfinish can be found. Pa per cylinders a nd m ost phenolics will allow far too mu ch leaka ge.

The distance between t he Collector an d th e base of the generator should be two or t hree t imes the

Collector diam eter . If the column is too close to the ba se, leak age an d spar king along the column 's

outer sur face will become a problem.

P O WE R S UP P L Y

Pr actical exciter volta ges ran ge from ar ound 5,000 to 15,000 for a ll but t he lar gest ma chines. The

giant Van de Gra aff Genera tor in the Boston Science Museum u ses 20,000 volts. The ma chines I

ha ve built, which ra nge from 4' ta ll to 15' long (horizont al), use a round 10,000 to 15,000 excitervolts.

One of th e simplest m ean s of obta ining th is voltage is to rectify the cur ren t from a 15,000 volt neon

sign tr an sform er (Fig. 11). If you're designing a fairly large genera tor, th e size an d weight of such a

tr an sform er will be negligible. A sma ller gener at or can use a sm aller, lower voltage neon sign

transformer and a voltage multiplier (Fig. 12).

The so-called "core a nd coil" neon sign tr an sform ers a re sm all, chea p, and fair ly light weight . These


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tr an sform ers a re usu ally ava ilable with outpu ts from 3,500 to 6,500 V. However, th e secondar y

midpoint ma y be grounded on some un its, which will cut th e usa ble volta ge in h alf. If th ere is no

midpoint ground, one leg of the seconda ry can be groun ded an d th e full voltage can be u sed.

Caution : If th e groun ded leg of a tr an sform er with no midpoint ground loses contact with earth

ground, it can d evelop ha lf of th e seconda ry voltage r at ing an d can cau se a d an gerous shock if

touched. For safety, add a 500 k to one megohm resistor in series with th e out put . (Oddly, th egenerators seem t o work a little better with little or n o resistan ce in series, even t hough the curr ent

deman d is in t he microam p ra nge).

Anoth er a pproach is to build a power supp ly consisting of a television flyback tr an sform er or a ut o-

mobile ignit ion coil, oscillat or, an d rect ifier (Fig. 12). It 's difficult to just ify th e cons tr uction effort

requ ired for t hese designs, however, because th ey provide only minima l savings in weight an d cost,

if any.

Although I've never tried it, a personal

defense "zapper " might be convert ed int o a

power supply. They're adver tized in maga-zines and sold in var ious gun stores. I'm

almost certa in that the output is DC. If not,

a high volta ge rectifier could ea sily be added.

The high voltage circuits mentioned above

prod uce d an gerous currents that can cau se

serious sh ock. If you're not experienced

working with high v oltage, find som eone to

help wh o is.

When you work on th e generator, unplug th e

ma chine an d short out the power supply torem ove an y residu al cha rge. If you use a

voltage m ultiplier, you m ay wish t o inst all a

500 meg., 1 watt bleeder resistor across the

output.

The power supply voltage sh ould be high en ough to form a faint corona on t he lower br ush es' points

when viewed in the dar k. No spark s should jump t o the lower pulley. Spark ing reduces the

ma chine's perform ance and can eventu ally dam age the belt. The dista nce between th e brushes an d

th e belt can var y from a roun d 1/8" to 1/2".

Five thousand volts will jump about 1/4"; 10 kV about 1/2", and 15 kV about 3/4".

The polarit y of th e su pply voltage will deter mine th e polarity of the Collector, i.e., a positive su pply

will pr oduce a positive Collector, a nd a negat ive supply will produce a negat ive Collector.

Fig. 11 - Neon sign transformer used as a high voltagepower supply for large Van de Graaff Generators.


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Page 13

Fig. 12 - Schematic for power supply using a typical neon sign trans-

former with secondary midpoint grounded to case. Transformers with

a secondary rated less than 12 kV will need a voltage multiplier.

Fig 13 - Cascade voltage tripler. Capacitors and rectifiers must have

a voltage rating twice the AC peak voltage. Capacitors typically

would be ceramic, 500 to 2,500 pF.

MOTORS

I prefer 1,725 or 3,450 rpm split phase motors or, for large generators, capacitor start motors.

Speed can be var ied by cha nging pulleys or by using a var iable speed pulley. Experim ent ers ma y

wan t t o use a n AC/DC motor so the speed can be ea sily varied over a wide ran ge. Once a good

operating speed is determined (see P. 10), there's rarely a need to vary it.

The 4' Van de Gra aff Genera tor described in th is man ua l uses a 1/6 h.p. split phase motor. The

large vertical ma chine pictur ed on P age 3 uses a 1 h.p. capacitor st ar t m otor, and t he h orizonta l Van

de Gra aff (Fig. 8), becau se of its wide, tight belt, uses a 2 h.p. capa citor st ar t m otor.


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Pa ge 14

The h igh voltage power su pply in F ig. 14 consist s of an au to ignition coil driven by an electr onic

circuit.

Power for th e circuit is provided by a 12 V. tr an sform er, full wave r ectifier, a nd filter capacitor (C1).

A 555 Timer IC produces positive pulses which switch th e power tr an sistor on a nd off. Ea ch time

the transistor conducts, current pulses through the ignition coil, causing high voltage to appear at

the coil's outpu t ter minal. The outpu t can be furt her increased with a voltage multiplier. The

ignition coil's outpu t is r egulated by R2 and R5, which cont rol pulse frequency an d power, respec-

tively.

Ignition coils requ ire experim ent al adjustm ent of R2 an d R5 for ma ximum voltage. Out put r an ges

from a round 4,000 to 10,000 volts, alth ough higher voltages m ight be pr oduced if one wer e to

stu mble across th e "perfect" coil an d design an impr oved pulse circuit. The au th or has us ed severa l

var ieties of inexpensive, comm on, r eplacement coils for brea ker-type ignitions, ea ch yielding a bout

the sam e voltage.

For m ore detailed inform at ion a bout using a ut o ignition coils and TV flyback tr an sform ers a s a h igh

voltage sour ce, see "Books an d Liter at ur e" in t he Appendix.

Fig. 14 - Ignition Coil High Voltage Supply. C1 = 1,000 to 2,000 mFd, 35 V; C2 = .01 mFd., 50 V; R1= 330 ohm, 1/4 W; R2 = 100 K; R3 = 100 K, 1/2 W; R4 = 100 ohm, 1/2W; R5 = 5K, 1/2W.


14/47

Page 15

MAINTENANCE

Dust, sha rp points, and hum idity ar e th e enemies of electr ostat ic generators.

Dust on th e Collector a nd column will ra pidly bleed off cha rge. Ha ir or lint can frequent ly become

lodged where th e support column ent ers t he Collector. If you can't see th e lint or du st, you can

probably hear it hissing a nd cra ckling a s it bleeds off char ge.

Avoid touching the column or belt. Ha nds a nd fingers leave oily acids tha t can r ender th e colum n

slightly conducting. Stubborn ha nd print s or dirt can be rem oved with dishwashing detergent, th en

by wiping the surface with rubbing alcohol on a lint-free rag (remember that Plexiglas scratches

easily). Do not use Windex or similar clean ers t ha t cont ain a mm onia or other electrolytes; they'll

leave a conducting film on t he column .

Sha rp pointed condu ctors in t he vicinity of th e genera tor will bleed away cha rge. Deep scra tches,

dings, or gouges on t he Collector su rface will prevent ma ximum char ge.

Hu midity will bleed off char ge along th e support column a nd th rough th e air. Hu midity also inter -

feres with char ge deposition on th e belt. Sometimes drying the belt and column with a ha ir dryer

helps r educe the effects of hu midity or moistur e. I've also tried placing moistur e-absorbing silica gel

in a porous cont ainer inside the ba se, but I'm n ot cert ain h ow effective this is.

PERFORMANCE SUMMARY

U se a ch a rge s pr a yer wit h an ou t pu t fr om 5 k V t o 15 k V. Adjus t sys tem to avoid spark ing between lower brushes and pu lley.

Use t he widest belt possible.

U se t he la rgest fea sible Collect or .

Use a h igh belt speed.

Mak e t h e d is tan ce bet ween th e Collect or an d base equ a l t o t wo or

thr ee times th e Collector diameter .

P rop er ly r adiu s t h e Collect or colu mn en t r ance h ole .

E xper im en t with br ush pla cem ent .

Keep Collector and column sur faces smooth and clean (do not use

Windex or clean ers cont ainin g electr olytes).

Avoid t ou ch in g colu mn an d belt .

Keep belt and pulleys clean.

Keep sh ar p poin ted con du ct or s a wa y.

Keep mois tu re con den sa t ion d own w it h h a ir d ryer if n eces sa ry.


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Pa ge 16

HOW TO BUILD A

4' VAN DE GR AAF F G E NE RATOR

Fig. 15 - 4' Van de Graaff Generator is de-

signed for classrooms and science shows.

Unit shown has a 12" dia. Collector.

The 4' ta ll Van de Gra aff Gener at or described on t he following pages can produce from 340,000 to

390,000 volts (depen ding up on the size Collector u sed) an d visible spar ks over a foot long. The

generator will provide enough charge for demonstr ations on hum id days, and is an outst an ding

perform er wh en conditions ar e good.

Virtually all of the high performance parameters set forth in the preceding pages are recognized in

its design. The ru gged, port able machine is perfect

for sm all science shows and classrooms. The

Collector slides easily on an d off the column , an d

the instru ment can be placed inside a road case forstorage or tr an sport .

COLLECTOR

The Collector cons ists of a 12" or 14" diameteralum inum flagpole sph ere (or flagpole "ball" in th e

tr ade vern acular ). The "ball" consists of two

hemispheres, the bottom h alf having a tur ned-in

lip over which th e top is placed. The 14" ball is

mu ch more expensive tha n t he 12", but it will yield

ar oun d 390,000 volts...50,000 more th an th esmaller diameter.

The support column entr ance hole is cut in th e

bottom hemisphere an d radiused by ha nd, and th e

two hemispheres are epoxied together.

The support column has a 5" O.D., so the radiused

hole will need to be about 5 3/16" in diam eter to

allow cleara nce.

Find th e center of the bottom hemisphere. Oneway to do this is to use a piece of #20 copper wire

and "guestimate" the distan ce from th e rim t o the

inside center. Run th e wire around the rim, ad-

just in g the wire un t il the correct lengt h is de ter -

mined.

Anoth er way is to mar k a 9 1/2" section on a length of wire an d ru n it from th e out side of th e hem i-

sphere t o the approxima te center. Run t he wire from severa l different locations around t he rim,


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Page 17

Fig. 16 - Scribe for marking column hole in bottom Collector

hemisphere.

ma rk ing each "center." A clust er of ma rk s will show the center. Once th e cent er is foun d, punch it

and drill a 1/4" hole.

Make a s cribe as follows: Cut a len gth of str aigh t wood 3/4" x 3" x 10" long. Drill two 1/4" holes

th rough t he wood 2 3/8" apa rt (Fig. 16). The holes must be str aight , so a dr ill press or dr ill guide is

recommended.

Sharpen the end of a 1/4" x 1 1/2" bolt and insert it into the end hole, with nuts and washers, as

shown. Bolt the scribe to th e hemispher e and adjust t he sha rpen ed bolt unt il th e scribe is level as itrests on the shar p point.

Rota te th e scribe and carefully score a circle in the hem isphere's sur face. Mak e the scra tch heavy

enough t ha t it can be easily seen.

Using a skil saw, cut a long th e scribed line. The resu lting hole should be 4 3/4" in diamet er, rea dy

to be radiused.


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Pa ge 18

Note: Fla gpole balls norm ally have a t hickness of about 1/16" (.0625"). The balls ar e ma de from flat

alum inum s tock tha t is placed over a spinning die or chuck. Dur ing the spinning process, a steel

tool is pressed a gainst th e alum inum , forcing it to conform to the sh ape of th e chu ck. The tool

creat es a series of sha llow, concentr ic rings in th e sur face of th e alum inum . These rings will not

redu ce the cha rge-holding ability of th e Collector so long a s t hey ar e sm ooth.

FOR MING THE COLLECTOR ENTRANCE RADIUS

The entr an ce ra dius is creat ed by ham mering th e edge of the lower hem isphere's entr ance hole

against a ra diused wooden die. Because t he a luminum is so ma lleable, this process is easier t ha n

you m ight expect.

The die is ma de as follows: Cut a r ing of 3/4" th ick plywood mea su rin g 5 5/16" I.D. an d 7 3/8"

O.D. Screw the r ing to a plywood disk 7 3/8" in diam eter an d, using a 1/2" ra dius rout er bit, rout

th e inside edge of the r ing (Fig. 17). The a ssembly can be secur ed for r out ing by screwing it t o a

work bench surface. Bevel th e out side edge at about a 45 degree angle. This can be done with a

router or with a disk sander.

Cut a plywood disk t ha t will fit sn ugly just

inside th e lower h emispher e (about 11 7/8" dia.).

This disk will be the bott om of th e die.

Using var ious t hicknesses of wood, ra ise th e die

ju st en ough tha t the hem isph er e, wh en placed

over it, just bar ely touches t he workbench

su rface (Fig. 18-C).

Atta ch t he pieces as shown an d screw th e as-

sembly to the workbench surface.

Using a small or medium size ball-peen ham-

mer, firm ly tap th e entr an ce hole edge all

ar ound th e perimet er, forcing it to conform to

th e ra dius of th e die (Fig. 18-C). Str ike only the

par t of the a luminum tha t should curve back

into the hemisphere.

Remove th e hem ispher e from tim e to time to check its fit on th e Plexiglas column . The fit sh ould be

loose enough th at th e hemisph ere will slide on a nd off freely.

Remove the h emisphere and file the r ough ha mm er ma rks smooth with a round file. Use sandpa perto smooth out the file ma rks.

ASSEMBLING THE COLLECTOR

The t wo hemispher es a re epoxied together so the Collector can be quickly slipped on a nd off th e

colum n. J us t about any epoxy, like th e common "Two Ton" epoxy, will work. "Five Minu te" epoxy

will set u p too quickly. I pr efer a gr ey past e epoxy, "PC-11" epoxy, which a llows plent y of workin g

Fig. 17 - Top view of wooden die.


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Page 19

Fig. A

Fig. B

Fig. C

Fig. 18 - (A) Cross section of

die (B) Dimensions (C)

Hammering hemisphere

against die to create radius


19/47

Pa ge 20

Fig. 19 - Bottom of Collector, showing radiused column

entrance hole.

time an d can be smoothed t o virtua lly eliminate t he seam .

Clean a nd lightly san dpaper th e two surfaces to be joined. Apply the epoxy to the r olled lip and

press t he two halves together . Weight s ma y be needed to keep th e halves tightly an d evenly to-

gether while the epoxy har dens. Wipe off excess epoxy with a ra g moisten ed with a cetone.

Before the epoxy har dens, check th e condu ctivity between th e two hem ispheres with a VOM. Al-

th ough I h aven't experienced an y condu ctivity problems, it's possible tha t t he epoxy could acciden-

ta lly insulat e one hem isphere from the other. If this ha ppens, it m ay be necessary to remove theepoxy from th e seam a nd t ry again.

After the epoxy has cured, carefully file and sand the seam smooth...no sharp edge should protrude.

The file mar ks a nd scrat ches a round t he seam should be wet sa nded with 120, 220, and 400 grit

sandpa per. If the Collector has a ny deep or u nsightly scra tches, wet sand t he dam age smooth a nd

th en p olish as described below.

P OLISHING THE COLLECTOR

For appearance, the entire Collector, especially areas that have been sanded, will need polishing.Use a 7", heavy duty 1,950 rpm polisher a nd a wool buffing pad. Use a fast -cut ting polishing com-

pound su ch as 3M fast-cut ting ma chine cleaner . An effective way to hold the Collector st eady while

polishing is to place it on a piece of carpet or soft cloth and kneel, holding the Collector between your

kn ees. Car efully apply the polisher, rotat ing the Collector as needed. Use special cau tion when

polishing ar oun d th e colum n en tr an ce hole, as t he polisher can sna g the Collector an d send it flying!

CONSTRUCTING THE BASE


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Page 21

The ba se is a box ma de of 3/4" cabinet gra de plywood with inside dimens ions m easu ring 20" by 16"

by 11" ta ll (Fig. 20). The t op consist s of two rem ovable pa nels of 1/4" Plexiglas. The front of th e box

is removable for m aintena nce and adjustm ents. The box inter ior a nd exterior can be painted,

stained an d varn ished, or covered with F orm ica.

Use wood screws and glue to assemble th e thr ee sides an d bott om of th e box. The front p an el is

screwed on bu t n ot glued. If Formica is to be applied to th e exterior, it should be done before begin-ning inst allat ion of component s. If you're a pplying Form ica t o th e inter ior, it mu st be done prior t o

assem bling the box. In case you're not familiar with Form ica techn ique, a cabinet shop should be

able to do th e job at a r easona ble cost.

Cut two braces of 3/4" x 2 1/2" ha rdwood an d insta ll th em flush with th e top, as sh own. Don't glue

the braces in place, as they will need to be removed from time to time when installing and adjusting

the components. They should be stained and varn ished.

After th e cabinet is const ru cted, inst all four swiveling cast ors (two with br ak es).

Cut two pan els of 1/4" Plexiglas for t he cabin et t op (Fig. 21-B). A 5 1/4" diam eter hole will be cut in

th e front pa nel to accomm odate th e Plexiglas support colum n. An excellent way to cut a clean ,

precise hole is to use a rout er a nd a simple guide, as described below.

ROUTING A P ERF ECT HOLE

Cut a piece of 1/4" thick P lexiglas or cabinet gr ade plywood 11" or 12" long a nd as wide as th e base

of th e router (Fig. 21-A). Un screw the rout er's base plat e and u se it as a t empla te for dr illing holes

in th e guide so th e router can be screwed to th e guide.

If the h ole you n eed to cut with t he r outer is 5 1/4" in diam eter , meas ur e exactly 2 5/8" from t he

outside of th e rout er bit (1/4" bit work s best) to a point on the cent er line of th e guide. Drill a 1/4"hole at t his point . Coun ter sink th e hole and inst all a 1/4" flat hea d bolt long enough to go all the

way thr ough th e mat erial you will be routing. Screw the r outer to the guide.

Drill a 1/4" hole in the material to be routed; place the guide over the material and insert the 1/4"

bolt th rough th e hole. The add ition of a n ut an d wash er will help sta bilize th e guide while the hole

is being cut .

Adjust t he router so th e bit will just pen etr at e thr ough th e mat erial. Loosen the 1/4" bolt enough so

th e router bit can be lowered slowly into the m at erial, allowing it to drill its own sta rt ing hole. Turn

th e router off, tighten th e nut on the 1/4" bolt "finger t ight", tu rn th e router back on, an d slowly

rota te it in a complet e circle, cut ting a 5 1/4" diam eter hole. Pr oceed very slowly as t he bit nea rs t he

end of its t ra vel so it doesn't wan der a s th e hole is completed.

This sam e technique can be u sed to rout out t he clamp t ha t h olds th e column in place (see below).

COLLAR


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Pa ge 22

Fig. 20 - Van de Graaff Generator cabinet


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Page 23

A

B

Fig. 21 - (A) Making a Router Guide that will allow cutting perfect circles. (B)Two Plexiglas panels that comprise the top of the cabinet. The 5 1/4" hole is forthe Plexiglas column.


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Pa ge 24

Fig.

22-PlexiglasC

ollarmountstotopofcabinetand

tightensaroundthecolumn,

holdingitfirmlyinplace.


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Page 25

The collar h olds t he P lexiglas colum n firmly in pla ce. It can be m ade from 1 1/2" th ick wood,

Plexiglas, or phenolic.

The r outer technique described earlier can be u sed to cut the clamp m at erial but, because of its

th ickness , the ma ter ial will ha ve to be routed from both sides. Dra w an outline of th e clam p on th e

Plexiglas, as sh own in F ig. 22. Rout th e out side circle first, st ar ting a t point "A" an d ending at point

"B." Mak e certa in you mea sur e to th e inside of the router bit when cutting the outside circle andmeasure to the outside of th e bit when cutt ing th e inside circle.

Cut t he tongue an d cent er notch using a ban dsaw (best) or jigsaw. You ma y find it easier to ma ke

these cuts while the material is still square, before routing.

Drill and coun ter sink five 5/16" holes in t he collar, as sh own. Make su re t he coun ter sink is deep

enough th at th e FH bolts will fit flush with or slightly below th e sur face of the Plexiglas. Bolts

protr uding a bove th e sur face of th e collar can bleed off char ge from t he Collector.

For a finished a ppear an ce, rout t he collar's out side edge with a 1/2" ra dius bit. Wet san d the edge

an d any scrat ch mar ks with 120, 220, an d 400 grit san dpap er. If a clear , high-gloss finish is de-

sired, polish th e clam p with t he 7" polisher a nd a polishing compoun d like Maguire's Machine

Cleaner . For th e highest gloss, follow up with Ma guire's Plexiglas Polish.

COLUMN

The column is fabr icat ed from a Plexiglas cylinder with a 5" O.D. an d 1/4" wall th ickness .

If you're fairly experienced work ing with P lexiglas, cutt ing th e cylinder sh ouldn't be difficult. Oth -

erwise, you m ay wan t t o ha ve the cylinder finished out by a plast ics fabricator.

If you plan t o cut th e cylinder your self, here a re some t ips:

When sh ort ening th e cylinder or squ ar ing-up t he end s, wrap a couple of tu rn s of com-

puter paper or lightweight poster boar d ar ound the cylinder a s a guide for ma rking a line

at a right a ngle to the cylinder's axis.

Use a special P lexiglas blade wh en u sing a r eciprocat ing saw to cut th e cylinder .

Rub au to wax or soap on the blade to keep it from sticking to th e plastic. Keep the sa w

flat again st t he cylinder. Cut s lowly an d let the blade cool from t ime to time.

Use special P lexiglas dr ill bits when drilling holes 1/4" an d larger.

Cut th e cylinder to 42" length, keeping both ends a s squa re a s possible. The top of th e cylinder will

need two slots 4" long and 5/8" wide for th e upp er pu lley sh aft (Fig. 23-A&B). The sh aft sh ould fit

snu gly, but sh ould not be forced. If the slots a re cut t oo na rr ow, use a file or sa ndpa per t o widenthem . Make certa in the slots ar e exactly 180 degrees apar t.

Four bru sh slots will also be needed (Fig 23-C&D). All brush slots, both t op an d bott om, a re of th e

sam e dimen sions (Fig. 23 "Inser t").

Two 2 1/4" diam eter holes should be cut nea r t he bottom of the cylinder to allow inser tion of th e


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Pa ge 26

Fig. 23 - Plexiglas column


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Page 27

Fig. 24 - Plexiglas column with belt and brushes installed


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Pa ge 28

Fig. 25 - Upper part of column. (A) Front of column showing aluminum tape,brush slot, brush, pulley, and aluminum contact strip. (B) Left side of col-umn showing brushes, pulley, connecting wires, and contact strips.

lower pu lley (Fig. 23-A&B), an d t wo bott om bru sh s lots will added (Fig. 23-C&D). The r ear bru sh

slot is invert ed an d lower th an th e front br ush slot (Fig. 23-C).

Make two aluminum Contact Strips 1 1/2" x 6 1/4" (Fig. 24-A&B). Thickness should be around 1/16"(.0625"). Drill 1/4" mounting holes in both the contact strips and the column, but do not attach the strips

until after the belt is installed. Countersink the holes in the column.

Apply two pieces of 2" wide alum inum ta pe to th e inside of the column as sh own in F ig. 24. The

ta pe will conduct char ges collected by th e bru shes t o th e conta ct str ips, and t hen to the Collector.

PULLEYS

The pulleys are ma chined from solid alumin um stock an d ar e 2" in diam eter a nd 3.6" long. A 1/8"

ta per is turn ed in the pulleys to help keep the belt centered. Ball bearings are pr essed into the ends

of th e u pper pulley, and th ese sh ould be r ecessed a bout 1/8" to allow r oom for sha ft collars (Fig. 26-

A). The u pper p ulley sha ft is st eel 5/8" dia. an d 5" long.

The lower pulley will ha ve two 1/4" or 5/16" set screws to tigh ten aga inst its sh aft (Fig. 26-B). The

lower sh aft is st eel 14" long a nd 3/4" diam eter .

It's a good idea to provide the ma chine shop with t he a ctua l bear ings tha t will be pressed into the en ds

of the upper pu lley (see Part s List). The shop may ha ve aluminu m an d shaft mat erial available.

BA


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Page 29

Fig. 26 - Upper & lower pulleys.

Two ball bear ing pillow blocks hold t he lower pulley. In order t o provide cleara nce for th e shea ve,

th e pillow blocks mu st be r aised a bout 3". Cut eight pieces of 3/4" ha rd wood 2 1/2" x 7 1/2". Two

sta cks of four pieces each will be drilled an d a tt ached t o the cabinet base t o raise t he pillow blocks

(Fig. 27).

Cent er a pillow block on one of th e pieces of wood, th en m ar k an d drill the m oun ting holes. Use th e

piece as a template t o ma rk a nd drill the rema ining pieces. Clamps an d a long drill bit will make

th e job easier. To provide stren gth a nd st ability, 3/8" bolts ar e recomm ended. Once th e pieces are

drilled, give them one or t wo coats of var nish.

ASSEMBLY

Cut a disk of 1/2" or 3/4" wood or Plexiglas t o fit sn ugly in th e bott om of th e colum n. This disk will

sta bilize th e column when it is mount ed in the cabinet. Drill and coun ter sink t wo 1/4" holes

th rough disk a nd bolt it t o th e bott om of th e cabinet (Fig. 27). You should be able to easily press t hecolumn on an d off the disk.

Screw the plexiglas top sections ont o th e box and insert th e colum n th rough th e hole. Pr ess the

column over th e disk. If the alignmen t is off, now is th e time t o corr ect it!

If the a lignm ent is o.k., slip th e locking collar over th e colum n. Pla ce a str ip of rubber 1/8" th ick

an d 15 5/8" long between th e colum n an d th e collar . The ru bber will serve as a gasket to prevent

the column from rotating and t o distribute stresses from the clamp. The rubber should be about the


29/47

Pa ge 30

Fig. 27 - Cabinet parts layout.

sam e height as t he collar .

Align th e collar with th e cabinet a s shown in F ig. 28. Slide a 1/4" x 5" bolt th rough t he clamp's

tongue an d tighten u nt il th e column is held firm ly. Mar k th e collar holes on the Plexiglas top.

Remove the a ssembly an d dr ill one 5/16" hole in t he locat ion in dicat ed in t he P lexiglas top (Fig. 28-

A). Drill all th e way th rough th e top wooden braces. Drill 1/2" holes in t he positions indicated in

Fig. 28. These lar ger diamet er h oles will allow the m ountin g bolts room t o move when t ightenin g

an d loosening t he collar .


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Page 31

Fig. 28 - Plexiglas top panels showing alignment ofcollar and sizes of mounting holes.

Remove the P lexiglas top, locate t he position of the wooden pillow block support s, an d m ar k a nd

drill eight 3/8" moun ting h oles thr ough t he bottom of th e cabinet.

Bolt th e support s in place along with t he pillow blocks and lower pulley. Slide the shea ves on t he

lower pulley shaft an d th e motor shaft. Position th e motor a nd dr ive belt according to Fig. 27.

Note: Some pillow blocks ha ve a ru bber gasket th at fits aroun d the bear ing. As th e lower

pulley must be grounded, it will be necessary t o wra p a str ip of aluminu m foil or

bare copper wire around the gasket so the bearing and pulley are in electrical contact

with the bear ing mount ing fra me. A ground wire will be at tached later t o the fram e.

Align the lower pulley, drive belt, motor, an d shea ves so th e drive belt is tight an d str aight . Mar k

an d drill th e motor mount ing holes. Be sure t o ma rk t he holes to allow room t o move th e motor for

future tightening of the drive belt.

Note: The motor sh ould be wired for count erclockwise rotat ion.

Mar k an d drill moun ting holes for the power sup ply an d power an d cont rol cables. Moun t th e

wheels.

B R U S H E S


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Pa ge 32

The bru shes a re m ade from clust ers of copper wire crimped or

soldered into th e ends of solderless term inals. The term inals are

then att ached to thr eaded bra ss rod or brass bolts (Fig. 29).

The cluster s of copper wire can be extra cted from ordina ry line

cord . St rip t he in su lat ion off several inches of line cord , cut off a

two inch length of wire str an ds, twist one end of th e cluster to-gether , an d inser t it into th e solderless term ina l. A "clust er" is

compr ised of around 100-250 str an ds.

Upper Brush es: (Two needed) Solder a solderless ter mina l to a 1/

4" bra ss nu t a nd wash er. A 1/4" x 1" FH br ass bolt will screw int o

the assembly from outside the column.

Lower Brush es: (Two needed) Solder a solderless ter mina l, bra ss

nut , and washer to the end of a 1/4" x 2" thr eaded brass rod.

During soldering, alignment of nuts a nd wash ers can be ma in-

ta ined by using steel nut s to hold the asssembly together. The

solder will not sick to th e steel nu t, which can be r emoved after

soldering. The upper bru shes can be soldered while th rea ded on a

steel bolt. When r emoved from t he st eel bolt, the a ssembly will be

perfectly aligned. The brush es will be tr imm ed an d adjusted

dur ing final a ssembly of the componen ts.

HIGH VOLTAGE P OWER SUP P LY

Any DC sour ce pr oviding 10 kV to 15 kV will work . The cur rent

requ ired is virt ua lly nil (6-10 microamps), so almost a ny sourcewill do. Oddly enough, I foun d a slight increa se in perform an ce if

th e cur ren t capacity of th e power supply is at lea st 1 mA. I can 't explain th is, becau se the curr ent

demand, including leakage, is only around 5 microamps, max.

An inexpensive, "gorilla pr oof" supply is described below. The t ra nsform er a nd r ectifiers can with-

sta nd sh ort circuits an d can p rovide more tha n 15,000 volts of either polarit y. For safety, cur ren t

limiting resistors a re placed in series with the outpu t.

The tr an sform er specified is a 6.5 kV "core an d coil" un it m an ufactur ed by Actown E lectr ocoil, Inc..

The compa ny ma nu factu res t op-quality tr an sform ers a nd sells factory-direct, so th e price is low.

Output from the transformer is doubled to approximately 15 kV with a simple voltage multiplier.

One leg of the tr ansform er's outpu t is grounded, an d although th is is not a st anda rd pr actice in the

neon sign business, th e technique works for t his low-curr ent power su pply.

To redu ce shock ha zar d, a 1 to 2 megohm , 6 W resista nce is placed in the groun d leg. A direct short

circuit will burn this resistor out, so make certain that the power supply wiring is correctly spaced

an d the lower brush es are far enough from the pulley tha t spar ks can not jump. A bleeder resitor

across th e voltage doubler isn't r eally needed, alth ough t he capa citors st ore en ough of a char ge for

an irritat ing shock if you come between the outpu t a nd ground. Always un plug the generator a nd

Fig. 29 - Brushes


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Page 33

Fig. 30 - High voltage power supply. (A) Schematic (B) Pictorial

short out t he capacitors when working inside the u nit.

The Collector will develop th e sam e polar ity as t he power su pply's outpu t. Before deciding which

polar ity to use, you m ight wa nt to review "Experim ent s," p. 40.

CHARGING BELT

The cha rging belt is m ade of gum ru bber 1/8" th ick, with an inside circum ference (or "IC") of 68".

Alth ough th e belt will have t o be custom m ade, th e cost will be fairly low...aroun d $20.00. A sup-

plier is listed in th e Appendix.

In s t a l li ng t he Cha rg i ng Be l t : Pla ce two 5/8" sha ft collar s on t he upper pulley shaft. Adjust th e

shaft and collars so the pulley is centered in the column and the shaft is even with the outside of the

column . If th e shaft pr otr udes slight ly past th e column , file it off un til it's flush. Apply a drop of

Loctite to th e thr eads of th e collars' set screws an d tighten . Set th e upper pulley aside.

Remove the lower pu lley. Tie a 1/2" or 3/4" nylon r ope ar ound t he cha rging belt an d lower t he belt

th rough th e top of th e colum n (touch th e belt a s litt le as possible). You m ay find th e tas k easier if

you la y th e column on t he floor or a cross a bed, keeping it fairly horizont al.

B

A


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Pa ge 34

Insert the lower pulley through t he column

an d thr ough th e cha rging belt (Fig. 31). Pu ll

the free end of the belt u p th rough the top of

the column an d carefully insert the upper

pulley th rough th e belt. (This opera tion will

requ ire two people, one t o pull the rope an d

one to push t he upper pulley under t he belt).

Lower th e pulley, placing th e sha ft into the

slots. Un tie the rope an d pull it from the belt.

Str aighten t he belt so it 's even.

I n s t a l li n g t h e C o lu m n : Slide the column ont o

the disk m ount ed inside the cabinet a nd a lign

th e colum n. Pla ce th e pillow blocks on th e lower

pulley shaft and loosely bolt the assembly in

place on the wooden supports (Fig. 32).

Note: Make cert ain tha t the pillow

blocks' bearin gs m ak e electrical con-

ta ct with th e pillow block fra me. If a

rubber gasket surrounds the bearing,

wrap some a luminum foil or ba re

copper wire ar ound the gasket .

Align th e assembly and begin tightening th e

moun ting bolts. Cent er the belt on both

pulleys and r ota te it a few times by hand.

Once a reasonable alignment is achieved,

tighten t he m ount ing bolts.

Atta ch th e Plexiglas t op and locking collar ,

an d align an d tighten t he entire assembly.

In s t a l li ng t he M ot o r : Place the V-belt on

th e lower pulley an d motor sheaves. Bolt the

motor in place and temporarily wire the motor

so it can be ru n to test the alignm ent. Apply

Loctite to the sheave threads before final tightening.

After th e assem bly is aligned a nd t ested by ha nd, switch th e motor on br iefly an d check for beltwan dering or vibrat ion. If th e cha rging belt wan ders, check to see tha t th e pillow blocks are tight ,

tha t t he front-to-rear alignm ent of the column is corr ect (twisting th e belt can ma ke it wan der), an d

th at t he pulleys ar e para llel. If th e overall alignm ent is fair ly close, the wan dering belt can n or-

ma lly be fixed by placing shims un der th e pillow blocks.

Once th e belt is balan ced, it usu ally sta ys th at wa y. (Surpr isingly, a balan ced belt can sometimes

Fig. 31 - Belt installation requires stretchingthe belt using a rope.


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Page 35

be thr own slightly off when t he char ging circuit is tur ned on. The electr ostat ic char ge on th e inside

of th e column is appa ren tly str ong enough t o somet imes pu ll the belt off cent er!)

Install the two aluminum contact strips shown in Fig. 24-A&B.

Be especially careful when insta lling ha rdwa re on the column . A nu t or bolt dropped inside th e

column will be difficult t o extra ct, and m ay necessitat e rem oving the en tire column .

I n s t a l li n g t h e U p p e r B r u s h e s : The front upp er bru sh should lightly cont act th e belt. Screw the

brush /nut /washer/ combinat ion onto the 1" FH brass bolt a nd insert the assembly into th e upper

bru sh slot, fitting th e bolt into th e counter sun k hole. Tight en th e assembly and check the length of

the copper wires.

If the wires need to be trimmed, remove the assembly and cut the wires as evenly as possible,

form ing a fan shape t ha t span s the width of the char ging belt, as shown in the dra wings. Reinsta ll

th e assem bly an d check the fit. The wires should lightly touch the belt. You may find it helpful to

use a screwdriver t o bend an d adjust t he wires.

Repeat th e procedure t o insta ll the r ear upper bru sh, but spa ce the br ush about 1/8" away from t he

belt. The rear brush sh ould line up approximately with th e front brush .

I n s t a l li n g t h e L o w e r B r u s h e s : The front lower bru sh should line up as closely as p ossible with

the a rea where th e cha rging belt separa tes from t he lower pulley as t he belt tra vels upwar d. (Fig.

24-C&D). When t he belt is moving, this ar ea will sometimes sh ift slightly downwa rd, as t he cen-

tr ifugal force tends t o pull the belt awa y. The bru sh sh ould be spaced about 1/8" awa y from th e belt,

but n ot so close as to allow spar ks to jum p to the pulley when t he power supply is tu rn ed on. Trim-

ming the brush wires for a perfect fit may be a bit tedious, but essential for high performance.

The lower rea r bru sh sh ould be positioned a s shown in Fig. 24-C. The bru sh sh ould be aroun d 1/8"from th e pulley. Both t he front a nd rea r bru shes will be conn ected to th e power supply, so th e rear

brush must also be adjusted so no sparks will jump between it an d th e pulley.

I n s t a l li n g t h e P o w e r S u p p l y : The core & coil tra nsform er can be screwed directly to th e cabinet

base or m ount ed in an aluminu m box. Mount the voltage multiplier on the side of the cabinet nea r

th e tra nsform er (Fig. 27). Use nylon bolts an d spacers to keep the mu ltiplier about an in ch away

from th e cabinet side. Keep all wiring and condu cting ma ter ials at least t wo inches from th e multi-

plier.

WIRING

Twist wires ar ound each end of the u pper pulley shaft a nd r un them inside the column to the alum i-

num conta ct st rips, as shown in F ig. 33-A. If you can't wra p th e wires a round th e shaft, wrap t hem

ar ound th e sha ft collar (th e sha ft doesn't r otat e...only the pu lley). Any convenient wire size will

work , but #16 or #14 will probably be easiest. Rout e the wires a way from moving par ts, an d ma ke

sur e th ey can 't vibra te out of position.

Conn ect a jum per wire between th e front a nd rea r lower bru shes (Fig. 33-B). Well-insu lated h ooku p


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Pa ge 36

wire will work , but 15 kV neon sign wire is pr eferr ed.

Run a length of 15 kV neon sign wire between th e voltage mu ltiplier outpu t a nd t he front lower

bru sh. This wire should be rout ed clear of all oth er wiring and condu ctors.

Conn ect a ground wire between one of the pillow block bolts a nd th e 5/16" bra ss groun d lug inst alled

in the r ear of the cabinet. This wire mu st ground th e lower pulley, so ma ke certa in tha t n o rubber

gasket material insulates it from the pillow block bearing.

Inst all the fuse and ter mina l strip, and bring in the a .c. power an d contr ol cables. The cables can be

secur ed with nylon wire stays an d str aps.

The rem ote switch box wiring is stra ightforwa rd. You can br ing the cont rol cable into the box an d

use a str ain r elief or, for a deluxe version, you can insta ll a militar y type conn ector t ha t will allow

you t o disconn ect t he box (see Par ts List). If you want to groun d th e box, you'll need to use a four -

Fig. 32 - Parts Layout


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Page 37

condu ctor cont rol cable inst ead of the t hr ee-condu ctor s pecified. The cont rol cable can be just about

an y length , but 8' to 15' fulfills most r equirem ent s.

TESTING

Connect th e ground lug to an ear th ground and att ach a han d-held electrode to the ground lug (see

"Experim ent s" for det ails on building and u sing a h an d-held electrode).

Leave the collector off. Tur n th e motor "on," th en th e power supply. The alum inum cont act str ips

should imm ediately cha rge and m ak e a cra ckling soun d. You should be able to dra w a steady

str eam of 1/2" to 1" spar ks between th e strips an d the ha nd-held electr ode. No spar king should

occur at t he lower brush es, an d the belt should run tru e.

Pla ce th e Collector over th e column an d level it by eye. Tur n th e genera tor on a gain. The Collector

should sta rt m ak ing a cra ckling soun d in 3-5 seconds, indicat ing full cha rge. Bring th e han d-heldelectr ode close to th e Collector. Fa t, noisy spark s 3" to 4" long should jump to the electrode. When

pulled farther away, the electrode should draw thinner sparks 12" to 18" long, depending upon

conditions.

Gener al layout for a 1.2 million volt Van de Gra aff Gener at or (photo on P . 3) is shown in F ig. 35.

Fig. 33 - (A) Wiring from upper pulley to contact strips. (B) High voltagewiring to lower brushes.

A B


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Pa ge 38

Fig. 34 - Completed 4' Van de Graaff Generator. (A) Rear view (B) Front (C) Front panel removed, showingbearings, wooden supports, and a front brush made from brass screen. (D) Rear view showing motor and aH.V. power supply circuit described on P. 14.

A B

DC

This genera tor is very similar t o the 4' model. The t op half of the Collector is rem ovable, so th e

upper bear ings are m oun ted outside the column , allowing for a slightly lar ger belt width . The powersupply consists of a 15,000 volt neon sign transformer with the center tap grounded and the high

voltage ta ken from one leg (see Fig. 11, P. 12). The bru shes a re m ade of bra ss screen, and pla cemen t

is identical to the 4' model, except t ha t n one of the bru shes t ouches t he belt; they're positioned a bout

1/8" awa y from t he belt.

The cabinet is Form ica over plywood. Fr ont , rear , and top panels ar e removable. Motor is a one

horsepower, 1,725 r.p.m., split pha se, tur ning th e cha rging belt at a bout 1 1/4 revolutions per sec-

ond. Spa rk ing dista nce to a 12" grounded spher e is ar ound 48", somet imes longer.

EXPERIMENTS


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Fig. 35 - General layout for a 1.2million volt Van de Graaff Generator

(photo on P. 3).


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Pa ge 40

1. F r e e -Air D is ch a r g e : Good conditions an d a very dar k r oom ar e requ ired to properly observe

free-air dischar ge phen omena . Allow time for your eyes to adjust to the dar k.

A positive Collector pr oduces a very int erest ing discha rge: a violet-colored st rea mer about 8" to

12" long will dart from t he Collector an d ter mina te in a bea ut iful fan sha pe. A faint, mu ffled

"sna p" accompa nies th is discha rge. When conditions a re good, the gen era tor will produce one of

these streamers every few seconds.

A negative Collector t ends t o produce fewer a ir dischar ges and , when t hey occur, th ey ar e more

concentrated and tend to form a more common lightning-like form, with minimal branching.

2. D is ch a r g e t o a H a n d -H e ld E le c t r o d e: Drawing long spar ks ta kes th e right configurat ion a nd

a bit of pra ctice. Un der good conditions, the 4' Van de Gra af can produce visible spar ks m ore

th an 12" long between th e Collector a nd t he pr oper ground electrode (Fig. 36).

Large diam eter electr odes work better t han sma ll ones. For maximum spa rk length, use a

discha rge electr ode 8" to 12" in diamet er. It's essent ial tha t t he electr ode's surface be smooth .

Att ach a sma ll acorn nu t or sma ll diam eter bra ss ball "bullet" to one side of the electr ode, as

shown. The nut or ball serves as a "dischar ge initiat or, assist ing in th e forma tion of spar ks.

Sta nd a bout th ree feet from th e Collector. Make su re your clothing is free of sha rp condu ctors

(pins, wat ch, etc.), an d keep your free ha nd by your side.

Tur n t he gener at or on a nd slowly bring the electrode close to the Collector, presen ting th e

smooth side of th e electr ode. A fat, loud spa rk will jum p about t hr ee or four inches to the elec-

tr ode. Pu ll th e electr ode back and rota te it so th e "initiat or" faces the Collector. With a little

pra ctice, you can dra w spar ks 8" to over 12" long from th e collector. The electr osta tic cha rge

Fig. 36 - Drawing sparks with a hand-held electrode


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Page 41

Fig. 37 - "Hair Raiser"

exerts a n oticeable force on th e electr ode, tu gging at it a s th e cha rge builds up. The long spar ks

ar e quite dim an d can be seen only in subdu ed lighting. However, they mak e a quite audible

"snap" as t hey str ike.

Hold the electr ode a pproximat ely 18" away. Occasiona lly, you will see very faint, r elatively fat

strea mers dischar ge between the electrode and th e Collector. These stream ers seem to have

distinct segments, or portions. The ma in cha nnel is perhaps t wo or t hr ee inches in diamet er.

There is sometimes a dar k ban d near one end, an d sometimes slightly brighter blue-white str ia-

tions appear t hroughout th e discha rge. The stream ers are so faint th at n early total dark ness is

required to see them .

3 . "H a i r R a is e r ": For young a udiences, this is undoubtedly the most enter taining demonstra tion

Van de Gr aa ff Gener at ors provide. Pla ce a pla stic (not wood or met al) step or stool 10" to 12"

ta ll beside the genera tor. Choose a "victim" with medium long, loose ha ir...th e finer a nd dr ier

the h air, the better . Have the person sta nd on the stool, keep his/her free han d by her side, and

place her other han d flat on t he Collector (Fig. 37).

Make sure the individual is not wearing a sharp-pointed, conducting object, like a hair pin.

Inst ru ct the individua l to keep her ha nd on th e Collector, as sh e can receive a m ild shock if her

ha nd is lifted. Stan d back five or six feet an d tur n t he generat or on.


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Pa ge 42

Fig. 38 - Electric Spinner

In a few moment s, her ha ir should begin t o rise. If her ha ir becomes ta ngled an d stubborn, have

her sh ak e her hea d a few times to loosen it. The demonst ra tion work s best if th e "victim" is ta ll

enough tha t her h ead is above th e Collector. When th e demonst ra tion is finished, bleed the

char ge from t he individual by bringing a sha rp-point ed, groun ded wire slowly toward her .

The "Ha ir Raiser" demonstra tes t he pr inciple th at like charges repel.

4. Lig h tn in g R od : This demonstr ation shows how Benjamin Fr an klin's lightning rod works.

Tur n th e gener at or on an d bring a sha rp-pointed condu ctor slowly toward t he Collector. The

point will mak e a hissing soun d as it a pproaches th e Collector. In da rk ness, you'll be able to see

a faint corona ..."Sain t E lmo's Fir e"...glowing at t he point. No spark s will jump t o th e conductorbecau se th e sha rp point bleeds the cha rge off before it h as a chan ce build up.

The effect can be dramatized further by taping several lightweight ribbons or lengths of thread

to the Collector's top. The r ibbons will stan d out a s th e Collector becomes cha rged a nd will

droop as cha rge is bled off. Try u sing some of th e very light weight , colorful, twine us ed for t ying

gifts. Atta ch five or six str an ds about 10" long.

5. R e ca lc it r a n t S t yr o fo a m : Have an other "victim" stand on the insulat ed plat form . Ha ve him

place one han d on t he Collector, and in t he other h ave him h old up a styr ofoam cup. Fill the cup

with styrofoam excelsior (the hemisph erical kind work s best). Tur n th e gener at or on. The

styrofoam will jum p out of th e cup, sa iling several feet. The foam sometimes st icks to oth erobjects before losing its charge and dropping off.

6. O r b it in g S a t e lli te s : Cut several sm all pieces of aluminu m foil into na rr ow tr iangular shapes

with ta bs at t he base. Twist th e tabs in opposite directions, so th at if th e foil were dropped, it

would ten d to rota te. Make t he tr iangles about 3/4" to 1" long. Pla ce the tr ian gles on top of th e

Collector a nd t ur n t he gener at or on. The foil trian gles will jump off and "orbit" the Collector

below th e seam , hitt ing the Collector from tim e to time.


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Page 43

Fig. 39 - Leyden Jar

The tr ick is to get t he foil shape a nd size just r ight, so th e foil spends a s mu ch time a s possible

in the air.

7. E le ct r ic Sp in n e r : A pinwh eel ma de from lightweight alum inum will spin slowly when placed

at op th e Collector (Fig. 38). Theoretically, the sha rp points form ions, which are r epelled. The

reaction causes th e spinner t o rota te.

8. L ig h t n in g in a B o tt le : Cau tion! This experimen t can caus e a shock. A Leyden Ja r is a capaci-

toran d can store a powerful char ge. The jar wa s invented (part ly by accident!) by Pieter von

Musschenbr oek in Leyden, Hollan d in th e 1700's.

The lar ger the Leyden J ar , the great er the charge it will hold. You can m ake as large a jar a s

you wish, or wire a number of them in parallel, but keep in mind that, if enough capacitance is

used, a lethal cha rge can be stored (See section on sa fety). I suggest u sing a r elatively sma ll jar,

approximately a pint, as shown in Fig. 39.

Hold a ground wire a gainst th e out side foil of the jar an d hold the cent er electrode close to th e

Collector. After a bout 10 seconds, rem ove the jar an d set it on a ta ble. Use th e shorting bar t odischa rge the capa citor. The spar k will be short but qu ite loud. The jar will also cause a fluores-

cent or n eon lam p to flash br ightly. Use high voltage wire to mak e the conn ections.

9. Ve r sor iu m : The Versorium wa s one of th e first electr ical instr um ent s. It's simply a met al rod

pivoted on a needle so it can rota te freely. Use a lightweight copper or bra ss tu be about s ix

inches long. Drill a hole at t he balance point, punch an indent at ion in th e tube, and insert a

sha rpen ed nail or needle. The nail can be mount ed on a Plexiglas base. Hold th e Versorium

nea r th e gener at or, an d one end will be att ra cted to th e Collector. Hold a char ged Leyden jar


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Pa ge 44

Fig. 40 - Smog Eater

near the Versorium an d ma ke it rotat e by moving the jar in a circle.

1 0. S m o g E a t e r : You can demonst ra te t he pr inciple of electr ostat ic precipita tion with th e "Smog

Eat er." Take a large glass or plastic conta iner an d insert a meta l rod with copper wire "whis-

kers " (Fig. 40). Glue a str ip of alum inum foil to the inside of th e jar an d ru n a gr ound wire

th rough t he jar to the foil, as s hown. Int roduce smoke from a cigaret te (sorr y!) or some other

source th rough th e plastic tu be. Conn ect a wire between th e Collector an d the r od, or simply

bring the jar close to th e Collector. Tur n on th e gener at or and, voil, th e smoke disappea rs. The

rod charges the smoke molecules, which are repelled from the rod and deposited on the alumi-

num foil.

11. E l ec t ro s t a t i c M o t o r : Two varia tions of electr osta tic motors a re sh own in F ig. 41. The Disk

Motor is r elatively complex, but offers higher perform an ce tha n t he sim pler "Pop Bott le" motor.

The Pop Bottle motor will rotate a t a round 200 rpm. Pr operly adjusted, and u nder t he right

conditions, the disk m otor can a chieve better th an 500 rpm . For publicat ions offering more

inform at ion a bout electr osta tic motors, see th e Appendix.

The key t o perform an ce is low-friction; th e spindles m ust be fitt ed to allow very free r ota tion of

th e disk or pop bott le. Ther e should be about a 1/8" gap between th e brush es an d th e foil seg-

men ts. Wiring should min imize electr ostat ic leaka ge.

12. Hi gh -Vo lt age Hu m a n : You can preser ve a char ge on yourself by donning ru bber boots a nd a

plast ic ra incoat . Elimina te meta l objects. Expose as litt le skin to th e air as possible. Sta nd on

th e insulat ed platform an d cha rge your self up. When you step down, your boots will crackle as

you walk. If you t ouch someone...you kn ow the r est. Be car eful, you can st ar tle your victims ;

an d don't even thin k about coming close to a compu ter !

1 3. C h a r g in g w i t h I o n s : Attach a short wire to the Collector and point it toward an individual

sta nding on the insu lated plat form . The person will become cha rged even if he's several feet

awa y. The cha rge from the Collector crea tes ions at t he sha rp ends of th e wire. The ions drift

thr ough t he air an d ar e initially attr acted to the person's body.

1 4. C h a r g in g b y I n d u c t i on : Place the insulat ed platform about four feet from the genera tor.


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Fig. 41 - Electrostatic Motors


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Pa ge 46

Have someone sta nd on it an d tur n on th e genera tor. While keeping yourself away from th e

Collector an d the individual, bring a ground ed rod in conta ct with t he person. Remove th e

ground an d tur n off th e gener at or. Touch the individua l with one input wire from a DC

microamm eter or a n eon lam p (lamp an d microammet er ha ve one wire grounded). The person

will have a cha rge, which will discha rge to ground th rough th e meter or lam p. The person's

char ge will be opposite th at of the Collector. (The electrode of the neon lam p th at glows is the

one r eceiving th e negat ive cha rge.)

TROUBLESHOOTING

1. B elt Wa n d e r s: If the belt wan ders to the r ight, for inst ance, add washers u nder t he left

pillow block until the belt runs true.

If th e pulleys ar e properly ta pered an d reas ona bly well aligned, the belt will sta y cent ered. The

belt itself mu st be accur at ely ma de. If it is very uneven, it will wan der a nd vibrat e.

2. S p a r k in g B et w e en t h e L o w er B r u s h e s a n d P u lle y: Move the brush es back un til the

spark ing stops. Spar king should not be a problem with the power su pply specified, but if itpersist s, the out put voltage of th e power supply mus t be reduced. The simplest way to reduce

voltage is to remove the multiplier and use the transformer in a simple half-wave rectifier

circuit.

A 10-wat t potent iomet er can be wired in t he pr ima ry of th e tr an sform er for br oad voltage con-

trol, but remember that a short circuit could quickly destroy it.

3. L ow C o lle c t or Vo lt a g e :

Collector a nd column mu st be free of dust , lint , fingerprints, and m oisture.

Belt mus t be clean and d ry.

Brushes must be correctly aligned (best al ignment is experimentally determined). No sharp conductors should be nearby.

Collector should be smooth, without sharp metal seams or gouges.

Power supply mu st produce enough voltage (10,000-15,000 V).

Humidity must be fairly low (using a ha ir-dryer on the column and belt ma y help when the

hu midity is very high).

Lower pulley must be at ground potential . Any rubber gasket existing between the bearing

an d its fram e should be wrapped with a st rip of alum inum foil or a piece of bar e copper wire

to ma intain electrical conta ct with the ground wire.

Brushes must be in their proper posit ions .

Belt mu st rotate in the proper direction; forward-facing part of belt tr avels upward.

SAFETY

The high-voltage power supp ly can produce a serious sh ock. Always unplug th e gener at or a nd

discha rge th e capa citors before working inside th e cabinet .

The electr osta tic cha rge th at resides on th e Collector is gener ally consideded safe for h um an con-

ta ct. Exceptions ma y include individuals wearing heart pa cemaker s. Keep in mind tha t although a

shock from th e genera tor's Collector is not su fficient t o cau se injury, th e shock can sta rt le.


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Page 47

The genera tor can cha rge capa citors, such as Leyden J ar s. If a sufficient cha rge is stored in a large

Leyden J ar or other capacitor, a da ngerous, or even fata l, shock could occur. How big a Leyden J ar

is consider ed safe? A pint -sized jar can d eliver an un comforta ble sh ock. A gallon-size would be

pain ful. Alth ough studies have been conducted to deter mine app roxima te ener gy levels tha t can be

safely taken by the body, the a uth or m akes n o claim regarding safety limits. J ust exercise great

cau tion when st oring a cha rge in any capacitor.

Static electricity from the generator can be damaging to computers and sensitive microprocessors.

Keep the generator away from electronic equipment, including diskettes, videotapes, and other

ma gnetic media.

Keep in min d tha t you can carr y a compu ter -dama ging char ge on your body for severa l minu tes. Be

sur e to groun d your self before u sing a compu ter .

A P P E N D I X

C o m p o n e n t s fo r 4 ' Va n d e G r a a f f G e n e r a t o r

1. Collector: 12" or 14" diameter a luminum sph ere. Source: W.F. Norm an Corp., 214-32

N. Ceda r Str eet, N evada, MO 64772-0323 (800) 641-2708.

2. Column: 5" diameter x 42" long x 1/4" wall Plexiglas t ube

3. Belt: 3 1/8" wide x 68" inside circumferen ce x 1/8" th ick gum rubber . Source: Texas Rubber

Su pply, Inc. P.O. Box 565067, Dallas, TX 75356-5067 (214) 631-3651. Ask for th e Belt Division.

4. Motor: 1/6 hp., 1725 rpm, split ph ase Dayton or equivalent (W.W. Grainger stock # 6k551).

Note: W.W. Grainger is world wide. To find t he st ore near est you, check Yellow Pa ges or call

(214) 637-2380.

5. Upper pulley: See PP. 28 & 29.

6. Lower Pulley: See PP. 28 & 29.7. Upper Bearings: Upper pulley bearings should be ball bearings for a shaft diameter of 5/8"

(Fafnir S7KDD or equ ivalent; W.W. Grainger stock # 1L006).

8. Pillow Blocks: Self-aligning, light dut y ball bearing (W.W. Gra inger stock #2X899).

9. Motor shea ve: 2" OD, 1/2" bore (W.W. Gra inger stock # 3X760)

10. Pu lley sh eave: 2.8" OD, 3/4" bore (W.W. Gra inger # 3X771)

11. V-belt for m otor: See P. 34. Best way to determ ine proper size is to wra p a 1/2" nylon r ope

ar ound th e sheaves with t he m otor in its proper location. The rope will give the circum feren ce of

th e v-belt.

12 . Power s u pp ly: Tran sformer

Rect i fiers

Capacitors

Resis tor(s)

PC board or Plexiglas

Nylon bolts & spacers

13. Fu se: 5 A. slow-blow

14. Two S.P .S.T. 10 A. toggle switches

15. Switch box: Radio Shack or, for a deluxe version, a cast a lumin um Bud E conobox type

CU-234 (Available th rough Allied Electr onics (800) 433-5700).

16. Power cable: Thr ee condu ctor #16 or #18.

17. Cont rol cable: Thr ee condu ctor #16 or #18


47/47

Pa ge 48

18. High voltage wire: 15 kV neon sign wire.

19. Cont act str ips: Cut from 1/16" (.0625) alum inum sh eet

20. Lockin g collar : Cut from 1 1/4" Plexiglas or phen olic

21. Top panels: Cut from 1/4" Plexiglas

22. Cast ers: Four 2" dia., swiveling (at lea st two should lock)

23. Cabinet : 3/4" cabinet-gra de plywood. Can be covered with Formica.

24. Term inal st rip: Available thr ough Allied Electr onics and m ost electrical supply stores.

25. Upper bru shes: Made with F .H. bra ss screws, solderless ter mina ls, copper wire "whisker s,"and brass nut s & washers.

26. Lower brush es: Made with 1/4" th rea ded brass rod, solderless term inals, copper wire

"whiskers," an d brass n uts & washers.

27. Conn ectors: Optional militar y style conn ectors for cont rol box. Allied Electr onics ha s

several styles to choose from.

BOOKS & LITERATURE

Dibner, Bern . Ear ly Elect rical Mach in es. The Bur ndy Librar y, Norwa lk, CT, 1957. This book is filled with

interest ing history, woodcuts, ph otos, an d dr awings of electr ostatic machines d atin g from pre-Von Guer icke

to Wimshur st.

Ford , R.A. Hom em ad e L ightn in g, Creat ive E xperim ents in E lect ricit y. TAB Books, Blue Ridge Su mm it, PA,

1991. An excellent "how-to" book concern ed ma inly with th e constr uction of a sectorless Wimshu rst ma -

chine. The au th or, R.A. Ford, developed a high performa nce model that can pr oduce a substa nt ial spark u p

to 10" in length . Considerin g the size of th e machin e (disks a re only 14" in diam eter ), I'd say it rivals a good

Van de Graa ff in performa nce! Book also cont ains mu ch a dditiona l mater ial and m an y sour ces for part s an d

information.

S cientific Am erican . "Possibilities of Electr o-Sta tic Gener at ors." Mar ch, 1934. An int erest ing ar ticle by

Nikola Tesla, who ana lyzes th e new electrosta tic genera tor built by Van de Graa ff. Tesla computes t he

voltage, cha rge, energy, etc. of th e machine an d elabora tes on its uses as a n "atom smash er." Unfort un at ely,

Tesla exposes his ignoran ce of th e new at omic physics, thin king of at oms as ba sically iner t, with litt le possi-

bility of an ything u seful coming from th eir being smash ed.

S cientific Am erican . Title un known. 1952 (?). This art icle can be foun d thr ough the Reader's Guide to

Periodical Literat ur e under th e heading, "Van de Graa ff Genera tors." The ar ticle gives generalized plans

an d pa ra meters for both friction an d extern ally-excited ma chines.

Popular Electronics. "200,000 Volt Van de Gr aa ff Gener at or." October, 1990. Article shows const ru ction of a

sma ll friction m achine an d includes several experiment s.

N at ion al G eograp hic. "Light ning, Nat ur e's High-Volta ge Specta cle." J uly, 1993. Great shots of na tu ra l and

ma n-made light ning. Includes excellent photo of a lar ge Van de Graa ff Genera tor at th e Boston Museum of

Science, as well as several interesting Tesla Coil discharges.

Va n d e G r a a f f G e n e r a t o r P a r t s & K it s

Two Van de Gra af

Documents

Hi-Perf Van de Graaff