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Pocket Van De Graaff generator

by mread, published

Pocket Van De Graaff generator by mread Feb 28, 2013

Description

A small Van De Graff generator, probably best not used in your pockets, and probably best not to run it near delicate electrical equipment.

Version 4

May 2013

This version uses ABS conductive filament from Rainbot3D.com, which greatly simplifies the top and bottom electrostatic combs.

The combs are completely printed, so no messing about bending and shaping wires. This also makes the parts much more reproducible and consistent.

The plastic has a resistivity of about 100 Ohm-cm. As printed, with 10% infill, I was measuring around 150 Kohms for each comb. As we are dealing with very small currents this is acceptable.

The bottom comb is in two parts, which acts as a clamp for the earth wire.

The top comb has a "shelf" such that the tin foil wrapped sphere rests on it to provide the electrical contact.

I had hoped to print the sphere with the conductive filament but I think the resistivity was too high.

The only wire needed now is the earth wire, I usually hold this while shocking myself.

Holder for battery pack added to the base.

All parts printed on my Rep2 in PLA, except the combs which were printed on my thing-o-matic mk6.

Recent Comments

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Nice! Thanks for the video
Lovely. Hey, is it possible for you to scale it up to something like ... youtube.com/watch?v=rNEY3Yv9kC8 ? By the way, put your video link in the description, it's cool.
Version 2 files added. This improves the top electrostatic comb.

New parts are Base_V2.stl and Top_Comb_Clamp.stl.

The top connection wire is stripped back a few inches, It greatly helps assembly if you wrap it in kapton tape ( or whatever you have) and the clamp holds it in place. It can them be cut straight and folded down. I hope the photographs will make it clear.

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Instructions


                                                        Parts:

1 Rubber band, I got a pack of 89mm long by 12.7 mm wide from Staples.

1 32 mm fuse, don't worry about the rating, it's just to form a glass rotor.

1 PTFE tape, to wrap around the printed rotor that fits on the motor spindle.

1 3V Motor, 25 mm diameter body by 30 mm body length. I got mine from Maplin, if you need to adjust for a different motor size I have included the 123D design files.

2 M3 x 19 screws

2 M3 bolts.

Aluminium foil to wrap the bowl in.

Wire, not sure what gauge it is but it's about 2mm in diameter.


The materials for the belt pulleys were taken from the Triboelectric effect table

http://en.wikipedia.org/wiki/Triboelectric_effect.

The top pulley is glass, using a 32 mm fuse, and the bottom rotor is PTFE tape, over a printed rotor with a bulge in it to make the rubber band self centre.

Instructions.

Print out one each of Base, Bowl, Clamp and Rotor. The rotor should press fit onto the motor shaft.

Wrap the rotor with the PTFE tape several times.

Bolt the motor into the base using the clamp and the screws and nuts.

Strip the ends of the wire, you need one long piece ( ~ 1m) and one piece about 20 cm.

The 20 cm wire should be stripped of insulation about 5mm one end and 7-8 cm the other end, the 5 mm end goes through the guide in the top of the base ( see photograph), and the ends bent down to form the electrostatic comb. The long stripped end is to make contact with the bowl.

The 1 m length should be stripped of insulation for about 5 mm and then pushed through the guide in the base to form the bottom electrostatic comb. Note that the combs should not touch the rubber, they should be 2-3 mm away from the rubber surface.

The other end of the 1 m cable goes to ground, I have mine wrapped around bare metal on a central heating radiator.

Wrap the Bowl in aluminium foil and push it inside the bowl so it can make contact with the short wire. Smooth the foil as much as possible over the bowl, sharp edges will cause charge leakage.

Fire up the motor and enjoy the sparks to your fingers.

I would welcome any suggestions to improving this thing.

Lovely. Hey, is it possible for you to scale it up to something like ... youtube.com/watch?v=rNEY3Yv9kC8 ? By the way, put your video link in the description, it's cool.
Version 2 files added. This improves the top electrostatic comb.

New parts are Base_V2.stl and Top_Comb_Clamp.stl.

The top connection wire is stripped back a few inches, It greatly helps assembly if you wrap it in kapton tape ( or whatever you have) and the clamp holds it in place. It can them be cut straight and folded down. I hope the photographs will make it clear.
HAHAHAH! an Arduino with a little speaker is missing from the design, to play some synthetized evil laughs when sparks are detected. Can you post a video?
mread - in reply to eried
I hope this works, I have n't loaded anything to youtube before.

youtube.com/watch?v=HAkm7koHVQ8&;feature=youtu.be
eried - in reply to mread
Nice! Thanks for the video
mread - in reply to eried
I know what you mean...

When I just had a PC in my spare bedroom it was the office.

When I had a MakerBot in the spare bedroom it was the workshop...

Now I have a laboratory... I`m turning into Dr Evil.
how big of sparks have you gotten with this? any hairs standing up on your head?
If I get the combs set up right about 1 cm long sparks, at a rate of about 1 per second.

Any hairs standing on my head ? Those days are long gone ! I have n't had long hair for many years.

I doubt the small generator could supply enough charge to take a large body to the potential required to get my hair lifting. Might be able to lift a few strands attached to the bowl though.

This is just a first attempt and I`m happy just to get sparks. I reckon the charge bowl needs redesigned, the combs need more accurate and consistent placement, and then I'll be in a position to start looking at different materials, such as a belt cut from a thin latex glove. different rollers etc.
What is the purpose of the PTFE tape over the drive pulley? I would think the dielectric properties of ABS or PLA would make this unnecessary. But this is a great thing! Plan to build one ASAP.
Glass and Teflon are the furthest apart materials on the Tribolectric scale that I had to hand.

The next iteration will improve on the electrostatic comb positioning as it is very sensitive to this. The strands should be as close to the rubber as possible without actually touching.
Glass and Teflon were the furthest apart materials on the Triboelectric scale that I had to hand.

The next iteration will have a better way of locating and aligning the electrostatic combs, it is very sensitive to the separation between the strands and the rubber.
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