massive VDG / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

massive VDG

Move Thread

LAN_403

PerksPlus

Tue Apr 28 2009, 05:03AM

Registered Member #2084 Joined: Sun Apr 19 2009, 04:31AM
Location:
Posts: 11

So After making a little, welfare Van Der Graaf generator I decided to try and make a massive less, welfare VDG.
aside from the size it resembles a plastic pop can, with a metal pop can as the sphere.

I don't understand why I'm only able to get really tiny sparks out of this ( less than 2 cm ).

The diameter of my cylindrical 'sphere' is about 1 meter. That would put my potential max voltage around 1 million. The belt and rollers are proportonate to the size of my sphere.
But with a 2 cm spark I think that only puts me at around 20kv.

I'm thinking that there can only really be 4 problems with this set up.

1. There is too much leakage/corona discharge on my sphere. (its about as nice and smooth as tin foil gets when wraped around something, though).

2. There are two strips of double sided carpet tape (it is probly slightly conductive) on my belt.

3. The fact that my sphere isn't a sphere.

4. Just thinking that maybe tin foil is too thin to hold a big enough charge.

5. small metal rims on my top roller.

6. my belt (vinyl) is fairly negative on the triboelectric series.

the top jug and top roller are surrounded with tin foil - I'm assuming that this is most likely why I'm getting tiny sparks. Can a little corona leakage really drop the potential voltage by about 98%?

Materials:

Sphere/Base. 3 plastic jugs (50 gallon) 2 for the base, 1 for the 'sphere's' structure.

Brushes, aluminum screen.

Rollers - Bottom - Teflon-tape-coated pvc pipe
- Top - a florescent glass tube ** there is a metal rim that my belt touches **

Belt - A Vinyl shower curtain **** this seems a little too negative to work great ***

Axels - threaded steel rods with skate bearings, rollers are held in place with nuts.

I'll post a pic when I've got some daylight to work with.

I guess what I'm asking for here is if there is a specific problem I should try to takle that would make the biggest differance, or would it be best to go through each and every potential problem.

Proud Mary

Tue Apr 28 2009, 01:45PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Aren't large VDG belts usually charged with a 50kV or so ion spray brush at the bottom?

As for the thinness of your 'sphere', this should make no difference that I can see, since the charge must be strictly on its outside. (Gauss's Law) This should hold true to any degree of thinness, so long as the material is electrically continuous (no holes!) until it becomes - or approaches becoming - a nanomaterial, when I would think it might start to behave in some other way which I shan't try to guess.

But I do know that every irregularity on the sphere, no matter how small, contributes to losses - even dust particles are considered unacceptable disturbances to the Gaussian surface on large professional machines.

Inadequate difference in the triboelectric series would result in lower potential if you aren't charging the belt.

I have read that excessive belt speed can somehow flick off the charge, but have no personal experience beyond book reading.

And as you say, there may be losses in every other sub-system adding up to one big loss to which humidity may be added.

Antonio

Wed Apr 29 2009, 01:12AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

A picture would help.
The most critical parts are:
The support of the terminal must be a good insulator. Turn off the motor and the terminal shall stay significantly charged for several seconds.
The belt must be a good insulator. Same test.
The terminal can't have sharp corners, and specially points.
The belt must be charged to saturation. Remove the terminal and see if you can draw small sparks from the belt, with the motor running.
The Teflon roller must be strongly electrized by contact with the belt material. Verify if it attracts hair, or a light thread, after the motor stops.
Your upper roller looks quite strange.

teravolt

Wed Apr 29 2009, 02:04AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I think your problem is the belt, white neoprean or some sort of nylon cloth belt would work. no rubber with carbon. the thicknes of your material for your sphier is not important you could use tinfoil on a baloon if you could hold the shape. the shape you have chosen should work but you must keep any projections from occuring. as the voltage builds up things like dust can spray off charge. soft polyethalean can hold quite a charge and is good for the bottom roller and aluminuim for the top. thease are the matearials that I used with 14" sparks. hope that helps

teravolt

Sat May 02 2009, 03:22PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I found good belt material cheap if you haven't found it all ready

PerksPlus

Mon May 18 2009, 04:24AM

Registered Member #2084 Joined: Sun Apr 19 2009, 04:31AM
Location:
Posts: 11

I totally gave up on the original project. I think it was most likely because my "sphere" was too leaky after doing experiments on a smaller VDG. Thinking about it now my design seemed a little sloppy anyways. I was using meter long, 4 inch diameter rollers. I plan on making a big one when I've got the funds to make it out of new stuff (instead of recycled brewery containers, threaded rods and skate bearrings) Thanks for the site though. I plan on making the next version tall, slender, with a respectable sized globe. So thoes belts look Ideal if I can get one about 20 ft long! thanks

btmarney

Fri Mar 19 2010, 06:37PM

Registered Member #2747 Joined: Fri Mar 19 2010, 02:38PM
Location:
Posts: 1

teravolt wrote ...

I found good belt material cheap if you haven't found it all ready

The listing is gone. Do you have a picture or description? I have been using packing belts but want to go wider.

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob