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A VanDeGraaff problem

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LAN_403

thedatastream

Sun Apr 29 2007, 09:54AM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

A drinks can works fine as a topload

DrZoidberg

Sun Apr 29 2007, 10:28AM

Registered Member #350 Joined: Mon Mar 27 2006, 05:14PM
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Posts: 106

Not sparks? Then what is it?
Replacing the pipe might help. But aren't toilet paper pipes made from cardboard? That won't work.
Do you have a multimeter? With that you can measure if your VDG produces any current at all.
A simple multimeter set to the 20V range should display something when connected to your machine. But you should connect it to the vdg before switching it on. And use a cheap one in case it breaks.

VDG

Sun Apr 29 2007, 09:01PM

Registered Member #668 Joined: Fri Apr 27 2007, 10:33PM
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Posts: 8

I'm not sure what are they, but I belive them to be some kind of St. Elmo's fire, or simply ionized air. I will try to replace the pipe I have with a plastic glass, like the one in the thread you have provided. And, by the way, Big thanks for all your help. One last question: must there be a ground connection for the lower comb?

DrZoidberg

Mon Apr 30 2007, 03:28PM

Registered Member #350 Joined: Mon Mar 27 2006, 05:14PM
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Posts: 106

Whatever it is, electricity is flowing from the belt to the brush. That's good. It means your belt, rollers and brushes are fine.
That just leaves the pipe and the can. A can should work for collecting the charge. Does the upper brush have contact with the can?
The lower comb doesn't necessarily need to be connected to ground but it mustn't be insulated. The charge on that comb needs to be able to go somewhere. Many VDG's have the lower roller, brush and motor in a metal casing. In that case the brush is connected to that. That's usually sufficient. the charge then finds a way to escape e.g. through the table the VDG is sitting on or simply through the air. But connecting the brush to ground is the best solution. Just remember that touching a grounded conductor always increases the risk of accidentially electrocuting yourself e.g. if though a faulty wire some appliance in your home gets electrified and you touch that at the same time you touch a grounded object you have a problem. Also grounding it makes the VDG less portable.
You can use yourself as ground. Touch the lower brush/metal casing with one hand and with the other you draw sparks from the can.

HV Enthusiast

Mon Apr 30 2007, 05:12PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

If you are looking for a nice sphere, Science First of NY has spheres up to 14" in diameter which are quite inexpensive.

VDG

Wed May 02 2007, 07:02PM

Registered Member #668 Joined: Fri Apr 27 2007, 10:33PM
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Posts: 8

Ok, two last questions: First, What size, approximity, the arc should be for a soft drink can? I can only seem to get 1cm at most, wich less then what I expected, and secondly, do the rollers and belt meterials have any effect on how far the VDG can charge?

GreySoul

Wed May 02 2007, 11:43PM

Registered Member #546 Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239

Hard to get an exact number for arc length given just the size of the can, without knowing how much power is getting built up in it... still, I'd probably be happy with 8-10cm arcs, 1cm is certainly not peak performance.

And the belt and roller composition are absolutely important, I'd say the most important aspects of a VDG. Without them the machine wouldn't do anything.

There are some good lists floating around that list the properties of different belt and roller materials. The rollers and the belt need to be as far apart on that scale as possible to peak performance.

-Doug

DrZoidberg

Thu May 03 2007, 02:31AM

Registered Member #350 Joined: Mon Mar 27 2006, 05:14PM
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Posts: 106

The maximum spark length for a VDG is approximately equal to the diameter of the sphere. But you don't have a perfectly shaped sphere here. A can has a rim which is bad. So I guess the maximum spark length is maybe 3cm. Using different materials for the belt and rollers might increase performance. Also the speed of the belt and it's width is important too. It doesn't really make a difference if you increase the charging current by using a better belt material or if you do it by using a wider belt or a higher speed. But the last 2 things are often easier to do.

Dr. Shark

Thu May 03 2007, 08:41AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Not quite true. Just like the support structure the belt must be absolutely non-conductive, otherwise the generator shorts itself out. I think Firkragg experimented with different compositions of rubber and found them all slightly conductive. Therefore you should pay a lot of attention to the belt material.

Would it be possible for you to post a picture of your VDG? That would make it a lot easier to spot what may be wrong with it.

VDG

Thu May 03 2007, 11:32AM

Registered Member #668 Joined: Fri Apr 27 2007, 10:33PM
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Posts: 8

Well, I don't have a camera that can transfer pictures, but I might loan one soon.

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