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4hv.org :: Forums :: High Voltage
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Inside the Van de Graaff

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Finn Hammer
Sun Jun 10 2007, 08:48PM Print
Finn Hammer Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: Skørping, Denmark
Posts: 741
Here is a Van de Graaff generator that I`ve just built:

The motor is a cute little 0.12kW 2900 RPM 3-phase unit in a 56 Frame, and the pulley is 100mm dia.
The flyback is used to create the corona spray for the lower comb.


1181505157 205 FT0 Base1 Resize


Front wiew:
Corona generator is on the green pcb.


1181505365 205 FT0 Base2 Resize


I would not have bothered you with this VDG, if it had not contained some novelty, and this is it:
The blue print contains the fiber optic components that allow the user to start the VDG by pressing a button positioned at the top of the terminal. The fiber is cut in 2 up the terminal, and a gobo connected to the on-off button allows light to pass when the button is depressed. This VDG is made specifically for hair raising duty.


1181505685 205 FT0 Base3 Resize


The spray and collector combs are made from stripboard and short needles:
The lower spray comb looks like this:


1181505857 205 FT0 Spraycomb Resize


The top electrode is made from IKEA bowls, and the inside looks like this:


1181506021 205 FT0 Top1 Resize


The white stuff is HDPE which I like because it is fantastic to machine.
Collector comb is conected to the top pulley, and the top spray comb is connected to the terminal. This way the belt is charged on both runs, so that it delivers double current.
The string of resistors keeps the top end from self exciting. This means that there is only output as long as the bottom spray is on. This makes it possible to remove the hands from the terminal as soon as the motor and spray is off, but while the belt is still coasting to a halt.
Here is the connection from the collector comb to the top roller:


1181506795 205 FT0 Top2 Resize


The belt is a conveyer belt from HABASIT, specifically non anti static. It is 0.7mm thick and it is 80mm wide.
Seen here with the top spray comb:

1181506957 205 FT0 Topspray Resize


This is the finished article:
!
1181507722 205 FT0 Final Resize



The generator charges with 50uA and is this enough to raise hairs?
Susanne has curly hair, like this:

1181507103 205 FT0 Susanne1 Resize


Charge her up, and her hair looks like this:

1181507177 205 FT0 Susanne2 Resize


Jette, on the other hand is fair haired, and charged to full potential she looks like this, on a day with 90% humidity:

1181507270 205 FT0 Jette Resize


Based on this, I conclude that for no questions asked hair raising, 250uA would be the way to go. Now I have a 200mm wide belt, put it on a 200mm pulley.......

That`s it, folks !
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Hazmatt_(The Underdog)
Sun Jun 10 2007, 09:32PM
Hazmatt_(The Underdog) Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Nice Job!

Are the drive pulleys convex (raised in the center) to keep the belt centered?
I ask because a firend of mine had a terrible time with the belt walking.
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Finn Hammer
Sun Jun 10 2007, 09:42PM
Finn Hammer Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: Skørping, Denmark
Posts: 741
Yes.

Both pulleys are crowned by turning a 1 degree taper on the outher quarter of the total length.
This is all it takes, and crowning should always be used.

Cheers, Finn Hammer
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Sulaiman
Mon Jun 11 2007, 01:40AM
Sulaiman Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Looks really good.

I have never made a VDG (and probably never will) but I am curious,
If the lower comb is positioned to spray the inside of the belt, could you omit the upper needles and just use the roller?
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Ken M.
Mon Jun 11 2007, 02:54AM
Ken M. Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628
It charges the outside of the belt not the inside if you look at image...1,3,and 4, you'll notice that the corona spray comb would charge the outside of the belt producing an obvious charge difference between the inside and outside of the belt. I think thats covers what your asking, if not sorry for the babbling.
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Part Scavenger
Mon Jun 11 2007, 03:38AM
Part Scavenger Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673
Just a thought I had about VDG's the other day if anyone cares... The ionizing brushes from laser printers would be perfect for VDG construction!
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Finn Hammer
Mon Jun 11 2007, 01:30PM
Finn Hammer Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: Skørping, Denmark
Posts: 741
Part Scavenger wrote ...

Just a thought I had about VDG's the other day if anyone cares... The ionizing brushes from laser printers would be perfect for VDG construction!

The brushes are one part that I`d like to be able to just buy.
Do you have pctures of it, so that I can see one without tearing my printer apart?
I have no idea where to look in the printer anyway, so perhaps you could guide me there as well.

Chees, Finn Hammer
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sparky
Mon Jun 11 2007, 02:33PM
sparky Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178
Along the same lines as a Van De Graff - I saw a very interesting device the other day... rather than using a belt to create the static it uses a powder blown through an acrylic tube network via an air compressor to make a very decent charge. It had a 3 ft dome attached to it ---- looked like a hybrid Van De Graff to me .... maybe someone here has seen something similar before. ???
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DrZoidberg
Mon Jun 11 2007, 03:12PM
DrZoidberg Registered Member #350 Joined: Mon Mar 27 2006, 05:14PM
Location:
Posts: 106
I have to agree. it looks really nice.
As far as I know even 5uA are enough to raise your hair.

I always wondered how much of an effect the second comb at the top has. The one that is connected to the top pulley.
I read that it doubles the current, but if I understand the working principle correctly it should only increase the current by about 30 to 50%.
Could you test that? I mean, only if the comb is easy to diconnect and reconnect.
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Finn Hammer
Mon Jun 11 2007, 04:31PM
Finn Hammer Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: Skørping, Denmark
Posts: 741
DrZoidberg wrote ...

I have to agree. it looks really nice.
As far as I know even 5uA are enough to raise your hair.

This depends on the kind of hair and humidity.
When I wrote "no questions asked" hairraising what I had in mind was that the generator should be able to raise the hair of a fuzzy haired old hippie right out of the late sixties, who hasn`t had a haircut since then. Or a wash for that matter.... smile

DrZoidberg wrote ...

I always wondered how much of an effect the second comb at the top has. The one that is connected to the top pulley.
I read that it doubles the current, but if I understand the working principle correctly it should only increase the current by about 30 to 50%.
Could you test that? I mean, only if the comb is easy to diconnect and reconnect.
Oh yes, I have ben testing and testing this over and over.
In principle, the system works by doubling the current. This occours when the charge density on both the ascending belt as well as the decending belt is at a maximum.
The charge density on the ascending belt is clearly at a maximum, because I can see excess charge leaving the belt at the point of tangency to the pulley.
And with only the collector comb in place, the current delivered is as expected: 32mA.
With the top spray comb in place the current is increased to 48-52mA and I have not been able to get it higher up than that.

Antonio Carlos M. de Queiroz wrote a small program called Elcal which does a fast calculation of what to expect from a VDG as well as other handy things.
Link2

Among all the silly (but funny, YMMV) things on Lateral Science you will find the standart text about Van de Graaff generators, written in 1938 by Trump, Merrill and Safford:
Link2

Cheers, Finn Hammer
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