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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.
Front wiew: Corona generator is on the green pcb.
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.
The spray and collector combs are made from stripboard and short needles: The lower spray comb looks like this:
The top electrode is made from IKEA bowls, and the inside looks like this:
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:
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:
This is the finished article: !
The generator charges with 50uA and is this enough to raise hairs? Susanne has curly hair, like this:
Charge her up, and her hair looks like this:
Jette, on the other hand is fair haired, and charged to full potential she looks like this, on a day with 90% humidity:
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.......
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.
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.
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?
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.
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.
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. ???
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.
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....
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.
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:
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