Date: Wed Oct 21 09:45:17 2009

Author: Santos Ramirez

Subject: Re: Van de Graff Generator Rollers / Re: Fun Fly stick

Post:


We also had a VDG that just would not work.
Tried all the things suggested here on tap-L (except
replacing the rollers) but no luck.

In a desperate move, took some Scotch brand Transparent
Duct Tape and put a single layer on the top roller.
Result - over 10 cm sparks...

(not sure how long the tape will last but at least it
worked for the lecture class)

Santos
TAMU-Physics



> Belts are often the issue. When adjusting the combs, if the combs are
> placed too close to the belt, the belt rubs the metal comb,
> impregnating the belt with conducting metal. You now have a short
> circuit, albeit at generally high resistance. But high resistance
> with the voltages of a VDG still means leaking off too much current to
> maintain a charge.
>
> Remember that the VDG belt is traveling very fast, so it will
> overshoot the static adjusted position at the roller/comb, once
> running. You will probably need a bigger gap than you would think to
> prevent this overshoot into the comb.
>
> What I found useful was a thorough cleaning with alcohol. Use a
> Kim-wipe on a meter stick which has been dampened with alcohol. Clean
> the column, rollers, and belt and let them dry, perhaps with help of a
> blow dryer. I always used Ethanol because we had cheap access to it
> at a university. Do not use rubbing alcohol as it contains water
> which also has to evaporate before the VDG will work.
>
> Next, take a very close look at your acrylic column tube. VDG's
> produce ozone which attacks plastic causing it to appear "crazed".
> these hairline cracks collect dirt making them megohm resistors from
> the top dome down to the base. Usually, the alcohol cleaning will
> clean the cracks enough to lessen the conduction.
>
> Or replace the column.I was able to copy the column onto a new piece
> of acrylic tube from local supplier. Drilling holes in the column for
> mounting is the biggest difficulty. You will need a bit intended for
> plastic. Either buy one, or grind off the cusps from your standard
> bit. Alternatively, use a manual drill and go slow. Trappe
>
> Quoting Michael Timmins :
>
>> It may be the black rubber belt. The best thing to do now is get an
>> electrometer and start rubbing rods with the belt to verify the
>> proper charge separation (that sounds nice, huh?). I'll have to get
>> one of these and play with it.
>>
>>
>> Mike Timmins
>>
>> Physics Dept.
>> University of Virginia
>> 382 McCormick Rd
>> Charlottesville, VA 22904
>> mat3q@virginia.edu
>>
>>
>>
>>
>> On Oct 20, 2009, at 3:56 PM, Irons, Stephen wrote:
>>
>>> Well, I replaced the teflon roller with Nylon which should take on an
>>> opposite charge from that of teflon, cleaned the grease off of
>>> everything and put it back together and am getting absolutely no
>>> charge buildup.
>>>
>>> I guess my next move is to play around with the positioning of the
>>> combs. Any other ideas?
>>>
>>> Thanks to all for your suggestions.
>>>
>>> -Stephen.
>>>
>>> On Oct 14, 2009, at 9:32 AM, Zani, Gerald wrote:
>>>
>>>> Keep the aluminum roller at the wand end for both positive and
>>>> negative
>>>> charge versions.
>>>>
>>>> Make an acrylic roller to replace the Telfon roller at the motor end.
>>>> Acrylic and Teflon will produce opposite the opposite sign of charge
>>>> when rubbed with most materials.
>>>>
>>>> Acrylic takes on a net deficiency of electrons (+positive charge) when
>>>> rubbed with most materials.
>>>> Teflon (and also PVC) take on a net excess of electrons (-negative
>>>> charge) when rubbed with most materials.
>>>>
>>>>
>>>>
>>>> - jz
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu]
>>>> On
>>>> Behalf Of Irons, Stephen
>>>> Sent: Tuesday, October 13, 2009 1:01 PM
>>>> To: tap-l@lists.ncsu.edu
>>>> Subject: [tap-l] Fun Fly stick reengineering
>>>>
>>>> Hello all,
>>>>
>>>> I bought two Fun Fly sticks a little while ago
>>>> (http://www.teachersource.com/ElectricityAndMagnetism/Electricity/FunFly
>>>> Stick.aspx?gclid=CLXZj_a9up0CFZho5QodJmXIjw
>>>> )
>>>>
>>>> and have wanted to reengineer one so that it puts the opposite charge
>>>> on the wand. So I finally got around to it this week. When I opened
>>>> one up I found a mini VdG generator, with a teflon roller at the motor
>>>> end and an aluminum roller at the wand end with a black rubber belt
>>>> connecting the two. I had the shop adjust them so I could reverse them
>>>> (teflon at the wand end and aluminum at the motor end). However when I
>>>> turned it on, pretty much nothing happened. I got no charge buildup at
>>>> all on the wand end. Is there something else I need to be doing?
>>>>
>>>> It looks like charge is being extracted from your body (an approximate
>>>> ground) and transferred to the wand end so it didn't seem like I would
>>>> need to rewire it.
>>>>
>>>> Any thoughts?
>>>>
>>>> Many thanks.
>>>>
>>>> -Stephen.
>>>>
>>>>
>>>> **********************************
>>>> Stephen Irons
>>>> Yale University
>>>> Director, Instructional Laboratories Department of
>>>> Physics
>>>> tel: 203-432-3664 P.O.
>>>> Box 208120
>>>> fax: 203-432-6175 New
>>>> Haven, CT 06520-8120
>>>>
>>>> COURIER DELIVERIES PLEASE USE
>>>> Yale University
>>>> Department of Physics
>>>> 217 Prospect Street
>>>> New Haven, CT 06520
>>>>
>>>>
>>>>
>>>
>>>
>>
>
>
>


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