Date: Tue Mar 31 16:43:20 2009 Back to Contents ------------------------------------------------------------------------

Author: Santos Ramirez

Subject: Re: VDG question


To Dave and Simcha and others-
Thanks for all of your comments.
I know I should have checked with tap-l first!

Will pass on info to prof.

I brought the VDG from the other building and checked it out.
The bottom "contact" is just a thin metal sheet with no comb
on it. The top contact is just a thin metal sheet with Vs cut
out on it and it is about 3 mm off the top surface of the belt.

After running it for about 1 minute, I noticed that the
wool felt covering around the bottom roller is starting to come off.

By the way, it uses two small belts.

This looks like a bad buy.


(any Welch reps reading this?)

> Hi Santos,
> I also vouch for the Science First works very well, just as
> Simcha describes.
> -Dave/RU
> simcha Segev wrote:
>> Santos, It may be too late for your professor but I bought lately a
>> large
>> VDG from Science First
>> at ~600$ and
>> it
>> look nice, work wonderfull in all humidity condition, produce long
>> sparks
>> ~25-30 cm and never faild.
>> I'm not familier with your cenco VDG but one major problem could be some
>> dust sticking on the isulator that hold the collector. Try to wipe it
>> with
>> alcohol. It might help. Check if there are some tiny "hair" dert
>> sticking on
>> the rubber belt. Other possibility is a bad comb contact (should be
>> close to
>> the rubber belt but without tuching) .
>> -- Simcha
>> -----Original Message-----
>> From: [] On
>> Behalf Of Santos Ramirez
>> Sent: Tuesday, March 31, 2009 9:52 PM
>> To:
>> Subject: [tap-l] VDG question
>> Tappers,
>> A professor here ordered a
>> Cenco Large Van De Graaff # CP33891-00
>> from Sargent-Welch last week (description follows).
>> Problem is - it does not generate very large sparks.
>> Has anyone else had problems with this VDG?
>> Is it fixable?
>> (We have 2 old (circa 1960) VDGs that work great and
>> the one ordered was the only one close in style to the old ones)
>> Santos
>> TAMU -Physics
>> ***************************
>> Generates 400kV. 105k More than Any Other Van de Graaff!
>> Based on the well-known Van de Graaff system, our newly improved design
>> features a large 28cm diameter collector sphere, a substantial 12.5cm
>> diameter x 56cm high transparent insulating column, a completely
>> enclosed
>> base with a variable-speed motor, and an integrated discharger on a
>> movable arm for controlling the length of the sparks and discharging the
>> sphere after use. The long column and the smooth finish substantially
>> reduce charge loss by leakage and spray discharges, which results in
>> improved reliability and greater maximum spark length. The generator can
>> develop voltages up to 400kV under favorable conditions. The low average
>> current of about 10žA or less prevents harmful shocks. Peak current
>> generated is about 50žA. Operates under all humidity conditions
>> encountered in the classroom. With 3-wire line cord and switch for 110V,
>> 50/60Hz.

Santos Ramirez
Technical Laboratory Coordinator
Physics Laboratory Center ? Heldenfels Hall
Department of Physics
Texas A&M University
College Station, TX 77843-4242
Phone: (979) 845-5236

From Tue Mar 31 16:43:20 2009