Author: Sam Sampere

Subject: Re: VDG question


You need to finish the quote. If I recall, when the SF VdG first came in, it didn't work well. When they spell the name wrong, that's not a good sign! You need to rewire the inside and make sure the bottom electrodes are connected to ground! They were floating! Fix that and your machine will work fine. Honest!


-----Original Message-----
From: [] On Behalf Of simcha Segev
Sent: Tuesday, March 31, 2009 7:05 PM
Subject: Re: [tap-l] VDG question

Santos, I "excavate" in the Tap-l history for the subject "Van de Graaffs"
and there are lot of information and experience of our taplers friends from
February 2007.
Most of them where happy with their Science First VDG, exept Ziggy "My
Science First Van de Graaff is weak compared to the old units so it sits on
the shelf." and Sammy "I've used it a couple times and have been pretty
disappointed in it" (sorry for quotation...).
There is also lot of advices for replacing the rollers to achieve
positive/negative charges.

-- Simcha

-----Original Message-----
From: [] On
Behalf Of Santos Ramirez
Sent: Tuesday, March 31, 2009 11:41 PM
Subject: Re: [tap-l] 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