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Author: Subject: Does the upper roller of a van de graaf generator needs to be inside the sphere?
Foeskes
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[*] posted on 6-8-2018 at 05:35
Does the upper roller of a van de graaf generator needs to be inside the sphere?


I'm currently building a van de graaf generator and many sources seem to suggest that putting the upper roller and comb inside the topload with a hole drilled in it makes the result better. Why is this the case and is it really nessesary?
I don't really want to cut the topload(made of ikea bowls) unless nessesary.

[Edited on 6-8-2018 by Foeskes]
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MJ101
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[*] posted on 6-8-2018 at 06:40


IIRC no. But you do need a top and bottom comb to couple charge from the top roller to the sphere.

Take a look here.

https://www.instructables.com/id/900000-volt-Van-de-Graaff-G...

Best of luck. :)
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Sulaiman
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[*] posted on 6-8-2018 at 07:08


AFAIK the terminal voltage is limited by corona discharge
and corona discharge initiates at sharp edges
or about 3kV per mm radius

e.g. even if no other sharp edges or points,
a two inch diameter roller with no shielding could not sustain more than about 75 kV.

If the roller assembly is shielded inside (for example) an eight inch diameter top load,
then the maximum voltage achievable would be around 300kV.

look carefully at the shape of the topload - there are reasons.
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