Re: THERABAND VDG BELTS?????????/ (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: Steven Roys <sroys@xxxxxxxxxx>


[Sorry for the delay in posting this.  I was on vacation with no internet
to be found :-( SRR]

---------- Forwarded message ----------
Date: Sun, 03 Jun 2007 22:28:53 -0300
From: Antonio Carlos M. de Queiroz <acmdq@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: THERABAND VDG BELTS?????????/ (fwd)

High Voltage list wrote:
> From: Ed Phillips <evp@xxxxxxxxxxx>
>
> ??? This is a pretty long post so I'll close it with the question I
> wanted to ask Antonio.? Some time back you mentioned a rule of thumb for
> estimating the maximum current which could be obtained from a VDG, given
> the belt speed and area.? Could you sent that again?? I'm curious to see
> how this little machine is performing.? The belt speed is about 780 feet
> per minute and the belt width is 5/8".? I get about 3 microamps current
> which seems pretty good for such a small and simple machine.
>   
Interesting comments.
About gluing, rubber cement really produces curling. I got around the 
problem by gluing pieces of
acrylic to the belt ends with a weak glue that could be easily removed 
later. I have also glued some
belts with cyanoacrylate glue. Works well with theraband and doesn't 
produce curling. The formula
for estimating charge current is:
I = e0.Emax.W.v
Where e0 is the permissivity of air, 8.85e-12, Emax is the maximum 
electric field in air, 3e6 V/m,
W is the effectively used belt width (m) and v is the belt speed (m/s).
If a current doubler is used, this current can be, ideally, doubled.
With your data, 780 feet/min = 4 m/s, 5/8" = 0.016 m. The resulting 
current is 1.7 uA. You probably
have a working current doubler. An insulated metal roller is enough. It 
becomes charged with leaks
from the belt and pushes opposite charge into the belt at the comb.

Antonio Carlos M. de Queiroz