Re: A Couple of Questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Terry Fritz <twftesla-at-uswest-dot-net>

Hi David,

At 12:34 AM 12/9/2000 -0500, you wrote:
>Hi Terry, all,
>
>I'm going to have to show my ignorance and ask you all a couple of
>questions regarding capacitor discharges. What is a dv/dt? I know 
>it has something to do with how rapidly a cap can discharge all of
>its energy in a very short time and the higher the value, the 
>faster the discharge and consequently, the better for us coil-
>ers.

dV/dT is simply the change in voltage divide by the time that change takes.
 A dV/dT of 10000V/uS says that these cap's voltage can change
10,000,000,000 volts per second before the current burns them up.  Let's
say we have a 2000 volt cap that runs at 200kHz.    

dV/dT = 2 x pi x Vpeak x frequency

Divide the above answer by 1,000,000 to get V/uS.

dV/dT = 2 x pi x 2000 x 200000 = 2513 V/uS

>
>Also, on the Maxwell cap specs page that Jim Lux so gracious-
>ly made available to us (thanks Jim), there was some spec 
>about 20% reversal current, or something like that. Can some
>one explain this to me? I would appreciate any responses on 
>this to help better educate this dum-dum. :^)

Apparently some caps don't like to go from positive to negative voltage.
This is not a big problem with polypropylene caps but some types of
dielectric tend to act a little like batteries and are not graceful about
voltage reversals.  Perhaps someone who knows more about this could explain
it to both of us better ;-))

Cheers,

	Terry


>
>Sparking in Memphis,
>David Riebe
>