Re: Capacitor Drain Resistors

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi Don,

At 12:32 PM 7/24/00 -0400, you wrote:
>Help!
>
>Please, can someone help me with a formula for calculating the correct ohmic
>value for drain resistors?  I have an assortment of 1 watt - 10k, 100k, and
>1megohm 10kv rated resistors that I can connect in series to achieve the
>correct value.
>
>     Capacitor:  .06uf, maxwell 40kv
>power supply:  15kvac, 240ma
>
>Don
>

The time it takes for a resistor to discharge a cap to a safe value (less
than 20 volts starting with 21kV)is about:

	T = 7 x R x C   or R = T / ( 7 x C )

So if you want the cap to discharge in say 10 seconds:

	R = 10 / ( 7 x 0.06 x 10^-6) = 23.8M Ohm.

The power dissipated is:

	P = V^2 / R   or   15000 x 15000 / 23.8E6 = 9.45 watts.

10 watts of loss (0.27%) will not hurt your coil's performance but will
discharge the primary cap fast enough to save you.  So you need to string
resistors in series to add to around 24Meg at 10 watts.

Cheers,

	Terry