Capacitor discharge

From:  Harri Suomalainen [SMTP:haba-at-cc.hut.fi]
Sent:  Monday, June 01, 1998 3:26 PM
To:  tesla-at-pupman-dot-com
Subject:  Re: Capacitor discharge

>I understand that using an NST and HV cap in series with the primary, the
>cap will discharge through the primary-chokes-NST which is a pretty low
>resistance path.

Even at such a case you should *not* rely on the cap discharging. There
be something wrong like a broken connection somewhere and the cap would
still be charged. I've seen this happen. Fortunately that was only with
charged 500uF cap :)  I learned from that one. Keep reliable bleaders
there always!

>This means that, after power-off, the HV and other capacitors are VERY
>to be still charged: how to discharge them safely?

Use a bleader resistor in parallel with the cap. That simple. Anyway,
tell you also that you should do that if there is dangerous amount of
stored. (Finnish regulations at least)

>1. A 10 Mohm HV resistor in parallel with each capacitor. This is what is
>in the capacitors employed in microwave ovens (they have got this
>INSIDE the cap can). But how that will affect the HV capacitor

Makes no difference. It is high impedance. Consider the rest of the

>2. A kind of delayed-relay battery that will short all caps through, say,
>100 Kohm resistors. But then you will have HV wires running through your

Make sure the shorting resistor in that case can handle pulsing. The case
mentioned earlier with a low-voltage cap was such a relay-shorted one.
perticular type of resistor just could not handle pulsing on and off
Finally resistor failed. Was not fun to handle that cap like it was

Harri Suomalainen     mailto:haba-at-cc.hut.fi

We have phone numbers, why'd we need IP-numbers? - a person in a bus