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Capacitor discharge
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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
HV
>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
may
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
400V
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
likely
>to be still charged: how to discharge them safely?
Use a bleader resistor in parallel with the cap. That simple. Anyway,
regulations
tell you also that you should do that if there is dangerous amount of
energy
stored. (Finnish regulations at least)
>1. A 10 Mohm HV resistor in parallel with each capacitor. This is what is
used
>in the capacitors employed in microwave ovens (they have got this
resistor
>INSIDE the cap can). But how that will affect the HV capacitor
performance?
Makes no difference. It is high impedance. Consider the rest of the
system...
>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
I
mentioned earlier with a low-voltage cap was such a relay-shorted one.
That
perticular type of resistor just could not handle pulsing on and off
frequently.
Finally resistor failed. Was not fun to handle that cap like it was
discharged.
--
Harri Suomalainen mailto:haba-at-cc.hut.fi
We have phone numbers, why'd we need IP-numbers? - a person in a bus