Re: Dont get zapped. ( safety shorting relays on HV ps outputs)

To: tesla-at-pupman-dot-com
Subject: Re: Dont get zapped. ( safety shorting relays on HV ps outputs)
From: Jim Lux <James.P.Lux-at-jpl.nasa.gov> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Mon, 14 Sep 1998 17:19:22 -0600
Approved: terryf-at-verinet-dot-com

T
> For really dangerous stuff like hv circuits it might be a good idea to
> have
> two lamps just in case one lamp gets blown out. Even with two lamps you
> should still check the switches too! Shorting the hv output might also be
> a good practice.

Shorting the output is standard practice for most commercial HV
equipment. You use a Normally Closed relay (often gravity is the force
that closes it). Then, power coming through the interlocks, etc, is used
to open the safety short. This is especially useful for systems with any
stored energy (like output filter capacitors), because when you turn it
off, the cap gets shorted. Actually, on one of my HV power supplies,
there are two relays. The first, with a series resistor, drops out
immediately to discharge the caps in a few milliseconds (without the big
flash and bang), the second, held up by a big electrolytic cap, drops in
a little later and applies the safety short.  In any case, a second or
so after kicking the plug out of the wall (or whatever), the supply is
safe.

I got tired of having the big bang everytime the power flickered and the
saftey interlock dropped the short on the filter cap.