|Subject:||Re: [Amps] soft start circuits|
|From:||"Ian White, G3SEK" <G3SEK@ifwtech.co.uk>|
|Reply-to:||"Ian White, G3SEK" <firstname.lastname@example.org>|
|Date:||Fri, 9 Jan 2004 09:21:10 +0000|
PAUL HEWITT wrote:|
I normally use these as the HV supply master mains switch in the amplifier and have never had a dv/dt problem.
What makes me nervous about SSRs as safety-critical circuit breakers is that if ever they do fail, they will almost certainly remain switched on (forever). In safety engineering terms, they are not 'fail-safe'.
Mechanical relay contacts may also weld shut, of course, but that's nowhere near as certain to happen. More than a century of industry experience makes it much more likely that the spring will pull the contacts safely apart.
(Maybe I've spent too much time around safety engineers. They are a simple, primitive tribe, who like technology that's obvious and sure to work... or if it doesn't work, is guaranteed to fail safe.)
If MOV's make you nervous, spark gaps are also suggested.
MOVs don't make me nervous at all - I use them, and love 'em. The key difference is that we don't use MOVs as circuit breakers!
I think I've posted this before but here it is again, Solid-state Relay Handbook with applications, by Anthony Bishop, (ex Royal Air Force, HI), from Crydom Company. This is an excellent book(224pp) and available from Mouser for under $20. It covers all types of switching for various loads and control side interfacing, (and MOV's, HI). Everything you wanted to know about SSR's but were afraid to ask!!
Thanks, Paul - I do need to find out more about SSRs, and will definitely get that book.
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