HI Ian
For safety I still use common sense, fuse every thing and use a plug! My
experience with mechanical relays here is the exact opposite, I've welded
them closed twice!! Not all faults occur on the tube side of the glitch
resistor unfortunately. Before I committed to using SSR's I spoke with two
of the local electricians that I use about them, zero failures! I also
don't do as John describes in his post, mix arcy/sparky mechanical contacts
with the SSR's, sounds like a good way to test the snubber circuitry, HI. I
would probably feel uneasy also with these in some of the Frankenstein
equipment John develops but in our "tiny" supplies I have no worries. Has
anyone with a Command, QRO or Emtron amplifier ever had a SSR failure? The
other tribe is just curious!
Cheers, Paul
PAUL HEWITT
WD7S PRODUCTIONS
QRO HOMEBREW COMPONENTS
http://wd7s.home.att.net
>
> 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.
>
>
> --
> 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
> Editor, 'The VHF/UHF DX Book'
> http://www.ifwtech.co.uk/g3sek
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