In a message dated 8/17/2005 9:37:49 P.M. Central Standard Time,
dennisberry@worldnet.att.net writes:
There has been a lot of recent discussion on Step Start circuits. Would one
of the 'hockey puck' or solid state relays work OK in this application?
They are usually available with 25 amp capability at a decent cost. I'm
curious if the solid state relays are susceptible to any RFI/EMI pick-up from
an
amplifier? Any experience with one of these devices?
Thanks for any comments,
Dennis
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I have used solid state relays for several years in this application with
excellent results. As usual though, there are some gotchas.
Most of us use capacitor filter high voltage power supplies. These power
supplies characteristically have peak current requirements five to ten times
the
average current draw. This is because the filter bank has to be recharged d
uring the short period of time that the ac half cycle voltage is between the
filter C voltage and the peak of the ac cycle.
At full legal power limits, a solid state relay rated at 25A will be under
stress due the high peak currents during key down periods. I have had 25A units
fail under these conditions. After switching over to 40A units I have seen
no more failures.
Also, there is a voltage drop across the solid state relay that generates
some heat. The relay must be mounted in a manner that the heat is absorbed for
long life; you can't hang one out in space like a mechanical relay.
I have had no rfi issues but my antennas are some distance from the power
supply location and that probably helps.
73/Gerald/K5GW
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