[Amps] Solid State Relays Again

Jim Garland 4cx250b at miamioh.edu
Sun Feb 9 23:44:17 EST 2014

Hi Jim,
I'm guessing the relay shorted because of a voltage transient, not  a
current overload. A possible culprit would be the inductive kick from the
plate transformer caused when the relay opened. You could try putting a
bidirectional TVS diode directly across the relay terminals to suppress a
large inductive spike. A reasonable choice would be Mouser  p/n
511-1.5KE300CA. Pretty cheap protection for $0.76. Also, you might consider
a solid state relay with a heftier 50A/480VAC rating. The Crydon D2440's
voltage rating might be a bit marginal for the application.
Jim W8ZR

> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Jim W7RY
> Sent: Sunday, February 09, 2014 8:14 PM
> To: amps
> Subject: [Amps] Solid State Relays Again
> I just had a solid state relay in my 8877 power supply short during the
> RTTY contest this weekend.
> I use 2 relays, one to short out the step start resistor, and the other
> one for the other leg of the plate transformer.  Both are controlleed by
> the WD7S triode board.
> The one that shorted is was NOT the step start resistor shorting relay.
> They are both Crydom D2440. They have been around a while because the
> defective one has a date code of 9425.
> Just trying to do some research and thinking of switching to mechanical
> relays.
> I looked at the archives and read a debate between Ian and Paul about
> this exact subject. Any new thoughts?
> 73
> Jim W7RY
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