[Amps] Solid State Relays Again

[Roger (K8RI)]

On 2/9/2014 11:44 PM, Jim Garland wrote:
> 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.
> 73,
> Jim W8ZR

We used a lot of solid state relays in industry.  I don't remember ever 
having to replace one so, I think Jim is right. It was likely an  an 
inductive kick that caused it to fail.  Back then, they were relatively 
new and for AC  "I think" we had back to back diodes across the relay, 
BUT that I quit in 87 and had been working almost exclusively with 
chromatography for more than 3 years prior to that. We did not build or 
design any of that equipment and given it was on the order of 30 years 
ago (give or take), I really don't remember much other than the basic 
theory and they were trouble free.

73

Roger (K8RI)

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