[Amps] Solid State Relays Again

Paul Christensen w9ac at arrl.net
Mon Feb 10 13:14:32 EST 2014

> A capacitor input type filter will cause much higher current peaks (5X not
> unusual) than the average current. This makes over sizing the SSR current
> rating  very important.

This is discussed in the linked Omron document titled "Solid State Relays - 
Common Precautions."


>From the text under capacitive loading:

"The supply voltage plus the charge voltage of the capacitor is applied to 
both ends of the SSR when it is OFF. Therefore,
use an SSR model with an input voltage rating twice the size of the supply 
voltage. Limit the charge current of the capacitor
to less than half the peak inrush current value allowed for the SSR."

Lots of guidelines and rules to follow when using SSRs -- a lot more than 
when using mechanical relays.  Also note the section on transformer loading. 
Since a typical plate supply is likely to be switched unloaded, special 
precautions are needed when selecting the right SSR for the job.

Paul, W9AC


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