Wednesday, 8 June 2016

Protecting Solid State Relays from Short Circuits



I have 4 SSRs on my board with a steady state current rating of 2A and a peak current rating of 9A (Relays are CPC1976). This product is meant to be a commercial one and the relays will be powering bulbs (CFLs, Incandescent etc) upto 100W @ 240VAC


My main concern is short-circuits. A lot of CFLs that I've used in my house short circuit for a small time when they fuse. The short circuit is serious enough that the circuit breaker trips. This will obviously fry my relays.


I can easily include a fast-acting fuse but that will be have to be replaced everytime the lights fuse! I could consider a resettable fuse but most of them seem to be too slow to act to save a semiconductor device.


What are my options here to have a resettable solution yet save my relays from damage?


One idea I had was to do away with the relays and use opto-coupler + triacs instead. Triacs are cheap and I can easily find some that can handle large amounts of current (obviously a short circuit will be more than they can handle). These may survive such short circuits with the addition of a resettable fuse?




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