Electronic – Standard Relay vs SSR vs TRIAC for Switching CFLs


I'm confused weather I should go for a standard electromechanical relay (EMR) or a sold state relay (SSR) to switch CFLs @ 220V with 100W max load. This is for a commercial product with the following objectives:

  1. Have at least 7 years of life (of continuous use)
  2. Resilient to short-circuits at the outputs of it's switching device (SSR, EMR or TRIAC).

The main concern here is the failure of the device: SSR will provide an extremely long life (if other components are up to it) whereas a EMR will have a relatively shorter life-span. However, it seems EMRs are more rugged to a short-circuit (till the circuit breaker or fuse pops, at least). A failure mode of CFLs I've found is that they sometimes short-circuit – either the internal wiring insulation fails or some other type of fault due to sub-standard components).

I suppose the question becomes: how long can I expect an EMR with a resistive electrical contact life of 100,000 cycles to work if the relay is switched 10 times a day?

Alternate approach that I had in mind: use a large TRIAC (rated for 30+ amps continuous) and a resettable fuse, rated for 500 mA, in conjunction with it. The fuse interrupts the current flow thereby saving the TRIAC from damage. Since the TRIAC is a heavy-duty one it has a higher likelihood of surviving such a failure.

Will the TRIAC allow me to have my cake and eat it too?

Best Answer

It might be on the optimistic side to expect the resistive life to apply to a CCFL load, however an overrated (eg. 10A or 16A) mechanical relay with any kind of a rating for a tungsten load will probably last just fine with a 0.5A CCFL load.

If it was purely a resistive load you'd probably get in excess of 10^6 operations. Check the life curves in the relay datasheets.