Hi all,

I've been asked to revise the design of an old product. One of
the queries is whether the relays can be replaced with solid state

Basically, the PIC controls 3 relays. An SPST on/off, which
switches 12V power to two DPDT, with a reversible DC motor
as the final load. I took the product on in 1999, and one of the
first things I did was to replace the unreliable FET arrangement
which someone had tried to implement. I'm told that every single
one of my relay versions is still in service and working well, so
that seems to have worked out OK

The SPST relay is 5A, the two DPDT are 3A, the motor stall
current is ~2A. The DPDT are activated before the power so
that they don't actually switch any current, just pass it

I've had a little experience with SSR and remember that they
tended to be at the lower end of the power range, and got very
expensive very quickly for anything over a couple of amps

Looking around Vishay, Omron and a couple of others, it seems
that is still the case. No power DPDT that I can see (not viable
options for this query anyway). A very few SPST at 2A, and
you'd need 4 for a DPDT, so that puts the cost well over relay
price

The SPST I could replace with a PFET, the DPDT would have
to be H-bridges + driver + protection. Sounds a lot more work
and expense than simple, reliable, relays

Has anyone experience with SSRs in this power range and/or
can suggest a component ?

TIA

Joe


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