Joe,

What is the DC Voltage of the motor? 12V?=20
If so there are ICs that include all the driving function of DC Motors and =
can handle easily 2A max.
the old L297L298 devices (H-bridge) should do what you need at a very decen=
t price, most likely less than the price of 3 relays.

My $0.02,
Jean-Paul
AC9GH



> On Apr 23, 2015, at 6:13 AM, IVP <joecolquitt@clear.net.nz> wrote:
>=20
> Hi all,
>=20
> 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
>=20
> 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
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> 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
>=20
> 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
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> 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
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> 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
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> Has anyone experience with SSRs in this power range and/or
> can suggest a component ?
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> TIA
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> Joe
>=20
>=20
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