On 26 Aug 2005 11:49:39 -0700, put finger to
keyboard and composed:

The project I am working on will need a relay for a 1/3 to 1/2 hp 240V
pump motor.

Have been trying to do my homework concerning possible solid state
relays to use.

So far the Teledyne S24A25 (zero crossing turn on) and the Crydom
A2425-10 (random turn on) seem quite similar except for the difference
in turn on.

Am wondering how much difference this actually makes?

I'd concur with those who recommend the zero crossing types. For an
inductive load ...

V = L dI/dt + IR

.... so if V=0 at t=0, then I=0 and dI/dt = 0.

This ensures the softest start.

A capacitive load (eg main filter caps in PSUs) will also benefit from
zero-voltage startup as I = C dV/dt.


- Franc Zabkar
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