How to spec a protection/flyback diode for a contactor's coil?

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1

I have an open drain signal output that I would like to use to turn on a Gigavac GX23B contactor (12vdc coil) when that open drain is active pulling to ground.

Unfortunately my open drain signal is limited to 175ma, and my contactor's coil inrush current is 3.9amps. The contactor does have an internal economizer but even when engaged the coil still pulls 230ma, well over my 175ma limit. I think a good solution is to use an SSR.

The Multicomp MC002254 seems to be a good fit, but its spec sheet shows that a protection diode should be put across the load.

How can I spec an appropriate diode for my application? The coil's back EMF is 55v, transients 50v, and reverse polarity 16v.

2

The rule is to have a diode that has the same or larger current rating as the relay.

Example:
If the relay coil needs 500mA to operate, 500mA or more rated diode is used.

3

That's without the diode. The diode has to support (only) the supply voltage and the actual coil current.

4

1N4004 gp rectifier will work in 99% of cases.
1N4004

5

This was brought to our attention.

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6

Faster release time can be achieved with resistors or Z-diodes which provide a load to the EMP where its energy is consumed. A diode in parallel will short cut and thus invalidate such circuits.

Remember that current will flow infinitely in a circuit of zero resistance.

7

Old joke, when in doubt, RTFM! LOL good catch

8

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