Surplus market blues

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Well they seemed like a good idea at the time

These relays contain a diode in series with the 12 volt DC coil.

No, not in parallel (used to stop back emf from shooting out transistors driving the relay coil) — series.

Connect the coil up backwards and nothing happens.

I have never seen this configuration before and no, of course I didn’t notice it *after* wiring four of them backwards then wondering why all four appeared bad.

If the issue had been parallel diodes, my current limited bench supply would have just gone into constant current foldback at like .6 volt and 200mA and thus alerted me to the problem… But it couldn’t be that easy now could it?

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