Quote:
Originally Posted by uwanna
The diode is not protection from "arc burn" but rather protection from
back EMF from the collapse of the de-energizing relay coil. It's meant to protect the solid state over rev protection ckt. Therefore, you are correct in that a diode would probably not be necessary as there is no relay coil with a SS relay.
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In my own work experience the first time I had a relay with a diode across the coil was for one purpose of protecting a high current circuit. The diode was installed to prevent relay chatter causing a momentary closing of contacts when the coil field collapsed and created a reverse current flow. The diode prevents the reverse current and preventing the momentary closing of the contacts. Under high current applications the non diode relay would arc the contacts and cause the relay to fail prematurely. Does this theory apply to the relay for the fuel pump? I believe that it does, a diode relay can be used in any circuit but a non diode relay in a high current circuit will suffer premature failure.