1. Find a high current bosch relay with a built in diode.
What does that diode do?
Does this mean the fan, when shut off, acts like a generator while still rotating?When the power is cut to an inductive load (fan) it creates a current spike in reverse. The diode give this current a path to flow so nothing gets damaged.
Does this mean the fan, when shut off, acts like a generator while still rotating?
And... as I understand, the diode is sort of a check valve for electricity.
You'll have to excuse my ignorance, I is a bit unedumacated in the arts of electrical engineering.
i was planning on just running a standard 40 amp relay without a diode on the fan. The way a relay works, there shouldn't be any reason for backflow...all a relay does is open or close a circuit, on or off, that should be it. So, if your switch is off, the relay should be open, effectively cutting off the output from the rest of the car.
FWIW, When I had the problem I mentioned above I cut the wires running to the thermal switch and haven't used it since. I never got around to adding a diode in and mine now has a delay before it shuts off. (Just enough to notice) I know it's coming from the fan because it stopped doing it when the fan was trashed. (It got shoved into the engine and the fan motor fried) The only explanation I would have is that apparently the relay will stay energized as long as there are amps flowing backwards through it. Might be because the relay is actually a large solenoid instead of the solid state relays I use for everything other than the fan.
Working out my wiring now, and i'm looking for a normally closed latching relay that will reset when input power is turned off. Anyone know where to find something like that?
Something intersting I came across in my search