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I wired electric 12V DC fans to my vehicle. Fans are relay controlled by the negative. Relays are controlled by a thermal switch. Fans, fans relay control and ignition are all fed through the same fuse box. If I turn off the ignition with the fans running, the engine won't stop until the fans are stopped. It looks like the fans generate voltage and are backfeeding my fuse box, hence, fans relays stay on and ignition keeps the engine running for a few seconds.

Can I put a diode inline on the fan circuit?

Would a flyback diode would stop the backfeeding?

Thanks

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3 Answers 3

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A series diode should work just fine. Make sure it's rated for the current. A flyback diode won't do anything useful.

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Just control the positive with the relays.

That is one reason why most car cooling fans I have come across are relay positive controlled. When you make millions of cars 1 diode adds a lot to the cost...

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It appears that power for the fan circuit is sourced from the 'On' terminal

of the ignition switch, as shown below.

enter image description here

The problem would be solved with the power being drawn prior to the ignition

switch.

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