[TR] auto fan controllers

Randall tr3driver at ca.rr.com
Wed Aug 28 12:59:17 MDT 2019


FWIW, I “rolled my own” using parts from the electronics junk bin.  Heart is a 741 style op amp IC, which drives a power MOSFET, which in turns drives a cheap auto relay.  Probably could have left out the relay, but I used it anyway.  The other key piece turned out to be using a voltage regulator IC to feed the whole thing (except the relay contacts).  Without the VR, the kickback from the fan motor would cause the relay to chatter under some conditions.  (Since the unit was already installed when I figured that out, I just tapped into the VR that also supplies my TR4 temp gauge).

For the sensor, I used an old GM (I think it was) gauge sender, which screws into the opening in the back of the water pump housing where the heater return goes (on cars with heaters).  Although I didn’t try it, I believe you could put a tee piece there and still hook up the heater return if you wanted to.

That’s probably not much help.  If I didn’t want to build one, I’d probably still be using the DeRale electronic controller, with a probe that just pushes into the radiator fins (like the one you linked to).  I ran one on a Stag for almost a year, but converted back to a mechanical fan as the electric pusher seemed to block air flow at freeway speeds.

Hayden offers a similar unit as well, which I’ll bet would also be more reliable and longer lived than your “economy” ebay find.

- Randall
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