Done! Electric fan speed control...I'm not an electrician in any way, shape, or form

[80stech]

Me thinks the best solution might be to eliminate the forward reverse switch all together. As long as the chassis ground is good shouldn't be a problem unless maybe it might generate some noise.

But yes, if the reverse switch is left in place the best thing would be to run the separate neg to the motor and then you might as well run the fourth wire out too!

Or leave the controller outside by the fan and only run the control wires for the knob into the cabin.
A length of cat 3 wire poked through the A/C evaporator line seal would probably do the trick.

[wpoll]

Originally Posted by 80stech

Me thinks the best solution might be to eliminate the forward reverse switch all together. ...

I was about to suggest that very thing - although it doubles as an ON/OFF switch. Maybe just removed the wire for the reverse operation?

[80stech]

Yep, just disconnecting the reverse wire would be a lot less technical and still leave off in place

Depending on how the circuit works there might not be a "reverse" wire and disconnecting any wire might be "Off"

[workingonit]

Originally Posted by wpoll

The audio engineer in me says maybe don't use the car body as the return path for the fan motor earth connection. While it will work (electrically speaking) you can't be sure what running decent currents through the car body will do to other systems. Any loose or bad earth connection could experience a raised voltage potential, causing all manner of odd issues.

And if you go down that route, then run a proper return for the power supply also - it's no big issue to run four wires through the firewall rather than two.

This is exactly the reason I started this thread, to get feedback from people with real experience doing things the right way, versus me just trying something new (to me) and hoping for the best.

I was sorta worried about causing a problem in another system (if I was to make the controller share grounds with a BMW module, and thus cause problems with it); and seeing no grounds in those two spots, in the Bentley, I thought they might be safe to use. And, in my racing experience, a bad shared ground can make for a bad day, so we isolated our grounds from others (makes a problem easier to trace). P.S. I have had automotive audio problems before I learned to not share circuits or grounds, so good suggestions!

Originally Posted by 80stech

If you hook it up like that then you risk blowing the controller if you hit reverse.
-and-
Me thinks the best solution might be to eliminate the forward reverse switch all together. As long as the chassis ground is good shouldn't be a problem unless maybe it might generate some noise.

But yes, if the reverse switch is left in place the best thing would be to run the separate neg to the motor and then you might as well run the fourth wire out too!

I wouldn't how just how to rewire the switch, anyway,so I will heed both of you guys' advise, and run the grounds out and separate them, one to battery ground (the power input negative wire), the other (power output negative to the fan motor) to a chassis ground, Will that work better?

[80stech]

NO, the neg motor output from the controller becomes positive in reverse so it needs to go to the motor only and NOT to ground.

[workingonit]

See what I mean, I know just enough to screw the pooch. Thanks for setting me straight, again!

[80stech]

yep, that's better just make sure that there is no ground hooked to the motor negative.

[workingonit]

Attachment 84024

Originally Posted by 80stech

yep, that's better just make sure that there is no ground hooked to the motor negative.

Ok, then, you're saying to make the controller negative output BE the ground, hooked straight to the motor.

I'll disconnect the fan negative from the existing chassis ground, then hook that wire to the controller negative output wire, with neither wire touching the chassis metal, right?





Edit, March 16, 2024

[80stech]

Yep

[workingonit]

Originally Posted by workingonit

...There's a three-position switch attached to the unit (forward-stop-reverse), but I'll only want it set to "forward" of course (though my fan is a "puller" by design), and I wonder if I accidently select the other positions, will the unit cause damage to the fan motor, running at full speed? Of course, the unit came with no instructions.
Attachment 84001 which is forward, which is reverse?

Originally Posted by wpoll

FWIW, that same style switch is often used on 12v halogen desk lamps - single-bar puts 6v on lamp, double-bar puts 12v on lamp.

Single-bar is half-power/speed, double-bar is full power/speed. Usually...!

Of course, that makes no sense in this application, so it may be wired to give forward and reverse, as you suspect.

*edit* - one of the video reviews on the Amazon page where you purchased the controller shows the reverse operation.

-also-

Originally Posted by wpoll

Looks like the double-bar is forward and the single-bar is reverse. He starts off with the forward direction (stated verbally) and the switch is set to the double-bar.

I finally found another polarity reversing switch, with a photo showing the positions for "forward/off (stop)/reverse", on Amazon. I searched Google for many hours to find a "universal switch markings code" list, but never found one showing the double-bar symbol...until now. One was listed on Amazon, all the time.


Of course, with the switch on my unit coming from China, there's no guarantee that it's wired the same as another.

Also, since the Flexalite fan is "brushed", it probably will run in reverse, with no harm done to the motor (perhaps switched by accident, or in testing). I've had many brushed fans that I've reversed, so perhaps this "puller" fan can reverse, too, but is designed for optimal airflow in only the advertised direction.