PWM Fan controller
Since BMW OEM double temp switch switching temperatures are quite high, I started to think if I could do a controller controlled by the ECU and varying the speed based on the coolant temperature and engine speed.
Since Autronic SM4 has some PWM outputs left, I decided to make a device controlled by O/P PWM2 output. Autronic simply measures the coolant temperature and varies the fan speed with the length of the pulse. After engine has been turned off and temp is high, fan is reversed to pull air out from the engine bay.
Graph shows how well the fan controller works, coolant temperature is pretty much stable 90C all the time. Blue is the O/P PWM2 ratio from Autronic. 100%=fan is stopped, 0%=fan is full speed.
James Colebourne
Posted at 2011-07-03 03:12:55
Nice addition, been looking to do something like this myself. What'd you use for the PWM speed controller? Most controllers I can use use a 1-5V input or only have a trim pot for speed control.
Administrator
Posted at 2011-07-03 03:35:07
Thanks for your query.
I'm using an output from Autronic to the controller together with a pull-up resistor to switched +12V supply. The Mitsubishi Lancer controller should work with 5V input. I use it to control the electric water pump and has worked flawlessly. Other good one is the controller used in Audi A6. It works really nice, it has a soft start system so it doesn't create spikes.