I have been following another thread for an automotive cooling fan controller but it has not "hit home" for me.
I currently have a purchased 2-speed fan controller that uses a temperature probe (thermistor, I assume) that plugs into the radiator coils. The controller connects to the probe and has a pot to adjust the turn-on temperature setting for the low speed fan. The output for the high speed fan is supposed to turn on when the temperature increases another 10 degrees. This "kinda" works. The controller is rated for a maximum current of 30 amps.
The fan is from a Ford Taurus I think, and has three wires for two speeds and ground. It runs at low speed with ground and the low speed wire powered and at high speed with ground and the high speed wire connected. Both the low speed wire and the high speed wire cannot be connected or powered at the same time. I assume that means it's a tapped winding on the fan? The low speed draws about 25-30 amps. The high speed draws about 50 amps.
Unfortunately, when the high speed output of the controller turns on it also keeps the low speed output on. I have remedied this with some relay logic using 70 amp relays so the low speed is disconnected when the high speed turns on.
I have two things I'd like to change for this setup:
1 - increase the differential between low speed temperature and high speed temperature to about 15-20 degrees instead of 10 degrees.
2 - add a soft start to the high speed so I don't blow the 70 amp fuse
Ideally, a PWM circuit to use one of the windings to produce an analog output (fan speed) proportional to the temperature would be great.
I'm fairly linear literate but know nothing about PWM. My analog designs ended about 30 years ago.
Jack
I currently have a purchased 2-speed fan controller that uses a temperature probe (thermistor, I assume) that plugs into the radiator coils. The controller connects to the probe and has a pot to adjust the turn-on temperature setting for the low speed fan. The output for the high speed fan is supposed to turn on when the temperature increases another 10 degrees. This "kinda" works. The controller is rated for a maximum current of 30 amps.
The fan is from a Ford Taurus I think, and has three wires for two speeds and ground. It runs at low speed with ground and the low speed wire powered and at high speed with ground and the high speed wire connected. Both the low speed wire and the high speed wire cannot be connected or powered at the same time. I assume that means it's a tapped winding on the fan? The low speed draws about 25-30 amps. The high speed draws about 50 amps.
Unfortunately, when the high speed output of the controller turns on it also keeps the low speed output on. I have remedied this with some relay logic using 70 amp relays so the low speed is disconnected when the high speed turns on.
I have two things I'd like to change for this setup:
1 - increase the differential between low speed temperature and high speed temperature to about 15-20 degrees instead of 10 degrees.
2 - add a soft start to the high speed so I don't blow the 70 amp fuse
Ideally, a PWM circuit to use one of the windings to produce an analog output (fan speed) proportional to the temperature would be great.
I'm fairly linear literate but know nothing about PWM. My analog designs ended about 30 years ago.
Jack
