Motor Protection

The cooling fan ECU monitors the speed of the cooling fans, from the current draw of the motors, and incorporates strategies to protect the motors from electrical overload if the fans are seized or heavily loaded (e.g. by debris or during wading).

When the duty cycle of the PWM signal indicates the cooling fans should be turned on, the cooling fan ECU initially outputs 2.5 volts to the motors to produce a SOFT start. When the cooling fan ECU detects the motors are running satisfactorily, it then increases the outputs to the appropriate voltages for the required cooling fan speeds. If a motor fails to start within 3 seconds, the cooling fan ECU turns off the output to the affected motor, waits for 5 seconds and then tries another SOFT start. If the second soft start fails, after a further wait of 5 seconds the cooling fan ECU outputs 6 volts to the motor in an attempt to get it started. If the motor starts, the cooling fan ECU then increases the output to the appropriate voltage for the required cooling fan speed. If the motor fails to start within 4 seconds, the cooling fan ECU turns the output off, then, provided the cooling fans are still requested on, periodically invokes the start routine in an attempt to get the motor running.

If a cooling fan is already running and then seizes or becomes heavily loaded, the cooling fan ECU turns off the output to the affected motor, then periodically invokes the start routine, while the cooling fans are still requested on, in an attempt to get the motor running again.

When one of the cooling fans is not running, the cooling fan ECU runs the other cooling fan at maximum speed.