SPAL UNIT QUESTION (MARK 8 FAN)

IIRC, the high speed setting uses a relay (triggered by a grey wire). Does that sound right to you? They have some schematics in the instructions showing this stuff but it's been awhile since I looked.

Good luck.

From *what I remember*, the spal does a a simple two speed "PWM" implementation for the fan. (PWM: Pulse Width Modulation technique.) On high, the fan gets the full "12V". On low, since it's a fan (motor), the need to do a PWM technique.

For an easy example, let's say they do the following:
They put out a 1000 pulses every second. Each pulse is "on" 3/4ths of the time and "off" 1/4th of the time. This results in a fan speed of ~3/4ths (not really, but let's say it does. . This is what you have to do with most electric motors to vary the speed. You can't just reduce the voltage. So, they do a "PWM" (Pulse Width Modulation) technique.

The MKVIII fan, is different. The fan motor has a "center tap" on the coil for the low speed wire. So, if you apply power to just the low speed wire, only half of the motor coil is getting energized. Therefore, it runs slower. That's different than the PWM technique that the DCC fan controller and the ?Spal? fan controller use.

The DCC fan controller is much more intelligent and it varies the pulse width according to the temperature. That way, the engine temp stays more consistent and you also use less power (fewer amps from the alternator, which means less HP needed from the engine to turn the alternator).

Hope the above helps! I've been doing this crud for 7+ years.