2 speed
there are 2 relays on that one
I think i would like to make my own PWM controller - have done some research and the control portion can be done with a PIC microcontroller and an LM35 precision temp sensor. seems that you can get parts that will operate from -40C to +125C (+150C for the temp sensor) so that is a fair enough range i think for automotive use. there is a power (high amp side) portion to this which i didn't get into yet but that should be straight forward once i figure out the schematics and code. the nice thing about it is that with the microcontroller you can basically program whatever ramp-up ratio you want and also whatever temp to rpm ratio and the percentage increase can be variable as well (non-linear i mean). I would have to be re-written but they are cheap enough that i can have 3 or 4 that can be swapped out on the road. I would also want to have an ambient (outside) temp probe and have the fan speed based on that, like in the winter most likely shouldn't be running at all or low speed compared to summer when you need more airflow to get the same cooling effect. And i'm also thinking some additional inputs like oil temperature (if there is an oil cooler in front of the rad), inlet air temperature (for the forced induction so it will turn on to run air thru the intercooler at low travel speed) and some other things might come up (like A/C control if I ever get one installed which is not very likely, or manual OFF/FULL override mode)
I just need time to work on it...
will probably cost more in the end than buying one from this guy but the fact he didn't answer any of my emails makes me look somewhere else.
I don't like the spal one due to lack of features.