I have the FM stage 1 fan kit in the car. I have both fans simply wired to the OE harness as the FM instructions describe. The fan comes on at 195 and off at 190, all working fine, but the Spal fans have a lot of initial power draw and if I am stopped at a red light or something when the car is stopped and idling then there a brief drop in RPMs when the load from the fan kicks on. I wanted to make a simple map in one of the Generic PWM Outputs to slowly ramp up the fan instead of 100% all at once. I tested the fan in the Output test mode on PWM2 and the fan works fine there for on/off input but when I try and do a % in the pulse duty cycle the relay in the fuse box makes crazy clicking noises no matter what Hz I try. Do I need to put another relay into the wiring someplace to make this work correctly?

 

You can't PWM a standard relay. The other problem with running PWM fan outputs on a megasquirt is that you're limited to 1000hz which is to slow. So even if you switch to a solid state relay it ends up putting a lot of stress on the motor shaft. I've seen posts on other forums where it actually broke the shaft.

There are some OEM fan controllers that accept a lower frequency input and then output at 18000 hz. IIRC they're found on some corvettes, Mercedes, and Ford fusions.

 

Ok. After I read this it sparked a fuzzy memory of something I've seen before and found this youtube vid describing what you had written. Have to decide if it's worth all the effort for something that's not really a big issue. Thanks.

 

Are they both turning on at once? I’d split them to two different relays and outputs, should help a lot.

 

No, they are not. One at a time.

 

Did you ever find a solution?