D9 print cooling fan only turns on briefly

Just printed a mount and added a 40mm print cooling fan to my prusa steel to help with overhangs but it only seems to turn on briefly even though I can see on the LCD that it should be going.

I've tried sending m106 through printrun and it only turns on for a moment.

The voltage coming out of D9 is 12.05 and the fan is rated 12V, 0.07A. I'm wondering if the trim pot on the pololu drv8825 is set wrong but going by the stepper logic I've set the voltage as .035 and while it goes for slightly longer it's certainly not continuous...

I must be missing something obvious

The fan isn't connected to any of the stepper drivers, so you're off on the wrong track there. The fan is driven by pwm and many fans won't run with low pwm settings, so maybe you're trying to run it at 10%?

Or the fan is just plugged in backwards

But yes some fans require a small capacitor across the terminals to do PWM at slower speeds

First try turning it on full speed M106 S255, if this doesn’t stay on, check you have the correct polarity.

Edited 1 time(s). Last edit at 03/22/2016 03:05AM by Dust.