RAMPS 1.4 and PWM-enabled fan. What do I need to know?

Hello All,

I've recently added a fan to my Prusa Mendel reprap. The fan I repurposed out of a non-functioning computer that was easily over 10 years old. I've noticed via M106 S??? commands that I don't appear to have PWM, which doesn't surprise, given where I got the fan. The fan is "all on" if I give a M106 S128 or higher, and there's no discernible difference between S128 and S255.

If I were to drop the $12 or so that such a fan might cost online, how would I ensure I'd have the PWM working? My current fan had just two wires which go straight into D9. The fan I might order has four pins. What are those other two pins for?

Anything else to watch out for? Any cheaper fans out there come recommended?

Thanks,
K

PWM control works just fine on my 2-wire fans. They are all of recent purchase. One has 3 wires, but I only connected the red and black. The third wire, I'm led to believe, is not to control the fan, but to report fan speed back to the controller.

I had to put a small capacitor across my fan terminals to get my fans working. Otherwise they just hum unless at full power

jbernardis Wrote:
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> PWM control works just fine on my 2-wire fans.
> They are all of recent purchase. One has 3 wires,
> but I only connected the red and black. The third
> wire, I'm led to believe, is not to control the
> fan, but to report fan speed back to the
> controller.

+1

3rd wire is a tach

Sounds good. Thanks everybody.

Anyone know what the fourth wire is for? And if I should stick to the three wire varieties?

lazzymonk Wrote:
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> I had to put a small capacitor across my fan
> terminals to get my fans working. Otherwise they
> just hum unless at full power

This sounds very good, and like it might even apply to me (because my fan doesn't go if I don't give it enough S???), but I don't know enough about electronics to figure out how I might solder a capacitor into the mix, and what might constitute capacitor smallness in this instance...

mine isnt soldered. it is just installed in the screw terminal on my ramps board where the fan connects.

A 1uf seems to work, but have tried bigger to with success.

Quote
lazzymonk
mine isnt soldered. it is just installed in the screw terminal on my ramps board where the fan connects.

A 1uf seems to work, but have tried bigger to with success.

What kind of capacitor did you use? electrolytic?