New 50 mm cooling fan has no modulation

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Mount PrintMore
Posts: 34
Joined: Mon Apr 14, 2014 4:09 am

New 50 mm cooling fan has no modulation

Post by Mount PrintMore » Sat Aug 30, 2014 3:55 pm

I recently ordered and received a new part cooling fan (50mm) from Makergear.
I have an older 12V/19V machine and I received a fan with a 12V label, as I requested.

However, when I try to use the fan, I get zero fan speed until I'm above a command of about 250, then I get full fan speed.

I must be missing something obvious here, any thoughts?

Dale Reed
Posts: 376
Joined: Thu Apr 10, 2014 1:39 am
Location: Cleveland Heights, Ohio USA

Re: New 50 mm cooling fan has no modulation

Post by Dale Reed » Sat Aug 30, 2014 9:59 pm

Mount,

Some brands of fans are not very tolerant of PWM speed control. These little fans have electronics in them to control commutation (reversing polarity of the magnetic field) --- that's how brushless DC fans work without brushes... On some, the electronics are happy to receive pulsed DC --- some are happy IF the pulsed DC is at or below certain frequencies --- and some are not tolerant of it at all.

The firmware on the M2s from the 12V/19V era (mine was a late one, received April 2013, a few months before the switch to all-24V) is set up with a fairly high PWM frequency -- somewhere above 20 kHz, so it won't be audible (to humans, anyway). I have seen some fans that won't run on that with a setting of less than about 220 / 255.

The newer Marlin firmware source code has a #define macro that lets you select a configuration for slower PWM --- about 400 Hz. I've found that every fan I've tried with 400 Hz PWM works fine and can be speed controlled down to about 25% (64/255). I actually got an Arduino and a motor shield to test this and was merrily collecting data when my cheapie laser tachometer stopped working. Got a new laser tach, but haven't had any time lately to test fans, or print for that matter... :-(

By the way, with the PWM at 400 Hz, none of the little 40mm and 50mm fans I tested really "buzzed" audibly at all. The sound of the fan was pretty much the same -- all you hear is the impeller pushing air, no power supply noise at all.

Long story short: there's a firmware solution for better fan speed control. I'm not on my printing PC right now to find where I got it, but searching this forum for "PWM" and "Marlin" should get you the articles where we discussed this and a link to the firmware (probably at github).

Dale

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