Print cooling fan not working properly
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Very cool, @red-sand-robot, I'm happy this helped
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@SnowCrash Thanks for that. I am running them at 25000hz and I think there is a slight improvement but still noticeable. I am guessing the fans that I got are not the best.
Kind Regards,
Sam -
@snowcrash said in Print cooling fan not working properly:
Hi @jckray,
Glad you got it sorted out.
Just thought I'd chip in about the issue of PWM frequencies for the benefit of anyone else struggling with pulsating fans and potentially reading this thread. 100Hz (or even 1000Hz for that matter) is way too low for PWM fan signals. Although there's no one frequency that's suitable for all PWM fans, conventional wisdom puts the number at 25,000Hz (or 25MHz), while some even opting for a little higher (around 30MHz). Often times, changing the frequency to that level makes a significant difference in terms of the fan's acoustics.
The 25kHz figure is quoted for 4-wire fans with a separate PWM input. You shouldn't use high PWM frequencies with ordinary 2-wire fans unless you use a series inductor followed by a parallel capacitor to smooth the PWM into DC.
Most 2-wire fans were never designed to be used with PWM, and it's amazing that they work as well as they do.
Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
http://www.escher3d.com, https://miscsolutions.wordpress.com -
@dc42 Is there any danger to the electronics from using a high PWM frequency (in the 25kHz range)? Or would the other danger be to the fan itself?
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The 25kHz figure is quoted for 4-wire fans with a separate PWM input. You shouldn't use high PWM frequencies with ordinary 2-wire fans unless you use a series inductor followed by a parallel capacitor to smooth the PWM into DC.
Most 2-wire fans were never designed to be used with PWM, and it's amazing that they work as well as they do.
@dc42, to pick up on @Red-Sand-Robot most recent question, while I completely agree with your second statement, I'm a bit baffled by the first.
What's the specific electrical/mechanical problem with using high PWM on 2 wire fans?
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High frequency PWM is ineffective if the fan has a capacitor across its power terminals. Switching losses in the MOSFET increase with PWM frequency, so if you do use 25kHz PWM to switch the power input to a fan, watch out for the MOSFET overheating.
Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
http://www.escher3d.com, https://miscsolutions.wordpress.com -
@dc42 said in Print cooling fan not working properly:
High frequency PWM is ineffective if the fan has a capacitor across its power terminals. Switching losses in the MOSFET increase with PWM frequency, so if you do use 25kHz PWM to switch the power input to a fan, watch out for the MOSFET overheating.
Thanks for the clarification. @dc42.
For me, this is one of those cases where theory & practice seem to diverge somewhat - at least in my experience. I've been working with every possible kind of fan for years now and run them off every conceivable (dc) supply type and although it's certainly true that some 2-wire fans really don't like to be PWMed, I never had a fan fail in the manner you describe. On the other hand, I've had quite a few 2-wire fans with which the noise level was significantly reduced when run in the 25-30KHz frequencies and they worked fine throughout their lifespan.
Perhaps I've just been extraordinary lucky in this context or possibly the danger here is very marginal. Either way, everyone's millage is different, as they say, and I guess each of us can make his/her own choices as to the level of risk they'd like to take and how to go about it.
