Maximum safe PWM Fan frequency

  • Hi!

    I'm setting my Duet Wifi 2 up, and I came to a problem with PWM fan. My fan doesn't like to run on low PWM frequency. I have set mine to 32kHz and now it is running fine from 1% to 100% of it's power. It's drawing about 160mA @ 12V at full speed. Should I change it because my mosfet can fail or it will run fine?

    Maybe it's better to use lower frequency and some filtering circuit?

    Best regards from Poland,

  • The mosfet normally switches in less than 100ns so it should be fine. 32khz is reasonable for that switching time.

  • Moderator

    I get the best sound out of mine at 30000Hz and they've been running like that for well over a year no problem.

  • @nhof @Phaedrux Thank You guys for help. I read that it should be kept low around 500Hz, so I was worried about some hardware problems.

    Best regards from Poland,

  • @petrzmax said in Maximum safe PWM Fan frequency:

    . I read that it should be kept low around 500Hz

    that is for non pwm fans as they might not work at higher frequencies

  • @veti My fan is Sunon EF50151B1 and it's not a PWM fan.

  • administrators

    Using high PWM frequencies, you may find that the speed range is restricted. It's all very well saying you can go down to 1% in the M106 command, but that 1% might give you 70% of the full-power speed.

    4-wire fans that use a separate PWM control signal are usually design for 25kHz PWM.

  • @dc42 That's true. I don't have full range speed control, but I prefer at least some control rather than not working fan. If there is some hardware solution to get this fan working at full range I will be more than grateful for some schematic etc.

    Best regards from Poland,

  • For a fan "full range" is usually limited by the lowest voltage the fan will run and start at (mind you those specifications are without any static pressure from a fan duct). But even at the lowest speed it will be running a lot faster than 1% of full speed.

    In this case 4.5V, so you could try to measure the voltage and pick the frequency that gives you the combination of a voltage close to 4.5V for the lowest setting and smooth running. Then you need to decide if you want 1% to be lowest possible speed, or if you want to approximate the % setting to % of RPM, say having 30% equal to 4.5V and the lowest possible speed.

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