Fan Header Amp and multiple fans on same pin support?



  • Each PC fan headers are good for about 1.0-1.5 Amps, if not a bit more (never want to get close to that limit because I'm terrified to get close to it given the cost of my motherboard.

    What is the max-ish (highest recommended) amperage on the fan headers? I have a few bigger fans that I've collected and would like to try to use, one turbine/centrifugal radial fan is 0.43 A @ 24v and is a monster so I want to use it for a bigger project. I also and making a few custom fans and air pumps, with the motors I have access to so I want to make sure I pick motors that are below the amperage level of the headers. PC fans I have are 0.15- 0.24A at 12v and am kinda trying to just filter out what I can and can't do. I'm a little concerned about the lack of flyback diodes, will it ever produce a negative impact to add one regardless for some peace of mind? I see 1.5A max for PWM, should I assume that is for the full on, or always on, fan headers as well?

    1.5A is nice for the PWM, so thank you for that, that is well within the realm of my needs. No issues with having several fans powered by the same PWM right? Assuming similar enough or same fans/motors below the amperage level? My PC shares fan headers so front two fans act as one, bottom two act as one and top two act as one so my PC thinks I have 3 fans when I really have 6. Which is what I want. That's with 3 pins rather than two, principle should remain the same though right?


  • administrators

    The recommended maximum continuous current is 1.5A per fan header, although 2A is permissible for short periods e.g. when the fan starts up. You can connect more than one fan in parallel as long as you do not exceed these current limits.

    Duet WiFi version 1.02 boards and all Duet Ethernet boards do have flyback diodes on-board. Flyback diodes are only needed when driving brushed DC motors or other inductive loads, not when driving ordinary brushless fans.



  • Thank you! I was unsure because the majority of the Faulhaber 2 wire DC motors we have at the lab I have been told are technically brushed motors, however, due to their superior design https://postimg.org/image/6bdxj3i3p/ their brushed motors exceed the efficiency of most other companies brushless designs. Knowing these are brushed without the understanding of why a flyback diode is needed caused me discomfort.

    Thank you, knowing 1.5A is the recommended limit and not the "blowout/break" limit is a relief. Should I make water pump powered by PWM, the initial spike in amperage to move the liquid or turn the pump on will not fry something. I will wait to purchase my next board for that though. As I learn more about the power of PWM I find so much more excitement in the potential applications, especially when already integrated into a CNC controller! 🙂

    Thank you kindly!



  • Please i need some confirmation about pins and wiring of the fans. What i understood from above. Can you use one 12v pin to power 2 fans and use 1 ground one ground fan always on. and 1 ppw ground for various speed fan? (ps sorry for my bad English)

    Thanks in advance!


  • administrators

    @ploegie said in Fan Header Amp and multiple fans on same pin support?:

    Please i need some confirmation about pins and wiring of the fans. What i understood from above. Can you use one 12v pin to power 2 fans and use 1 ground one ground fan always on. and 1 ppw ground for various speed fan? (ps sorry for my bad English)

    Thanks in advance!

    Yes, two or more fans can share a single positive supply wire.



  • @dc42 thank you for the reply


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