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I have an 18V system and I need to run some fans off of the 18V rail. I've been using 24V fans with PWM control and they work fine (although are slower than their fully rated 24V speed). Now we can't seem to get enough 24V fans to build the next batch (even without PWM, they are out of stock everywhere). Would running a 12V fan on my 18V and never going above 66% PWM work? Or will this fry the 12V fan instantly? Or will it work for a while but with reduced fan life? Short of finding more 24V fans or the world inventing 18V fans, what's the best way here?

I don't have 12V available on the system, nor do I have enough room to add a DCDC that is large enough to handle the current for all of the fans.

A loosely related SE post

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  • \$\begingroup\$ Does the survival of your system depend on the fans? \$\endgroup\$
    – Wesley Lee
    Sep 29, 2020 at 0:48
  • \$\begingroup\$ Without an engineering specification of the fans, this is an off topic question on the (ab)usage of an undocumented product. If the only spec you have is "12v" then the answer is no, because these are electronic modules, not simple DC motors. \$\endgroup\$ Sep 29, 2020 at 0:58
  • \$\begingroup\$ Do you mean "12V fan" or "12V Fan Control Board". Can you please sketch or draw how/where you are proposing to apply the 12V / 18V and PWM? \$\endgroup\$
    – P2000
    Sep 29, 2020 at 2:56
  • \$\begingroup\$ I was thinking of 12V DC Brushless Fans such as from this digikey search: digikey.com/short/zwq1rq \$\endgroup\$
    – Casey
    Sep 29, 2020 at 3:59
  • \$\begingroup\$ Taking the first fan in the list (datasheet delta-fan.com/Download/Spec/AUB0812VH-SP00.pdf), the operation voltage is 10.8 - 13.2Vdc. My question is will this fan be damaged by either power it with 18V and using the PWM pin to limit the output to 66% of max or to use an nFET on the ground leg to do PWM, as drawn by @P2000 below. \$\endgroup\$
    – Casey
    Sep 29, 2020 at 4:02

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4 pins fans are brush-less motors, the same as low noise fans. Those fans have electronics inside and they may not tolerate higher voltage. DC motor with no electronics works fine with higher voltage PWM.

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    \$\begingroup\$ This hints at the truth: if it would work is not possible to know without the specifications of the particular fan controller. If the specs say it's not allowed then knowing if it would actually work would require knowing the design margin of those specs... \$\endgroup\$ Sep 29, 2020 at 0:58
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    \$\begingroup\$ In reviewing the datasheets from my digikey search (digikey.com/short/zwq1rq) list of 12Vdc brushless fans, the operating voltage for 12V fans seems to always (or usually) be in the 10V to 14V range. This suggests 18V would be a bad choice. \$\endgroup\$
    – Casey
    Sep 29, 2020 at 4:05

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