Can the polarity of standard CPU 12VDC brushless fan be reversed? For my application it is fine if the fan is not broken afterwards. Please see the image of the fan below:
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\$\begingroup\$ You want it to spin in reverse, or work normally with a reversed polarity? \$\endgroup\$– HandyHowieApr 27, 2022 at 15:00
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\$\begingroup\$ @HandyHowie I am already happy if it doesn't break. I thought that it just reverses since there should not be any circuit. Is that correct? \$\endgroup\$– Marco BobingerApr 27, 2022 at 15:02
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1\$\begingroup\$ @MarcoBobinger A BLDC motor will always have a circuit--it's actually a permanent magnet synchronous motor, a type of AC motor, along with drive circuitry that converts incoming DC to AC. \$\endgroup\$– HearthApr 27, 2022 at 15:06
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\$\begingroup\$ Computer fans have an electronic driver in them. It's not just a motor there. \$\endgroup\$– DKNguyenApr 27, 2022 at 15:09
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\$\begingroup\$ @DKNguyen and Hearth thank you. That answers the question then I guess. I cannot open the an to check if there's some reverse polarity protection but I'm pretty sure there isn't. \$\endgroup\$– Marco BobingerApr 27, 2022 at 15:18
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2 Answers
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Can the polarity of a 12V brushless CPU fan be reversed?
For a simple fan such as you show in the question the answer is probably YES. It all depends on the type of controller being used to drive the fan. Some simple two wire fans use a circuit somewhat like this:
Notice here that there is a series diode in the circuit, so this could sustain a reverse voltage without damage (though obviously it won't spin).
Other fans may or may not sustain reverse polarity without damage. If the fan has an rpm indicator or has speed control then the inbuilt controller is much more complex.
You could set up a test for the different fan types to find out the capability, or try to find the schematic to assure yourself of the capability.
Here is one datasheet for a two wire fan I found which clearly specifies it has reverse voltage protection.
answered Apr 27, 2022 at 15:21
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The fan will not run in either direction if the input power polarity is reversed. It will probably be damaged. It would be difficult to get into the internal motor control circuit without damaging the fan. Even if you could do that, it is not likely that you could modify the circuit to reverse the fan. The direction of air flow is easily reversed by turning the fan around. That can probably be done without modifying the mounting arrangement except to change the position of the guard.
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\$\begingroup\$ Yes, thanks. This can be concluded. \$\endgroup\$ Apr 27, 2022 at 15:21