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I have a 3d printer with a 24 volt PSU. I am looking to upgrade a pair of fans on the printer, and there is a much larger availability of 12v fans then there are 24v fans.

There are 2 common instructions I see to use a pair of 12v fans with a 24v supply. One is to use a buck converter to convert 24v to 12v and power the fans in parallel. Another recommendation I see is to wire the 12v fans in series to a 24v PSU.

My gut says wiring the fans in series is not the best option. I anticipate that the fans will not drop voltage evenly, causing them to run at different speeds, and wear unevenly. Also, if one fan stalls, it will draw stall current, dropping much less voltage and overvolting the other fan. But I'm not sure if that's really a big deal for these little cheap fans, and worth doing for sake of not buying extra parts.

Is there any other significant disadvantages of wiring fans in series like this? Is parallel definitely the better option?

And is there a significant difference if I need these fans to be controlled through PWM of the return path? I know that PWM control can not be done through the buck converter, and there has to be special consideration like in this diagram.

enter image description here

For sake of argument, Here is the fan I have in mind and here is the PSU

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Always match the voltage of the power supply and the voltage of the fans. Wire fans in parallel.

Never wire two motors (such as fans) in series. When one stalls, the other one will see twice the voltage, damaging it, especially if it has electronics inside.

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The buck converter will work in most cases.

If you are concerned about reliability or EMC or losses then the series scheme has some merit.

You should not just connect in series. These brushless fans take current in ripply pulses. When you measure this with a scope and a 1 ohm burden resistor you will see. Electrolytic capacitors of 470 microfarad will deal with this. Now the fans will run fine. We did this, however when you stalled one 12V fan when running 27VDC the other speeded up and its continuous voltage rating was exceeded by 1 VDC. I sorted this by designing a simple voltage balancer. The voltage balancer only wasted power when things were not normal. When the fan voltages were within 700mV no power was wasted. This scheme that I was asked to do 28 years ago went into production with no hassles.

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