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12V fan PWM control using 24V fed motherboard

war4peace

Dec 14, 2022
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Hello all,
I have been researching this for quite some time, and I received quite a few answers on various communities, however there were conflicting answers which went head to head, therefore I thought maybe I should ask true experts.
I have a few 3D printers with motherboards using 24V from AC/DC PSUs. The printhead requires more cooling (part cooling fan), and I want to use a 40x28mm 12V powerful fan, such as the Delta PFB0412EN-E, or Sanyo Denki 9GAX0412P3S001, or even the Sanyo Denki 9HVA0412P3J001 (I own all of them). Any of these fans are PWM controlled (4-wire fans), and the Tacho and PWM wires need to be connected to the motherboard (or a toolboard) in order to be controlled. Unfortunately, the boards are all 24V and even though they do have 12V output ports, those are not rated to the power consumed by those fans (for example, the Duet 1LC Toolboard supports maximum 800mA on its 12V port).
I also have a DC/DC Mean Well PSU (24V to 12V, 6.5A), as well as another AC/DC Mean Well PSU (outputs 12V, 7.1A).
My question revolves around how to power the fan in such a way to avoid issues. 12V and ground wires would come from any of the two above PSUs, and PWM and Tacho wires are connected to the 24V board, but I'm worried about whether this would work well or is there something else I need to do? I was told I should connect the 24V PSU ground with the 12V PSU ground in order to avoid issues. Would that be enough?
Please let me know if you need further information, I'd be happy to provide it.

Thank you!
 

Harald Kapp

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I was told I should connect the 24V PSU ground with the 12V PSU ground in order to avoid issues.
That's the correct way to wire this. But only the grounds ;)
Try to make sure you have a single point where the grounds connect. Typically one would a the ground pins of one of the twoe (or more) power supplies to connect all grounds at this single point (also called star point).
If you have only one fan to be powered from the 12 V supply, you can make this ground connection also at the fan (but then not at the power supply - keep it to a single point).
When you create multiple ground connections, you create so called ground loops, which can lead to irrational and irreproducible behavior of the circuit.

You also need to make sure the PWM and Tacho signals match between the fan and the controller board.
The pwm signal is typically 5 V, so the controller needs to issue a 5 V pwm signal.
The tachometer signal is usually open collector and can be connected to any input that provides the necessary pull-up resistor. Current into teh tacho output is limited, so you have to check the current from the tacho input of the controller board into the facho output of the fan.
See e.g. this info.

Without delving deep into the datasheets of the components you linked, I assume that the fan should work perfectly with the motherboard as this interface is well standardized (nobody would risk to destroy a PC only due to a mismatch between fan and motherboard).
motherboards using 24V
The 24 V is definitely not used for the logic part of the motherboard. There will be voltage regulators down to 5 V or 3.3 V. These are the operating voltages usually employed by microcontrollers and/or digital logik today.
 

war4peace

Dec 14, 2022
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Joined
Dec 14, 2022
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Thank you for your reply.
I was planning to connect the grounds from the PSU output grounds for the 12V and the 24V PSUs. Looks like this is the right way to go.
It's a single fan, nothing complicated there.
About the Tacho and PWM wires, they are color-coded, and the PWM connector on the toolboard is documented. The port is standardized, no problem there.
You are correct about the various voltages in the motherboard itself, what I meant was the motherboard is powered by a 24V PSU and the power outputs from the motherboard (to fans and heaters) are 24V as well.
With all being said, I believe connecting 12V and 24V PSU output grounds using a single wire would suffice.
 
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