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How to convert digital fan to analog knob?

brandontran

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Hi Folks,
I'm not an expert with electronics but I hope experts can guide me in the right direction on what part is needed. I have a fan I like, the digital panel that is on it died. No big deal, I'll just take it apart and add an analog knob switch for 1, 2, 3 speeds or variable is fine as well. As I dug into this fan, I learn the complexity of brushless motors and that I can't just simply hook up power to it. So I then learned about how it has a controller and if I connect 2 wires the fan comes on full speed. I made a diagram of the 3 wires I'm working with. These wires came from the digital panel. I cut them and then touched the wires to see what they would do.
  • I have 3 wires
    • A is +
    • B not sure what it is
    • C is -
  • These 3 wires were connected to the digital panel
  • Connecting A and C makes the fan turn on full speed
  • If I multimeter A and C I get 4 volts
  • Motor is 24V DC Brushless and the controller is a black box to me right now.

What components can I use to have a knob to turn that makes fan go slow, medium, fast or variable is fine as well? I learned that a potentiometer only varies resistance and tested with multimeter which was cool. I found a potentiometer and wired it up for kicks. Any pro would know that didn't do anything. The fan was full speed all the time.

So do I need to vary the voltage 1-4V to make the speed of the fan change via these control wires?

I'm curious if something like this would do the trick. Also not sure how to wire it up...

Thanks for any help.
 

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BradtheRad

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Manufacturers must want to maintain secrecy about 3-position motor speed switching, or 3-position electric blankets, etc. There could be more than one method, each hard to figure out and hard to fix.

Some motor types change speed according to supply voltage or current, some types according to AC frequency.
Your motor may be the type where two wires provide supply rails, and the third wire controls speed. If you give more information then it may allow our resident experts to assist you toward completing your repair job.

Does the motor nameplate specify 24VDC? It's a question whether internal driver circuitry requires 24V or whether 24 is safe maximum. Installing a buck converter can only work if the driver circuitry is versatile enough to run at various supply voltages.
 

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