Resistor to reduce voltage for motor

[steveggz]

I need to power a small 20mm mini 5v fan. I have a 5v mean well power supply but I want to use a resistor to lower the voltage to 2.80v. I tested the fan at 2.80 volts (with a vaiable power supply) and it was the quietest while giving enough air. Is it possible to just put a resistor before the fan to lower the voltage to 2.80v? Everything online talks about using a resistor for LED's. I don't get it, can you only use a resistor with constant current?

My power source is 5v 6A
My mini fan is rated at 5v .150 but I want it to run at 2.80v (Its draws around 50mA at that voltage according to my variable ps)

[basinstreetdesign]

No problem and Ohms law will solve it for you.  You can use a series resistor to reduce any voltage source AC or DC.  That statement comes with BUTs, but it is still true.

If it is true that your fan draws 50 mA when driven by 2.8V then the resistor needs to drop 2.2V at 50 mA.  So the resistor value you need is 2.2 / .05 = 44 Ohms and it needs to handle  ( 2.2V )^2 / 44 = 0.11 Watts of power.

The closest standard value available is 43 Ohms and a 1/4 Watt resistor would do fine.  You can get it almost anywhere electronic components are sold.

DK has them for $0.10 for just one but I'm sure that you can get it many, many other places.

https://www.digikey.com/product-detail/en/yageo/CFR-25JB-52-43R/43QBK-ND/2121

[chrisl]

you can try using 3 diodes in series or a 43 ohm 1/2 w (or even a 1/4 w) resistor..

[fourtytwo42]

These fans often require more current to start so the diode solution maybe better than a resistor, trial and error is king