I want to replace the two noisy 24v brushless fans on my printer with high performance silent 12v fans, more specifically Noctua A4x10 FLX
The 3D printer hot-end fan is on continuously with 24 volts, so I can use a DC regulator such as LM2596 to achieve a constant 12v to power the fan. The part cooling fan on the other hand uses variable voltage to adjust the speed of the fan during the printing process (Probably between 14-24V). I would like the 12v fan to be able to vary it's speed just like the 24v fan does. From what I understand using a LM2596 will not allow the voltage to vary and will just continue to put out solid 12v.
Is there a way to allow this variable fan speed functionality to translate to a small 12v fan? Is using a simple voltage divider circuit the answer?
UPDATE:
Thanks to Dampmaskins comment it looks like the variable speed part cooling fan is in-fact PWM. In that case is it possible to convert 24v PWM to 12v PWM?
Best Answer
You could theoretically use a simple series resistor as a voltage divider to produce 7-12 volts over the fan but in practice it may get problematic. You should test the fan behavior versus 14-24V input voltage range.
As a more robust solution you could use a mosfet as a variable resistor. Use a green LED to bias the mosfet base and basically use the mosfet as a source follower. Replace the LED with diodes and/or another LED depending what you have available and what's your gate threshold voltage. You could also use the same idea with a transistor and a single diode, in fact a transistor would work better with the more predictable base voltage.
The transistor/mosfet will run hot so it should be a chunky TO-220 style, not petite TO-92 package one.
Edit: I guess a simple 220R series would do the same job but you need at least 3/4W resistor and it'll get piping hot.