What can i use to drive 12v fans from a different power source


So i've got a small project with some PC fans that are DC driven only (no PWM).
Now i could just drive them directly from the PC fan headers (maybe with a max of 2 or 3 per header) but seeing as im limited by current then and the amount of fans (and they'll need to be the same speed anyway) i'd love to have them all driven from a higher current source but still controllable from 1 signal.

What is available to me to basically take the 0-12v DC from the PC fan header and use it as a "signal" in (to what ever piece of electronics would work), then have that produce a matching 12V out, but at a higher current ability/off the main power supply directly?

Thanks :slight_smile:

A simple 12v relay is probably your easiest solution... something like image
This can handle up to 10A.

But a relay is either on/off, not variable......

For example. If i hook a standard 3 pin (+, -, Tach) to the PC fan header and set the software to DC Control, the software can change the speed of the fan by adjusting the voltage coming out of + between 0 and 12v

ie, if it was a 2000rpm fan, 0v would be stopped, 6v would be 1000rpm and 12v would be 2000rpm (and levels between, ie 9v ~1500rpm, or say 4-5v ~800rpm).

That fan header has a limit of 1 amp (so 2-3 fans depending on draw). I'm looking for something that'll take an external power source (say directly off the main PSU), and put out a changing 0-12v DC signal to drive all the fans based on the fan headers "signal" puts out (like an amplification, or a voltage follower where its referenced to a higher current supply).

Can you please show a schematic of what you're trying to do, which micro controller you are using and the code you are using. These are essential to make the forum members help you.

Do you want to control the speed of a 12V PC Fan with a microcontroller? I do have a solution for that.


All the fans of that type I have used, ALL have electronics built into the hub of the fan and you can PWM the DC supply all you want and it will not change the speed of the fan.

They likely have, but.... Suppose You connect power sup GND to fan GND. Then connect the second cable to power sup positive and hold the other end in Your hand. What happens if You make a short, some 1/10 of a second contact to fan positive? The fan makes like a "jump", rotates and stops.
Using a quite low frequency (I think was some 25 - 250 Hz) PWM is possible to speed control even electronical fans. The sales people said "Impossible". I said: "Come here and look". That design is used in commercial, heavy machines since 20 years.

These are 100% DC controlled fans, though I'm yet to see a fan that doesn't respond to DC voltage control. Just most have PWM control built on.

Regardless PWMing a DC controlled fan doesn't really work, often the fans fail the spin properly at low speed or they actually make high pitched noises. They respond to stepped DC voltage control.

Is there really nothing on the market that'll generate a matching 0-12v signal from a strong power source based on a 0-12v signal from a weaker one?

I guess I'll have to just tie 2-3 fans together and run them directly from the fan headers then...

Digital pots perhaps.

Sure there is but they will likely be very special and costly. Consider reply #6 and make some tests!

Oh yeah sure that'd be possible, not 100% sure how well it'd work with 120mm sized fans just because of the motor speeds and general quality, I 'think' to get sufficient control (with lower speeds) with PWM Iike that is usually when they start making high pitched noises.

Kinda sucks these fans don't have PWM onboard. I think I'll just have to go with stacking them onto different fan headers and tie them together with software, just easiest way it seems. I figured there'd be something simple out there that operated like a Mosfet but was able to vary output voltage up and down depending on signal input (like an OpAmp type setup that could handle decent current)

Oh well.....