3 pin PC fan

I have a 3 pin PC fan with led and would like to know how to use it outside a desktop PC. It has 3 wires (all black) and if I connect 2 specific ones off them to 9V battery the led will turn on but the fan wont. If I connect the third one to the positive of the battery the battery will tilt a little bit (like 1 or 2 degrees) and then go back to its original position.

I couldn't get analog reading from the third wire. I tried to output a PWM signal (analogWrite from 0 to 255) directly from arduino to the third wire but nothing happened.

Is there any thing I can do to make it run?

They did make it hard by making all wires black. Normally it will look like:

Which also shows the connections. So hold your connector the same way and you know where to connect the power. The tacho signal is a feedback signal from the fan, leave it disconnected.

Two things to note:

  • A 9V battery is very weak, it might be to weak
  • By random poking around you might already have destroyed it :wink:

Thanks for you reply
I have another one that I didn't mess up with and I connected it like the image to 12V but still the led turns on but the fan not. As I said I tried to analogRead from the third wire but I'm only getting random numbers so I don't think its for feedback. Every time I connect the third wire to power the fan tilt a little bit does that mean any thing?

I tore one down and got this circuit:

What confuses me is the 4 coils with only 3 wires coming out of them! What type of motor is that? Can I control it using arduino instead of the built in circuit?

All DC motors have multiple coils, and 2 wires are sufficient to run most of them. You may have a special stepper or BLDC motor, with 2 pairs of coils, which deserves a special ESC or inverter.

Wow, I just looked again and seems like I used the only Google Image with the connections the other way! (And he, don’t remember what you can Google right?) Seemed like a nice image. ::slight_smile: All others are

Photo’s (did you use a potato?) seem like a normal fan. And looks like I see S (tacho), + and - on the PCB. This seems to be in the same order as the above image.

As I said I tried to analogRead from the third wire but I’m only getting random numbers so I don’t think its for feedback.

I did say it’s feedback, not that it’s analog :wink: It’s a pulsed signal. From the top of my head to GND and you need to supply the pull up.

But if its only for feedback connecting the power wires should turn the fan on, right? But it's not running so I think it should be the third wire controlling it somehow. Don't worry about the image I connected it based on numbers not colors.

I don't have an esc can I do it with arduino only? I have some MOSFETs

Alright, wasn't really clear in my post by implicitly asking a question. Is it a fan from a normal PC?

If the answer is yes, the change of the third wire being control is slim to none.

And what is that 12V supply?

And did you reconnect it like in the last image? (Hope connecting it wrong didn't break it ::slight_smile: )

And I never came across a standard fan that needed an ESC...

But I see photo's of the fan disassemble... Why? And are you trying that same fan after reassembling it?

I have 2 fans one is still as I got it and the second one is disassembled. I contacted the seller and he said not to connect it to battery. The 12V battery is 3 18650 connected in series. Voltmeter shows around 12V. I'm sure that I connect it as the image.

I have 2 of this fan:

And 2 of this heat sink:

After disassembling one off each, both the heat sink fan and the normal fan behave the same and look the same from inside.

Three 18650 might be a bit high but should be fine.

Okay, really for a PC. That makes the third pin (of the bottom fan) a tacho signal and nothing to do with driving it.

The other fan is a 4pin fan so that is a little bit different. It does have a PWM in pin but as far as a read (never tested it), it should just do full speed without a PWM signal.

2 pins of The 4 pin connector are connected to positive and negative of the 3 pin connector and the other 2 pins are just empty.

So the led works but the fan isn't. Is there a way I can use it by controlling the motor directly using arduino and MOSFET? I don't have an esc.

Sounds a bit like the fan is dead. Either DOA or by tinkering...

Yes and no. You could make your own driver if you are skilled enough. But no, doesn't sound like you can do that now if you have to ask where to start. To be fair, I wouldn't attempt it either :wink:

Do you have some old stuff laying around with a standard 12V fan in it? Old PC, old power supply etc. I would first try to run that and next buy a new fan. Or buy new fans anyway, they are cheap :stuck_out_tongue:

Unfortunately I don't have any. I bought these to make a mini cooling refrigerator with peltier. I thought it would be an easy project but now the fan made it complicated. Anyway thanks for your help I'll buy different fans :slight_smile: