I need help with a small computer fan

I have this motor from an old server

It has 8 wires leading to standard 4 pin fan connector.

If I connect black to Ground, Red to +7.5v then only one fan is spinning at very high speed (and loud).
But, if I connect White (Control) to Ground and Red to +7.5v both spin nicely and quietly

According to data sheet, it is 12V, Yellow is Sensor and that White is Control,
so I am connecting Control to +

Do you know if I could run it like that without breaking something?

Hi davidco, welcome.

You have the datasheet, all necessary information is supposed to be in there.
I don't have it but you do.
And i have no idea what part it is (it says san ace 40, but that's all i can make of the picture).

If you need help with the contents of the datasheet, supply or point to it.

Thanks for the welcomes MAS3
I thought I pasted the datasheet... here it is:

The thing is, there was a reason I replaced that fan from the computer years ago, thinking it was broken. Maybe that is why connecting power to Red and Black spins only one. But then power on "-" and "control" still spins both. Do you know why this works and would it work for months without issues?

Lead Wire


  • red
  • black
    Sensor yellow
    Control brown


  • orange
  • gray
    Sensor purple
    Control white

Seems quite clear to me.
It's a counter rotating dual fan.
I'm guessing the counter rotation is supposed to reduce noise.
The datasheet also mentions PWM, so some more guessing is that you can put a PWM signal to the control wire, and regulate the fan speed that way.
The sensor tells your system the spinning speed of that fan.
By putting control to +, you are putting 100 % PWM (or speed) to it.
I don't know whether there is a pull up in the fan which would assume full speed if the control wire is open, but that wouldn't surprise me.
The datasheet doesn't tell anything about that, but it does tell you all about rotation speed and PWM, and airflow and PWM.

If you need both fans to rotate, put 12 volts to red and orange, and GND to black and gray.

I will then connect power to Control and GND, and if it breaks, I have a second fan to operate properly on Red and GND
Thanks! I have learned a few things from your answer.

The counter-rotating is for aerodynamic performance. Server fans are not designed to be quiet,
they are designed to shift a lot of air against more back-pressure than standard computer fans.

You can split that fan into two independent units. Slice the sticker at the join and then rotate the two fans against each other. There’s little feet on one that lock into slots on the other.

There’s no wires crossing the join. You have to connect both fans to power to have them both function.