I have a couple of server power supply units, namely HP DPS-1200FB. Those PSUs are working just fine (given their mileage) but the DC fans appear to be wearing out so I decided to replace them.
The original fan installed in those PSUs is a Nidec 40mm DC fan with four wires: GND, +12V, Temp and Rotation control.
When I was ordering replacement fans I explicitly asked for only two wires: GND and +12V because I prefer them to be running at full blast all the time.
When I install the replacement fans, the PSU runs for a couple of seconds and then turns itself off. My guess is it checks the RPM reading on the fan, does not get any data and thinks the fan is malfunctioning.
Is there a way to fool the PSU that it actually has the fan installed even though it only has two wires? I attached a picture of the original fan termination for reference.
Best Answer
four wires: GND, +12V, Temp and Rotation control.
From the datasheet I deduce that instead of Temp and Rotation control there are Tacho (pulses indicating the fan's speed) and Control which probably feeds a PWM signal to the fan to control the fan's speed.
This means that this fan uses quite "standard" signals. My bet is that the supply just wants to see the "Tacho" signal so that it knows that the Fan is spinning.
I also think that you could just a standard 4-wire CPU-cooler fan (and optionally ignore the PWM Control input or use a 3 -wire fan and then not connect the PWM control signal. That 3-wire fan will then just rotate at maximum speed but will provide a Tacho signal to the supply making it operate.