My attempt at creating a circuit board that enables 4 PIN aftermarked fans on HP ProLiant servers

[radioman]

The TACH/RPM signal from a after marked fan is two pulses per revolution. It's "open collector", so the fan provides a pulsed ground connection at described rate. This signal is used to control a P channel mosfet ( Q1 ) that is used to turn optocoupler ( U1 ) off and on. U1 delivers voltage in pulses to the smoothing network ( D1,R1,R2 and C1). It takes 3.5 seconds to discharge C1 down to 6 volts from 12V DC. From what I have read, rotation detect is a simple DC voltage signal.

Sadly I have no possibility to test the circuit out, but it should work on HP ML series towers from G5 to at least G8. I don't know if it will work on other models. It should be fairly easy to make a test setup on a Veroboard/stripboard or similar. The HP fan connector can be salvaged from a dead fan, and used to connect to the motherboards fan connector.

I take NO responsibility if anyone destroys their motherboard testing this circuit!

HP fan connector pin out:

Standard PWM 4 pin pinout:

 

Circuit schematic:

 

[brwainer]

If HP’s PWM is 3.3V and a standard fan is 5V, will the fan (or most fans) be able to use the lower voltage PWM signal?

[radioman]

1 hour ago, brwainer said:

If HP’s PWM is 3.3V and a standard fan is 5V, will the fan (or most fans) be able to use the lower voltage PWsignasi

According to the document 4-Wire Pulse Width Modulation  (PWM) Controlled Fans:
PWM Control Input Signal  
The following requirements are measured at the PWM (control) pin of the fan cable connector:  
PWM Frequency: Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kHz  
Maximum voltage for logic low: VIL = 0.8 V  
Absolute maximum current sourced: Imax = 5 mA (short circuit current)  
Absolute maximum voltage level: VMax = 5.25 V (open circuit voltage)

So 3.3V PWM should work because its within the outlines ( logic high) specified in that document. It looks like it is a TTL level signal.

[Allcrafter]

Is the wire connected to gnd of new fan's plug? (More look picture)

upu

[Allcrafter]

Sorry first was wrong picture