Hence, the first two pins on the right column are 5V pins, perfect for powering your 5V fan. In both the regular Pi and the Raspberry Pi Zeros, the SD card is defined as the “top” of the Raspberry Pi. Let’s establish what is the “top” of the Raspberry Pi. In which case, you’d want to connect the positive (usually red in colour) to a 5V pin. In all likelihood, you will probably have a 5V fan. This is important because you’ll plug the leads into different GPIO pins on the Raspberry Pi depending on voltage.
You can determine that by viewing the sticker on the fan.
The above schematic lays out the theory, but I just don't know what to make of that 4th pin discrepancy.First, you will need to know if your fan is a 5V fan or a 3.3V fan. Unfortunately, I don't have a multimetre or anyone to borrow one from. It's not my picture, I just posted it because it shows the same connector key ridges layouts side by side, left is how the HP fan is, keys on either side, right's a regular PWM. Judging by the below diagram, the first three pins should be fine, but it's that last " or +5V" bit on the fourth pin that has me worried - forgive me, my electronics lessons are long behind me, but if the motherboard "puts" that 5V on the 4th pin where the Noctua's expecting a PWM signal, would that cause a problem? Noctua's got a little article here outlining the two different solutions, but they don't actually spell out whether I can safely plug a PWM fan in a DC header.
I guess my main question is - ignoring the ridges, which I could just file off, would plugging a 4-pin PWM fan in a non-PWM, voltage-controlled 4-pin header still work properly or at all? Both the HP fan and the Noctua are listed as 12V and HP won't have developed their own new standard, so that header's gotta be either PWM or DC-based. Click to expand.It's not my picture, I just posted it because it shows the same connector key ridges layouts side by side, left is how the HP fan is, keys on either side, right's a regular PWM.