Hi!
There are no doubt better forums on the internet for this type of question, but I don't like registering on dozens of forums for every question I might have, so I try my luck here first.
I recently bought a Corsair Hydro H45 to replace the old stock cooler. It performs very well and my computer no longer sounds like a commercial airliner at take off under load. Now to the potential problem. The unit has two connectors, one for the fan and one for the pump. The pump connector is an ordinary three-pin fan type connector. Now, I assume I should get an RPM reading from the pump since it has three leads, but I don't. I tried a different connector on the motherboard, but with no difference. The pump is working, because I momentarily disconnected it and saw the CPU temperature immediately start to rise, but I don't get and RPM reading (like I do from the fan). I wrote to Corsair support, but the support didn't provide me with a clear answer either and there is no info in the documentation or specifications that I have found whether the pump outputs RPM or not. Anyone else here with that unit who can give me a definitive answer? I have tried Google of course, but with no luck, just some results that might indicate that it does have a sensor.

All the best!

It depends on the type of motor, the control, and the feedback. Only DC motors need feedback, and this leads to power supply inefficiencies. AC and stepper motors don't need feedback. AC usually is fixed to the AC frequency. There is a slight slippage, typically 3% but they are accurate enough. Stepper motors usually use 4 motor leads but could be reduced to 3, and you don't need feedback, because the frequency you drive them at sets the speed. So they have internal feedback. One lead only is very poor feedback. But cooling was in the very early stages when I worked on hardware last, and I can't help you unless you get details.

It sounds like you have a cooler and it's working. Rule #1 of maintenance states: "If it ain't broke, don't fix it!"

Hi and thank you for your reply!

I'm well aware of rule #1 But I'm more of the philosophy that if something isn't working optimally or the way it's designed, then fix anyway. I'm thinking two things. One, that since I can set things up in BIOS to let the computer warn me if the RPM of a fan (or in this case the pump) drops below a threshold, then if there is a speed-/tach-/RPM-sensor (whatever is the correct term), I can set things up to be alerted should the pump ever fail. And two, that if the pump unit is equipped with a sensor and that isn't working, maybe there is more to the unit that isn't up to scratch (for example if the leads hasn't been soldered satisfactory and the power to the pump will fail next).
What I think is a bit strange is that there is no mentioning in the specifications whether there is a sensor or not. I'm happy with the product itself, but not with the manual, which is a bit like IKEA's manuals with just drawings and no text.
3-pin fan connector on pinouts.ru: https://pinouts.ru/Motherboard/MbCpuFan_pinout.shtml

OK.

Going by the link, your 'spin sensor' most likely gives 1 digital pulse per revolution. Quite possibly an open-collector thing, So you put a resistor to your VCC, (12V, 5V, 3.3V, whatever, and the pulse pulls it down.