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Question Can the cpu water pump be on the same header with a fan?

Jun 21, 2020
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The fan and the water pump are both 3 pin and I want to y split them into a single header. Will it work?
 
Jun 21, 2020
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Pump draws @ 0.2A. Each fan pulls @ that. The issue being that a simple aio pump requires a constant 12v, not variable voltage. So that would require the fans to run at 100% also.
I didn’t think I’d mind the fan running at 100%, but it got annoying fast. Thanks.
 

Karadjgne

Titan
Ambassador
If you had a pwm fan, it wouldn't be an issue, the 3pin pump would run at a constant 12v.

However. You only get 1 speed reported from any splitter, and thats whatever is on the master leg. So you'd get no idea of what speed (if any) the pump is running at. That works the same if you connect the pump directly to psu, splitter, hub.
 

Paperdoc

Glorious
Ambassador
Karadjgne has pointed to one good solution. Most water pumps are designed to run on 12 VDC at full speed all the time. To do that OFTEN they make use of a small quirk of mis-matched fan systems. Any 3-pin "fan" (or pump) connected to a 4-pin header that actually is using the new PWM Mode for fan speed control will always run full speed. So, IF you were to replace the fan with a 4-pin model and get a 4-pin fan Splitter, you could connect both of them to a single header and make it all work. IF you choose that, I recommend you plug them into the CPU_FAN header, and then ensure that the PUMP unit is the one plugged into the splitter output arm with all 4 of its pins. That way the only speed signal sent back to the CPU_FAN header will be the PUMP speed. That does nothing fof speed control, but that header pays special attention to the speed signal it gets to detect FAILURE of the attached device. In an AIO system, the PUMP is the most important unit to monitor for failures, since that could cause rapid overheating of the CPU. The 4-pin PWM-style FAN you connect to the other Splitter output WILL have its speed controlled properly IF you go into BIOS Setup and ensure that the CPU_FAN header is configured to use the PWM Mode of control - NOT the DC Mode and NOT the "automatic" Mode setting.

IF the FAN involved is used on the radiator of the AIO system (and thus should have its speed controlled according to the CPU internal temperature), the other solutions possible are:
(a) Fan to CPU_FAN header, and connect the Pump to any other 4-pin header NOT used for something else, and configured to use PWM Mode of control so that it always provides the 3-pin pump with a full 12 VDC supply; or,
(b) as above, but pump connected using an adapter the a 4-pin Molex or SATA power output directly from the PSU, so that it gets a fixed 12 VDC power supply.

Option (a) means you could "see" the pump speed, but its possible failure might not be detected. Option (b) would NOT send the pump's speed signal anywhere, so you will never know what it is AND nothing can ever detect its failure.
 

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