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January 9

Question about PC cooling fans

I am replacing my 10-year-old PC with something a bit more modern. and have a question about the new(er) PWM fans. My old system just fed 12V to the fans with no speed control.

The CPU cooler I have chosen has 3 PWM fans, and the motherboard has a single 4-pin PWN CPU fan connector. The pins on the MB are:

1 GND
2 Voltage Speed Control
3 Sense
4 PWM Speed Control

I believe pin 2 lets me use a 3-pin voltage control fan, but my fans are all PWM.

My question is this: assuming that I stay within the current limit, is it OK to connect all of the fans in parallel? Or do I need a small fan controller? That sense pin concerns me; I doubt that it will be able to sense the fan speed of three fans connected together. Is the sense line even used on a PWM fan? --Guy Macon (talk) 18:18, 9 January 2019 (UTC)[reply]

AFAIK the sense line is unrelated to the type of speed control the fan uses. It's used assuming the fan and mobo support it. Note that it has nothing to do with the speed control or otherwise the operation of the fan, it's simply so that you can monitor the fan speed. In the 3 pin days, there was no problem using fans in parallel provided you didn't exceed the current limit although because of the way the sense works I doubt connecting all the senses work work and indeed most commercial parallel connectors only connected one of the sense connectors to the motherboard. I think this remains the case in the 4 pin days, but I admit I'm not sure. Nil Einne (talk) 10:43, 10 January 2019 (UTC)[reply]

I had a quick look and found this. [1] It sounds to me like using the fans in parallel should work even with 4 pin fans although you probably understand it better than me. (To be clear, as with 3 pin fans you should only connect the sense on one fan although I don't think it will damage anything if you connect both, instead your fan speed won't work properly.) Again I think it's how most commercial ones designed by anyone competent are made [2] [3] [4] [5] BTW the first source reminds me of something I think I've read before, it's not entirely connect that the sense is unrelated to the fan speed control I guess. The sense works better when you use the 4th pin for speed control, if you simply PWM control the voltage as was common in the past, the sense may not work properly although again this doesn't affect the speed control or the fan in any way unless your system actually uses the reported speed in some way besides simple monitoring. Nil Einne (talk) 11:50, 10 January 2019 (UTC)[reply]

Thanks! I don't see any downside to disconnecting the sense line to two of the three fans when using four-wire PWM fan control, So I am going to do that. --Guy Macon (talk) 16:21, 11 January 2019 (UTC)[reply]