Making sure I understand PWM connections

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johnstac

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Feb 23, 2007
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I have ordered quite a few Noctua 140mm PWM fans to replace the stock fans in my new case. I want to make sure that I am not getting confused about the connections. I read that there can be a concern abut connecting to many fans to any one motherboard fan chassis. Are they referring to the 3 pin type because they put a load on the motherboard whereas with 4 pin fans, it is okay because if I connect the power to another source I can use the 4 pin for a signal without any power to the motherboard? (That was a mouthful) I think I have got this wrong so I need some help figuring it out. I am thinking that as long as I connect the molex to a different power source, I can still connect the 4 pin connector to a splitter with as man 4 pin fans as I would like to control from that one chasis. Is that correct?
 
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i7Baby

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PWM (eg CPU cooler) fans have 4 pin connectors. Voltage (eg case) control fans have 3 pin connectors.

The connectors are made so that you can join 3 pin with 4 pin connectors. In this case, the PWM line isn't continued through the 3 pin cable.

See http://en.wikipedia.org/wiki/Fan_control

Most modern motherboards allow one or two pwm fan headers for cpu fans and 3 or 4 3 pin headers for case fans. You can run 2 fans off each case fan header using a splitter eg http://www.amazon.com/StarTech-Power-Splitter-Cable-TX3SPLIT12/dp/B002DY7M1G
 
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johnstac

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I thought I understood everything you said until I checked the last link you posted. All of my case fans will be 4 pin so I don't think that one will work. I will look for another though. Thanks.
 
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