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Very Odd, Slowing CPU Fan With Fan Controller NOT attached to CPU fan


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I have a bizarre situtation. My PC case has a fan controller with mutiple 3 pin fan connections and an external speed control knob. I have attached two auxiliary fans to it. The other front, rear and CPU fans are attached to 3 pin connectors on the MB. When I use the fan controller to reduce fan speed (noise), the auxiliary fans AND the CPU fan slow. Of course, CPU temp goes up. My brand new HX650W is connected to the fan controller using a standard 4 pin molex power connector direct from the PSU. Nothing else is attached to this power cable. Why would this happen? How can I fix it?

Thank you..........Steve


Lian-Li PC-V354 case


Intel DP55SB MB (micro-atx)

Intel I5-760



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I did some testing as you requested. I found that the CPU fan speed did not change when there were no fans connected. Also, any change seemed imperceptible with or without the power connected to the controller with no fans connected. The front fan is a 140mm fan with blue LEDs. This had a barely perceptible change on CPU fan speed. The second fan exhausts to the top of the case. This is 140 MM case fan, no LEDs. It seems to have more of an effect on CPU fan speed. Here's the problem. Both fans have a more perceptible effect but, here's the disclaimer, the speed change seems to vary more or less at different times between high and low on the controller. I am wondering if it is the user (me) that is having the perception variances. As for CPU temp rising, it's a "duh" thing. The secondary fan is perpendicular to the CPU fan and about 2-3" from it. So if this fan spins slower, less heat is exhausted and CPU temp has to go up. It is probably not a slower CPU fan. With fans on high, CPU temps are 160-2F and 165-7F on low.


Not sure if there is a plausible explanation for this. I will look for a new 140mm case fan with a lower amperage rating and better bearing. I will also build a Y connector to connect both front 140MM case fans to the 3 pin connector on the MB. It should be able to handle the amps.


Can you think of any explanation for the variance in fan speed? Feasible power drain? Doubtful. CPu voltage never changed. Grounding issue. Would it matter?


Thank you.



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I would plug the fans back into the controller one at a time and see if its a particular fan that is causing the variances or if it could be the fan controller itself. I am really not sure how the PSU could cause this, but if all else fails we can certainly try replacing it for you.
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