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Reducing fan speed

V

vidrazor

n00b
Joined
Dec 2, 2010
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I have an old Mad Dog slot cooler from my old Prescott system, and I thought it might come in handy sticking it next to my graphics card in a system I just built. If you look at these specs, you'll see it runs a bit noisy, and I was thinking of slowing it down to somewhere between 50-66%, using something like the cables supplied with a Noctua NH-D14. I know airflow will go down quite a bit, but it's just some auxiliary airflow for the graphics card, which is a basic MSI R4350.

Does anyone know what size resistors would do this for ~50% and/or ~66%? I would imagine a series connection vs parallel is needed. How bout using a trimmer pot? What spec for the pot would I need? Series? Parallel? Does it matter?

Thanks for any info on this.
 
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theres a cheaper easier way of doing it. there use to be a diagram here on the forum or some googling might find it. if you take the 2 wires from the fan. cut the connector off. then take one of the 4 pin molex connectors. depending on the wire each one has a different voltage. red and black will give you 100% speed. i know that for sure. but i cant remember which wire is the 5v. if you can find that one you stick the red wire into that and the black into the black it will slow the fan down. do some googling you might be able to find what they are but thats how i had my old thermaltake 90mm jet engine heatsink setup back in the athlon XP days.
 
basically 12v is the yellow wire and the black wire next to it is -12v

5v is the red wire and the black wire next to it is -5v

caution: some claims this is dangerous... however I have never seen any proof of this

and for 7v you do this: 5v(red) from power supply to negative on fan, then 12v(yellow) from power supply to positive on fan
 
Thanks for your replies. Seems to me just sticking a resistor or trimmer pot is simpler, I just don't know what values of resistor I'd need or, if using a trimmer, whether it's better in series or parallel.
 
A pot would work, but they don't do well in warm environments, as they handle heat very poorly, and wear out when turned too often. Personally I would just use 7V trick (fyi the black wire is not - anything, its just reference). However if you want to use resistors, just figure out what voltage you want the fan to work at (9v, 5v, whatever). Then I would use the 0.15A max rated current and ohms law to figure out what resistor would give me that much voltage drop. For example for it to run at 9V, you need to drop 3V. So take voltage/amperage=resistance, in this example 3/0.15=20. This means you would need a 20 ohm resistor in series with the fan.
 
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