View Full Version : How to undervolt my delta black label fan
02-09-02, 08:48 PM
I was told that I could lower the voltage of my fan and make it run a bit slower to reduce the noise.
Is this true and if it is, how is it done?
By placing a resistor in the +12V line. The higher the resistance, the greater the voltage drop and hence the slower the fan. Keep in mind that as the fan slows down, the effectiveness of the heatsink goes down and the hotter your CPU will run. If you use a fixed value resistor, you will get only 1 speed reduction to choose from. If you use a variable resistor, you can vary the speed continuously from full speed to almost stopped.
02-09-02, 10:07 PM
Or you could try this, attach the ground from the fan to the 5 volt power supply molex connector and leave power wire on the fan going to the 12 v yellow wire on the power supply molex connector . This will give you a 7 v mod ..mind you it wont cool quite as well but it will reduce the noise.Here is a 7v mod molex adapter I made...
To mimick your setup, I placed a ThermoEngine with Delta 38cfm fan on my HSF test assembly. With the CPU running at 70W and the fan at full speed, the temperature of the Athlon XP core, as measured with the internal thermal diode was 41C with the ambient air at 21C. That calculates to .28c/w. Using a rheostat, I started reducing the fan voltage from 12.1V downward. Here's the results:
12.1V 41C .28c/w Loud as you might expect
11.0V 42C .30c/w Considerably less shriek
10.0V 43C .32c/w No shriek
9.0V 44C .33c/w About like a YS-Tech 27cfm
8.0V 45C .35c/w As loud as the Water cooled rig I'm typing on.
I suspect that your Tbird is running more wattage and the inside of your case is hotter than 21C, so your temp will probably be higher, but the relationship of temp to the fan voltage will not change. Good Luck
02-10-02, 05:42 AM
You're right Hoot, my case temp runs around 26-29c after running prime95 for about 6hours but my cpu temp won't go past 39c.
I'll have to hook up my 120mm fan again to see if the case temp drops.
Thanks for the responses.
Hoot's solution above is great. I have used a 25 ohm 3 watt rheostat from Radioshack for months on my Swiftech MC462 with the 80x38 moderate screamer that comes with it. It works great. I can crank it up for gaming and slow it down to where it is nearly inaudible when I'm surfin'.
02-11-02, 04:57 PM
I chose the 7v mod on my delta and its great. I get good temps. Just make sure you have an inlet and outlet fan. But my computer is noticeable quieter then before. And temps rose only 2 degrees. The rheostat is another alternative, but from what I hear the rheostat itself gets hot. And plus with the 7v mod its very easy and can be reversed when needed.
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