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Claudius 18th June, 2002 07:51 PM

Reduce fan voltage without power loss?
Here is what I was thinking:
Instead of using resistors to drop the 12V line to 7V, replace the ground line with the 5v line. That will give you a voltage difference of 7V (12v - 5V) without any power loss.
Does this sound like a good idea? Or is there a problem with doing this?


The Spyder 18th June, 2002 07:54 PM

FYI- Everybody does this- yes it is a good idea, but it is not the best for the PS, but dosent seem to affect it-

Aedan 19th June, 2002 11:06 AM


Originally posted by The Spyder
it is not the best for the PS, but dosent seem to affect it
As long as the load on the 5V line exceeds the load that the fan will present, the PSU won't even notice. It's when the load on the 5V line is less than the load that the fan presents that odd things will happen.

The only way I see that happening is by unplugging the mobo and any other perpherals. The likelihood then is that you're under the minimum load that the PSU requires anyhow.


reddeathdrinker 19th June, 2002 12:13 PM

Power = Current * Time

So as long as your current is constant, you won't lose power.

But remember that Current = V/R, so lowering your voltage lowers your current at the same resistance. You'll therefore need to lower the resistance in some way (resistors in parallel, prolly) to keep the current the same.......:insert smiley for "Too much effort"?::)

Best thing is go from a fast small fan, to a slower large fan, for the same cfm........

Claudius 19th June, 2002 03:09 PM

Actually Power = Current * Voltage.
Since I = V/R, this can also become P = V^2/R, and since V = IR, P = I^2 * R as well.

It is resistance that affects power (in a system with a linear I-V characteristic of course). Thats why I would avoid resistors.
Actually, The real reason why i want to get the 5V line involved is because it's much easier ;)

drow_elf 20th June, 2002 04:17 PM

mmmmh basic electricity formulas.... yummy!

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