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  #1 (permalink)  
Old 28th February, 2003, 11:39 AM
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Question Fan voltages - am I slowly breaking my PSU??

In my quest for the quietest pc on the planet I have sussed that if you change the pins on 12v fans over the 5v leads from my psu, they run quieter than a small mouse running on silk, but...

I'm planning on running 3*12v 120mm fans (for my rad on the w/c kit) at 5v.

Will this put overload my shiney Enermax 350W psu?

I understand that if you lower the voltage the current increases to match the wattage, but is this case on the psu? will the wattage lower as a result of a rated component connected to the wrong power input?

Cheers!!

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Old 28th February, 2003, 06:05 PM
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AFAIK, many 12v fans won't spin at all on a diet of 5v. 7v would be safer, to the best of my knowledge.
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Old 28th February, 2003, 10:36 PM
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Re: Fan voltages - am I slowly breaking my PSU??

Quote:
Originally posted by DevilDoll
I understand that if you lower the voltage the current increases to match the wattage, but is this case on the psu? will the wattage lower as a result of a rated component connected to the wrong power input?
If you keep the wattage the same, then a change in voltage will affect a change in current.

However, as a fan has a basic resistance to it, lowering the voltage will lower the current, and hence lower the wattage required to run it. (Lower voltage = Less work done spinning the fan = lower wattage)

Áedán
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Old 1st March, 2003, 06:36 PM
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Thanks Áedán, so if the resistance remains the same, with the current & voltage dropping as a result, no major worries then.
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Old 18th March, 2003, 12:04 PM
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If you are concerned about running them from the 5V line(it shouldn't actually be a problem). There are two other ways of doing it- You can run a pair of fans in series off the 12 V line- thus each is getting 6Volts, or as someone else mentioned you can connect the fan to a 12volt line but ground the fan on the 5Volt line and run them at 7Volts.
I have tried all these combos and they work without sending the PSU up in flames.
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Old 18th March, 2003, 10:09 PM
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Cheers Lord V, am running them at 5v without any problems. (Didnt even consider the 12v serial setup, but i like it so much my soldering iron is warming up right now....)

btw I replaced my enermax psu with a ZalmanZM400A-APF and man, if it wanst for the power led i wouldnt know its powered on
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Old 19th March, 2003, 11:08 PM
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This 12-5=7 business has confused me a little. Surely it would mean a current is flowing up the 5V line (the wrong way). So if something usually ran from the 5V line, it wouldn't get anything cos the current would be going the wrong way? If you see what I mean.

Or does the currentgo from +12V down to +5 and then through any 5V components down to +0 ground?
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Old 21st March, 2003, 09:55 AM
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Stigweed- think your second explanation is correct.
I find it easier to view the thing in terms of water piping. Voltage= water pressure, current(amps)= water flow rate. Don't know what would happen if you put too much into the 5V line and it overflowed.

Devildoll- I am assuming the fans are identical (ie same resistance) to put them in series and get 6V on each.
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Old 21st March, 2003, 02:47 PM
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Yeah, both fans are identical Bi-Sonic 120mm...
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