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Old 7th December 2002, 11:59 PM   #1
JBL is offline JBL  Canada
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Arrow Removing fan???

I've been using a computer power suplie to power opamp and similar circuit. I've found no inconvenient(electricaly) on doing so.

I would like to use one to power all my low level electronic for my audio system(including preamp, active xover and maybe auxilliary circuit in power amp someday.)

But I hate the noise of the fan. Would it be possible to just remove the fan from the psu.

I would not use the 5 volt output at all and much less than1 amp from the +-12 volt. I think that the PSU will survive.

Any tought?
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Old 8th December 2002, 12:31 AM   #2
OliverD is offline OliverD  Germany
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Switch-mode power supply units often need a minimum load to function properly. Be careful, especially if you do not use the +5V line. Also check the power ratings for +12V and -12V. They are often different, since +12V is needed to power the drives' motors, while -12V is NOT used by many modern main boards.

You can try removing the fan. Carefully watch the temperature of the power devices in a worst case scenario (high load, high ambient temperature). If you think you (and the power devices) can live with it, there you go.

Otherwise try mounting the power devices of your computer PSU on a big heatsink mounted on top of the PSU case, connecting them by wires as short as possible. Isolate them from each other and from the heatsink. Connect the heatsink to earth. Use shrink tube to isolate the pins from each other. This approach worked fine for me when I had to make a server as quiet as possible.

Again, watch the temperature carefully and figure out whether you need a heatsink even bigger.

CAUTION: There are power devices in a switch-mode power supply unit working with HIGH VOLTAGE! You have to ISOLATE all devices from the heatsink properly. Also, don't do these modifications unless you fully understand what you are doing and are aware of all possible RISKS.
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Old 8th December 2002, 01:03 AM   #3
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Jonathan, would it not be easier and more compact just to build a proper power supply?

This is my attempt, as you can see it is not very tightly laid out, yet is only 150mm long and gives 500mw per side.

Sorry for the fuzzy photo, I didn't use the macro setting and the batteries ran flat just after I had taken and downloaded this shot
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File Type: jpg dscf0023.jpg (45.2 KB, 113 views)
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Old 8th December 2002, 01:06 AM   #4
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Oops, just noticed I broke a couple of the inlet wires whilst posing the board for the photo... B****r
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Old 8th December 2002, 01:22 AM   #5
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hehe wasn't able to wait...
Removed the fan and made it work a nearly full power. Work fine. Become hot but not as much as I tought.

Second every computer power suplie I've experimented with in my live(that represent at least 6) didn't need an external minimum load(was probably provided internaly). So that problem is removed from the list in most case.

Also the protection on those thing render them nearly indestructible. Made them suffer the worst possible load condition. Never had a failure. And they d'ont cost much even new.
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Old 8th December 2002, 10:13 AM   #6
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Why not just run the fan off the 5v rail instead of the full 12v? There will still be plenty of air for what you want, and it will be way quiet too!
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Old 11th December 2002, 02:05 PM   #7
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the -12volt current output is only limited by the diodes used... The +12volt uses 2 diodes (in the one 3 pinned package) that is mounted on a heatsink, while the -12volt jut has small (probably about 1 amp) diodes mounted on the board.. also, the value of the filter capacitors, ohh, and the filter chokes...umm.. yeah, thats all.. So, in theory (and practice) you could get half the +12volt current into the -12volt, and half into the +12volt.... which in some cases may be 6amps each way.. not bad...
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