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 Post subject: How about external power supplies -- why or why not???
PostPosted: Sun Dec 29, 2002 11:12 pm 
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Joined: Sun Dec 29, 2002 9:10 pm
Posts: 44
I've been thinking it would be a good idea to put the power supply outside the system. Seems that the benefits would be:

- isolation: no vibration from fans to be amplified in case
- better cooling: more space in case, better airflow, lower temps
- easier to cool, mod: seems that you could do more tricks to cool the power supply if it were external, like a big 120 mm fan or something else creative.

The way my desk is set up I'd have room for a big external power supply, so it wouldn't be a problem.

The biggest potential drawback that I can think of (save for actually finding or building one) is the distance. I'm by no means an electrical engineer. But, I wonder if there'd be a problem running the DC current an extra few feet, say 5 or 6?

Also, I did a search of the forums here. Was able to find one single entry thread titled External Power Supply. It linked to a page that showed a picture of one at some Asian trade show.

So, is an external power supply a worthwhile idea?


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 Post subject: Re: How about external power supplies -- why or why not???
PostPosted: Tue Dec 31, 2002 9:28 pm 
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Joined: Sat Nov 09, 2002 1:45 pm
Posts: 149
RickStrobel wrote:
I've been thinking it would be a good idea to put the power supply outside the system. Seems that the benefits would be:

- isolation: no vibration from fans to be amplified in case
- better cooling: more space in case, better airflow, lower temps
- easier to cool, mod: seems that you could do more tricks to cool the power supply if it were external, like a big 120 mm fan or something else creative.

The way my desk is set up I'd have room for a big external power supply, so it wouldn't be a problem.

The biggest potential drawback that I can think of (save for actually finding or building one) is the distance. I'm by no means an electrical engineer. But, I wonder if there'd be a problem running the DC current an extra few feet, say 5 or 6?

Also, I did a search of the forums here. Was able to find one single entry thread titled External Power Supply. It linked to a page that showed a picture of one at some Asian trade show.

So, is an external power supply a worthwhile idea?


few things:
believe or not, PSU fan moves lot of air in your computer case. without PSU, you need some exhaust fan anyway unless you intend to keep the case open (assuming you're going for fanless system).

i don't think vibrational noise from PSU is any significant. psu fan noise is by far the greatest obstacle. but you won't be circumventing this.. because you'll have to install an exhaust fan anyway to keep things moving.

if you put psu outside of case, there'll be absolutely no need to go overkill on the cooling (i.e. 120mm fan). stock one running at 7v should be fine because there will be no additional heat from the rest of the computer. this is of course, you want the 'extreme' cooling... but if that's the case, you're in a wrong forum :D

have fun! keep the ideas coming...


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 Post subject:
PostPosted: Wed Jan 01, 2003 1:32 pm 
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Joined: Mon Dec 09, 2002 5:00 pm
Posts: 12
Running the power supply outside of the case and extending the DC cables will cause some additional resistance. By definition there is 1 ohm of resistance in 1 foot of pure copper #10 AWG wire. So extending your cabeles will add marginally, more than one ohm per foot since you will be using smaller wires than 10 guage. and the wire is not 100% copper. There will also be additional resistance due to the extra set of connections if you splice into, or extend the original power cables. (This can be avoided if you REPLACE the cables rather than extend them.)

Either way, there will be some additional resistance that will make your power have to work harder to do the same thing as before it was relocated. If you have a GOOD power supply with a a bit of wattage to spare, placing the power supply outside of the system shouldn't cause any problems as long as you don't have it really far away and do a good job of making the connections.


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 Post subject:
PostPosted: Wed Jan 01, 2003 2:25 pm 
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[quote=By definition there is 1 ohm of resistance in 1 foot of pure copper #10 AWG wire. [/quote]

10 gauge copper wire gives ~1 ohm/1000 feet


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 Post subject:
PostPosted: Wed Jan 01, 2003 10:35 pm 
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Joined: Sun Sep 29, 2002 9:05 pm
Posts: 228
Location: Powell River, BC, Canada
One of the only things I can think of with respect to putting the PSU outside the case is that various electrical noise can leak out of the wires, running back from the computer to the PSU. Normally the PSU has some line filtering that aids in keeping EMF inside the case, where it can't feed back out of the 120v power cords, but the mobo and other internal components usually have no filtering (ferrite beads, capacitors, etc.). These parts could be supplied by you, and theoretically should be put just inside both the computer case and the PSU case, so that the power wires in between the two cases don't act as an antenna for the noise. Using grounded/sheilded cable would also help; in effect a "flexible extension" joining the two cases.

Manufacturers need to be fussy in order to meet FCC regulations that cater to all markets. But in practice, I have this sneaking suspicion that electrical noise with computers is a very minor issue. It doesn't seem to bother anything much, nor does the computer seem adversely affected. However, high power radio gear (HAM, VHF, etc.) can beat up nearby equipment if proper shielding isn't there. Also, sensitive audio gear could possibly pick up and amplify computer electrical noise (even poorly shielded microphone wires inside a computer case can do that).

On my own system, I have just one fan on the PSU, set deep inside the case instead of out at the very back. I think it helps keep the noise down a bit, and it also helps that that one lone fan serves to ventilate my whole case. If you are worried about PSU vibration, then I think that it would be better to isolate the PSU fan properly. Any other significant PSU vibrations are most likely caused by a problem with the PSU, and shouldn't be happening in the first place. Other minor PSU buzzing would be less audable with the PSU mounted inside the main computer case.

On the other hand, if you want a very compact case positioned in a work space for easy access to drives, I can see how a long remote PSU would help keep heat and noise further away, as well as maximizing the working space inside the case. In that situation some extra filtering capacitors at the computer end would be wise to help with high frequency voltage regulation problems that could arise given the extra supply lead length (especially on 3.3v & 5v lines). Given the present status-quo of IDE and FDD interface standards, I see that approach as generally more viable than trying to remote mount the drives. I kind of like the idea of a slim / book-sized PC with the mobo mounted back-facing-forward or back-facing-sideways, to give easy access to the many I/O ports that are usually built on to the mobo. I think that is how I will build my next system (including custom built case).

Happy new years, Crisspy.


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