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Old 04-06-2009, 09:38 AM   #1
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High current switching supplies

I'm looking for a unit in the form of a power 'brick'.

Optimally, it is able to handle 20 amps at 12v. More would be nice if possible. I've found the large supplies with screened cases and such. I love those supplies for clean power but I don't want something that big. I don't need a 5v rail from the supply as the major load is from the CPU and video card which use the 12v rail primarily. I see cheap 10 amp ones on ebay but not 20+

Here is the application. I have a Dell GX270 (Small Form Factor measuring 4"x12"x13") desktop system. I love the small size of this thing but it limits my power supply options to... well, nothing really. I can only run the stock 160w power supply so this makes me need to either use an external supplemental power supply, gut the 160w supply and use a full size power supply for power tunneling through the stock supply, or open the stock supply and upgrade the regulators.

Using an external supply I feel is a bad idea. It makes for a big, heavy cable running into the back of the computer with a bunch of wires and it ruins the portability of the computer. The regulator upgrade MIGHT work if I can get heat sinking into that case but that is unlikely because of the size.

Those two reasons have led me to the supplemental supply. It will have a circuit that kicks it on and off with the system but can supply the processor load circuit and the video card with power.

This is the system specifications(pending power supply) *=maximum:
2.4GHz P4 HT 256k (3.2GHz P4 HT 512k* due to thermal limitations)
2x1GB PC3200*
200GB 7200rpm SATA HDD
128MB AGP Radeon x1050 (AGP 256MB Radeon HD 3450)
Creative Audigy SE 7.1

That's pretty much it. Not a blazing fast crazy computer but plenty for what I need. Light gaming with HD movies to come due to the new video card's ability to output component 1080i. This, however, will be my last upgrade as I've reached the thermal limitations of this system except for a blu-ray DVD for when it gets retired to HTPC-only use.
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Old 04-06-2009, 10:46 AM   #2
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All the places I use you already read about in that supplier thread. 20A seems like a tough find. Could you use two of the cheapo 10A ones in parallel? Crack the cases and consolidate them perhaps?

Every time I use a power supply calculator online it gives me what seem like very inflated values. Anybody know a good one?
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Old 04-06-2009, 02:48 PM   #3
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I might be able to do that. I could use two for the processor because it is a 4 pin setup that has two grounds and two 12v rails. Tonight I'm testing if a 60w 12v/5v combo supply I have is enough to run the video card. If it is I'll be able to use that for at least the card. If I could get my input connector to stay at around 9 wires or so it might not be that bad.

I'm going to have to do some testing. ATX specifications for the 'P4 connector' is 1 amp minimum and 13 amps max with a surge of 16.5 amps holding > 11volts for 10ms. I think a large capacitor could more than supply that and 13 amps is the max specification. I could use a single 12v/10a supply and see how loaded it gets. If I do that, I can get my wiring down to 1 sense pin, 3 ground, 2x12v rails, and a 5v rail. 7 pin connectors aren't hard to come by. I'm sure ratshack even carries that kinda stuff.

That would give me 180 watts of external, fanless power supply in a custom DIY box.
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Old 04-06-2009, 04:07 PM   #4
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Do you have a UPS? If it uses a 12v battery maybe that could handle the surges for you. The capacitor idea definitely sounds reasonable if you've got a good supplier.
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Old 04-08-2009, 05:27 AM   #5
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I've done some rough testing. The video card runs great off 2 amps 12v and 2 amps 5v from the switching regulator I have now so I believe the processor will run fine off of 10 amps.

Also turns out that I NEED a switch in line with the adapters so they turn off when the power supply turns off. With just the video card getting external power the dvd drive stays in an active error state unless the second supply is unplugged.
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Old 04-08-2009, 05:49 AM   #6
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Can you use a relay hooked to the power supply to control the adapters? I don't know about you, but having to remember to throw another switch every time would drive me crazy.
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Old 04-08-2009, 05:55 AM   #7
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A solution that requires less effort than relays would be to use the switch on a power strip, unless the computer automatically powers itself off (a la ATX). For auto-poweroff, it should be possible to pull the signal from the wire that tells the power supply to shut off and send it to the other power supply too.
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Old 04-08-2009, 06:11 AM   #8
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I actually do the powerstrip thing myself. I've arranged my devices by function on a few of them so I can turn off anything I don't need. For example, if I'm running a simulation at night or doing some other computational task, I can kill everything but the computer itself. If I'm downloading something big overnight, I can just kill the speakers monitor, and my skype phone. Simple and a little crude, but it does the trick.
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Old 04-08-2009, 08:56 AM   #9
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I'd actually prefer to not have the supplies come online via main power switching as I don't know what kind of start-up surges they may have.

The way I was thinking of doing it was to run a 12v line from the existing power supply to a couple of double pole relays in the main box that activate when the system is turned on. There will be a slight delay but not enough to make a difference I don't think.

This is also the preferred method if one day I am away from home and the power blinks and the computer itself doesn't come back on but the power brick does. Right now I have the computer set to automatically come back on in the event of a power loss but you never know.
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Old 04-08-2009, 09:03 AM   #10
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There's plenty of pinouts and documentation on ATX power. You should be able to just tap the wires that signal the power supply to power up/power down and use them for the second power supply.

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