300w or better external PSU?
January 20, 2011 8:15 PM   Subscribe

How can I find a "laptop style" power supply that is good for more than 120 watts?

I built a cool little Intel Atom powered computer for my garage about a year ago. I got this power supply for it and it works great! Its really cool to not have a traditional power supply.

I will be in the market for a new desktop fairly soon here and would like to use a similar "brick" external style psu, but cant seem to find where to get them.
Im looking for one that will handle normal desktop wattage, no less than 300w or so.

Question 1 - Does one of these even exist for consumer purchase (I know they exist, ive seen them in some dell desktops)?

2 - Where would I find one?

Thanks a lot!
posted by Esefa to Computers & Internet (12 answers total) 2 users marked this as a favorite
I think that the product you want to buy is physically impossible.

The problem is cooling. The Laws of Thermodynamics require that a significant percentage of the power going through the unit gets dissipated as heat. If something the size and shape of a laptop power brick is generating 200-400 watts of heat, it's going to get really hot, and start a fire.

Anything that can yield the amount of output power you want will have to be relatively large, and will have to have a cooling fan. That's the only way it can be safe.
posted by Chocolate Pickle at 8:36 PM on January 20, 2011

Its definitely possible. I failed to mention that I dont care how big it is (within reason), since the beauty of these is that they can happily reside under a desk or anywhere else out of view.

Here is a fanless 600w "external" power supply. I like it but its not quite what im looking for since this one needs to be fairly close to the computer (and its more power than I need).
posted by Esefa at 8:53 PM on January 20, 2011

I think Chocolate Pickle is a little off the mark: the power isn't used in the power brick itself, so there's not an issue with heat. But unfortunately I don't know of a suitable PSU.

It could help to know what voltage you need to get out of it.
posted by anadem at 8:59 PM on January 20, 2011

Thanks for the response anadem. I have no clue what voltage ill need.

Im currently looking at a Core i5 2300 with a mini-itx mobo and a laptop hard drive. Pretty minimal power requirements but I dont want to be near the limit of a power supply's range.
posted by Esefa at 9:24 PM on January 20, 2011

the power isn't used in the power brick itself, so there's not an issue with heat. But unfortunately I don't know of a suitable PSU.

But the power supply transforms the power from one voltage to another, and those pesky Laws of Thermodynamics say that such an energy transformation cannot be 100% efficient. Power supplies dissipate a lot of heat; it's impossible for it to be otherwise.
posted by Chocolate Pickle at 9:47 PM on January 20, 2011

What I was referring to as being impossible is the kind of little-black-box-plugged-directly-into-the-power-bar which powers ever laptop I've ever owned, except at the kind of power level you want. That isn't possible. (Or rather, that can't be done without safety hazard.)

If you won't mind that the box is big, and that it's got a cooling fan, then there are no such physical difficulties.
posted by Chocolate Pickle at 9:50 PM on January 20, 2011

How about a server power supply like this or this?
posted by xedrik at 9:54 PM on January 20, 2011

So that would be a 12V 25A PSU. While it won't shed 300W of heat, you're not going to find a fanless power supply at that power rating period. It will have a fan. it will also output 25A which is why you don't find many because that's a lot of potential current. Don't let your pet rabbit chew on those wires.

Radio Shack used to carry this power supply for some mystery application - possibly high-current quick-charging of RC car batteries. I dunno. But they don't seem to sell it any more, they only have the manual.

But in general such things are simply not made. External laptop PSUs top out around 100W or so. It's basically a cooling thing. You could buy this cheap PSU and put it in a box with a fan but I'm not sure how that's any better than a standard ATX PSU in terms of noise or convenience.
posted by GuyZero at 9:56 PM on January 20, 2011

Both of those server PSUs have fans and are both designed to be enclosed in a case. They're probably not rated to run exposed from a safety point of view. Also, they have stubby little connectors that won't reach very far.
posted by GuyZero at 9:57 PM on January 20, 2011

Thanks for the replies all. I guess I was running under the assumption that given the size of the 100w external that I own now, 3 or 4 times the power (and 3 - 4 times the size) should be no big deal.

I really just cant accept that it isnt possible to build one, with enough surface area (using fins), im sure its possible even without fans. It would definitely be big though, not ridiculously big, but you wouldnt want to lug it around.
I think the real problem is that there is no market for them. Understandable. Too bad though, it would be nice to have a decent system that could be mounted to the back of the monitor.

Thanks again!
posted by Esefa at 10:23 PM on January 20, 2011

Well, if I'm doing the math right, the PSU for my work laptop is capable of 240W and it doesn't get abnormally hot. It's useless for your purposes since it puts out 19.5VDC at 12.3A, but it's not actually an insurmountable technical challenge since the rest of the DC-DC circuitry is contained in the very limited confines of a laptop.

That said, the biggest I can see on my usual source for goofy stuff like this is 180W at logicsupply.com. However, that said, if you're looking at something small like that perhaps you want to consider the portable equivalents in a mini-ITX board anyway, which would significantly drop your power demands. You wouldn't be able to get the current generation of video cards to run on it, but that might be acceptable for your purposes.
posted by Kyol at 10:42 PM on January 20, 2011 [1 favorite]

Radio Shack used to carry this power supply for some mystery application

Hey, I have one of those! I use it to power a car-stereo style amp.

If you can add a beefy capacitor downstream of the supply, you'll get better performance, if the power demand is not exactly constant, which it probably isn't.
posted by StickyCarpet at 11:45 PM on January 20, 2011

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