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Why Aren't PC Power Supplies External?
An Anonymous Coward asks: "After years in the computer industry it just occurred to me: Why don't computers have external power supplies? The lions share of the heat and noise from a computer are generated from the power supply. Why not take it out of the case and run just the 12 and 5 volt lines into the case, leaving the heat and noise tucked down under the desk somewhere? Perhaps there is some electrical law that makes that a bad idea, but I can't think of it." One stumbling block is that a power supply brings in more than the 12V and 5V lines, it also provides the power connectors for the motherboard, internal peripherals and external fans. However, these could be provided by the case. If a standard form connector from external PS to the PC is designed, might we be able to avoid further incompatibilities like AT/ATX? It's an interesting idea for future designs, but I wonder if there are other stubling blocks out there. Thoughts?
I would like to see DC wall sockets. For efficiency reasons, power should be transported over long distances via AC. Once in the house, there would be one large AC -> DC converter. Jacks in the wall would have pins to select one of a few available voltages.
Look around your house/work at how many separate AC -> DC converters there are. I think centralizing would be more efficient. You could have battery backup and very clean power.
DC power is easier to use (most of the time). Telco racks are DC for a reason.
In 1981 the Sinclair ZX81 had an external power supply. You reset the machine by pulling the plug from the back and reinserting it, or you could just wobble the 16K RAM pack for the same effect.
I can't wait for my new PC to have the same feature.
Not hardly.
These days, Most heat is generated from the CPU, and most noise, believe it or not, is generated from those cruddy little CPU fans. A lot of noise is also generated from extra case fans you may have trying to improve airflow in your case. P/S fans are often much quieter than those other fans in your system.
I've thought of this idea before, and I also think it'd be a fantastic idea. Just keep in mind, the P/S also needs to be cooled, so that external box will have fans in it, and once it's outside the case, it'll be making some noise, too. I remember my Amiga 500 fondly, though, as it's power needs were such the external P/S didn't need any fans...
We had some X-terminals with external power supplies. They had a habit of breaking, so we tried to source some new ones. 80 quid (thats over $100 in USA money). I was stunned. 80 quid for a black box transformer.
Anyway, the thing had the pinout of the connector printed on the bottom, so I hacked off the cables, soldered on some standard molex connectors, and wired three of them up to a standard PC power supply running in an empty case.
Back to the question. An Xterminal is a pretty low-power-usage device (no moving parts, and the monitor was on a mains cable) and that seemed to need an expensive PSU. A comparable unit to power a PC as well would be ridiculous...
Baz
I know PCs don't draw very much power, either, but if the power supply were external, you'd have to include special internal cables, a power socket (or two or three) on the case for these connectors, and some stylish, fancy case for the external power supply. All of which would drive up the cost of the machine $20 (which is a lot these days).
The real issue here is that Intel and the hardware manufacturers are deliberately picking case designs that require several fans to cool correctly. It's as if these engineers never heard of the word convection.
The answer? Buy a decent, quiet power supply, and some cooling fans. Note that pcpowercooling.com has a new cooling fan that includes a thermistor. The fan spins only fast enough to keep cool, so it actually spins slower, and quieter, most of the time.
Most people don't care if they're going deaf from that little whirring noise, and OSHA's rules don't apply to the home....
Jim,
Not arguing your line loss figures, but you can always use a power supply with remote sense lines to make up for the line loss. I used to work in electronics, and we HAD to do it on some of our higher power boxes. When your pushing 120 amps of 5VDC with a +- 50mV spec, you have NO choice
-- 73 de KG2V For the Children - RKBA! "You are what you do when it counts" - the Masso
Wow, something on Slashdot I'm actually semi-qualified to answer! ( I used to design server-class power supplies)
There have been some good answers, but the biggest reason PC power supplies are internal rather than external boils down to $$. Well, that and safety, but then safety boils down to $$. And then technical, but that's also solved by $$.
There are at least four voltages produced by PC power supplies, with currents on the 5V line up around 12-20 Amps. The regulation of the 5V line measured on the motherboard is about +-5% or better (+-250mV), which at 20A would work out to about 0.012 Ohms of resistance split between cable and connectors. 14 guage wire (similar to an extension cord) has a resistance of 0.0026 Ohms per foot. So, about 5 feet of wire would chew up all of the allowed resistance with nothing left over for connectors. I've been loose with my numbers, but you get the idea.
Now imagine a cable from the power supply to the computer with 8-10 wires, all the size of those in a standard extension cord. Now, imagine paying for all of that copper.
The old AT-class and now the ATX class supplies are commodity products. This means that the design is stable, has been engineered and cost reduced to death, and are now being manufactured in low labor rate locations with component parts being negotiated to sub-fractional pennies.
Custom power supplies used to be priced in the $1 per watt range (in large volumes). PC power supplies are well down below the $0.10 per watt range and going lower. Anything new will have to survive being compared against a mature $15-20 solution.
Cheers,
Jim
Hmmm... I was envisioning more of the C-64 style of power supply (or the same thing found on many printers and some computer speaker sets). Standard 3-prong plug -> 2/4 ft of wire -> Fairly Large box -> 2-6 ft of wire -> power-hungry box. Lets you have control over the placement of the power converter, and doesn't use up any extra plug space. Wall warts are only good for low wattage apps. Wouldn't be all that nice for a 100-200W multi-voltage supply...
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As an owner of a A1200 (that's Amiga, folks), which had an external powersupply (actually, so did the A500, and A600), they SUCK! Why?
Trying to find a place for it was always a pain, because the cables came out front and rear. It was a nightmare. If it weren't for the location of my desk at the time, it could've been stepped on or tripped over. It was the only thing I hated about my A1200.
As far as noise is concerned, I doubt the fan in the power supply is noisy. I have a test setup right now with an ATX powersupply sitting out openly on my desk, and when it is on, it is all but inaudible. Even in a case, I doubt it it very loud (BTW - why all this talk about loudness? I don't mind the sound of computers - give me the thrum of a computer room A/C and powersupply system for company any day!).
I can only see one way having an external supply would be a good thing, and that would be if it had plugs for everything - no more wall warts, only one AC plug, everything else plugs into the powersupply. I am imagining something like a beefy looking power strip - it could even have a built in UPS for certain components. I would be even willing to bet the monitor could run off of such a system (maybe - I have a portable tube based TV that runs off a 12 volt/1 amp wall wart - of course, it has a small screen - maybe a larger monitor couldn't do it).
I would think you could actually build something like this yourself - getting large amperage bare power supplies isn't a big problem, so just build a case, add some custom cables... The only issues I can see you running into would be possibly noise (electrical) and voltage/current drops/sagging (from excess length of runs for the cables)...
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Doesn't Apple's G4 Cube have an external power supply? I assume that is part of how they managed to make the Cube so quiet (and so small).
So when this system was new, I gradually decked it out with one too many gadgets. Multiport serial boards, CD-ROMs, hard drives, tape drive, I don't know, but at some point it started needing more power than the dinky little supply in the mini-tower case could provide. And I couldn't find a supply with enough juice that would fit the enclosure.
So I got a big supply, set it on top of the case with the cover off, and ran the wires down to power the motherboard and all the rest. With a spot-fan on the CPU, no worries there, and nothing else gets hot enough to cause any trouble.
Maybe this approach wouldn't work on these newfangled, high-MHz, noise-sensitive systems they've got these days. Or maybe it wouldn't be a problem, as it isn't for me. Someone would have to try it.
Incidentally the system is still overpowered for what it does... it runs a dialup BBS and has a custom alarm clock from hell to get me up in the AM. (Wasn't that one of the apps CmdrTaco wanted in the BorgBox?)
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Aside from power requirements of most modern expandable computers introducing the need for cooling, interference is an important factor.
When you have an internal power supply, the case shields against outside and emitted interference. You can shield the external power supply, but it is harder to effectively shield the multiple DC conductors that must go from the power supply to the PC. Inside the case, it is a much more controlled environment. This helps with stability a lot, considering components in modern PC's have to have over 1GHz of timing accuracy. Also, you don't have to make a cosmetically pleasing case for an internal power supply (unless your chasis is translucent), but you have to make it less than an eye-sore if it sits on the floor or desk. That extra casing introduces more costs.
The main reason _I_ would like an external power supply is for my server rack (in progress). I've got 5 pcs in rackmount cases (of varying sizes), they're all watercooled (read: NO fans at all in the cases except for the powersupply). Now, if I could buy a 1 or 2-u powersupply that would run that many boxes (and preferably be designed for watercooling itself - I can dream can't I ;) I'd be in heaven. If we had external power supplies for desktops, there would already be some type of standard (hopefully) connector. Thus, large capacity PS's could be designed with a little scalability in mind (picture a power hub with multiple ports).
Why not attack it the redneck way ? Just buy a truckload of molex extensions and chain them together until you have about 12ft of unshielded power wires dangling around.. that way you could hide the case away and screw the cdroms and tape drives directly onto your desk thanks to the extra long power connections.. as a bonus it will automatically kill your roommate's cat in seconds as soon as it sinks its teeth into it.
-Billco, Fnarg.com
The technical term for the little transformer built into a plug (so you can only get one into a wall outlet, or half as many on your power strip as it has outlets) is "wall wart". Their efficiency is often hideously low, and it's a pity that there aren't Federal regulations restricting how much power they're allowed to waste (especially when the device they are powering is in the off or standby state).
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I can't say I want anymore power supply devices lying around my desk. So please don't suggest that they make another. Its wonderful and unusual that they make proper UL listed power supplies for computers. Most cheap things don't want to plug into the wall. Currently, I have One AC-DC for the scanner One AC-DC for the external zip drive One AC-AC for the DSL modem One AC-DC for the PIC16F873 board These dongles either take up cumbersome space or they take up way too much space on the powerstips. Happily the printer, monitor, and computer all plug in normally. On the other hand... If they could link all of these peripherals up to the same power supply, that'd be pretty cool. I wouldn't mind having just one external power supply if we could plug all the devices into that. Unfortunately daisy chaining is frowned upon in DC power supply situations. So that means a spidery nest of power cables no matter what we do. Is there anyway out of this? How about a tesla-coil right above the computer ;)
I'd give mega frankenstein points to anyone
who made a working computer system using
a tesla-coil.