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DC Power Supply for Desktop Computers?
cmowire asks: "Given that
inverters waste a lot of power and using solar and battery power is getting to be more attractive given power shortages, are there any DC power supplies that can be bolted in place of a standard ATX power supply and tied to a battery/solar panel combo? I know that it's pretty trivial for a laptop to work like that, but I'm more curious about doing that for a desktop system."
Amtrade has several DC power supplies available... they ain't cheap, though... the cheapest one listed is $85.50, and prices go UP, UP, UP from there...
Of course, you'll need to be able to feed that UPS battery with a slightly higher DC Voltage than the battery's own voltage to keep it trickle charged, and that source of DC will have to be able to supply enough current to drive the computer and monitor and keep the battery trickle-charged, and it's probably at this point that you'll realize distributing power via 120 Volt AC around the average home and letting each device convert it according to that device's needs is much more practical.
Another possibility is to rebuild your computer's power supply, eliminating the AC side of it and replacing the isolation/step down/switching transformer and associated switching transistors with something that's the same on the secondary side but uses lower voltage-higher current transistors and fewer windings of heavier wire on the primary side, unless you can put enough solar cells in series to achieve about 170 to 200 Volts DC.
You may have realized by now that I'm trying to point out that although what you want is possible and an interesting thought exercise, it suffers from a pretty high lack of practicality.
Using DC is going to almost invariably mean lower voltages than the wall socket, which means higher amperages for the same wattage, which means thicker cables keeping the current source and the computer near each other or even thicker cables to prevent voltage drop.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
Avoiding the conversion to 110 Vac seems attractive, but (as has been mentioned above) modern power inverters are more efficient than you might think. The main advantage of reproducing the ac line voltage is the ease of just plugging things in, with no modification to their wiring.
I bought a "Smart UPS 1000", made by APC, on Ebay for $65. To provide 300 V-A (see comment #14 above concerning power factor) for fifteen minutes, this unit uses two 12V sealed lead-acid batteries that weigh about ten pounds apiece, connected in series.
A power supply that ran on 12V would be more versatile (solar cells, vehicle power, etc.). I think a practical approach would be this: switch the 12V through a transformer (higher frequency for a smaller transformer) and rectify it to make around 270Vdc. It would not have to be very well regulated, by power supply standards.
Since monitors and ATX power supplies start out by directly rectifying the line voltage to make 270Vdc, (which they use as the input to their various switching power supply circuits to produce the different output voltages), their line cords can simple be plugged your 270Vdc output. You don't have to worry about polarity, because the full-wave line-voltage rectifiers will direct your 270Vdc properly to their reservoir capacitors.
Thus, you don't need an inverter, and you don't have to listen to the BUZZ of an inverter.
You'd have to check for any line-operated fans in the equipment, though, and replace them with dc fans.
Everything should be made as simple as possible, but no simpler. -Albert Einstein
The entire point of the power supply in most computers is to convert AC to DC: the components in the computer take DC power directly. If you already have the DC power, you could almost (modulo deriving the right voltage levels and some power conditioning) hook up all the components directly.
The item (or items) you are looking for is called a DC-DC power converter, possibly combined with a moderately sized capacitor to smooth out any sags or dips (you'll also need something to filter out surges, maybe a zener diode or some such). For most of the computer all you are worried about is producing 5 V and 12 V feeds, which shouldn't be a big deal, but for some components (CRTs and the flourescent backlight on most LCDs) you will need to produce some very high voltages (in the kV range, at least). For high voltages you will need to go back to a real power supply and an intermediate AC stage (aka, a switching power supply, which is what you already have in all such applications). Then the question is, do you replace the one that you already have in your CRT or LCD monitor, which is expecting 50-60 Hz, 110V (or 220 V, or whatever the local flavor is) AC power, or do you roll your own that can take whatever DC voltage you happen to have handy?
Ultimately, it is probably much simpler just to convert your local DC source into a nice 60 Hz, 110 V AC signal and continue using all your equipment in an unmodified manner. The conversion, both in your DC-AC converter and in the computers' power supplies, is pretty efficient these days, so don't worry too much about lost power there.
Not counting the monitor problem, the best bet might be to go with a DC-DC power supply. A friend and I recently had the opportunity to put our server in a telco grade colo and we had to scour the net to find such a beast. We were able to get a -48V DC input power supply with a standard form factor that dropped right into an ATX case. It has the standard voltages and connectors of a regular ATX supply on one side and a -48V DC input on the other. Unfortunately, our company went out of business a week after we got it hooked up but it worked great in the meantime.
I can't remember the exact output wattage, but we had it hooked up to a 5 amp fuse running an average number of components w/o trouble. I'm no EE but I imagine you could easily run it off a battery bank if you had an existing photovoltaic array and distribution system. If you didn't need a monitor, you'd be all set, otherwise, you might as well stick w/inverting to AC and using standard components as an earlier poster had suggested.
Unfortunately, I don't have the link w/me but I'll put it up when I find it.
I'm trying to sell it (moved back to an AC colo) so if anyone is interested, drop me an email.
Dan Bernstein wonders why power supplies don't come with an internal UPS.
-russ
Don't piss off The Angry Economist
Sound and serial ports (sometimes)...
(quoted from somewhere)
"RS232 data is bi-polar.... +3 TO +12 volts indicates an "ON or 0-state (SPACE) condition" while A -3 to -12 volts indicates an "OFF" 1-state (MARK) condition.... Modern computer equipment ignores the negative level and accepts a zero voltage level as the "OFF" state. In fact, the "ON" state may be achieved with lesser positive potential. This means circuits powered by 5 VDC are capable of driving RS232 circuits directly, however, the overall range that the RS232 signal may be transmitted/received may be dramatically reduced.
The output signal level usually swings between +12V and -12V. The "dead area" between +3v and -3v is designed to absorb line noise. In the various RS-232-like definitions this dead area may vary. For instance, the definition for V.10 has a dead area from +0.3v to -0.3v. Many receivers designed for RS-232 are sensitive to differentials of 1v or less."
--
"It's tough to be bilingual when you get hit in the head."
The -12v isn't used by most components, but a lot of sound cards DO use it. (I happen to know because my -12v lead came loose, and the only thing that went wrong was my audio out picked up a whole lot of noise and reduced its volume 90%.)
Time flies like an arrow. Fruit flies like a banana.
Whatever you try, don't use those cheapy seventy dollar inverter critters from the local Rat Shack. They make enough interference that some laptops and handheld radios cease to function near them.
crap and i just bought one of those off ebay - oh well, luckily it was only 15$ - guess we'll find out if it was a good investment when i hook my $3000 system with all my crucial data with no backups to it
Two wrongs don't make a right, three lefts do!
errr... dude, you wouldnt want to read the post first would you? thats what he wants to do... skip the middle man, use a dc atx powersupply.. he said the inverters use too much power.. read it again.
stuff
Not so! One can directly raise DC voltages with a switched-capacitor circuit. You can also reduce and invert DC voltages with clever switched-capacitor circuits.
Now, getting the voltage necessary to drive a CRT out of a 5V power supply this way would be a royal pain.
Unless you really enjoy screwing around with electronics, I'd recommend just using an inverter and plugging in your hardware unaltered.
But if you're willing to go to the trouble and expense of modifying your computer, why not just shell out the extra bucks and use a laptop?
I stole this sig from someone cleverer than me.
DC voltage conversion is a subject in itself. Reducing DC voltage is fairly easy, but involves losses and inefficiencies. The only way to raise DC voltage is to chop it up into AC and run it through a transformer. Chop it up right and you get an inverter.
Anyone with a bit of experience in power supplies should be able to figure out what is needed, it is fairly basic electricity. The main concerns I see are ensuring that the supply has enough capacity and getting isolated supplies so you can get both + and - 5 Volts.
And, oh yes, the monitor. Not so easy here. Traditional CRTs require a high voltage that can only be generated from AC. Even DC powered TVs have a built in inverter.
So are the new LCD panel screens DC powered? No particular reason why they shouldn't be. Just the cost consideration there.
So it can be done fairly easily, just a case of bodging the parts together and getting an inverter for the monitor or a DC powered monitor.
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Find a couple of older 386 laptops and strip the dc converter/regulator boards out of them, wire the outputs in parallel, and mount appropriately.
This should get you by, although if your PC has a large power draw you may need more than two. If you don't have spare laptops laying around you can find similar circuits available from Marlin P. Jones or All electronics.
Whatever you try, don't use those cheapy seventy dollar inverter critters from the local Rat Shack. They make enough interference that some laptops and handheld radios cease to function near them.
*whup* "Get along, little electrons. Heeyah!"
Look over at www.mp3car.coma t= P
http://www.mp3car.com/hardwarecats.asp?Type=H&C
There you go.
First of all you don't need another PSU, just a filter as others have mentioned.
;-)
You can purchase large solar panels which can produce 400 W 12V in direct sun, but these are large and often cost several thousand dollars. And, the very important question of night is also an issue.
A good alternative is a solar battery. It's a solar cell connected to a large DC NiMh or NiCd battery, which is continually trickle-charged (batteries don't care too much about current/voltage variations). This way, you have non-sunlight or low light level access and relativly consistent power. These units often come with a DC-AC converter, which means all you would have to do is plug in your computer (or any other appliance for that matter). These are also expensive, around $500+ for anything good.
I worked on a project which used a small version of a solar battery in remote monitoring embedded computers. We used the LART Intel SA-based MIPPs 200 MHz devices with 802.11 communications. They worked very well with solar batteries, and uptime for each node was almost 100%.
Of course, there is a question of why you would want to do this when you have plenty of juice piped in your home. For me at least, power interuptions are negligable and for the other times when I really need 100% I use APS. This approach would be difficult to scale, as I don't see any solar powered datacenters and I'd question the reliability of solar devices powering critical systems as compared to a good, multiple grid power input and backup systems.
You don't live in California, do you?
"I'll just chip in a bit for RedHat: I actually have that installed on my university machine." - Linus, '95
Zippy Technologies makes DC-DC powersupplies that can take -24v DC and N+1
redundant power suppluies that do -48DC.
Sold under the EMACS brand (no kidding!) I've seen the ATX for 190$ on the web,
this is probably the extreme end of the spectrum (though if you need DC applications,
you got $$$.)
Found a site, Arise Computer Inc, who have a whole page full of ATX power supplies that should suit your needs. Looks like they've got 5 on this page which will take DC input - just select one that's got the input voltage you need and away you go!
You can accomplish anything you set your mind to. The impossible just takes a little longer.
Most PC power supplies are switchers which operate by rectifying the line voltage and running it through a chopper to drive the primary coil of a small toroidal transformer. The secondary coils yield +5, +12, -12 and the other outputs required by the computer; the chopper duty cycle is regulated to keep the output voltage correct. It wouldn't be much of a trick to use a different primary coil (heavier wire, fewer turns) and chopper designed to operate off 12 VDC instead of 135-350 VDC. Voila, 12-volt-capable PC power supply. Mind the input connector, that thing is going to draw some amps.
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I bought one of those surplus laptop supplies from Marlin P Jones. It was DOA. Nice looking unit, though. So I used an inverter. Much easier to hook up, and now I can blend margaritas in the back of my Jeep at field parties =|> .
Those purpose-built 12V ATX power supplies are nice but too pricey for a homebrew system.