12VDC ATX psu for PC

Hi, Can anyone perhaps please point me to a circuit diagram for a ATX PSU for a PC with a 12VDC supply voltage(+/-300W)? I've got a 12VDC backup system, solar and wind, and do not want to use an inverter. The 3 & 5V rails are not a problem, but the-12V, +12V seems to be. Should I step up the 12V to 24V with an DC-DC converter and then split it to 12V-/0/12V+? Will this be more efficient than a 12VDC to 220VAC Inverter? Thanx in advance,

-- WalkTall

Reply to
WalkTall
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I am not so sure that the 3 and 5 volt supplies are going to be as little a problem as you think - bearing in mind the current needed and the efficiency that you probably want for a solar/wind system.

You are going to need an converter of some type - so a simple dc >dc converter feeding dc to a standard atx supply seems the simplest solution. It can be very high efficiency

- and a fairty rough and ready design as the atx supply will handle the regulation. /Most/ atx supplies will run fine off dc. This is likely to be the most efficient solution - unless you custom design switch mode converters for each output voltage.

Look at the current loads of the 12 volt supplies. Had they been similar, a split 24 v supply might have been worth considering - but they aren't so it isn't.

For a solar wind system, my starting point would be a laptop anyhow. I have several /old/ laptops functioning as 24x7 servers (some with RAID USB2 external drives for the extra storage/fault tolerance) - they save a considerable amount on the electric bill over a year.

Reply to
Palindr☻me

Is the +12V available regulated well enough, or will it require better regulation to meet the ATX standards? I assume you're planning on using linear voltage regulation for the +3.3V and +5V rails. You will need to know the amperage used by your PC for each of the regulated voltages for a proper design.

The -12V is hardly used; a simple switching DC/DC converter should work.

You'll also need the on/off control circuits if you want to duplicate the ATX supply functions as seen by the PC. The PC uses the +5V SB for the "turn-on" circuit.

There are commercial ATX PSU's with 12V input, but they are expensive.

Reply to
VWWall

I've seen 12VDC PC power supplies for sale at computer fairs. I think the target audience are people who put a PC in their car as the basis for their car audio system.

All rails are regenerated, as the swing on a car supply from less than 10V during starting to 14.5V charging is far too much for any PC rail to sustain directly.

Reply to
Andrew Gabriel

As Andrew Gabriel noted, there are 12 VDC input power supplies available.

But also note that ATX power supplies are more complex than what you apparently are giving them credit for! It just is not reasonable to build your own when it is a commodity device. You can't spend thousands of dollars on engineering just one device, but a company that will sell hundreds of thousands of them can.

That said, rather than find one that runs off 12 VDC to begin with, I recommend a 220 VAC inverter to power a standard off-the-shelf ATX supply. Given the same economies of scale apply to 12 VDC units vs inverters that do to a home constructed unit, I'd look for the 220 VAC inverter simply because it gives you a vast choice of ATX power supplies. Your intended use might be a bit more stressful than what the average power supply experiences, and you want to buy a *quality* ATX supply from a well known brand name manufacturer.

Half assed engineered ATX power supplies aren't worth using, whether you design it or someone else does. The difference in price is relatively small (especially compared to the replacement cost when the power supply fails and destroys half of the units it is powering).

Reply to
Floyd L. Davidson

Thanx all, I think that Palindr?me idea will be the best solution for me. I've got a couple of ATX PSU's lying around to experiment with. (Any circuits for dc to dc converters?) Should it be a 12VDC to 220VDC inverter or can I tap in somewhere on the PSU PCB to supply it with a lower voltage, say 24VDC? (I'm not so clued-up on Switchmode Power Supplies) I've got grid power on site, so the supply is more for power failures than anything else, but I would like to make it as efficient as possible. My Solar/wind system is 12VDC, charging a bank of batteries. Mostly used to power lights, my PC and a 12VDC capable TV, the essentials ;-) for now, but I would like to use it more permanently in the future as I expand it. Money IS a problem, so I would rather build than buy.

WalkTall PS - Apologies for the late post, but I only go online about twice a day.

Reply to
WalkTall

To paraphrase Floyd (for which I hope he will forgive me)

12v to 110/240 volt inverters are so cheap that it really isn't worth prototyping your own - unless you are into electronics in a big way. The (new) cost of the components is going to be more than the cost of a new commercial unit. (300W 12>240V inverters are on sale in the UK from 15GBP).

OK, you can use bits from an old at/atx power supply to save money and make one very cheaply, but see below.

I would only be leading you astray to describe what you could do to a standard atx supply to get it to work from 12V input. It simply isn't worth doing. Modding it to give different outputs is a different matter - and much safer, to boot.

Similarly, a 12V to ~220V 300W DC-DC converter isn't difficult to design and build but, if you have to ask how, you probably shouldn't be doing it - getting it wrong could easily be a fatal mistake. Plus a home-brew, without all the gear to set it up, isn't going to be as efficient as a commerical unit. If you really want to do this - investigate buying a kit from one of the many kit designers.

Reply to
Palindr☻me

Why use a DC-DC converter, when that requires first a DC->AC inverter and then an AC->DC conversion... and your ATX power supply will run off of AC. Just use a DC to AC inverter, and skip adding an extra AC->DC part, because it is already built into the ATX power supply.

You do need to find a basic primer on switching power supplies.

You also want to make it reliable. Efficient won't mean much if it fails often...

Building is not necessarily less expensive. You can't build an ATX power supply for the price you'll pay to buy a brand new one. The same is probably true of DC to AC inverters.

Reply to
Floyd L. Davidson

LOL, it depends what you mean by "AC"! A DC to "high frequency" rectangular wave inverter is going to be a lot smaller and generally more efficient than one with a 50Hz output - however, if you feed that into an unmodified atx supply, the "mains" filter built into the atx supply will have to be either disabled or removed. If you leave it in place you have to run at 50Hz or thereabouts. Unless - you take the output of the high frequency inverter and simply rectify and filter it.

If I needed to produce the solution and couldn't buy off the shelf for some reason (eg, the input voltage was non-standard, or I had to produce one over the weekend when the shops sere shut..) - then I would go for a high frequency design and get it to produce the right dc for the atx supply input - rather than design a 50Hz solution..This is particularly the case if my starting point was a scrap bin full of AT/ATX supplies - they have the transformer cores needed for a high frequency, not 50Hz, solution.

The most common sense approach is as, I think everyone, has been suggesting - an off the shelf inverter, feeding into an off the shelf atx supply.

Reply to
Palindr☻me

The input circuit of an ATX PSU rectifies the mains voltage, using a voltage doubler in the case of 115V mains. In either case the voltage applied to the switching circuit is ~320V DC, which is the peak AC voltage. You can by-pass the rectifiers, but you must obtain the 320V DC from somewhere. A 12V DC to 320V DC converter can be built, and if correctly designed, would be somewhat more efficient than a 12V to 220V AC inverter.

Unless you wish to experiment, the best bet is the easily available inverter! You could rewind the high frequency output transformer from an old ATX PS to make the transformer for the 12V DC/320V DC converter, and even use the ATX input capacitors as well for the ~320 V output. The switching mosfets would be entirely different, and a new driver and regulator circuit would be needed.

You might find a surplus UPS with a 12V battery and 220V AC output which could be modified.

Reply to
VWWall

All of the above is correct, but has nothing to do with what I suggested! :-)

That is *exactly* what I suggested. (Twice already...)

Reply to
Floyd L. Davidson

My fault, I hadn't realised that the," Why use a DC-DC=20 converter..?" was one of them rhetorical thingies...My post=20 was addressing this question, not questioning your suggested=20 solution.

I was going to say , "as you suggested" - but didn't want=20 not to give credit to everyone else that suggested the same=20 thing (me included, lol). So I had hoped that you would have=20 recognised yourself in "everyone"..I had added the paragraph=20 to emphasise that I was agreeing with you....

--=20 Sue

Reply to
Palindr☻me

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