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# How does one convert an ATX mains powered power supply into one powered by 12V DC (DC-to-DC power conversion)? Answered

How does one convert an ATX mains powered power supply into one powered by 12V DC? This should be a pure DC-to-DC power conversion and should remove and replace the AC transformers stage thus in no way introducing any form of mains equivalent AC.

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You can use an inverter to convert the 12 volts to 110 the just plug in as normal. Some inverters will not run computers and will damage them, but some inverter will run computers. The second option is to design a 12 volt supply that has outputs that plug into the atx power rails in the motherboard.

If you go this route (which is certainly the simplest, off-the-shelf, answer), look for a "sine wave" or at least "modified sine wave" inverter; those are generally safe for most electronics. Square-wave inverters (which is what the older/cheaper units tend to be) are more likely to cause trouble.

Though actually, that's an interesting question. A modern 110/220 autoswitching power supply *might* handle square-wave input reasonably well; filters have gotten larger and if it can handle 220V it can probably handle the higher energy in each 110V peak from square wave. I'd be willing to try it -- but I'd try it on a junker machine first!

I've been experimenting with this to with no success at all. Here is an old DIY-version.

I thin MkII is exactly what he is looking for.

This should be a pure DC-to-DC power conversion and should remove and replace the AC transformers stage thus in no way introducing any form of mains equivalent AC.

It means that we can't use either an inverter or a beaucoup switchmode DC DC converter (my preference would have been to use a 48V in multi-output converter, but eh...)

So...

It all depends on what the secondary is coming off the ATX power supply's transformer.

You'll need to match the values at its output to successfully bypass the AC stages, so the first thing to do is power it up, case open, and measure the output of the secondary(s).

Further, the source will need to match the current delivery needs for the power supply's regulation circuits.

Since the ATX delivers +5V, +12, and -12, and since they all use a shared common. you probably need something like 2 supplies, 1 to feed the positive voltages, and another to power the negative side. Further, since the current draw is unbalanced, the positive side battery packs will need to have significantly greater "heft", than the negative side. The imbalance can in part be calculated from the output ratings that are usually imprinted on the case (+5V @ 30A, +12V @...) The cell-blocks would be connected in series to present the positive and negative voltages using a shared common, and boosting the positive side would be done by connecting positive-V cell-blocks in parallel to compensate for the disparate current drain between positive and negative sides.

I'm not sure using 12V unit-cells is the best way to think about it, since my expectation is that the transformer is outputting something in the area of +/-18V, to give headroom for the regulation stages.. You may have to change that to 6V units or even right down to the constituent 2V cells so you can provide the required power without further losses due to the need for pre-regulation.

If your thought is to directly power the ATX regulation stages from a single 12V source by DC-DC feed only, I'm almost positive that it will be a wasted thought. However, all you have to do to find out and prove me wrong is bust that ATX power supply case open and start measuring the transformer secondary voltage(s).

Of course, I'm assuming that you have the capability and skill to perform the measurements safely. If you have no skills in this area, I urge you to ask someone who does to perform the measurements. There's a reason why they slap that warning label on the side of power supplies.