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What voltages i can obtain from ATX by combine the outputs? Answered

I have not opened an atx, to measure the outputs to understand. I google it and i find like -12 with +12 you get 24V, -5v and +5V you get 10V but no one say all the outputs. What happens if i connect +12V with -3,3V, or others.

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petercdBest Answer (author)2013-12-20

All the atx voltages on the outputs share a common ground/earth, so nothing can be combined to increase or decrease existing voltages, what you see is what you get.

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danyelo (author)petercd2013-12-20

So then why when you connect -12V with +12V you get 24V? This question is from the perspective of making a power Supply!! This is what i talk about: http://i41.tinypic.com/14b6p77.jpg , but are more other combination to obtain other voltages and i want to know them before i begin to disassembly the ATX .

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petercd (author)danyelo2013-12-21

What you're measuring is a potential difference between -12 and +12v and there's a difference between theory and practice, theoretically there is 24v according to your meter, but practically you wont actually have a load working at the combined 24v for any practical length of time.

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steveastrouk (author)danyelo2013-12-21

Because you will STILL have +12 and -12 with respect to 0V, and 24 V across the ends. You WON'T have 24V with respect to ground, and you'll only be able to take current at the maximum rating of the lower rated supply - so if you have +12@10A and -12@1A you will be able to have a 24V @ 1A output.

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rickharris (author)danyelo2013-12-21

Your confusing your terminology - If you measure between + 12 and -12 you will measure 24 volts.

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darryl.kinslow (author)2014-09-02

You don't get different voltages by combining the different voltage outputs. You'll blow up your power supply. -5v means it's a ground for a 5v output, combining it with a 5v output will just route the 5v directly to ground. Combining different voltages will burn out the lower voltage capacitors on the lower voltage outputs as you will be feeding a higher voltage to them from the higher voltage outputs. This is also why you cannot just take a cable and plug it from one computers usb port to another.

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iceng (author)2013-12-21

But if you have two ATX and do not let them touch frame to frame,
you can get 48VDC !!!

BTW I think the -12 is the lower current and
that is the current rating you are to expect as the output of 24 or 48VDC..
If you try to pull more current .... Expect something to fail

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MrRedBeard (author)2013-12-20

Some power supplies work fine when combining the voltage sources because they have isolation circuits integrated, If your power supply does not have isolation circuits built in it may cause capacitors to blow after a short period of time because they're not rated for what you might be pulling. Do note that combing 12 with 12 or 5 with 5 may work fine but combing 12 with 5 on a psu without isolation circuits may burn out the capacitors with a load due to the 2 sources being unbalanced.

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