PC ATX supply use and loading

:

reading the wikipedia page:

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seems you need to drive the power_on pin to low and also connect the +3.3V_ sense to a +3.3V line.

Bye Jack

Reply to
jack4747
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This document

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suggests that there will be minimum load requirements on both 12V outputs, the 5V output and the 3.3V output. Based on the power specification of the PSU, you might want to try loads giving minimum currents for one of tables 3 thru 6.

You'll have a fair amount of heat to get rid of.

Sylvia.

Reply to
Sylvia Else

Seen a goodly number of Youtube "presentations" showing an ATX supply as a (potential) power source. Common representation is the basic box with banana connectors for the

+3.3V, +5V and the +12V and NO load. Claims are like "useful bench supply".

IN PRACTICE: I tried all of the following combinations of loads on the +5V and

+12V1: no load, 1K, 100 ohm, 10 ohm, 1 ohm. In most cases, the supply "burped" and shut down. In only a few cases, it stayed on for up to 30 seconds.

Have not tried leaving the +12V1 open and the various loads on +12V2.

Goal: to draw from 10mA to 10A at (about) 12V.

So, any pointers how to get (one of the ATX supplys) to work on a continuous basis with stated output?

Reply to
Robert Baer

No sure if you are just making use of an old unused PSU but if you are prepared to buy a new PSU you can find ones that can run regulated with no external load required. Think they might be referred to as 'Haswell compatible' or similar (as these CPU's can drop their power requirements very very low).

Reply to
Richard Jones

I think that depends (a lot) on the actual power supply's design.

I just brought home some small supplies out of a server to use as 12V "battery eliminators" (12V @ 70A). They run well with NO loads on ANY of the outputs.

YMMV.

Reply to
Don Y

Yes, though the OP's is presumably not one such, or he wouldn't be having difficulties.

It's generally easier to find out what one has to do to stop something working, than what one has to do to make it work. The OP's sensible course is to load up all the outputs, and then see how much of the load can be removed from each, being aware that there may be an interaction between them.

Sylvia.

Reply to
Sylvia Else

Sure, plenty instructions are all over the internet:

I've converted a few for various dumb reasons. No big deal. However, I did run into a few obstacles:

  1. Check for bulging capacitors and high ESR caps. They're epidemic in used ATX power supplies.
  2. If you're going to draw high currents from the 3.3v or 12v outputs, make sure your wiring and terminal posts can handle the load.
  3. Test the power supply with a maximum dummy load and leave it run for a while. Find out what it does when it gets hot. Having it crap out, shut down, blow a fuse, oscillate, or catch fire is not a great idea. Also check for ripple and noise on the various outputs.
  4. Look at the power supply PCB. If it's crammed with parts and looks complexicated, it's probably a good power supply for a conversion candidate. If the PCB is sparcely populated, it's probably crap.
  5. The push button power on/off is ok for PC's, but rather dangerous for a bench power supply. I suggest adding an AC line power switch (and fuse).
  6. Metering is nice.

  1. Banana jacks suck. Use a real power connector or spade lugs with proper cables.

Good luck.

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

Have you seen these dual display, digital meters? They are small enough that you can use one for each output. Unfortunately, the lowest current I found was 0-10A You can also find 0-50A and 0-100A.

DC-0-30V-10A-Voltmeter-Ammeter-Red-LED-Panel-Amp-Digital-Volt-Gauge-/

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I bought a pair of them to rpeair a HP 6253A power supply with damaged meters.

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Reply to
Michael A. Terrell

Sure. I use them for all kinds of strange things. I even have one installed under the hood of my car. Mostly, they are connected to various solar charging schemes.

As usual, there are problems.

The meter may show 3 digits, but no way is it accurate to one LSB. I've connected a bunch of the USB volt/amp meters in series to a load. In theory, they should all read the same voltage and current. I didn't keep score, but the numbers were all over the place. I would guess(tm) about +/-0.5V accuracy.

The combination volt/amp meters are positive common with current sensing on the negative line. See wiring diagram near the bottom of: Note that the positive (red) wires are common and that the shunt is inserted in the negative (black) line.

For example, if I were to measure the output of a solar panel, with the meter inserted between the panel and the controller, I would be faced with the impossibility of grounding both the controller and the negative wire of the panel. The same would be true for the OP's ATX power supply. He could ground the ATX negative line(s) or the load, but not both. As far as I can tell, they're all like that.

There's also a problem of how to supply power to run the meter, but that's easily solved with a floating DC-DC converter.

I've had to resort to using seperate voltmeter and ammeter devices, with at least one DC-DC converter. I haven't spend any time finding a better or more elegant solution. Suggestions are always welcome.

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

Robert Baer prodded the keyboard with:

Hi Robert,

Connect the green wire to any black wire. This will switch the PSU on. You also may need to draw around 50 to 100 ma from the 5 volt line.

Somewhere kicking around I have some connectors that plug into any of the four pin plugs with 47 ohm resistors wired between the 5V and ground. In the early days many PSU wouldn't start up without a load on the 5V rail.

HTH.

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Best Regards: 
                      Baron.
Reply to
Baron

If about 12V is what you really want, you might be better off finding surplus laptop power supplies.

Michael

Reply to
mrdarrett

Try loading the 3.3V line. I know folks who have done this for battery charging, and they claim it works.

Or, buy something surplus from MPJA that just does the job.

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Reply to
Tim Wescott

Theres a schematic here

Typically a load on the +5v rail, like a Floppy disk drive, should start them up,

Cheers

Reply to
Martin Riddle

You can buy that breakout board $13.80 and acrylic case $4.00 from Seeed Studio:

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

the +3.3V_sense to a +3.3V line.

  • I had ASS-u-ME-d that the use of the power on pin was a known given. So i am the ass for dewing that. There is a 3.3V sense line? If so,it seems to be a well-guarded secret not on the web. Perhaps you mean that i should be loading the +3.3V line instead of the 5V line?
Reply to
Robert Baer

Hot stuff fer sure. Basically the problem is that both 12V outputs must be loaded along with the +5V lines and the Youtube "articles" gloss over the necessary loadings. Thanks.

Reply to
Robert Baer

This IS anew supply and the article that Sylvia gave suggest that external loads ARE required in the real world.

Reply to
Robert Baer

May i read in a few qualifiers: "small supplies" and "out of a server".

Reply to
Robert Baer

  • I use a toggle switch there for "on" and "off".
  • Like i mentioned, i have tried all kinds of loading combos (EXCEPT on
+12V2 and 3.3V).
Reply to
Robert Baer

Thanks, everyone; all of the above should get me (and the supply) on track.

Reply to
Robert Baer

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