Rigging a PC power supply

[mechanicalbrain]

Let me do a little explaining before i ask my question to save myself hassle down the road, just bear with me. Frequently when I do electrical work for our team and I want to test a part (just to see if its physically running) I connect it to a little homemade 6 volt battery pack however the pack isn't rechargeable so I end up paying a fortune on batteries, also it wont provide power to everything (at least not for a decent amount of time). So anyway a week ago I was playing with the PC power Source and I realized "hey most of the voltages that this outputs are same voltages FIRST parts run on." Recently Ive been using it to test out some of the older parts (Sometimes a multimeter just won't do), after I removed the Molex connectors and crimped on some alligator clips. It's been working fine and it won't damaged anything, however to work it has to be connected to a motherboard. So far Ive been solving this problem by using a real old board I had on a shelf but when season starts I don't want to carry it everywhere with me. Is their any way I can rig a power source to run by itself?

[sciguy125]

I used an ATX power supply on one of our team's projects. They have a minimum load in order to work. Without this load, they quickly stop working. It has something to do with the inductors needing a minimum current in order to work properly. I'm not well versed in power supply design, so I can't give you much more detail than that.

I ended up connecting some power resistors to it. You'll have to look up the specs for your supply and figure out the correct load. Depending on your exact situation, you may be better just finding a cheap supply somewhere.

[mechanicalbrain]

Well I do kind of want to use a PC power source. It has the perfect outputs and i have like four of them just sitting here collecting dust. I might just have it run some other device all the time like a light or fan. Maybe use it to power a electrical "workstation". Thanks I didn't realise they needed a minimum load.

[Andy A.]

Originally Posted by mechanicalbrain

Well I do kind of want to use a PC power source. It has the perfect outputs and i have like four of them just sitting here collecting dust. I might just have it run some other device all the time like a light or fan. Maybe use it to power a electrical "workstation". Thanks I didn't realise they needed a minimum load.

Ok.

This page has a good deal of information about PC power supplies.

I haven't, in the quick research I've done been able to figure out just what signal to pin 14 it requires to keep the supply on. Perhaps a short to the 5v or 3.3v line?

I'll keep looking.

Anyway, if you want a portable power supply, why not just get an adjustable supply? PC supplies vary a great deal in quality, and some are downright junk. Or, use a battery and construct a voltage regulator to step down to whatever voltage you wanted.

I'd hate to have to drag around a atx supply, especially if you have to get it through airline security (a box with lots of wires coming out of it)!

-Andy A.

Edit: I did a bit more searching, and found a whitepaper on the ATX specs. It seems that pin 14 has to be held at ground for the supply to stay on. Check out the paper .

[Tristan Lall]

Easy: just take a paperclip and connect the green wire to any black wire. The rear power switch (if so equipped) must be on. (I will assume your power supply is ATX; if it isn't, then this won't necessarily work, and won't necessarily be safe.)

Yes, I've done this. There was neither smoke, nor fire.

Here's an independent verification of my story:

First, power the thing up. You can make an ATX power supply that isn't connected to a motherboard turn on by grounding pin number 14 on the big motherboard power connector. It's easy to spot that pin, because it's the only one with a green wire going to it.

Use any handy bit of wire - like the paper clip in this picture - to connect pin 14 to any ground contact. The ground contacts are the ones with the black wires going to them. Presto, the PSU will turn on.

From dansdata.com

[mechanicalbrain]

Originally Posted by Tristan Lall

Easy: just take a paperclip and connect the green wire to any black wire. The rear power switch (if so equipped) must be on. (I will assume your power supply is ATX; if it isn't, then this won't necessarily work, and won't necessarily be safe.)

Yes, I've done this. There was neither smoke, nor fire.

Here's an independent verification of my story:
From dansdata.com

Thats perfect! Ill give it a try tomarrow and see if i can't get this working.

[sciguy125]

What I forgot to mention was how I made my switch. I got an adapter then chopped it up. There's 20-pin and 24?-pin motherboard connectors. I had a 20-pin supply, so i bought an adapter and cut the 24-pin connector off (I only needed the 20-pin). I could have just bought the connector and some pins, but they were only sold in 50-packs.

I wired up a switch between 14 and ground. The rest of the wires went to fuses for the respective outputs. There's also 3 signal pins if you want to use them. They tell you when the supply is on, plugged in, and when the power output is good (or bad, I can't remember which). You can connect LEDs to them. This gave me a nice dongle to connect to any ATX supply.

[mechanicalbrain]

Originally Posted by sciguy125

What I forgot to mention was how I made my switch. I got an adapter then chopped it up. There's 20-pin and 24?-pin motherboard connectors. I had a 20-pin supply, so i bought an adapter and cut the 24-pin connector off (I only needed the 20-pin). I could have just bought the connector and some pins, but they were only sold in 50-packs.

I wired up a switch between 14 and ground. The rest of the wires went to fuses for the respective outputs. There's also 3 signal pins if you want to use them. They tell you when the supply is on, plugged in, and when the power output is good (or bad, I can't remember which). You can connect LEDs to them. This gave me a nice dongle to connect to any ATX supply.

Sounds cool I might just do this tomorrow. I know i have all the necessary parts in my workshop.

[BrianBSL]

Another option is to use an old AT power supply - I have a couple from old PC's that have since been recycled. They require no minimum current and no pin-shorting to work. I used to use one as a basic bench supply before I got a real one.

[Dave.Norton]

Originally Posted by BrianBSL

Another option is to use an old AT power supply - I have a couple from old PC's that have since been recycled. They require no minimum current and no pin-shorting to work. I used to use one as a basic bench supply before I got a real one.

I'd be careful with an old AT supply, power supplies have gotten much better, many of those old supplies wouldn't regulate unless they were loaded, which would let the magic smoke out of anything you are working on.

[Joe Johnson]

Another thing to keep in mind when you eventually get tired of that big honking connector with just 2 shorted wires is that if you cut it off and just connect the green wire to a black one (perhaps even inside the power supply housing to keep it clean), often the supplies won't work. I found out the hard way that on some supplies you have to see which wires are joined at the connector and reconnect those wires as well.

For a PowerUp! 6100D model (cheap with loads of current capability), there are 2 orange wires and 2 black wires joined at the connector -- the power supply just will not work with out both those pairs wires joined (in addition to the grounding the green wire trick).

Good luck.

Joe J.

[mechanicalbrain]

Originally Posted by Dave.Norton

which would let the magic smoke out of anything you are working on.

Heh Ive let that magic smoke out of so many electronics that my mentor calls me smoky (I'm not joking he really does). Well it works fine. I'm going to house it in a tubaware and put in switches so i can turn off wires and not half to worry about contact. Thanks all this is perfect for a quick power source.

[mechanicalbrain]

Originally Posted by Andy A.

Ok.

This page has a good deal of information about PC power supplies.

I haven't, in the quick research I've done been able to figure out just what signal to pin 14 it requires to keep the supply on. Perhaps a short to the 5v or 3.3v line?

I'll keep looking.

Anyway, if you want a portable power supply, why not just get an adjustable supply? PC supplies vary a great deal in quality, and some are downright junk. Or, use a battery and construct a voltage regulator to step down to whatever voltage you wanted.

I'd hate to have to drag around a atx supply, especially if you have to get it through airline security (a box with lots of wires coming out of it)!

-Andy A.

Thanks for the page it actually helps allot. I have a decent power source and i have an adjustable power supply... which has fried many a electronic when it was accidentally set to the wrong voltage. Also most 12volt battery packs are rather large (yeah ive seen small ones refer to next line) and I don't want to have to keep charging them. Plus over time they wear out and 12volt rechargeables aren't cheap. Finally im not worried about airports. I live in Virginia which is a short drive to regionals and a (slightly longer) drive to nationals. We don't go through airports but i cant see them taking a power supply if you checked it in.

[Rickertsen2]

Short green wire to any ground(black) wire and it will whir to life. Just makes sure its not a Dell power supply. In the past they have been known to use proprietary pinouts/color schemes with standard connectors.

[mechanicalbrain]

Originally Posted by Rickertsen2

Short green wire to any ground(black) wire and it will whir to life. Just makes sure its not a Dell power supply. In the past they have been known to use proprietary pinouts/color schemes with standard connectors.

Yeah I used a DELL by the way DELL uses a gray wire (not white either).