ATX power supply to drive a 12V DC motor?

Some Psu won't even start up without a load on the 5 volt rail !

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Best Regards:
                      Baron.

Check out the latest version of Nut&Bolts where there is an nice article on using the PS for thngs.

Nuts & Volts?

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Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Thank you all for your comments and suggestions, they've been most helpful.

Yes, and that was not intentional...........

On second thought, I have further questions (see below) before I buy the parts. Here is some info about one of the supplies I have:

Model: WIN-400PE DC: 400W

7.5A/4.5A AC input (230V 50/60Hz): +3.3V 15A +5V 30A +12V 15A

-5V 0.6A

-12V 0.6A

+5VSB 2A (what is VSB?) +3.3V & +5V MAX 200W 2.03 (ATX12V standard?)

- Is the 10ohm 10w resister ok, should I go lower (eg. 7ohm 5w)? The link above states a fix to get a higher voltage by wiring two 1ohm 10w resistors in series

- Is there an issue with using the PS on/off switch to turn it on and off? Or, do you recommend I connect the green and black wires to an on / off switch (SPDT)?

- Is there a problem with using a small heat sink on the resistor (if I can find one small enough), rather than heat sink compound?

Regards,

Michael

5V stand-by.. used for powering peripherals that can wake up the computer when there's activity.

I suggest you experiment with resistors. Some ATX PSUs I've tried didn't even need a dummy load to function correctly.

Shouldn't matter. If you use the main on/off switch, remember to make a permanent connection between green/black.

As long as the resistor doesn't get too hot, any method will work. If you can still touch the resistor after using it for a while, you're OK.

By the way, does your PSU have short-circuit/overload protection ? If not, I'd put a fuse in there as well, otherwise you risk blowing up the PSU.. or put a suitable light bulb in series while you're playing around.

Thanks for the info. I don't know if it has short-circuit/overload protection, how can I check this? If it doesn't, will the fuse be wired to the green and black wires on the large PS connector?

Regards,

Michael

No! Put a fuse in series with the load, ie your motor!

--
Best Regards:
                      Baron.

I'll be connecting the power supply to a motor speed conroller (the motor will be connected to the speed controller), so the fuse will be in series with the controller - is this correct?

Regards,

Michael

Bar>

If it has short circuit protection, the manufacturer will tell you so. It should be in the instruction booklet (if you have that), or possibly on the sticker on the outside of the case, or google the model number on the internet. If you can't find anything, assume it's not protected against overload/short circuit (many of the older models aren't)

The fuse needs to be connected between the +12V output of the PSU and the rest of your circuit. Suitable fuses can be found in the automotive parts section of a local store, if you can't get find them in your favorite electronics supply store.

Get a few 12V automotive bulbs, to make dummy loads. Even use one across the +5 supply - it probably won't light, but will provide a load. You can either get sockets at the auto parts, RS, or you can solder right to the bulb bases.

Start the supply by grounding the green lead, as others have said, and take some measurements.

And please bottom-post. :-)

Good Luck! Rich

Many, many years ago, IBM XT power supplies needed a dummy load or they wouldn't operate properly - they'd go into overvoltage shutdown, or whatever the problems they had with 250W switchers in the 1970's.

I don't know if that's still necessary, but I'm so old I only heard about that green wire a couple years ago. ;-)

So, is the green wire just ON/OFF, or is there a T FF inside the PS?

Thanks, Rich

The green wire is just on/off, the T FF is on the motherboard.

Just on/off.

The flip-flop that converts the ATX momentary power switch to a push-button toggle is on the motherboard.

Bye. Jasen

I used a different PS than the one I described above. I made the following modifications:

- green to black

- 10w10ohm resistor on the 5v supply

This supply also has a switch, so I didn't bother connecting an additional one. I did a quick test to determine whether it works and it does. I haven't taken measurements, as I've run out of time tonight, but even so I'm real happy that it works. I still need to buy a fuse for the short circuit protection also.

Regards,

Michael

Here are some readings:

+12V supply output is 11.94V +5V supply output is 5.14V +3.3V supply output is 3.41V

Regards,

Michael

Good advice.

PC power supplies don't seem to be as fussy as they used to be about having a load on the 5V rail. I often use jumpered ATX supplies to run random devices (including 12V motors) on my bench, & they always fire straight up - even when the only load is the internal fan (12V).

Not in my experience.

Just jumper it & power it up. If it works, you'll hear the fan start running. If not, it won't hurt the PSU.