AT power supply question for non-pc use. 2

[johningram]

If i had an old AT power supply and wanted to use it to power a 12 volt product that took around 12 volts and anywhere from 1-30 amps could it be done?
My power supply says the yellow wires are +12volts and 10amps and my 12 volt apliance can be used in a way so it takes only 10 amps or less. Would this work?
My second question is, if it would work, if i can take 2 AT power supplies and team them together to produce 12 volts and 20 amps? And could i team 3 together for that matter?
My third and final question is could i use the AT power supplies 12volt 10amp output to charge a car battery? Ive seen many battery chargers that were only 10 amps. Would this work? If not is there a small inexpensive circuit i could use to modify it to charge a battery?
Thank you very much!

 

[SkipCox]

This page will get you started understanding the pc power supply:

http://www.epanorama.net/links/psu_computer.html

Car battery chargers usually output 13.6 to 14.0vdc. A pc powersupply is regulated much closer to 12vdc and likely wouldn't do a car battery much good.

Skip

http://home.comcast.net/~scox9/index.html

 

[Snickle]

And it's much much easier to blow a PC power supply if it doesn't have a proper load on it. Usually needs both of the motherboard plugs attached to the board plus one drive, floppy will do.

 

[edfair]

ATs were better at regulating with just the 12v used. I've done it for half a day or so without blowing one. And that is no guarantee that the next one I tried would not have smoked.

You could parallel two or more, but you need to put some resistance in serial with each one to eliminate the possibility of one supply affecting another's regulation. May drop the voltage a bit at full load.

You probably could modify a power supply to get up to 15 to 17 volts for a battery charger. But you'll have to study some electronics to figure out how. Just about every manufacturer does it a little differently. And then you blow your battery because it charges all out rather than cutting back when the battery nears full charge. It is questionable enough that I use a charger rather than any of the 15v supplies I have laying around.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[etarhan]

I haven't checked the link provided by SkipCox, but it's very likely that you will find valuable information there concerning PC power supplies.

I would also advise in the favor of checking the google for the words "battery charging". I'm sure that, just as I have experienced, you will find some very valuable information concerning charging the Lead-Acid batteries. It's generally much more than applying 12V to the terminals of a battery, although one needs to know what your specific and exact application will be. In some cases, even a step-down transformer and a single diode are enough, but the general requirement is quite more sophisticated.

I wonder if you have ever read the label on a PC power supply, particularly the current supplying capability of the 12V output.

I would definitely advise against playing with the internals of a PC power supply, in order to adjust the voltage levels of the different sections. Not counting some odd ones, it is not designed for adjusting the outputs. You just kill it successfully, that's all.

Last word: Don't think that you're the first guy to brilliantly think of using a power supply to charge a battery. I've thought of this before yourself, and I don't think that I'm the first, either.

Good luck,
Engin

 

[ceh4702]

You may want to look at some other options than a PC power supply. Radio shack and some other places make Power adapters that convert 120 or 220 to 12 Volts. They use to sell kits for running things like a Car Stereos and CB's designed for 12 Volts so you can move them between an automobile and your house. The hard part is the ampage you want. However, there is probably some electronics supplier somewhere that makes some kind of power supply to fit your needs. They do make some 500-600 watt computer power supplies that probably have a high enough rating designed for servers with multiple drives.

The probem is that a computer power supply is more complicated and has to have a load to start, and supplies power at +-12V, and also at other voltages, and their rating is a combination of different voltages to add up to a combined wattage/Amps. More power is designed to go to the 3.3V for the Processor.

If you do not like my post feel free to point out your opinion or my errors.

 

[edfair]

I've used them. When the battery is dead, and the service call awaits, you do what you can to kick the car off. But I have since bought a charger, and I also carry a portable power pack for problems on the road.

 

[kiddpete]

To echo those who already commented, car battery chargers are built to charge batteries. Their circuits are designed to slow and stop the charge as the battery nears its capacity. Overcharging causes the sulphuric acid in the battery to start boiling which generates sulphuric acid fumes. If you know what these smell like, you can smell them several feet away from the battery. These fumes can explode.

 

[johningram]

Thanks guys.
Yesterday i found a small site that informed me how to put a load on the +5 volt side using a resistor.
So last night i went home and tried it out. I connected a bunch of 12 volt pc fans (like 4 little ones and 1 big one) instead of a resistor to the +5 volt output since that is the one that needs to have a load or the power supply will fail. The fans needed a push start but the 5 volts was able to spin them all and even a halogen 12v 30 watt bulb all at the same time as i had my car audio amplifier running off the 12 volt yellow wire. But i did turn the bulb off for most of the time. It seemed to work fine and the power supply stayed cool. However, im not sure if that means its doing ok or if it will fry soon or what? But it did make my car audio amplifier work. Its a 4 channel amp and i have 2 of the channels bridged to a subwoofer and the other 2 going to a pair of polks. Its turning out to make a great PC speaker/sub setup. It worked great at a much higher volume than i even needed.
But the voltage stayed around 11.7 volts and when bass hit it would drop to a little over 10 volts. Is this bad for the power supply? In the car it can happen safely and as long as it doesnt go to 9volts then its ok. And if it goes to 10volts alot or constantly then thats bad. But i dont know the affect that will have on the power supplies life.

Also i would like to know more about how to team them together. Thats the info i really want.
Also what could i use instead of a resistor to keep the +5 happy without taking to much power away from my 12 volt side. It would affect the 12 volt side right? Also is the standard connectors 5 volt the one i need to put a load on or is it the motherboard 5 volt wires? I thought they were all the same.

MY power supply says the yellow wire is 12+volts and 10 amps.

 

[johningram]

Oh ya its an AT power supply

 

[SkipCox]

PC fans normally run on +12vdc but, due to noise, can be wired to run at a lower voltage. Here's the how:

http://www.radiativenz.com/guides/fanvoltmod/index.shtml

A psu converted for bench use:

http://web2.murraystate.edu/andy.batts/ps/PowerSupply.htm

the resistor used to load the psu:

http://www.radioshack.com/product.a..._name=CTLG_011_002_014_004&product_id=271-132

and a test of 21 power supplies:

http://www.tomshardware.com/howto/20021021/

and finally, the resistor wired to plug into a psu molex connector...forgive the quick .xls drawing:

http://home.comcast.net/~scox9/tester.xls

Be careful when screwing with these...if you touch the wrong component at the wrong time you will dance, cuss and wonder why you ever had anything to do with a computer.

Skip

http://home.comcast.net/~scox9/index.html