Computer power supply converted to a 12v DC power source

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Computer power supply converted to a 12v DC power source

Postby Dee Bee » Fri Dec 17, 2004 9:13 pm

I did some web research, got hold of a PC power supply and was able to convert it to a a 12 v DC power supply. This may have an application to Teardrop setups if the 12v DC load does not draw too many amps. This home made rig can handle about 6 amps on the 12v DC line.

Here is the positive side....It cost me $8.00 to complete the project! For the difference in price, maybe I'll hook it up in my future TD to drive just a few cabin lights using shore power instead of the battery. Better yet, I'll figure out away to use a double pole, double toggle DPDT switch so the same 12v DC cabin light circuit can be run with the power supply or the battery system with just a throw of the DPDT.

Here is link to my project

http://www.nfdc.net/home/cbdb/12%20V%20Power%20Supply.htm

DEE
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Postby Arne » Fri Dec 17, 2004 11:24 pm

DEE, I fly radio control planes... To use the field charger, I connected the field charger output to a r/c transmitter, the input to a 12v battery.... the battery was connected to a battery charger which was plugged into a.c.

It was a tedious set up:

115v.......battery charger..... battery......12v field charger.....r/c battery..

Now:

115v......converted computer power supply.....12v field charger....r/c bat.

Where you used resistors for a load, we use 2 1257 12v auto lamps (could be 1157)..... but much nicer to flip a switch than run a lot of wires.. and you are right, the price is right... sometimes we can find them in the dump in discarded computers...
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Re: Computer power supply converted to a 12v DC power source

Postby TonyCooper » Thu Dec 23, 2004 12:19 pm

Dee Bee wrote:I did some web research, got hold of a PC power supply and was able to convert it to a a 12 v DC power supply. This may have an application to Teardrop setups if the 12v DC load does not draw too many amps. This home made rig can handle about 6 amps on the 12v DC line.

Here is the positive side....It cost me $8.00 to complete the project! For the difference in price, maybe I'll hook it up in my future TD to drive just a few cabin lights using shore power instead of the battery. Better yet, I'll figure out away to use a double pole, double toggle DPDT switch so the same 12v DC cabin light circuit can be run with the power supply or the battery system with just a throw of the DPDT.

Here is link to my project

http://www.nfdc.net/home/cbdb/12%20V%20Power%20Supply.htm

DEE


I just did the same. Took 30 minutes and with my 300 watt supply I can draw 14amps at 12 volts. Thats enough to power my entire 12v system. I intend to wire it up to my 110v shore power and run off the PS while charging the battery. Another plus is that it is smaller than the average converter. BTW, adding a second 10 ohm 10W resistor in parallel resulted in output voltage going up. It is now at 11.94 v output, was 11.75 with a single resistor.
Tony

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Re: Computer power supply converted to a 12v DC power source

Postby Dee Bee » Sat Dec 25, 2004 6:20 pm

I just did the same. Took 30 minutes and with my 300 watt supply I can draw 14amps at 12 volts. Thats enough to power my entire 12v system. I intend to wire it up to my 110v shore power and run off the PS while charging the battery. Another plus is that it is smaller than the average converter. BTW, adding a second 10 ohm 10W resistor in parallel resulted in output voltage going up. It is now at 11.94 v output, was 11.75 with a single resistor.


Thanks for letting us know that you had success with your project! I am curious to know how much it cost to make the conversion. Mind telling us a ball park number for comparison to comercial power supplies?

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Postby Arne » Sat Dec 25, 2004 7:05 pm

If you can get the power supply for free. Stop into your local computer place and see if you can get one out of a junker, or look in a dump, that's what I did>... then I have 2 light bulbs hooked up... it needs some resistance to crank up... I'll put a pick in my album.....

So, it can be between free and $15.00.....
www.freewebs.com/aero-1
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Re: Computer power supply converted to a 12v DC power source

Postby TonyCooper » Sat Dec 25, 2004 8:25 pm

Thanks for letting us know that you had success with your project! I am curious to know how much it cost to make the conversion. Mind telling us a ball park number for comparison to comercial power supplies?

DEE


I have less than $10 in it. Two 10 ohm 10 watt resistors and a little heat transfer compound. Both found at radio shack. I also splurged and bought a matching switch to power it off/on. I had the 300 watt power supply from my previous computer.

A converter will cost you anywhere from $75 to hundreds of dollars. My power supply is also physically smaller then most converters. The fan is a little louder then I'd like. I think I'm going to use the +12 (as positive) and +5 (as negative) to get to +7v to slow it down a bit and quiet it.

To whoever started this thread - Thanks! A good idea ...

To all - Merry Christmas!
Tony

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Postby myjeepcherokee » Sun Dec 26, 2004 4:09 pm

I too modified a pc power supply for my tear, but instead of using resistors to put a load on the power supply, I instead used the bulb in my amp meter to put a constant load on the supply. It puts out 10amps at 12 volts. I used it this past weekend for over 20hrs and no problem with heat or anything!

Picture here:
http://tnttt.com/album_ ... pic_id=715
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Postby Eric Adams » Sun Dec 26, 2004 9:49 pm

I am electronicly illiterate (to a point). I can use a voltmeter and figure out what is coming out of which wires, etc. I took apart a 250W PC power supply I have extra (freebie, nada...etc) and seperated out all the +12V, +5V, and GROUND wires. Spliced each group together seperately and ran the ground and +12V to each seperate terminals. Is this enough?? Run my 12Vdc items off this without any other alteration? It is a old AT style power supply that has a long thick black cable that has a switch on the end of it (ON/OFF).

:)

Why add the resistors if all I need is 12Vdc and that is what the output reads?
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Postby TonyCooper » Sun Dec 26, 2004 10:27 pm

Eric Adams wrote:
:)

Why add the resistors if all I need is 12Vdc and that is what the output reads?


The old AT style power supplies don't need to be modified.

The new ATX style power supplies are much more intelligent and will not supply power without a load present on the +5 volt line. In fact adjusting the resistance of the load will actually slightly raise or lower the 12 volt output by a few tenths of a volt.

Regarding the post about using a light bulb to load the power supply ... What happens when the bulb blows? Some cheap ATX power supplies will damage themselves without a load on them.
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Postby Eric Adams » Sun Dec 26, 2004 10:31 pm

Is there a Watt to amp conversion?

Say my PS is 250W. ???
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Postby Dee Bee » Mon Dec 27, 2004 12:17 am

Why add the resistors if all I need is 12Vdc and that is what the output reads?


PC Power Supplies are built around a "switching" circuit. Because of this design, most of PC power supplies require a load for the unit to power up properly. Without a load, usually on the +5V line the PC power supply is built to shut itself off. This is especially true of the newer ATX style. The purpose of using resistors is to imitate the load of the hard drive, so the power supply cycles up to full output power. If the power supply doesn't sense a load the ATX styles shut off.

Some PC power supplies can be damaged if you try to power up with out a load.

By the way--remember if you plug in the power supply to house current the black cord of the older AT style power supplies always has 110 AC in it even when you have it switched off.

The power supply total watts (200 watts, 300 watts etc) is a rating of the max. design wattage of all circuits coming from the power supply. There is a smaller maximum wattage for each 3.3 v, 5 v, and 12 v line generated by the power supply. Some power supplies have circuits that also supply "stand by" power to the computer mother board. There are also outputs that are measured in "negative volts!" You will never get all the watts on one line ( for example on the +12v DC line).

Most power supplies have info on the unit labeling that will tell you how many max amps are designed to flow on each voltage line. Even on a 300 watt PC power supply, 8 amps max is typical for the 12 v DC line.

Watts = Volts X Amps

12 volts X 8 amps = 96 watts

So you can see that the power from these PC power supplies is limited. You will never be able to run high amperage devices from a single PC conversion. IF you try to pull to many amps through a converted power supply it will over heat and probably shut down. Be aware of the max amp rating and keep within the design capacity of the wires for that line. I have found that I will be able to run cabin lights and a fan off my conversion. Not much but it is all I want.

There are helpful links at the bottom of my page. Read about all the various approaches to this project. There are different solutions depending on what kind of power supply you are working with.

http://www.nfdc.net/home/cbdb/12%20V%20Power%20Supply.htm

It is possible to boost the volts and the amps, thus increase the watts but it is a more extensive conversion as the following link shows. On this web the way watts were increased was by combining three power supplies. Make sure you know what you are doing if you try this or you'll just get smoke.

http://www.qsl.net/i0jx/pcsupply.html


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Take it step by step. Be Safe. Don't be afraid to read and learn. Hope this helps!

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Postby myjeepcherokee » Mon Dec 27, 2004 5:53 pm

I feel pretty safe using my light bulb to supply a load on the power supply. I have my power supply on a switch and only use it when I need to be running off of shore power so I will rarely not have a load one the supply when it is on. I just view the bulb as extra assurance that if I for some reason dont have a load on it that it will be ok.
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