Making a bench testing power supply from a computer P/S

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ABQTBird
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Making a bench testing power supply from a computer P/S

Post by ABQTBird » Tue Jul 23, 2013 12:49 am

It is often useful to have a safe power supply that you can use to test parts on your T-Bird such as window motors, starter relays, bulbs, switches, clocks, horns, radios, etc. Using a car battery is not recommended as the current potential is far too high and any device connected to it must be protected with a fuse. Battery chargers also make poor power supplies as they too do not offer overload protection either. A computer power supply is ideal for bench testing. It is extemely sensitive to short circuits and will shut down immediately when a fault is detected. A typical 400W power supply offers about 17A or more of current at 12V, enough to test just about any electrical part in the car.

Here is what you need for a basic setup:
*An ATX type power supply. These are the most common and have been used for at least the past 10 years. You can get them from Newegg.com for about $20:
http://www.newegg.com/Product/Product.a ... 6817170016 or, in my case, I have a computer shop near me that sells used power supplies for $10-$15.

*A 10 ohm 10W ceramic resistor. These can be found in the drawers at Radio Shack for about $2.50 for two. RS also sells them on Ebay for $1.21: http://www.ebay.com/itm/360682691965?ss ... 1439.l2649

*A small single pole single throw (SPST) switch. This is another Radio Shack item that you can get for about $1.50.

*Solder and a soldering iron, a wire cutter and stripper, heat shrink tubing or electrical tape, and two part epoxy, JB Weld, or silicone adhesive.

Here is the power supply I used. It is an old 350W model that can provide 17A at 12V. Another useful aspect is that you can also get 5V for testing instruments or driving electronic circuits if you are interested in that sort of thing, and 3.3V which you can use to test LED's without using a resistor:
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Layout the power supply and you will see a lot of wires. The yellow wires are 12V, the red are 5V, the orange are 3.3V and all the blacks are ground. There are some other colors that are not needed.
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Cut all of the wires off of the large 20 pin connector. The purple, gray, white, and blue wires are not needed. Pair one of the black wires with the green wire, and another black wire with a red wire.
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This is optional, but if you want you can open the power supply and cut off the purple, gray, white, and blue wires at the circuit board. This is safe. just avoid the very large capacitors on the other side of the power supply. They will not have a charge in them anyway if the power supply has not be on in the past day or so.
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Glue the 10 ohm resistor to the cooling slots on the side and allow it to harden, then cut the leads off to about 1/4".
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Solder a black and a red wire to either side of the resistor and cover the connections with shrink tubing or electrical tape.
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Solder the green wire and a black wire to the small switch.
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Cut off the remaining connectors and group the colors together. You can stop at this point, but keep in mind that if you are testing a high current part such as a motor, you will want to group several wires together and use a heavier gauge clip lead to attach the 12V and ground wires.
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If you want to make the job a little neater, you can use binding post terminals, which will require drilling holes in the power supply. Just make sure they are well insulated as some of the ones at Radio Shack are designed more for plastic project boxes. I chose to use barrier terminals which gives a little more flexibilty with the attachment of clip leads. These can also be obtained at Radio Shack. I spent about $10 on these. Notice how I have grouped the wires together and run a jumper between them. This will allow for the highest current flow without heating any single wire.
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Here you can see each of the voltages provided:
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Finally, some tests. Here is a power window motor I found in a box of parts. It tested good.
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How about a headlight bulb:
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If at anytime you short the power supply, fix the circuit and turn the switch off and back on. There is also a switch on the back of the power supply, but it may not reset it.
Last edited by ABQTBird on Wed Jul 31, 2013 3:04 pm, edited 1 time in total.
Tom in Albuquerque
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vince
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Post by vince » Tue Jul 23, 2013 11:58 am

Wow! thanks
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john6t6
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Post by john6t6 » Wed Jul 31, 2013 3:00 pm

Thanks ABQTBird! This is great, I have several items that require testing, and this will do the trick.
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55Greg&Amy
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Post by 55Greg&Amy » Wed Jul 31, 2013 3:23 pm

Thanks, after seeing this post I promptly dug out an old computer power supply and built one and it works great. My car is 6volt and I have been using a 6volt battery to test my window, seat and blower motors for a while but no more.
Greg Minnich
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ABQTBird
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Post by ABQTBird » Wed Jul 31, 2013 3:30 pm

My car is 6volt and I have been using a 6volt battery to test my window, seat and blower motors for a while but no more.
Will you use the 5V for testing? I would imagine it should work, just at a lower speed for motors.
Tom in Albuquerque
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55Greg&Amy
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Post by 55Greg&Amy » Wed Jul 31, 2013 5:55 pm

The 5v worked just fine for testing the extra motors I had laying around.
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SGTCornewell
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Post by SGTCornewell » Sun Apr 06, 2014 8:16 pm

the 5v can also be used to test certain sensors on newer engines. computer controlled sensors often call for a 5v reference signal from the computer and don't like to get 12v put through them.

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Post by sseebart » Fri Jul 04, 2014 6:54 pm

I've been wanting to make this ever since I saw the post. Finally had a chance this week, and it works great.

FWIW, the Radio Shack near me didn't have most of these parts. I ended up sourcing most of the materials at Fry's Electronics.

Just a few mods for my unit. I glued the PS down to a board so the whole unit will stay together. I also labeled the voltages, as my memory is not what it used to be. I don't care for crimped on connectors, so I soldered all the connections. Otherwise, I followed the directions pretty closely:

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What finally got me going on this was the need to test some gauges for my 62 F-100. Started with a working, but beat up temp gauge from a t-bird--putting 3.3 volts to it:

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Since that didn't fry anything, I tried out the fuel and temp gauges for the pickup, they also tested good. 3.3v on both of these, too:

Image

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~Steve

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55Greg&Amy
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Post by 55Greg&Amy » Fri Jul 04, 2014 8:37 pm

I attached everything to the power supply to make it easier to transport to the work area. I use alligator leads for the positive terminals. Image Image Image
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SBurney
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Re: Making a bench testing power supply from a computer P/S

Post by SBurney » Wed Aug 30, 2017 9:03 pm

I thought this was a pretty genius idea. Here is my 2nd version. The entire thing is self contained, and I added a dpdt switch and a power light (an led connected to one of the 3.3v wires) to it. The reason for the dpdt switch is because I'm working on the windows in my car and I need to 'blip' the window motors to get them on and off of the regulators.
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Steve Burney
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