Computer Power Supply Conversion

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saboo
Posts: 483
Joined: Mon May 18, 2009 3:48 pm

Computer Power Supply Conversion

Unread post by saboo » Wed Mar 15, 2017 11:14 am

Simple directions to convert a computer power supply for a battery charger power supply.

Ideally you will get a power supply that has a rocker switch on the back. This means that once built, the power cord can be plugged in and the switch used to turn the device on or off. Otherwise you will have to unplug the cord as the switch.

Open case.

ADDED EDIT HERE. Change relates to the brown wire.

There is a large bundle of wires coming out the back. Unsolder all power wires from the main board except 2 Yellow, 3 Black, 1 Red, and the 1 green and on some power supplies, the brown wire. If the brown wire is there do not unsolder it.

Solder the green to a ground pad after cutting the length to suit. The black wires are coming from ground pads. This enables the power supply. EDIT The brown wire is often tied to the orange wires at the motherboard connector. This is a 3.3 volt sense line. Without it, some power supplies will not start. It needs to be cut long enough to be soldered to the 3.3 volt line. Orange was the 3.3 volt line. So solder the free end to the pad on the power supply board, where the 3.3 volt lines were.

Solder 1 Red to the center of a single filament automotive tail light bulb. Solder 1 Black to the brass base of the same bulb. Leave the wires long enough so you can wrap the base in black tape and mount the bulb in the hole where all the wires used to come out. This is the dummy load needed on the 5 Volt rail. It also acts as the indicator light. Try to find a single filament 12 volt automotive bulb. It should be 10 watts or more.

Decide where you are going to mount the Red and Black receptacles. Cut 2 yellow and 2 black wires to a length to suit.

Drill holes and mount the receptacles. Use a meter to check that neither are shorted to the case.

Solder a single Yellow wire to each of the Red jack receptacles.

Solder a single Black wire to each of the Black jack receptacles.

So now there is a single wire to each of the receptacles.

Make sure that no wires are bare or shorting.

Plug in power cord.

Light should come on.

Should be 11-12 volts across a Red and Black jack receptacle.

Pull plug.

Assemble the case again.

Retest output.

Charge your batteries.
Nothing like the smell of electrons in the morning ;-)

saboo
Posts: 483
Joined: Mon May 18, 2009 3:48 pm

Re: Computer Power Supply Conversion UPDATE

Unread post by saboo » Wed Jan 02, 2019 6:25 pm

Some people had followed the above directions as originally posted. When they were finished, the units would not power up. Since then I have had a similar issue.

It turns out that all of the ATX power supplies that I had modified, up until a couple of years ago, just worked. The reason is that later power supplies have a 3.3 volt sense line. You can tell if the power supply that you are going to modify requires this line. It will have a brown wire tied to an orange wire in the 20 position or 24 position mother board connector. See one of the attached pictures.

The appearance of the inside of the power supply is shown in some of the attached photos.

In the post above I have added revisions to reflect this requirement. I apologize if you spent time and then found your power supply would not work.

In addition I have a picture of the 12 volt tail light bulb mounted in the cable outlet hole of the case.

Finally you can see a case with 3 pairs of 12 volt banana jack receptacles.

I hope this added information helps.
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Nothing like the smell of electrons in the morning ;-)

saboo
Posts: 483
Joined: Mon May 18, 2009 3:48 pm

Re: Computer Power Supply Conversion

Unread post by saboo » Wed Jan 02, 2019 7:06 pm

More Pictures
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Nothing like the smell of electrons in the morning ;-)

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