Bench Power Supply




About: Professional work in various electrical and mechanical fields, obscure sense of humour and typically willing to help... Currently under contract designing environmental monitoring equipment.

Re-purpose a Computer power supply into a Quad output Bench supply.

I have been using this to test a multitude of different circuits and devices!

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Step 1: Materials

You will need to know basic soldering skills.

A computer power supply.
Several eyelet wire connectors.
different coloured binding posts.
An LED(i used an old computer power led)
Power resistor. 10Ohm 10W should work.

Optional is a cigarette lighter adapter (CLA).

Step 2: Disassembly

Observe proper precautions when disassembling a power supply.
Make sure it is not connected to mains
Make sure that it is fully discharged.

Remove the cover screws.

Remove any chassis connectors.
Remove the mainboard screws.

Remove the power supply circuitry from the metal chassis.

Cut all the output wires to about 6-8 inches from the mainboard.

Step 3: Identify and Connect

The output section of the main circuit board may be labeled. If it is not The following rules may apply.

Red = +5V
Orange = +3.3V
Yellow = +12V
White(as shown) = +12V
Blue = -12V
Purple = not used
Grey = Power on LED
Black = Common or Ground

Thin orange = 3.3V sense
Thin Red = 5V sense
green = Power on

Separate and bundle the wires accordingly.

The sense wires on my supply are directly between the orange and yellow in the picture.

Group the wires together and fasten them with solder or crimp eyelet connectors.

Any exposed connections should be covered with heat shrink to taped to prevent shorts.

The green wire must be connected to ground.

the thin orange must be connected to thick orange.
The thin red must be connected to thick red.

You should connect a resistive load (some supplies require this for proper operation). I chose a 10Ohm 10W power resistor. it needs to be connected on one end to the 5V red wire and on the other to ground. I soldered this in place then protected the conductors with heat shrink.

I chose to use a CLA and wired this directly to the 12V (white) V2 section of the supply. The ground was connected to a black wire.
The CLA was positioned into the existing wire loom hole in the back of the supply. It is held in place with a rubber grommet.

If you choose to you can connect an LED between the grey wire and ground. use an appropriate sized resistor for your LED,

Any unused wires should be sealed from shorting by covering the exposed ends with heat shrink or electrical tape.

Step 4: Drill the Chassis

You will want a nice way of transferring the power from the inside to the outside.
I used binding posts. The colours chosen were all that the local store had in stock.

Drill holed in a convenient place on the chassis to attach the binding posts to. The rear of my supply was the only place.

Secure thee binding posts to the chassis using the nuts provided.

Drill a hole in a convenient place for the LED mount.

I drilled using standard bits and a step bit. If you haven't used a step bit before, you are definitely missing out on the joys of nice round holes in sheet metal.

Step 5: Test and Enjoy

Test the power connections with a multimeter.

Once you have verified that there is no short and the voltages are placed to the binding posts that you wish, reassemble the chassis.

Label the binding posts for future reference.

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68 Discussions


2 years ago

I'm part-way through making this, and I'm new to this kind of project.
The 300w power supply I'm using has 7 yellow wires labelled 12V1 8.0A,
and 2 black-and-yellow wires labelled 12V2 14.0A. If I connect these two
lots of wires separately (ie. to separate binding posts), does that
mean I can have two 12v supplies with different current (ie. one at 8.0A
and one at 14.0A)? Also, I successfully ran the power supply for more
than half-an-hour with no load before turning it off, so does that mean I
can get away with not having a resistor to provide a load?


Reply 3 years ago

Some supplies will not start or operate properly without a load. This was done as a standard measure to allow for proper operation and voltace reading. I hope that this helps.


4 years ago on Introduction

What is the difference between 12v and -12v? Also can i connect more Voltages together eg 3.3v and 5v for 8.3v?

1 reply

Reply 4 years ago

Nope.voltage means the potential difference.if you connect +5v and a +3.3v you'll get a result of 1.7v (5v-3.3v)
+12v and +5v = 7v
+5v and -5v = 10v and so on


4 years ago

So you don't need to connect all the same wires? Like I have 2 doZen or so ground(black) wires, which is a major PITA to try to solder all of them(except the one to the resistive load) to one tiny banana plug post. I can just cut them short and seal most of them off?

1 reply

Solder several together to get a good ground point but most can be
blunted and sealed off. I usually use 5 or 6 together to get an
excellent ground lug.


4 years ago on Introduction

Don't have any pictures but thanks for all the help putting this project together. Now with this project under my wings I can go forward with others. Again, thanks for your time and effort.

1 reply

4 years ago

he, awesome project but where do you need the resistor and resistify load( sorry don't exactly know how to write it) for?


5 years ago on Introduction

Thnaks for the cleare instruction. Now I want to build it but I have a question about the type of banana plug I should buy. Are any good for instance or do I need to worry about a specific type. I'm not that experienced in electronics and don't want to burn the house down. ;-) Thanks in advance


5 years ago

very nice thx. just found I had to out heat shrink on the banana plug terminals to stop them shorting on the chassis


5 years ago

I didn't said constant current. I need variable current circuit. Which is require to study the characteristics of components. This can done by using simply POT but it cause heating after 0.5-07A. Conventional Power supply had this feature.

Constant current control requires quite a bit more complicated circuitry. It might me a good idea at this point to spend $100 to purchase a regulated variable supply.


5 years ago

Can u tell me is it possible to have current control ? And if, then how. Please reply soon..


5 years ago

can be a charger of lead acid battery for battery truckn