Introduction: Bench Power Supply

Picture of Bench Power Supply

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!

Step 1: Materials

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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.


Rofey (author)2017-02-04

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?

Lockheed95 (author)2016-01-06

why do you need to use a load?

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.

Mesut.DD (author)2015-10-18

good power supply

Random_Canadian (author)Mesut.DD2015-10-22


kaunder made it! (author)2015-07-30

Great instructable! Here is my result.

itge13 (author)2015-02-13

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

arukshan (author)itge132015-07-04

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

erik.savoie.3 (author)2015-06-18

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?

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.

tgattsiii (author)2015-01-21

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.

I hope you get lots of use from. and enjoy your project!
Sorry for the late reply!

russ_hensel (author)2015-01-09

Just a note to let you know I have added this instructable to the collection:
Encyclopedia of ATX to Bench Power Supply Conversion
Take a look at about 70 different approaches to this project.

Mistercrazyboy21. (author)2014-12-12

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

PaulB10 (author)2014-10-11

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

silence444 (author)2014-09-03

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

palashdaking (author)2014-03-07

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.

Random_Canadian (author)2014-02-23

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.

palashdaking (author)2014-02-11

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

jayz01982 (author)2014-01-15

can be a charger of lead acid battery for battery truckn

charles543 (author)2012-07-07

What is a CLA?

PCfreak (author)charles5432013-09-18

CLA = Cigarette Lighter Adapter

It is the type of power socket that you have in your car.

Klaudiuszm (author)2013-02-18

Great instructable! Definitely going to look into making my own. Couple of quick questions though, how safe is this? And how can i limit the amperage going out?

I left one on over a weekend with no issues. Current limiting would need the addition of a breaker or fuse. I have found that of you go over the rated for the power supply it will need to be reset by unplugging the supply for 10 seconds. This may be limited to the supply that you use. An in line fuse from the hot side would definitely give you the protection that you are looking for.

About safety in general, would I get shocked by this if I accidentally touched a terminal?

You will need to treat this like you would any low DC voltage supply. You need to be careful around ay electrical potential. However at the voltages in this supply you will not experience an electrical shock like you would with house mains. Usually any DC voltage below 48V is usually not labeled as being a risk to health and safety. If you are concerned please feel free to pick up a book on basic electronic principles.

bpfh (author)2012-07-07

This is one thing I cannot get my head around. Negative current. Would that mean that the power is coming from the ground rather than going to it ?

bpfh (author)bpfh2012-07-07

Negative voltage, sorry , not negative current.

chamunks (author)bpfh2012-07-24

depends on the situation really. the negative side on a battery is the side the current is leaving the battery and the plus side of the battery is the side that is technically the ground or collector. There are some situations where this gets confusing though so you might need to look into the specifics someone whose more confident in their knowledge of this might be able to chime in here but i hope this helps.

lourens01 (author)bpfh2012-07-16

The easiest way I can explain it, is to think of Voltage as a reference to 0V. If you take two 12v Batteries and connect them together, ie one negative pole to one positive pole, you effectively have a 24V battery. Now, if you take this connection and make that your 0V you have have a 12v on the one side and -12v on the other.

In Telecommunication it is a common practice to use -50v. This means that you have a Positive earth instead of a negative earth. A motor car, and almost everywhere else, we use a negative earth.

I hope this helps.


bpfh (author)lourens012012-07-17

I think I got it : So the telco in your example would be using a 100v supply with 2x50v supplies in series, they can go between 0/50, -50/+50 or 0/100v, depending how they cable their battery systems (3 connections 0, 50, 100v) whereas in a car we are running a plain 1x12v (for example) and your only possible connectors are 0 and 12v.

Thanks for the explanation!


DustyJK (author)2012-07-23

why not take a little extra time and wire in some usb ports for usb chargers.
It should be similiar to some of the altoid chargers.
Sorry for bad spelling ;B

ingkiller (author)2012-07-18

i made this, just like you said.
but i'm getting like 0.4 volt from red, 1.9 volts from yellow, about 2 volts from orange. i have no idea what went wrong. the supply i'm using is a compaq from an old pentium 4 pc i got for free from school.
there is one wire i got, you didnt mention. its a red/white one.
i hope you can help.
greetings ingmar

sconner1 (author)2012-07-07

When I get 'round to building mine I'll probably throw on a couple ammeters on the most used voltages.

ak47freak (author)2012-07-05

How do you go about discharging these units?

sconner1 (author)ak47freak2012-07-07

For quick insurance you could also use a low value resistor to the connector pins with the unit unplugged of course. The resistor is better than just shorting the pins to ground because you prevent sparks and damage.
Drain each volt rail separately.
Connect the v+ and v- (any color wire other than black) to ground (black) for a few minutes. It shouldn't take long, there isn't much storage capacitance in these switching power supplies.

Keep in mind the different voltages have different current capabilities.
+12v and +5v have the most
+3.3v and -12v have very low current available
Read the label on your unit and label the outputs of your finished unit.

mattmahn (author)ak47freak2012-07-06

Leave the PSU disconnected from EVERYTHING for a couple of days.

Trike Lover (author)2012-07-06

Another useful addition, if you're working on radio equipment, is a pair of Anderson connectors to +12 and Gnd. A lot of mobile amateur radio and commercial radio equipment now comes with Anderson power-pole connectors as standard equipment.

There are chassis-mount Andersons available, but most people don't have any on hand, even if they have Andersons to fix or convert equipment power leads. if you drill a couple of holes side by side in the chassis back plate, file square corners to fit the Anderson pair, and then glue in the shells with some 5-minute epoxy, they sit nicely next to the CLA socket. Solder the metal inserts to +12 and Gnd, wires inside the case, slide them in until they lock, and you're all set.

VAustin89 (author)2012-07-06

I have been contemplating on building one, since I like to build small guitar amps and guitar effects, would this power supply do the job? or is it just too much for my intended application?

Trike Lover (author)VAustin892012-07-06

I built a multi-stompbox supply using a computer supply and some LM7809 regulators. I used the +12 volt DC output of the computer supply to feed the 7809's, and each regulator feeds one stompbox. ( You have to be careful of the +/- on the power plugs - not all pedals are the same).

Pedals don't draw very much current, so I probably could have put 2 or 3 pedals on the output of one regulator. But, I got a bag of 20 7809's for about $3, and so power to each pedal is separate. I put a 100 uF electrolytic capacitor and a 250 k resistor across the output of each regulator for extra filtering. No magic to the 100 uF cap value - I just had some sitting in a drawer.

I also had one pedal that used four AA batteries, but it runs fine on the +5 volt output of the power supply. If necessary, I would have added a LM7806 regulator to run that box, but it works fine on 5 volts so I didn't bother.

Trike Lover (author)Trike Lover2012-07-06

I forgot to mention that I put a fuse in the + lead running to each pedal plug, I carry some spare fuses in the pedal box. Better a 60 cent fuse than *phunt* and bang goes a $60 pedal.

Trike Lover (author)2012-07-05

If you want to add an ultra-deluxe touch you can permanently mount two inexpensive DMM's, one for voltage and one for current. Double faced foam tape works well. Power supply for the meters themselves can be made using LM317 variable regulators, or LM78xx series fixed regulators, if the required voltage is not available in the PSU. These DMM's go on sale for as low as $3.00 apiece, and they add a nice touch as well as being functional. You will need to make up a couple of short jumpers with banana plugs to connect the meters to whichever supply output is in use. You can measure two different voltages, or voltage and current for one circuit - and you never have to go looking for them!

ksexton1 (author)Trike Lover2012-07-06

I'd say use for a real easy meter setup. it's powered by the voltage it's measuring, 3.2-30V, using very little current.
They also have panel mount voltage and current meters.

Trike Lover (author)ksexton12012-07-06

Ksexton1 - yes, those 460's are very nice, and not expensive (shipping costs more than the displays, LOL). I have used Adfruit displays in building projects for my ham radio shack. They look good and work well.

I mentioned the DMM;s mainly because they;re on sale right now uber-cheap where the author and I live. They;re not as elegant as the 460 displays, but they are flexible in function and inexpensive (right now, at least). If I had not seen those DMM's on sale at PA I would probably have incorporated a 460 or similar just for convenience.

I also have some WWII-vintage analog voltmeters and ammeters with the right ranges - but mounting them means cutting big round holes, or improvising some other mount. I may use the old meters if I ever build a Steampunk'd power supply. They look very "art-deco" in their Bakelite housings. They even have internal bulbs, so a there's a nice orange glow.

jimdkc (author)2012-07-05

I've seen several implementations of this idea. Yours is one of the cleanest. I have a power supply that I'm not using and was planning to make it into a bench supply. I'll probably include a ground for each output (on standard 3/4" centers) and try to find binding posts to match the power supply color codes (red +5, orange +3.3, yellow +12, and blue -12 -- DigiKey or Mouser electronics are likely sources). I particularly like your inclusion of the car cigarette lighter adapter! I hadn't thought of doing that!

Trike Lover (author)jimdkc2012-07-05

If you search on EBay for "20pcs Binding Post 5 color" they are also available in multi-colored sets. Shipping cost may be less depending on where you live.

jeffeb3 (author)2012-07-03

Why did you tie the 5V red to ground using a small 10 Ohm resistor?

1up (author)jeffeb32012-07-03

Switching PSU's like these should always have some sort of load connected, so the resistor is on the 5v line to draw about 500mA.

endolith (author)1up2012-07-05

If the power supply required a minimum load, then it would already be built into the power supply.

About This Instructable




Bio: Bit of a background in various electrical and mechanical fields, obscure sense of humour and typically willing to help...
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