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

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).

Comments

[Klaudiuszm]

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?

[Random_Canadian]

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.

[Klaudiuszm]

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

[Random_Canadian]

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]

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]

Negative voltage, sorry , not negative current.

[chamunks]

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]

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.

Lourens

[bpfh]

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!

Cheers!
Daniel

[DustyJK]

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]

Hey
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

[charles543]

What is a CLA?

[Random_Canadian]

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

[sconner1]

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

[ak47freak]

How do you go about discharging these units?

[sconner1]

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.
Done.

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]

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

[Trike Lover]

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]

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]

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]

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]

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]

I'd say use https://www.adafruit.com/products/460 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]

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]

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]

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]

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

[1up]

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]

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

[robbied]

This isn't quite accurate. When plugged into a computer, there is always current drawn on the 5V rail. This switches the regulation on for the 12V. You will need some resistance on the 5V rail if you want regulated 12V with some amps.

[nadav]

Theres a post on Dangerous Prototypes (ill try and find the link) where they say that its not always necessary. So first I would test your PSU to see if it needs the resistor, cause if it doesn't then it'll save you money (a tiny bit), power, and most of all heat.

[arnefl]

Nice work.
I have a few of these and they are wired a bit different. I make use of the power supply's ability to be in standby mode. In this mode they can deliver 2-5 amps 5v. And as soon as something is connected, that use power on the other connections, the power supply brings itself out of standby mode and power up. I save a lot of energy when using this version. (I also have a button to force it out of standby with a power resistor)

When in standby it uses almost nothing, and still delivers quite a bit of 5v. current. When powered up they use from 10-30 W, doing nothing. (if nothing is connected)

[gezer2u]

Could you do either a instrucable or provide a link so we can see how to do this.

Thanks

[arnefl]

It's quite easy.. On this one, a Dell, I connect 11 to ground. I connect a +5 to a power resistor, then to a switch, and from it to ground. This is the "force On-button. I leave it off.

Pin 6 is the one giving lots of +5 volt when in "sleep mode". (also sometimes called VSB)

When plugged in and in sleep mode, I can draw lots of current at +5 from the pin 6. If I connect anyting demanding current on other pins, +12, +5 etc. the power supply turns itself on and out of sleep mode. I never need to "brute force" it out of sleep mode with the switch.

[gezer2u]

Thanks!

[arnefl]

A simple current regulator
http://www.eleccircuit.com/lm317-lm338-lm350-current-regulator-calculator/

[Revanchist]

Hi everyone, I've been looking for a great project such as this, one thing I have a question is, how would I go on to adding a negative 5 volts? would it be similar to how you added the -12V? since some of my projects require bipolar power supplies that would be amazing to use... although +12/-12V would also work, I like working with 5V for the Arduino....

[Trike Lover]

There are several simple current limiter circuits on the Radio-Electronics site, here:
http://tinyurl.com/7aq4qlx
[Open in new window]

The simplest one uses two diodes and a resistor, and others are shown using one or two discrete transistors. All could be added on the output(s) of this supply if a person felt it necessary.

There are also several Op-Amp IC's specific to this purpose, readily and cheaply available. A Google search for "current limiter IC" or "current limiter op-amp" will turn up several examples, most simple to build, and with manufacturer-supplied data sheets that include circuits and, in some cases, board layouts.

Fixed or adjustable current designs are all over the 'net, and it's no problem to incorporate one on an output circuit if it's felt to be necessary.

This is a nice, clean adaptation, and a most interesting Instructable. Props to the author.

[pollux64]

I agree totally with @ArtemKuchin about the current limiting. I have blown-up two supplies because of that. Recently I implemented a current limiter according to http://www.chirio.com/switching_power_supply_atx.htm (In Italian, but workable with Google translate)

Every supply is a little bit different but this gives you an idea of what to modify.

[ArtemKuchin]

The main problem with all these home made lab power supplies built from ATX PS is the absence of current limiter. I use a cheap real lab PS and current limiter in it saved tons of devices for me. Current limiter is a must have for a lab supply. If it is not there then it is just a toy, dangerous toy. Sorry to be "tough" on you, but that's life.