Introduction: A Most Useful Power Supply

By
About: Founder of The Science Experience.

Have you ever needed multiple voltages when working on a project and all you have is a variable power supply? Here is one solution to the problem that is inexpensive to make and easy to use.

Supplies

Bill of Materials:

Case – Small ammo box from Harbor Freight $4.66 Power supply – free

Computer power supply - free

Computer 120V (or 240 V) power cable

Banana plugs – Amazon

Banana jacks – Amazon

Various banana plug to connector parts – Amazon (see picture)

I admit to being a little lazy so I purchased 3 sets of 10 ft red/black 18 AWG wires from Amazon.

Hook-up wire – free

SPST Switch to turn on and off the power supply (A computer power supply uses a touch switch to turn on the power to the circuit board in the computer. As I do not have a board attached, I needed this switch to turn on – and keep on – the power supply, and of course, to turn it off when I was finished.).

Tools:

Drill Large hole cutter (2.5” or 63mm)

Small hole cutter (1.25” or 33mm)

Various drill bits

Solder

Soldering Iron

Shrink tubing (for all wire connections – especially when you are going from a group of wires to a smaller or single wire. .

Step 1: Introduction

Have you ever needed multiple voltages when working on a project and all you have is a variable power supply? Here is one solution to the problem that is inexpensive to make and easy to use.

Step 2: Why This Approach to Power?

My projects usually require a combination of 5 volts and 3.3 volts, with the odd 12 volt requirement thrown in. I have worked with computers since the mid-70s and for the last 30 years the most consistent part of a computer has been the power supply. They have developed to the point that even the least expensive ones are well regulated and very efficient. For this project I chose a reliable (and used) power supply that I had laying around. I wanted three fixed and filtered voltages – 12V, 5V and 3.3V with enough amperage to power whatever I was working on. I also wanted the power supply to be portable and easy to use.

Step 3: Balancing Loads

There are a lot of wires coming out of a computer power supply so it is important to keep track of which ones you are going to use and how they will be connected together to connect to the banana jacks. One of the calculations I did was to determine the size wire I needed to carry the amperage that would be supplied on each line without a drop in voltage. I divided the black ground wires into three bundles and connected each bundle to the three ground banana jack connectors on the power supply. That way I had a solid ground for all three voltages, even if I used them at the same time.

Step 4: Portability

All of the cords and connectors shown will fit in the space between the power supply and the outside of the case including the cables needed to connect AC power and the 3 supply voltages.

Step 5: Switch to Turn on and Off the Power Supply.

Step 6: Airflow Is Important

Air holes on the airflow side of the power supply.

Step 7: Back of Ammo Box

Holes cut in the back for the fan output and power cord connector.

Step 8: Securing the Power Supply

Use a few short screws to hold the power supply to the side of the case.

Be sure that they are not long enough to touch the power supply circuit board!!

Step 9: Mounting the Power Switch

A computer power supply uses a touch switch to turn on the power to the circuit board in the computer. As I do not have a computer motherboard attached, I needed this switch to turn on – and keep on – the power supply, and of course, to turn it off when I was finished. Be sure the leads are long enough to allow the lid to open all the way but not so long that they get caught when you close the lid.

Step 10: The Finish

I now have a power supply that supplies most of my power needs on a project that provides the following:

12 V @ 15A regulated

5V @ 18A regulated

3.3V @ 20A regulated

Total power used at one time cannot exceed 250 watts. I work a lot with Raspberry Pi and Arduino but I have never had a project that required that much power.

All of the voltages are regulated to within 5% of the voltage listed, which is within the tolerance of any project I have worked on so far.