Diy Power Supply Modification Using SMPS

Hey today in this instructable I will show you how I built my first every power supply. There are plenty of power supply conversion videos on the internet. Few of the features of this project are highlighted in the image above.

Now before you build this project I would like to bring this to your notice that I wanted to build a power supply that had both fixed and variable voltage outputs with current reading. I made the project but I was not able to get the current readings accurate on the display. Initially I thought something was wrong with my display or the resistances of the DPDT switches caused that. But very soon I found that the Switch mode power supply I salvaged from my PC was unable to provide a constant voltage for a longer time. I was still not sure what the exact matter was. But then the SMPS went completely into coma and I could not test the DIY power supply. Now I am a lazy person and hence chose not open the Power Supply to fix the problem. Instead I built a simple fixed one for temporary usage. You can find that online very easily. The only reason I am sharing this version here is to give you some idea how I made this variable + fixed Power Supply. And this might work for you if you salvage a "Working" PSU. So let's see the build process.

Step 1: Gathering the Supplies

Let's take a look at all the components. I will just list them here one by one. (You can refer the images above)

1. An old SMPS (Switch Mode Power Supply)

2. Buck Boost converter

3. Voltage Current Meter Display

4. Double Pole Double Throw (DPDT) Toggle Switch

5. Rotary Switch ( I was unable to find the desired product in my locality so I had to use this one )

6. 10K Potentiometers with Knobs

7. Binding Posts & Banana Connectors

8. Rocker Switches

9. Crocodile Clips

10. Heat Sinks for the Buck Boost Converter IC's

11. Led and a 220 Ohm resistor

12. MCB (optional)

13. USB/Micro USB port/DC Jack (optional)

Along with the above mentioned things you will also need some tools.

Tools : Soldering station, Heat shrink tubes, Drill machine, Metal cutter, 2.5 mm flexible wires, Spray paint, Sand paper, etc

Step 2: Voltage Levels of the SMPS

The SMPS has various different multi-colored wires. Each wire corresponds to a different voltage level. The above image will give you an idea about the voltage levels.

For this project we will use most of the wires except the -12 V (Blue).

The SMPS turns on when you connect the green wire to the black wire.

Note : Some SMPS have a brown sense wire. That wire needs to be connected with a 3.3 V supply.

Step 3: Circuit Diagram

The connection diagram for this project is shown above. You would not want to connect all the stuff together without testing it first. So for that follow the first diagram which will show the basic Variable Voltage part of this power supply.

Also do read all the points on the next image. They will help you to understand the connections.

Step 4: Building the Power Supply Case

This was the main part I wanted to highlight of this project. Building a case from scratch can be pretty difficult sometimes. So here is what you can do. If you have two casings of the SMPS then just join them together side by side and cut the center part for passing the wires and for air flow from one side to other. Refer image 3 for that.

Then make some holes for the connectors, switches and V-I display. If you are using an MCB then make one cut out for that too.

Now paint the casing with some spray paint.

Then install all the electronics and close the box.