How to Fabricate a Lunch Box Into a Dual 0-12VDC Power Supply.

Preface:

Hello and welcome to my Instructable.

I am a first year Electronic Engineering student and was given the opportunity to build a power supply. I was immediately fascinated but wanted to make more than a run of mill project. My original idea was to use a cigar box and pack as much into a small space as possible. As a former UPS worker, Tetris enthusiast and skilled in Unwrapping and packing UV maps I felt confident I could meet the challenge.

Well, after a embarrassing and brief brush with the law over the definition of "FREE", I retired myself acquiring unwanted cigar boxes from Tobacco shops. By the way, It was misunderstanding but i digress. This is the part of the story when our hero is introduced to the audience. One Saturday I was cleaning my apartment and by cleaning my apartment, I mean starting to clean and finding a lost item and reminiscing with it for the next 3 hours. This item was in fact the lunch box shown. A discarded Christmas or birthday present now finding new life as the inspiration I needed to complete an idea. I hope you can find inspiration in this Instructable after all isn't the reason we're all here to make something cool?

The first goal of this Instructable was to make a functional, dual 0 -12 VDC power supply. The concept was to use a single 10:1 step down transformer and two voltage regulators to create dual 0-12V variable DC outputs and a variable 0-24VDC output. Secondly, I wanted to recycle an old STAR WARS replica lunchbox as the housing for the power supply. Hopefully this Instructable will peak your interest in electronics and help guide you in your own power supply projects.

To build the power supply,as shown in the circuit, you will need the following parts:

2 x 10,000uF Cap - Link

6 x 1N4001 Diode - Link

1 x 10:1 Step-Down 12V Transformer - Link

4 x 10uF cap - Link

2 x 120 Res - Link

2 x 500 Potentiometers - Link

2 x 1k Potentiometers - Link

2 x 1k Res - Link - Link

4 x Terminal Blocks - Link

1 x Slow Blow Fuse - Link

1 x Toggle Switch - Link

1 x Fuse Holder - Link

1 x LM317 Voltage Regulator - Link

1 x LM337 Voltage regulator - Link

You will additionally need the following:

3 Prong US Plug AC Power Adapter Cable Cord

IEC 320 C14 Male Plug 3 Pins PCB Panel Power Inlet Socket Connector

1 x breadboard to assemble the circuits

Cables (wires, alligator clips, etc as you need) to make the connections

Soldering Iron

You may also want:

Dremel

Cutting disk

Drill and various drill bits -

Desoldering Iron

Multimeter (for testing)

Oscilliscope (for testing)

Needle nose pliers

Step 1: Prototyping the Power Supply

The included pictures will help you prototype the power supply step by step.

The layout is designed for a permanent build on a prototype board. Some modifications have been made.

Important Note:

When doing a permanent build I grounded the outside rails of each voltage regulator and the terminal blocks on the underside of the board.

Once you have completed the build I highly recommend using a heat sink on each of the voltage regulators. If you keep the output voltages low the remaining voltage will fall across the regulators and they will get HOT.

Now would be a great time to test the output of each regulator.

A single 1K potentiometer can be for each of the voltage outputs.

Step 2: Permanent Build of Circuit

I am adding a designated parts list:

Voltage Regulators:

317 - LM317 Voltage Regulator
337 - LM337 Voltage Regulator

Fuse:

F1 - 1A 250V

Potentiometers: (Link for more information on using potentiometer as voltage divider) *NOTE the potentiometers used in this circuit are being used as variable resistors.

P1 - 500 ohm
P2 - 1K ohm
P3 - 500 ohm
P4 - 1K ohm

Resistors:

R1 - 120 ohm .5W
R2 - 1K ohm .5W
R3 - 1K ohm .5W
R4 - 120 ohm .5W

Capacitors:

C1 - 10,000 uF 35V Electrolytic Capacitor
C2 - 10,000 uF 35V Electrolytic Capacitor
C3 - 10 uF 50V Electrolytic Capacitor
C4 - 10 uF 50V Electrolytic Capacitor
C5 - 10 uF 50V Electrolytic Capacitor
C6 - 10 uF 50V Electrolytic Capacitor

Diodes:

D1 - 1N4001 50V 1A
D2 - 1N4001 50V 1A
D3 - 1N4001 50V 1A
D4 - 1N4001 50V 1A
D5 - 1N4001 50V 1A
D6 - 1N4001 50V 1A

Step 3: Constructing the The Rectified Output From Transformer

I was able to recycle a transformer with a bridge rectifier already attached. I kept two of the diodes on the board and placed the 10,000uF caps directly into the PCB.

1N4001 diodes can be used here instead of the recycled ones I used.

Red = Positive Voltage

Black = Negative Voltage

For the ground wire I drilled a hole into the PCB, scraped away the green coating and soldered the wire to the secondary of the transformer.

Green = Ground

Step 4: Transforming the Lunch Box

The next steps will be less of a step by step how-to and more a visual journey of my design and build.

I will say that planning is very important. The tin lunch box was very delicate. I used masking tape to protect the paint when drilling and cutting the tin.

Step 5: Final Thoughts

I had a lot of fun with this project. The project not only re-enforced many electronic fundamentals but it made me seek further knowledge of unfamiliar components.

I am aware I didn't explain many of the electronic characteristics. I could have but it would have been riddled with grammar and spelling errors. Besides, many other authors have done a much better job than I could ever have imagined.

I can however , leave you with some links if you would like to expand your knowledge.

Transformers -LINK

Rectifiers - LINK

Voltage Regulators - LINK

Final Final Thought-

I am trying to work on my communication skills so any and all questions will be answered in the comments. I will also be editing the post as I see fit. Just like like this project was an opportunity to learn more about something I was unfamiliar, this post will also be a learning experience.

Thank you for viewing,