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

11,732

175

21

## Introduction: 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

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

### Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

## 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.

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,

B

Thank You

Mr. S and Mr. E

## Recommendations

141 9.7K
81 7.5K
195 12K
Large Motors Class

14,629 Enrolled

## 21 Discussions

I have made a few corrections and added a designated parts list. Thank you again for all the feedback. If you are having trouble with this project I will add any steps that will help you complete the build. I check daily.

I like the way you have made this go down to zero, with the diodes D3 to D6. I think it would have been nice if you'd explained how the supply works, what each part is for, if you have in mind beginner enthusiasts as your audience. Speaking of which, you want to "pique" my interest, not "peak" it! :)

http://blog.dictionary.com/pique-peak-peek/

Nice work. The vintage lunch box ramps up the cool factor.

There is a connection error at your first diagram.

Could you explain to me the best way to create a split power supply so that I have 12v and -12v rails? I'm attempting to repurpose a Class D audio amp IC from an old rear projection TV. I've found the datasheet and it requires a split power supply.

Scott, this circuit actually provides a -12 and 12 v output. The outputs share a common ground. I would look at the transformer part of my instructable. It will show a 10:1 step down transformer half way rectified.

I noticed that. You might want to update the title of your instructable, it's misleading.

Im not sure why this is misleading. In a DC context the current is constant.

nice work, i most probably will make this, as a power supply is very essential to most projects.
as a suggestion i would recommend adding a voltmeter in the center of the front of your lunch box (has good space) since you'r dealing with 2 variable voltages. 1 led volt meter with a switch (to switch between output 1 and 2) is enough. u might need a 5v regulator for it, lm7805 should do fine.

overall very nice project, thanks for sharing.
PS : making mistakes is only human, so grammar mistakes can be fixed, and more explanation would make beginners better informed and gives them a clearer view of the components and their role in the circuit.

The problem I ran into was that many cheap mini 3 wire Digital volt meters are unreliable from 0- 2.7 ish Volts and any thing above 10V. I agree, it would be nice to have a reference to the output voltage.

I would have loved to but I ran out of room in the lunch bow.

To elaborate on the connection error in the diagram:

The '337 input should connect to the anode of D2, not the cathode as shown. As drawn, D2 and C2 have no function, and the 337 will receive AC input, which will let the smoke out.

I made the correction to the first diagram and the tranformer diagram. Thanks again.

UGH, you are correct. I will make the correction immediately. Thank you!

I will be making all corrections and adding a designated part list this evening. Thank you for all your feedback.

Try Drilling Extra Vent Holes 1/4Inch from each other in the corners & mount 12V DC PC Fans (About 1 1/2 inch in size) to remove the Heat better.