Hello,

so this is my first instructable, any tips for making things clearer or fixing these instructions are welcome. I study mechanical engineering and am not too deep into electronics but tried my best. If you have any improvements, feel free to share them in the comments.

My motivation to this project was the need for sound when doing my off-grid camping tours. I also wanted to use the device for charging mobile devices like my phone, flash light or GPS, and came up with the idea of using the most common interface, a USB port.

I also needed a device that was super sturdy and a water resistant as possible and ended up with an old ammo-box. Starting with this box, I slowly gathered the parts I needed for my project. That was eight months ago. I started a first build mainly from weak wood, and little time, just throwing the components into the box. This barely survived my first trip, and I started all over, modelled it all on CAD and made a better faceplate from aluminium.

***no native speaker here, don't hate, but feel free to correct me***

Step 1: Parts and Tools

The parts needed for this project may be different for you and your needs. Here is what I needed for my build:

Ammo-Box (I got mine from Amazon) you can choose any box that fits your needs
Audio Amplifier from Amazon (Mini Hi-Fi PAM8610 Audio Stereo Amplifier 2X10W Dual Channel D Class Module)
Speakers (8Ohm) I had these at home, but you can get them online
Lead Battery 12/6V (I ordered these from amazon)
Solar modules 2 pcs, 5W each (more amazon!)
Step-Down power-converter (DC-DC) 2 pcs, these are very cheap and extremely useful in many projects, get some more, if you order online
Digital volt/amperemeter (my choice from amazon)
USB-Hub
Any type of plug/jack connection for your solar modules
Threaded rods (4mm x 100mm, 8 pcs), I got these at a local store (1000mm piece, cut it myself)
A couple of switches, get them at radioshack or your local electronics store
Captive nuts, 2 pcs
Stereo plugs
Wicked roofer's screws (see picture)
Aluminium/wooden sheet/plate to hold all the components
A variety of nuts and bolts, zipties, wire, shrink tubing

Tools needed:

Basic soldering tools
Plies
Coping saw (if you have advances tools available like a laser-cutter/water-jet use these!)
Drill and various drill-bits
Printer (if you want to print the template)

Step 2: Making a Plan

Before starting to build i should have made a plan.

I did not, and it went terribly wrong, and it died on my first camping trip.

After that i decided to make a good plan, and do some CAD sketches, to see if it all fits and to make a proper layout of the top plate.

The images above show all the details, I hope it is easy to understand.

It took some serious time and effort to model all the parts and arrange them, but as I am very happy with the result that I have now, i don't have any regrets on investing that much time.

I also added the 3D-data for you to download. If the .igs file format is not working for you please leave a comment and let me know what you prefer!

solar_boombox.igs
Download

Step 3: Electrics

Fortunately I electrics are not too difficult for this one. At least I made a very simple and cost-efficient approach to all the parts.

The Solar Modules:
I got two 5W 12V modules from amazon. These have a max. of 0,28A and max. 18V. As I wanted a consistent charging voltage of 14V, I decided to wire the two cells in series, and convert the voltage with one of my DC-Converters. The buck-converters are rated for 1A output. If the modules produce the max. power of 5W the output of the converter is at (2*5w)/14V=0,71A wich is still below 1A.

The Batteries:
I chose to get two 6V sealed lead batteries because they add up to 12V, are easy to charge, cheap and robust. They have 4,5Ah each, wich leaves us with an estimated power of 12V*4,5Ah=54Wh. That should be enough to charge my devices and listen to music for a good while! Charging time at full sunlight is about 54Wh/(2*5W)=5,4h. If we count in all the losses and the lying on the data sheets, the batteries might be full after a long day of bright sun.

The wiring:
I wired everything in parallel, and the batteries in series to get my desired 12V. I hope the schematic makes it all easy to understand.

Step 4: Top Plate

I started with the top plate. I printed the plan I made in CAD and glued it to the plate.

Then I put the box on the plate and drew the outline. I cut the marked pieces and the outline roughly and tried to fit the speakers and the threaded rods.

After being very happy about the clean look this has, I started grinding the plate until it fit snug inside the box. This takes quite a while, but it's worth it.

Now you can already add all the components like switches, jacks and the audio cable to the top plate. For the audio cable I used an old headphone cable, and soldered a stereo plug to the side where the cans normally are. So I ended up with a cable with plugs on both sides, that I secured with a simple knot behind the hole in the plate.

I added the template for download

deckplatte.pdf
Download

Step 5: Lower Plate

To hold the heavy batteries, and the little electronics we have, I made another plate. This time I used some thin wood I had lying around, and that is easy to cut. I used the same template as for the first plate, and only cut the outlines and the eight holes for the threaded rods to connect the plate with the whole construction.

Then I screwed the DC-DC converters to the board. This looks a little ghetto, but it works just great.

I fitted the batteries to the board and marked the outlines. Then I drilled the holes for the cable-zippers to fix the batteries.

Step 6: Bring It All Together

Now I cut two small wooden pieces and drilled two holes that matched the space between two threaded rods. These two pieces will fix the interior electronics inside the box, so they won't fall out. I measured the distance from the lower end of the threaded rods to the middle of the wooden pieces and placed it all inside the ammo box.

Then I drilled from the outside of the box right through the box and the wood. This way I make sure, that the two holes match, and it all fits tight.

In the next step I put the captive nut in place and test-fitted it outside the box, so it would not fall off, when inside the box.

To finish the build, I put the insides into the box again, and fixed it all with the two screws.

I also added two hinges to the solar panels, so they would fold nicely and cover the glass-side

In the future I probably give the box a nice paint job and get some leather straps to fix the solar modules to the box for transportation.

I hope u liked this instructable and enjoy building your own solar boom box charger!