Solar Bike Stereo




 In this instructable I will show you how to make a solar powered bike stereo box that fits in a milk crate, which you may already have on your bike!  This instructable assumes you have some proficiency in woodworking and soldering, and is really about the solar to battery circuitry and the options it provides.  This system could be used for any variety of applications that run off 12v DC.

In designing this project the box went through many phases, first it was battery powered, then the solar was added, and more extra bits kept finding their way into the box.  Because of this the photos will appear somewhat inconsistent, so I have provided some easy to read drawings for clarification.

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Step 1: Materials

  Parts you will need:
car speakers
solar panel (Sunforce 5watt trickle charge)
milk crate
tompsons water seal
milk crate
DPDT switch
M-F Audio Cable
Power jack and plug (to match whatever your amp comes with!)
8 threded inserts
assorted screws
  Tools you will need:
Soldering Iron
Table saw
Screw driver

Step 2: Cut List

I used 5/8" MDF and my box is waaaay heavy, you could easily do this with 3/8" or 1/2" MDF to save some weight but it will change the dimensions of your sides bellow.
  Cut sides:
1: 12" x 12" bottom
2: 12" x 9+7/8" sides
2: 10+3/4" x 9+7/8" speaker sides
1: 13" x 14" top
1: 10+3/4" x 9+5/8" divider

Step 3: Speakers

Cut holes in the center of two of your sides to match your speakers.  You can use a hole saw if your speakers are small enough, or drill a small hole and use a scroll or jig saw.  Solder about a foot of wire onto the speaker terminals and screw them onto the inside sides of your speaker sides so that they fit on the holes you just made.  You can round over the outside edge of your holes with a 1/4" round-over router bit.

Step 4: Glue Up

Glue the sides and speaker sides together to make a box.  Glue the diver in the middle flush with the bottom.  Finally glue the bottom on the box.   (You might want to make sure the box fits the crate before you glue it up, you may need to shave a 1/16" off all the pieces depending on the accuracy of your crate.)  Should look like the picture when viewed from the top.

Step 5: Fit the Top

For the top, put four of the threaded inserts into the top corners of the box and drill through holes that line up on the top.  The top should over hang about an inch past the back.  The top should also be the same size as the solar panel.  Mark the mounting holes from the soler panel on the top and install the other four threded insterts on those spots.  You should now be able to screw the top onto the box, and the solar panel onto the top.  I used 1" 10-32 square drive machine bolts for all of these.  You can optionally add a 1/8 pice of plexy glass with the same mounting holes as the solar panel on top of the solar panel to protect it.

Step 6: Connectors

Layout the holes for your power input jack, audio input, and switch on the front side of your crate.  Make sure they align with holes in your milk crate, I used one of the handle holes for everything.  Drill the holes and install the parts. 

Step 7: Solder

Solder everything to the switch based on this schematic.  What this all does is let you switch between running the amp of the battery versus running the amp off the included AC adaptor while the solar cpanel charges the battery.  This is important becasue you don't want the solar panel charging the battery while the battery is in use.  If the box is not connected to AC putting it into AC mode serves as a generic off mode, but the battery will still charge.  The solar panel comes with alligator clips; I just cut those off to use the wires.  All of the grounds (black wires) can be soldered together, just the positive (red) wires have to go through the switch.

At this time you might want to consider any other possible uses for 12v DC.  For instance, you could add a 12v car cigarette lighter outlet to power any accessories you hay have for one of those.  I took apart a 12v car to 5v usb adaptor and added that to my box so I could charge my usb capable accessories.  (You could even charge your ipod while it plays over the speakers.)  Just connect any 12v additions to the power cable that goes to the T-amp.

If you can, use speaker wire or some other shielded wire as it will cut down on the likelyhood of all your cables becoming antennae for background noise.

Step 8: Cables

 Connect all the cords and speakers to their appropriate inputs on the amp /  bettery / solar panel.  You can run the cables over the divider since it is 1/4" short where needed.

Step 9: PolyFill

The battery should sit in one speaker well and the amp in the other.  Fill the remaining space loosely with poly fill.  The divider prevents the speakers back noise from canceling each other out, and the polyfill keeps the back noise from bouncing back out the front of the box.

Step 10: Assembly

Put on the lid, panel, etc.  And put the box in your crate.  Finish with Thompson's Water Seal.  Won't be really waterproof, but will help if you get caught in the rain.

Step 11: Control

I use an iPhone mount on my handle bar and run a 1/8" to 1/8" sterio audio cable along my brake cables to the box.

Step 12: ROCK & ROLL

You're done baby, and now you've got a stereo system that can rival any car's, but mounted on your bike!  Sweet!

Get the Tunes Remote or Tango iPhone app and your friends can easily DJ music on your device, great for parties.

The Boom Bike was made possible by generous support from the ASU GPSA Graduate Research Support Program.

1 Person Made This Project!


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23 Discussions


5 years ago on Introduction
Heres a couple vids on the one I built.

I kept it a bit simpler than is shown in the site by leaving the switch off. I used Velcro to mount the amp and used its volume and switch. I have not built the lid yet but plan to make 2, one plane and the other with the solar panel.

I'm not using the solar panel most of the time because the battery will last a couple days so unless I'm camping with it, I don't think it will be too useful. I also want to keep the weight down. I'm not completely done with it yet. Im considering adding a phone charger in there and might use a cigarette lighter (male/female) setup as for it.


9 years ago on Introduction

And also, why do you not want to solar panel to charge the battery when the battery is in use? would that not be beneficial? or the point for that matter? from what i am reading it seems like in order to use this, the amp is not powered when the solar panel is charging?

4 replies

Reply 9 years ago on Introduction

 Right, if the battery is charging via solar, you have to run the amp through AC/DC.  The only reason I do not have the solar panel constantly charging the battery is because the solar panel operating instructions specifically said not to use the battery while it is being charged.  Don't know why.


Reply 9 years ago on Introduction

i asked my coworker about why you wouldnt want to charge the battery while its in use, and he mentioned that the battery's memory could get messed up by it discharging yet remaining at the same capacity. makes reasonable sense.

you've inspired me to create my own. i do not have a bike yet, but i frequent the beach and the wilderness so this is F***ing fantastic! thank you and keep up the good work!


Reply 7 years ago on Introduction

Sealed Lead Acid Batteries don't suffer from memory effect ... only NiMH and NiCad batteries have this problem. This leads me to wonder why the operating instructions say that? Perhaps this causes a problem with the built in charge controller on the Solar Panel? Does it even have a charge controller, or does it only have the diode to prevent reversal?


Reply 7 years ago on Introduction

after doing some Googling here is my best guess of why the warning exists.

If your amp is drawing 2 amps and you have it hooked up to the battery (not charging), then the battery will supply the full 2 amps---simple.

If you are charging your battery at the same time that your amp load is on, then your panel will supply .375 amps (optimally) and your battery will supply the remaining 1.625 amps.

Now for the BUT --- If your amp is on for too long and your battery can't supply the necessary current, then the amp might start trying to suck more power from the solar panel than it can provide---potentially causing overheating and damage to the panel(?).

PV arrays on houses are hooked up to batteries that are constantly being used, so I don't see there being any problem with charging a battery while there is a load attached. House arrays have better backup systems like a charge controller or a generator that can kick in if the batteries are getting too low. Since we probably don't want a generator in our milk crate we'll just have to mind our battery a little more closely.


7 years ago on Introduction

so great...I love it. Where in the box did you connect the grounds that you soldered together?

Also, am I correct in interpreting that there is nothing attached to the negative terminal on your battery?


1 reply

Reply 7 years ago on Introduction

Thanks. I think I soldered all the ground leads to a connector that plugs into the battery's negative terminal.


8 years ago on Introduction

Fantastic project with totally awesome results! I was wondering though, would it be possible to use a smaller solar panel? I realize the charge time would be increased, but the application I have in mind would be best with a smaller panel. (also a little cheaper) Sunforce seems to make durable panels, so this was the panel I had in mind -

1 reply

Reply 8 years ago on Introduction

I don't see why not. The total amp hours of your battery will determine how long it takes to recharge. With a smaller panel it could take more than one day to recharge a decent sized battery.


Reply 8 years ago on Introduction

I scavenged a lot of it, but basic run down is:

$60 - solar panel
$50 - Amp
$20 - Battery
$70 - Speakers (Car audio I recycled from another project)
$20 - Other stuff (wire, switches, MDF, etc)
$220 - Total

But you could probably save a bunch using different speakers


9 years ago on Introduction

How long would it take the battery to charge from being completely dead? How long does the music last once it's at full charge? Thanks!

All I can say is, Flogging Molly rock and should rightly be played from a moving speaker in public places!


9 years ago on Introduction

 I had a thought about making the boom box so its always charging a battery when its playing music in the sunlight. i came up with using two batterys and no ac/dc plug bc i havent figured out how to wire it. i'm having a hard time wrapping my head around how you soldered all the ground wires together and just put the positives in the switch. i plan on using a knife switch for aesthetics, and thats got me all confused. could you help me out? i drew up this diagram of how i am thinking it should go. 

thank you in advance!

SBB Diagram.jpg
1 reply

Reply 9 years ago on Introduction

 That looks like it would work for two batteries, neat idea.  I really did just solder all the ground leads together.  Yes, it was a big lump of wires all in one place, but yes it does work that way.  You don't have to worry about the grounds being switched on and off - it's important that they connect to the same ground so you don't build up charge somewhere else in the circuit.


Reply 9 years ago on Introduction

 It's a good question.  The way I have it set up, no.  The solar panel has a built in reverse diode and cut off so it doesn't over charge the battery, which would be a problem if you just connected the battery to the AC.  I imaging with an appropriate battery charging circuit you could throw something it there that would let you charge the battery off the AC, too, but that's what the sun is for!

Nicely done! I really like the fact you now have a self contained "sound cube" that could be taken anywhere there is sunlight. Just ploop it down, add an MP3 player, instant party.