Introduction: Solar Charged Stereo Cooler
This instructable outlines a portable solar charging station, stereo, and LED light that is built into a playmate cooler. It is an all-in-one portable unit, as you can charge your phone or tablet with solar power, fill a room/beach/field with music, and also have an area light.
You can set this up at your home for everyday charging of your devices, and easily bring it with you for a day on the beach, on a camping trip, or anywhere else. It can be very useful during power outages, or even be a prime source of power in an off-grid cabin or home.
The design of this unit is very flexible, and you can choose features or expand on this to meet your specific needs. You can also take advantage of using scrap parts for its construction, with old car audio components, scrap wood, and spare wire that you might have lying around. I've found that you can borrow from a lot of "car accessories" that are 12V DC powered, or even use a small inverter for AC loads, to use this solar power for a wide range of devices.
Step 1: Parts
I chose the 16 Quart Igloo Playmate cooler for this build, since it's big enough to hold everything, but still small enough to carry with one hand. The roll top is also quite useful, and makes access to everything very easy. (~$20, Target/elsewhere)
I used an scrap laminated bookshelf to mount everything on. I've used thin plywood for this before, but a thicker piece of wood makes the acoustics much better. (free/scrap)
Any standard 12V auto/marine stereo deck will work. I used a basic marine unit, since it somewhat more water resistant than a standard car deck. The cheaper units are "Mech-less" and have no cd-player. You could reuse an old unit, and go pick up a used deck from a junk yard / scrap exchange. ($30+ depending on features, Amazon/elsewhere)
I used a pair of 5.25", 150 Watt, 2-way marine speakers, which fit quite nicely given the playmate dimensions. While you could use regular car speakers, marine speakers are waterproof (in theory) and are usually built to take more impact and abuse. Again, this is a spot where you could pick these up on the cheap as used car parts. (~$20, Amazon/elsewhere)
Small 12V AGM lead-acid batteries are very easy to find, as they are used in computer UPS units and fire-alarm systems. Like all batteries, their capacity is rated in Amp-Hours (Ah). Choosing the battery size is a trade-off between Ah capacity and weight, as this is by far the heaviest part. I chose to use two 12V, 8Ah batteries (wired in parallel for a total of 16Ah). At moderate volume, my stereo draws approximately 1 Amp, so in theory I could play music for 16 hours if I drained the battery from 100% to empty. Admittedly, this is overkill, you could get by with 5 - 10 Ah. (~$20 for a 8 Ah battery)
Solar panels are getting cheaper by the day, and you can find a small one on eBay or elsewhere fairly easily. Since the battery is 12V, you want a solar panel that is rated for 12V. The "open-circuit voltage" of a 12V solar panel will be around 18V, but the charge controller will prevent overcharging. The size of the panel should depend on the battery size. As a starting point, I would suggest matching the wattage of the panel to the amp hour rating of the battery (10 Ah battery, 10 W panel), but also considering what loads you will have (a stereo will draw 5 - 20+ W). A 10 W panel will have an effective charging current of approximately 0.6 amps (10W / 18V), which will charge your battery from half to full in about 8 hours of full sun light. I used a 10W solar panel, but this will depend on your needs. (~$35 for 10W panel, ebay)
If you want to charge the system with a solar panel, you will have to use a charge controller to connect it to the battery. These devices regulate the battery voltage and disconnect the solar panel when fully charged, preventing overcharging and damage to the battery. Find one that has a current rating greater than the "short circuit" current rating of the solar panel (the smallest you will see are typically rated for 5 - 10A). A basic unit will do, but I chose a nicer one that has the PCB sealed in epoxy, making it moisture tolerant.
Some units will have a low-voltage disconnect (LVD) function, which will shut off the loads if the battery voltage gets too low, preventing damage to your battery. ($20-$60, Amazon/elsewhere)
- Multiple DC toggle power switches ($5)
- Fuses and fuse holder for different DC loads ($10)
- 12V cigarette ligher socket for accessories ($5)
- Short lengths of wire (scrap/free)
- Drawer handle, to pull the faceplate out ($2)
- LED lights ($10)
Total project costs:
- As built: $250
- Basic components, with same features: $150, (less with used audio parts)
Step 2: Speaker Mounting, Battery Placement
A dremel works well to cut through the cooler, as it's soft plastic and foam. When cutting out a pattern, I like to draw the shape on a piece of paper, and rubber cement it to the piece. This makes it easy to follow the lines as you cut.
Once the holes are cut, pop the speakers in and screw in the 4 screws for each speaker. Drill pilot holes, but set the screws BY HAND, as the foam is very soft and it would be easy to strip it away with a drill. Apply a bead of caulk around the edge of each speaker to finish it up, making it more water resistant.
Choose a place for your batteries. Use some scrap packaging foam to prevent the batteries from sliding around. Foam is lightweight, and easy to change in the future. I've found that more secure mounting isn't really necessary, but you could always put in a bracket to hold them down if you wanted to.
Step 3: LED Strip Placement
Mounting lights on the cooler is entirely optional, but it's a nice feature to have if you want an all-in-one unit for power outages, camping, ect. [Another option would be to plug in 12V DC lights to the auxiliary socket on the faceplate.]
These surface mount LEDs are cheap, waterproof, and come with adhesive on the back. Start by cutting 3 or so strips of equal length, and solder leads onto each of them. Encompassed the solder joints in a little hot glue, and then covered it up with some heat shrink tubing if you have some.
Note where you want to run the power wires from the fuse block up through the faceplate, and into the cover (probably one end of the cooler or the other). Then removed the sliding cover to the cooler (just pop off the white caps, and remove the single screw on each end). Drill a hole for each LED strip, keeping the hole just barely big enough to fit the wires. Next, feed the leads through the hole, remove the adhesive backing, and slap them in place. Add a little caulk to seal each hole.
Using wire nuts, connect all of the positive (+) leads together along with a ~2 ft wire so you can connect them to the fuse block later on. Do the same for for all the negative (-) leads. Secure these far enough from the edge so that the top can still roll freely. Put the lid back on.
Step 4: Component Mounting on Faceplate
Cut the the wood you are using to the proper dimensions, and checked to make sure it fit in the cooler nice and snug (you'll have to round off the corners to get it just right).
I drew out my faceplate on Inkscape, using the correct dimensions for each component, and allowing enough spacing between each. Also include holes for wire access to the charge controller and solar panel. Keep in mind the faceplate will sit on top of the speakers and the battery, so you will have limited space above these components. Again, I printed this out and rubber-cemented it to the wood.
Next, drill out the holes on the template. Then, cut out the rectangle for the stereo. I used a coping saw for this, but it would probably be easier with something like a jig saw if you have one. Once all your holes are cut, peel off the paper template and start putting everything in!
Step 5: Wiring
Now you can start wiring everything up.
There are basically 3 different circuits (1) loads, (2) batteries, and (3) solar panels. For each of these, you will connect everything in parallel to the charge controller, which isolates each circuit from the others. You MUST have a dedicated fuse installed in series with the battery. For the loads, instead of having individual fuses for each load (as shown), you could also lump this into a single fuse for all the loads. Other than that, the theory of it is pretty simple.
In practice however, it is difficult to keep everything organized and wired properly. As you can see, it can quickly become a jumbled rats-nest. I like using crimp on connectors, and they are fairly common amongst auto/marine 12V devices. I recommend lots of zip-ties and adhesive pads, or whatever suits your preference.
Follow the specific wiring instructions for your stereo unit. These units will typically have two connections to power. One is meant to remain attached to the battery, regardless of on/off state to retain the onboard clock and radio presets - the second serves as the control signal to turn the unit on and off (which I would recommend you will wire in series with a toggle switch). Other than power, you will have connections to your speakers, as well as at least one for an antenna. You can easily just solder/crimp on an extension to the antenna lead, which has typically worked fine for me, but you can also buy a dedicated (marine) antenna for this purpose.
Step 6: Testing
While I haven't done an exhaustive test of the battery life yet, I have gotten several hours out of the unit without recharging it. Assuming that you have enough sun to re-charge it every couple days, there would be no need to charge it from the grid (although you always could).
The solar panel that I bought perfectly fits on-top of the faceplate (out of dumb-luck), and is a great way to store it during transportation. I've also found that the top of the cooler is a great place to store your phone when you're on the beach, and can keep it dry and out of the sand (not to mention charging it!).
I've used a standard SAE plug to connect the solar panel to the system, and a 2' cord wired into the panel's junction box. With this approach, you can use standard 'battery charger' SAE extension cables (15' for example) whenever you need the a greater distance between the cooler and panel. This allows you to get the panel in the sun while you keep the cooler indoors.
You can store the extension cable and any other accessories below the faceplate, as long as you've kept it easy to access.
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