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In this instructable I will show you how to build a sealed battery box. It's not completely water tight but rain is no problem for it. Since building this I have found it to be a great mobile power supply for many things even running power tools while camping where there are no electric hookups.

The intro pics show it in 12v (series) & 24v (parallel). The switch in this instructable is a DPDT switch and it is the heart of the setup. One thing to note is that since the time I put this battery together I found that the switch in the pictures was expensive and it had a fatal (to the switch) mechanical failure. I will post the part number and where to find it but I'll also provide the replacement switches that are cheaper and work better. Here is what you will need to buy or acquire to make this exact setup:

  • A junction box from The Home Depot (Find/Buy it here) *The bigger version is the only link online. Go in person to the store to see the one I use in this ible.
  • Dual Polarity Dual Throw (DPDT) switch (Original: Find/Buy it hereOR Better ones: Find/Buy it here)
  • Wire. I prefer 14 gauge but 18 gauge from a standard computer pcord18/3 will do (Find/Buy it here)
  • Plugs... male & female connectors. (Find/Buy it here)
  • Quick connect terminals (Find/Buy it here)
  • Batteries. I use 12v batteries. I have SLA/Li-Ion/LiPo because I like them but the choice is yours for what you want. The link takes you to where I get them locally. (Find/Buy it here)
  • Epoxy (Find/Buy it here)

Step 1: Cut the Wire to the Right Length

It's pretty straight forward. I used the diagonal length of the box so that the wires will have no problem reaching anywhere in the box. You need to cut 3 red and 3 black segments. You will also need a small piece no more than 3 inches. So the final total is 2 for each battery, 2 for the external plug and a small 3 inch piece for internal wiring. You could shorten the wires that go to the external plug if you want I just wouldn't skimp on the battery wires.

Step 2: Solder the Clips on the Ends

Bust out your trusty soldering iron and attach the ends on. They are crimpable too but I don't own a crimping tool so solder it is. You could also put clips on the small segment of wire if you want to make it easy to remove.

Step 3: Place External Plug and Make Hole for Switch

I apologize for lacking some detailed pictures with this part. It's up to you to drill a hole the right size for your switch. The detail I would have liked to have more pix of is the epoxy although I do assume that you have certain skillz learned in grade school or shop class... like gluing things together...

So, cut the holes to fit the plug and then mix your epoxy and put it around the edges. It sets in minutes but should be given 24 hours to cure completely. Don't glue yourself to it because it's not pretty.

Bust out your favorite drill bit set and find the one that best fits to make the right size hole. I put a piece of electrical tape down to make a tighter seal around the edges and then I cut the exposed tape with blade and it looks nice and clean. Attach the optional rain cap to the switch if this is the kind you choose to use even after I warned you. ;)

Step 4: Wire Up the Switch

This is the very important part. The wiring is easy but if done wrong it can cause a short and some very bad results. For this part I will be passing the ible time to DieCastoms and he will show you how to wire up a SIMPLE Parallel/Series Select Switch.

Once you finish with his ible you only need to make sure you don't get your battery leads mixed up so I had some zip ties handy. You can use whatever you want to pair them up accordingly.

Step 5: Place Your Batteries in the Box

Again, pretty straight forward. Put the battery in the box no lotion required. Secure them in however you want. Ultimately I just stuffed old newspaper between them and it was very snug. Velcro could be a good way to go too...

Step 6: Close It and Test It

Attach the clips to the batteries and place the cover on the box. This one has screws so you know what to do there. For testing we get the volt meter out. The switch has 3 positions (On-Off-On) series, off and parallel.

Congrats! If nothing burned then you did it right! Feel free to adapt all sorts of things to that like an Ebike or a drill or anything you like!

Step 7: Update: the Better Switch

As I mentioned, the switch had a mechanical failure. Here are the pix of the new switch and the setup. Much cheaper and no failure yet. I like to keep on top of my comments so don't hesitate to ask questions or if I you may need more clarity on things. Enjoy!

<p>can you charge the batteries through the wiring?</p>
<p>Yes, I have a good 12v charger that I adapted a plug to. all I have to do is make sure that it's in 12v mode on the switch and charging goes great. Since this post I've used this to power an electic chainsaw in the middle of nowhere and it did excellent!</p>
<p>I must say, I have been pleased that my simple Ible has seen action over the past TEN years that it's been up, but I am Honored that you have referred your own readers to it! I've had it used in a swamp cooler, an EBike, a massive RC car, even an electric guitar over the years and never cease to be surprised when I get a new question about it, so long afterwards!</p><p>I LOVE that you've built your supply within a junction box, it is not an idea I would have had! It looks like you've done a very tidy and clean job of it! I'd be curious about adding a recess in the top cover so that the switch and the socket are below the top surface but otherwise, I might copy your idea in-turn!</p><p>Last, I am curious what the mechanical failure actually was? A switch that is &quot;Make before Break&quot; makes contact with the second set of contacts before breaking contact with the previous set when being switched and will eventually fail due to electrical arcing (temporary shorts). Break before make switches will overcome that, and so will 'center-off' switches.</p>
<p>Copy away just post &quot;I made it pix&quot;! I've used these junction boxes for lots of things including blanketing a small city with distributed wifi. They just rock and they are waterproof if you do things right. I like your idea of a recess and would love to see pix of that when you get it made. As for the switch failure, I didn't see any evidence of burning or heat issues for arcing but I did find that the orange plastic on the switch just cracked and it was the part clipping it to the metal piece so the whole thing just fell apart underneath. It was just a mechanical failure. It was during a camping trip so maybe it got bumped in transit to the campsite then when I was switching it the plastic gave way. Still sad about it because I did thing the first switch was sexier but I need something reliable and if cheaper then the better.</p>
<p>Nice work!</p>
<p>Thank you very much. It was an enjoyable exercise in creativity.</p>

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Bio: I'm a DIY ideas man. I constantly strive to create my own products including tools. I'm actually a master of misusing/reusing things ... More »
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