A few years back I made some 12-volt battery packs following a design made by a friend. Since then I have used these batteries on different occasion with great success. So today, I am going to post the original article with some additional suggestions that I have learned from practically experience.
Here is the first article on battery packs
You can make your own
A friend of mine made some battery boxes using 50 cal ammo cans and 12-volt burglar alarm batteries. They are very nice compact units that will provide 14 amp hours of power. I have built a couple of them and they work well. I have used them to power 12-volt lights, but they have many other potential uses.
What they consist off is a 50 cal ammo can in which you drill a hole for the female half of the cigarette charger. The hole should be about 1 ½ inches from the top of the can. You then take two 12 volt 7 amp hour batteries and wrap them in Saran wrap. Place the Saran wrapped batteries in the can next to each other. Fill the can with spray foam insulation. It comes in a spray can and you can get it at Home Depot. You don’t want it to cover the batteries, just hold them in place. The reason for the Saran Wrap is so that in the future you can exchange the batteries without removing the foam.
Now complete a simple parallel circuit running from the two batteries to the cigarette charger. Place
a 15-amp fuse in the hot side (the red wire) just before the charger. There are a couple of different ways in which you can charge the box. One way we have used is to take an old 12-volt wall charger and attach the male half of a plug that will fit the cigarette charger. The second way is to use a solar charger. To preserve the maximum life of the batteries the rule of thumb is to never charge more than 10% of the charge of the battery. In other words, these two batteries total 14 amp hours, so you should never charge at a rate of more than 1.4 amp hours. This is about a 20-watt solar panel. If you are using a bigger panel, you will need a controller.
We are currently working to improve these units, if you have any suggestions they are welcome.
Since then we have made a few changes although I am still using the original design, some friends are using the improved versions.
- The new plastic ammo cans work well and are lighter.
- I always crack the top open when using or charging the battery pack. The friend who uses the plastic ammo box has drilled small vent hole in his so that he can use it or charge it with lid closed.
- Soldering makes a better wire connector than the blade connectors.
- You can use different size batteries such as the UNIVERSAL POWER UB12220 12 VOLT, 22 AH SEALED AGM BATTERY which provides more amp hours.
- I used a standard spray foam insulation which will burn.. I suggest that you use Fireblock Insulating Foam Sealant
These battery packs work every bit as well as some of the very expensive ones currently being sold on the market. With a little bit of thought you can make these in larger sizes. In a few days I will post more information on how I have been charging these battery packs with solar panels.