Imagine you're out camping, or just living in your van full time, and you really need to fix something. Like when your hammer breaks and you can hardly get the remaining pieces of wood out if it before fitting a new handle. Or you just really want to make and build something awesome (this is instructables after all). Wouldn't it be great to have some power tools on hand?
Problems with power tools is that they need electricity. Even battery powered tools need to be recharged quite frequently, and the chargers usually only work on 120/240V. Let's find a way to make them work on your 12V off-the-grid solar power in your van, or just the normal 12V system in your car.
Step 1: Stuff You Need
Of course, you need some battery powered power tool. I have a Bosch battery powered drill that I used a ton, so we'll use that for reference.
Then, you need a charger that can work with your battery and operates on 12V. I've had this one from Hobby King for a while, and just recently find out it also works great for what I'm describing here. It also came with a bunch of different cables for connection to the battery you want to charge, including one with alligator clips, that I'll be using on my battery.
My charger came without a cable, so I got one to connect the charger to the solar system in my van. It has a standard 12V car plug on one side, and a 5.5mm/2.1mm DC plug on the other side.
Lastly, it's good to have a multimeter on hand for checking battery polarity.
Step 2: The Battery
There are different types of batteries, and they are charge in different ways. So it's good to know what battery type we're dealing with.
My batter powered drill is a few years old already, and uses a NiMH type battery, rated at 12V. Those batteries are usually made up of multiple cells, each of which is rated for 1.2V (standard voltage for NiMH cells). So we're dealing with a 10 cell NiMH battery here. Luckily my charger can handle that sort of battery. If you're buying a new charger, make sure it can deal with your type of battery as well.
A lot of newer battery powered tools use Lithium Ion batteries. Lithium Ion batteries are usually also made up of multiple cells, with a default voltage of about 3.7V per cell. They are a bit more tricky to charge, because different cells charge at different speeds. RC batteries have special connectors to deal with that, but our power tool batteries normally don't, so be extra careful when charging those, and choose a lower charging current in the next step.
Step 3: Figure Out the Polarity of Your Battery Contacts
Your battery will have two or more contacts. You need to figure out, which contacts are used for charging, and what their polarity is. On my battery, there are two contacts, one on each side, which are used for charging. I took the alligator clips from the battery charger, and hooked the banana pins on the other side of the cable into my multimeter (set to measure DC voltage, up to 20V).
Now it should show you a voltage somewhere around the rated voltage of your battery. If not, you should try some different contacts. If the voltage is negative, as in my first picture, the alligator clips are connected the from way, so just switch them and you'll be good to go for charging.
Step 4: Charging
Plug the charger into your 12V van power socket. Do not plug in the battery yet. Choose the proper battery program, in our case "NiMH Battery", then the "Charge" mode. There's usually other modes as well, such as discharge, which should be explained in further detail in your charger's manual.
The charger will ask for the current you want to charge your battery with. The original charger charges my battery in about 3-4h. With a 3000mAh battery, that means it puts at about 1A of charging current into it (well, not quite, there's a bit more math behind this, but let's not make it too complicated). I like to play it a bit safer, and have enough time, so I set the charging current to 0.5A (less current is also good for your battery lifetime).
After having set that, plug the battery into the charger, and start charging. This might take quite a while, but the charger will most certainly let you know with some annoying beeping when the battery is fully charged.