NOTE: I wrote this 'ible before I had a comprehensive understanding of electronics. This is a rather bad idea and will most likely wreck your battery. It seemed intelligent at the time. Oh well, live and learn.
Adding a jack to the battery of a cordless tool so you can run it off of wall current and keep it close to full power all the time. This might not be the brightest idea to do with NiCd batteries, but if you have a skunked battery you can't lose much.
I decided to do this project with the Black & Decker Firestorm 18V system, but you could do it with nearly any cordless tool set.
Things you'll need:
-Cordless battery and charging unit
-Soldering iron and solder
-Something to dismantle your battery (In this case Hex wrenches and Torx bits)
-Two wire quick-disconnects (they usually come in male-female pairs)
-Power drill and bit
-Knife or x-acto
You may also want:
-Hot glue gun or epoxy
Step 1: Dismantle Your Battery
-This will void every sort of warranty you could hope to have. Proceed at your own risk
-Discharge your battery before working on it. This should be a no-brainer
Each battery is made differently, so I can't give specific instructions on how to take it apart. Mine involved really annoying hex screws that refused to budge. Then I realized they were Torx - hey this is a learning experience. So I got a Torx10 bit and took it apart.
You should be left with two halves of a case, the cells, and possibly some springy do dads.
Step 2: Find Your Anode and Cathode (+ and -) and Wire the Quick Disconnect to It
Locate your anode - this is going to be usually white or red. If you've forgotten your cell setups, this is the positive terminal. In my battery there was a white wire for the anode and a common cathode (a plate that just connects all of the cells' cathodes).
Drill a hole in the side of the battery casing so that it's convenient to run a cord out of.
Run the wires of the quick disconnect trough the hole. It doesn't matter which one you use, as long as you use the opposite one for the wall unit end. For my example, I used the female, so the wall unit will be male, so on and so forth.
Wire positive (red or white) to positive and negative (black) to negative). Solder the wires, being careful not to damage the cell.
Step 3: Reassemble Your Battery
Put the battery back together. You will probably have to force it a bit in order to get the wires to fit in the casing. Also, make sure to put back any springs or things that lock the battery to the tool. I used QuikGrips to hold it together while putting the screws back in.
Step 4: Modify the Wall Adapter
Now to modify the power cube to attach to the battery. Since you're going to be drawing a bit more current, you will might have to replace the original cable. Mine was mysteriously cut a while back, so I used the opportunity to upgrade to an extension cable.
Cut the power cube from the part that clips to the battery. If you're going to replace the cord, leave about 1.5" on the power cube end. Otherwise, cut it 1.5" from the battery clip and skip to soldering the quick disconnects.
If you decide to replace the cable, cut it to the length of cord you want. About six feet is good for most uses. On each end, make a cut about 3" from the end so you can open the outside case like a pea pod. Pull the wires out, and cut out the ground if there is one. Cut 1.5" off of the black and white wires and strip the last half inch. You should be left with two 1.5" wires with the last third stripped.
Strip a half inch of the wires from the power cube, and solder those to the ones coming out of the cable. Do the same for the quick disconnect (male) at the other end of the cable. Wrap each of the interior wires with tape, tuck them inside the cable, and tape all around that.
If you still have the battery clip, you can solder on a (female) quick disconnect so that you can still use the charger as is by plugging the clip into the modified wall unit.
Since quick disconnects usually come in pairs, you might have a leftover male adapter. You can use this as an auxiliary charger, say if you wanted to charge from a lead acid battery, or zap it with an arc welder to reset the cells.
Step 5: Finished! - Using the Power Tool
The battery and charger should be all set now. NiCd batteries are a pain in the ass sometimes because of dendrites and charge memory and stupid stuff like that, so I think the best way to use this system is charge the battery full, then use it with the cord most of the time. The wall unit as is doesn't have the capacity to run a power tool by itself, but the fully charged battery gives it the extra oomph. In between usage, the battery recharges, effectively allowing you to use the tool at full power all the time. Of course, if you have it running nonstop for long periods of time, it's gonna run down; furthermore this is a bad idea because you might overheat some of the components.
I've found that with moderate usage my tools have, if anything, more power than they did before. I haven't put them through serious testing yet, but when I do I'll post an update.
Pretty much the main reason I used the original batteries is they keep the electrodes in place. Given more time and money, I would have gotten some 18V capacitors and replaced the cells with those.
This is my first instructable so let me know what you think!