I bought myself a cheap cordless drill 7 years ago, and it has been a fantastic tool, considering the price I paid. The only problem with it was that a few years back one of the two batteries it came with died, followed by the second one recently. I had a look around for replacement battery packs, but the only option I found cost as much as a new drill would.
Not wanting to throw away what was essentially a perfectly good drill, I had a look around the Internet to see if I could convert my cordless drill to run off AC power. Unfortunately I didn't find anything remotely useful, but I did find this Instructable that showed how to convert a drill to lithium batteries. After reading through it, I decided I'd have a go at converting my drill to use LiPo batteries. I decided that I wanted to be able to make the conversion without taking the drill itself apart. This is how I did it.
Step 1: Tools and Materials
You won't need too many tools for this:
- Wire cutters
- Soldering Iron
- Hot glue gun
You'll need the following parts:
- LiPo Battery (see below for some notes on what to look for in a LiPo)
- Battery connector to suit your chosen battery
- LiPo Voltage alarm
When choosing a LiPo battery, the first thing to do is check how many cells you'll need. My drill had a 14.4V battery, so I need a 4 cell (or 4S) LiPo. The next choice is battery capacity, which to some extent will be determined by the space inside the existing battery pack. You'll need to make sure whatever battery you pick can fit inside your drill's battery pack. My existing battery had a 1300mAH battery, so I figured if I had something at least as large as that I'd be good
Step 2: Take the Battery Pack to Pieces
The battery pack on my drill was held together with 5 screws, and easily separated into two pieces when these were removed. The battery is connected to the top half with two wires, which I clipped off as close to the battery as possible. With the battery out I turned my attention to the connections at the top of the pack. The existing wires are soldered to the connectors, so it would be a simple matter to replace them with the XT-60 connector for my new battery.
At this point I measured the space inside the pack to determine what size LiPo pack I could fit inside it. After much browsing of web sites I settled on a 2200mAH ZOP Power LiPo from a Chinese retailer. Sure, I'd have to wait nearly a month to get it, but it was stupidly cheap.
Step 3: Attach the New Battery Connector
The new battery has an XT-60 connector, so I removed the battery connectors, soldered them to the appropriate style connector and replaced them back in the top part of the battery pack. At this point it's really, really, really important to make sure you keep the positive and negative wires in the right place. I marked the inside of the battery pack before removing the original wires to make this easy to remember. Trust me, if you get it wrong you could end up letting the smoke out of your drill.
Step 4: Fit the New Battery
Having received my new battery, I proceeded to install it in the bottom half of the battery pack. It was at this point that I discovered that my measurements weren't exactly accurate, and that the battery didn't fit. In the end I cut out the screw mount at the end of the battery pack. I figured that one less screw wouldn't be a big issue.
With the battery now fitting snugly, I cut a small notch for the batteries balance cable to come out through. We need access to the balance connector for charging the battery, as well as connecting the voltage alarm to. It's important to use a voltage alarm, as discharging a LiPo battery too low will cause it to fail, often in a dangerously spectacular fashion.
With the notch cut I reassembled the battery pack, making sure that none of the wires were pinched, or that the battery was being squashed. I took the voltage alarm, connected it to the balance cable and hot glued it into place. With that done I plugged it into my drill, and prepared to test it. It was a huge relief when the drill worked as expected.
Step 5: Charging the Battery
Prior to this I've never charged a multiple cell liPo battery before, so wasn't sure if I needed to connect the charger to both the balance cable and positive and negative wires. After a bit of playing around I found that I needed both connected for my charger to charge the battery. I was now stuck, because to access the battery's XT-60 connector would require taking the pack apart.
I considered making an adaptor that could plug onto the battery pack, but remembered that my drill had an adaptor that connected to the battery, and had a socket for a power pack to plug into. I took this apart, and found that there was no fancy circuitry inside, just a diode for protection, a red LED and a resistor to limit the current through the LED. This meant I can simply use this to plug my liPo charger into whenever I need to charge the battery. Score!
Step 6: Final Thoughts and Conclusion
There's one thing to consider that I haven't yet mentioned. LiPo batteries have a discharge rating (C rating), which affects how much current the battery can deliver. Too low a C rating could limit the performance of the drill. I was unable to find any information about what a suitable C rating for a drill would be, so I opted to get a fairly high (65C) rated battery.
Altogether this project cost me just under $35 Australian, much cheaper than either a replacement NiCad battery pack, or a new drill. I'm extremely happy that I've been able to resurrect what is a perfectly good drill, and not have to add one more bit of rubbish tot he local land-fill. My next task is to put a 5S LiPo in my father-in-law's cordless hammer drill that he's misplaced the charger for.