Introduction: Fix a Broken Power Plug on a Cordless Drill

When I first got my 18 volt cordless drill, I had come concerns about charging - you had to plug the adapter directly into the drill, and the center pin was extremely long and tiny, so eventually the pin snapped off inside the adaper and the drill stopped taking a charge. I fixed it by removing the broken plug from the drill and replacing it with some quick-disconnect fittings I had lying around the shop.


- 1 broken drill
- 1 matching wall wart
-  Lineman pliers in lieu of a crimp tool
- Screwdriver
- Multimeter
- Wire connectors
- Spare wire
- Pocket knife

IMPORTANT: This is a DC circuit. DO NOT CROSS THE LEADS. If you're not sure what you're doing, get someone experienced in DC circuitry to help you.

Step 1: Taking Apart the Drill

I started by removing the battery and taking the case screws out of the drill. Make sure you note which screws come out of which holes, as some of them are longer than the rest. Also, take care with the trigger assembly - mine came apart when I was putting the drill back together and wouldn't reverse direction until I fixed it.

Once you get the drill apart, you can see it's an elegantly simple device: a motor, a relay and transistor to control it, a power source and a switch. The power plug is wired directly into the connector for the battery.

Step 2: Wiring

The first step in rewiring is to determine the polarity of the adapter. If you're lucky, the polarity of the barrel connector is marked either on your drill or on the adapter; I was not so lucky.

If you're unlucky like me, start by removing the connector, making sure to leave enough wire on the connector to hook the multimeter lead to.  Set your multimeter to continuity mode, then clip one end to one of the wires coming off the connector. take the other end and touch it to the outer barrel of the connector, then the inner sleeve to determine which is the contact point for that wire.  Turns out on my drill, the wire with the stripe was the positive lead... good thing I checked!

Next, check the wires connecting to the plug on the drill - on mine, the red wire running to the center pin was the positive lead, and the barrel was the negative. So, for me that means the wire on the adapter with the stripe needed to connect to the red wire in the drill.

I wanted to make sure I could charge and use the drill safely, so I wanted to A) use covered connectors, and B) make sure it was impossible to cross them, just in case someone other than myself needed to charge it. I used a red barrel connector for the positive lead, and the blue spade connector for the negative.

There wasn't enough wire in the drill assembly to be able to have the connectors fit, so I used a bit of spare wire and a couple crimp connectors to extend the plugs outside the drill casing.

Step 3: Reassembly and Final Thoughts

Put the drill back together and charge it up!

Some things I learned through this project:

- Make sure the connectors you use are good quality and the right size for your project. Also, invest in a quality crimp tool if you haven't already.

- Use shielded connectors to minimize the risk of a short circuit. Since the connectors I used are only shielded on the drill side, I have to make sure I unplug the wall wart before disconnecting it from the drill. Small price to pay for not zapping my wrist every time I go to build something.