Introduction: Extending the Life of a Cordless Drill (by Adding a Cord)

Is the battery of your cordless drill dying? Do you want to use it for long periodes without having to wait for the battery to recharge? Don't spend your money buying new batteries, add a power cord instead!


Well, batteries are expensive.

Cordless drills are often sold for very little money, but they lock you in to a battery system from whatever manufacturer you bought, and those batteries are expensive. There are of course other brands that sell replacement batteries, but these usually carry a lot less charge, and aren't much cheaper. These are even more of a scam than the batteries sold by the original manufacturer.

Okay, so are you ready to give it a try?

Step 1: Materials & Tools

For this project, I assume you are at least familiar enough with electricity to know that simply plugging the drill in to the mains power of your house isn't going to work, and that you have soldered before. I will give an alternative method if you don't feel comfortable with a soldering iron, but if you have access to one, I recommend using it.

The tools and materials required for this project:

  • Old battery from your drill
  • Soldering iron & tin wire (or a few terminal blocks if you don't feel comfortable soldering)
  • Wire strippers (if you don't have one, you can also use a pair of scissors or your teeth)
  • Two short lengths of heat shrink tubing (can also be replaced by two short lengths of electrical tape if no heat shrink tubing can be found)
  • Screwdrivers
  • Multimeter
  • 12v power adapter*

*Finding the right power adapter can be hard. It needs to be 12V DC with around 10 Amps.

Unfortunately, not all power adapters list the same specs in the same way on the same place.

First, you need to look at the OUTPUT voltage, not at the input.

The voltage is usually a number between 3 and 24 followed by a capital V.

(you need to find one with 12V)

Second, determine that the adapter is DC, and not AC.

AC voltage is very different from DC voltage, and will most likely break your drill, so pay attention. AC is marked simply "AC" ore more commonly with a little wave ( ~ ). DC is either marked DC or with a line with three dots under it ( ⎓ )

Third, and probably hardest, find an adapter with enough amps to support your drill. Depending on the speed of your drill, you wil need an adapter with around 10 amps. Fore some slower drills 5 amps could be enough, but if you have to go out and buy an adapter, I recommend going with 10 amps to be safe. the amount of amps is either given by a number between 100 and 900 followed by mA (milliamps) or simply a number between 1 and 999 followed by a capital A.

100 mA is equal to 0.1A

Please note:
I am no expert, and although I have tried to explain this as simply and clearly as possible so that anyone can follow this guide, I take no responsibility if you break your drill following this guide, or electrocute yourself. Always be careful wen playing with electricity, and don't touche the high voltage stuff unless you know what you are doing.

Also note:
Soldering irons get really really hot. Don't toch the metal part when plugged in and for at least the first half hour after unplugging it.

Step 2: Disassembling the Battery

The first thing to do is to take apart the battery for the drill to reuse it's plug.

Locate all of the screws on the outside of the battery casing and undo them. These may be six sided star-shaped screw heads called "Torx", so you may need to buy a specific screw driver, or find as many flat headed ones as you can find, stuff them in, and hope for the best (done it before, sometimes it works, sometimes it completely destroys the head of the screw).

If you've undone all the screws but can't get it open, look for hidden screws under a label of plastic seal. these can be hard to get to, but with a small knife or flat screwdriver, they can usually be removed so you can get to the screw.

If you don't see any screws at all, the casing may simply be held together with clips. Put a strong piece of plastic or an old credit card into the seam, and try to pry it open. If that doesn't work, you may have to use a bit more force and saw open the casing.

Be very careful with the batteries inside when using a saw.
We don't need them, but they can contain chemicals you don't want to get on yourself or on your floor.

Step 3: Disconnecting the Battery Cells

Inside the battery should be a series of battery cells chained together. Sometimes they can be inside another protective casing, this can also be removed.

There should be a black wire and a red wire going from one end of one of the battery cells, to a metal part of the connector plug. Desolder or cut off these wires on the side of the battery cell, not on the side of the plug!

If both wires are the same color, you wil have to do a bit of extra work:

Find the battery charger, and turn it on. Using a multimeter, measure the DC voltage coming from the plug the battery normally connects to. If the multimeter reads somewhere between 12V and 16V, mark the wire on the battery connector corresponding to the connector with the red wire from the multimeter as "red", and the other wire as "black". If the multimeter is reading somewhere between -12V and -16V, (a negative voltage) mark the wire on the battery connector corresponding to the connector with the red wire from the multimeter as "black", and the other wire as "red". (so the opposite colours to the multimeter)

In my battery, the metal parts of the plug where totally separate from the plastic housing of the battery, and without the battery cells in the housing, the connectors of the plug simply fall inside. If this also happens to you, use some hot glue or super glue to secure the metal connectors inside the plug so they don't fall out.

Step 4: Connecting the Power Adapter

Start by cutting off the original plug from the adapter, and stripping the rubber insulation. Depending on the type of adapter, you either have two wires coming from the adapter, or one thick wire.

If you have an adapter with two wires, the rubber insulation needs to be removed from both. Start by pulling the two wires loose from each other, then strip both wires individually.

For single wire adapters, you wil most likely find a copper or silver outer layer, covering another layer of rubber insulation. Twist the loose strands of copper or silver wire from the outside into one ticker wire, and strip the inner wire. Don't cut of the loose strands of copper or silver, this is part of the wire, not part of the insulation. Usually, the inner wire is the positive wire, and the outer wire is negative.

Now, to determine what wire from the power adapter is positive and what wire is negative, connect the red wire from the multimeter to one exposed wire from the adapter, and the black wire from the multimeter to the other exposed wire from the adapter. Set the multimeter to measure DC voltage, and plug the adapter in (make sure that the wires from the adapter aren't touching each other, this will short out the adapter)

If the multimeter is reading 12V, the red wire is connected to the positive of the power adapter, and the black wire from the multimeter is hooked up to the negative (mark the wires on from the power adapter)

If the multimeter is reading -12V, the black wire is hooked up to the positive and the red wire to the negative.(mark the wires on from the power adapter)

If the multimeter is reading nothing, it's either not set to the right setting, not making a good connection with the power adapter, or the power adapter isn't working properly.

Now that we know what wire we need, it's time so solder!

Add a bit of tin to the end of both exposed wired from the power adapter and from the battery connector for the drill, and slide a piece of heat shrink over the wires from the power adapter.

Solder the positive wire from the power adapter to the red wire from the plug of the drill.

Solder the negative wire from the power adapter to the black wire from the plug of the drill.

Slide the two pieces of heat shrink over the soldered joints, and heat them until they properly insulate the wires.

The solder-free alternative:

If you don't feel comfortable using a soldering iron, use the same method described above to determine the positive and negative wires from the power adapter, and connect the positive wire to the red wire from the plug of the drill using a terminal block. Connect the negative wire from the power adapter to the black wire from the plug of the drill in the same way.

Step 5: Test It!

The drill should now be functional again! Partially re-assemble the battery without the battery cells inside, and plug the empty battery casing in to the drill. Plug the power adapter into a power outlet, and press the button!

The drill should work as normal, but it's never going to run out of batteries again!

Step 6: Not Working?

If the drill only works at low speeds, but suddenly stops at full speed, the adapter is not powerful enough.

Try using an adapter with more amps.

If the drill is not working at all, double check that the correct voltage is sent to the correct connectors using a multimeter. If the multimeter reads no voltage at all, one of the wires isn't connected properly, or the adapter isn't working.

If the multimeter reads a negative voltage or the voltage is on the wrong connector on the battery, one of the wires is connected to the wrong connector, re-solder the wire to the correct connector and try again.

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