Convert a Perfectly Good Cordless Drill to a Corded One




Convert a cordless drill to plug into a 12 volt battery pack when your battery packs die.

About twenty years ago, I sprang for a state of the art, best that money could buy, a Porter Cable 12 volt cordless drill. (the highest voltage then). It came with a charger, steel carrying case and two nicad battery packs. I got a lot of good use out of it over the years. About eight years ago, the battery packs started to die. I bought one new one for $50 or so, which has since died. At that point, I ended up with three dead batteries and a really nice drill that I couldn't use.
I intend to rebuild two of the batteries with new NiMH cells eventually, but for now, I decided that as long as it is a 12 volt drill, it can run from a 12 volt battery pack, of which I have several. This battery case was fairly easy to convert. Some of them may be harder or easier than mine.
You will have to open it up and engineer it to hold the contact plates firmly in place with the wires attached. If you want to do this with a drill that is less than 12 volts, you will have to determine a way to drop the voltage to a safe level. Putting a resistor in line is the simplest way. If your drill is a higher voltage, I don't know of any simple way to provide a higher voltage.
At every step of the wiring, it is a good idea to check the wiring with a continuity tester or ohmmeter to determine that the connections are complete and that there are no opens or shorts.
Before chopping, cutting, drilling, examine the components to determine the best path for the wires. It is a good idea to mark the ends of the base and top of the case to prevent confusion.
If you have problems with my instructions, drill a hole through your hand, set your hair on fire or burn down your house, all correspondence regarding these issues should be made to my attorney. You will be promptly awarded 16.4 million dollars after sending the appropriate handling fees to his PO Box in Nigeria.)


Step 1: Parts and Tools

Parts List
Main Components:
- One old battery pack
- One cigarette lighter plug and cord, the heavier the better. Mine looks like about 14 gauge and holds a replaceable fuse in the plug. The cord

is about seven feet long. Try to find a cord that is long enough to comfortable reach the battery pack from where you will be working.
- Short length of rubber hose for strain relief that the cord will fit snugly through, about four inches.
- Fuse - fuse size is not critical. It is mainly to prevent a short circuit from causing a fire or meltdown. Probably a 5 amp would work. If it blows,

go larger.
- inline fuse holder (if your cord does not have one built in.)
- 2 or 3 tie wraps to secure the cord and strain relief

- electrical tester for checking polarity, voltage, continuity.
- Soldering iron
- Screwdriver
- Diagonal cutters
- Drill

Step 2: Prepare Battery Case

Determine the polarity of the contact plates. Fortunately mine was marked on the outside of the case. If your battery pack has any capacity at all, you can read the polarity with an electrical tester. If you get it wrong, it will probably still work but the direction switch will work backward. Worse case is if there is a diode that prevents it from working at all. It is a good idea to mark the polarity with tape or a sharpie to prevent confusion. (I am an expert on confusion and can supply references)
Open up one of the batteries and extract the cell assembly. Clip off the lower cells that fill up the main body. Throw them away. No, don't throw them away. Rechargeable and button batteries should be disposed at authorized battery collection sites. Take them down to your local Radio Shack and make them throw them away.
Remove the thermal sensor, the small metal thing tucked between the cells that is wired to the third contact plate(or leave it in if it isn't in the way). This leaves two dead cells, that hopefully are not too nasty and corroded, that fit into the "tower" that have the contact plates attached. If your cells are not usable, or the case is a different shape, you might be able to carve a block of wood that fits the case and can hold the contact plates. Silicone caulk, Friendly Plastic or Fimo might also work.

Drill a hole that the hose will fit through in the base of the case. Thread the wire into the hose and thread both through the hole. A knot can be tied in the cord, or tie wraps added to be tightened later to prevent the cord from pulling out and straining the soldered connections.

Step 3: Wiring

Solder the wires to the remaining cell assembly, either to the connection wires, contact plates, or the body of the cells (Not really desirable if you can avoid it. If you do this, be advised that applying high heat to a battery cell may have unpredictable results. At least wear protective glasses and clothes. Performing work using electrical tools naked is generally not a good idea. Same with cooking bacon.)

Step 4: Preparing Case

Make a spacer block that will fit snugly in the space left by the removed cells to hold the remaining cell/contact assembly firmly in the tower. I made mine from assorted blocks of wood with a tunnel carved in one to allow passage of one wire to the other side. This can be made from a single block of wood, friendly plastic, paper mache, etc. Just be sure it is hard enough to resist the pressure of inserting the case.

Step 5: Final Assembly

Pull the wire out through the hose and tighten tie wraps. Assemble parts, carefully juggling the block, wires and screws. Be sure screws don't poke into the wires. As you put all the parts together , Close case and screw together.

(note: There is no next step. Do not click on that button. Don't say I didn't warn you.)



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    30 Discussions


    2 years ago

    I went a step further than this. One doesn't always have a a car handy, and a 12V battery is a bit heavy to lug about. So I made a much smaller lightweight replacement using six 500 Farad supercaps wired in series. This will happily keep you going with a hundred or so medium sized screws into pine before requiring to be recharged.

    This is where supercapacitors really come into their own. If you use a constant current charger capable of supplying 20 Amps, it takes about 30 seconds to charge.(I built my own. Two transistors, a handful of resistors and a fan cooled PC processor's heat sink I had hanging around) and off you go for more happy trouble free screwing! My charger will work from a car battery or a mains supply (I bought a mains 20Amp 12v supply from the internet for about £15 and tweaked it a bit to supply 17v)

    Supercapacitors make lousy batteries. They hold a much smaller charge, and have a high self discharge rate. But they can supply current at up to 1,000A or more and be charged in seconds rather than hours. They are a fraction of the weight and size too and this makes up for it in this application. The high current capability makes the screwdriver able to supply MUCH higher torque than the original batteries too, should you want need it.

    My supercapacitors are mounted in a plastic box and weighs a bit more than a pound. It is about 6" by 4" by 3" and was manufactured by Messrs Tupperware. I added a cheap digital voltmeter to it as a sort of fuel gauge. The energy it contains is proportional to the square of the voltage so it is not exactly linear, but it gives you an idea of when to go charge it up again with experience.


    10 years ago on Introduction

    (Not to be condescending, but if you don't know what "VOM" stands for, you probably should not be doing this.)

    Erm... sorry, but you are being condescending. I didn't know what VOM stood for (although given context and the letters I took a shot in the dark that proved to be right) but I've never heard those called VOMs, only multimeters.

    Saying "if you don't know what this is for then you shouldn't be doing this" is OK if you are talking about a pair of scissors or a marker or something equally obvious, but using it on terminology that otherwise-well-informed people might not have heard just alienates people. Someone asked me what "flex" meant on one of my Instructables- I had to tell them it meant wire, and if you dont know what wire is for then stay the hell away from electrical projects, but it was just a difference in terminology.

    Ranting aside, this looks like a good project. Now we just need an Instructable on how to deal with the people who say "hurf durf why did you attach a wire to a cordless drill now it's not cordless any more hurr".

    5 replies

    Reply 3 years ago

    Lol at a small power supply able to supply 200 amps...That's a HUGE 12 volt supply.


    Reply 10 years ago on Introduction

    Okay, I took out the condescending comment. I assumed that VOM was a well known term with anyone who would be doing this. I do think that if anyone is not familiar with basic tools used for this project, they may have a - shall I say - less than positive experience. Maybe there should be a site-wide disclaimer indicating that if anyone is attempting a project that is beyond his skills, it may turn out to be more entertaining than she expected and let them have their fun. I've had many entertaining hours exploring my limitations that way! I explained why I attached a wire. For all I care, they can look stupid publicly and don't deserve any response.


    Reply 8 years ago on Introduction

    True, if someone isn't familiar with these things already, it'd be hard to learn them all at once. That being said, I've used a multimeter quite a bit but have never heard of a VOM before now :)


    Reply 8 years ago on Introduction

    Sorry for my inconsideration and rudeness. I've now removed all mention of the offensive "VOM" term. Anyone who reads any of this are now responsible for their own safety. If anyone still has problems with my originally well intentioned desire to share a good idea, please let me know and I'll delete the entire post and immediately commit seppuku (and try really hard not to bleed on anyone).


    Reply 10 years ago on Introduction

    Thank you very much for this instructable. I have a battery drill that holds a charge long enough to drill through a sheet of plywood. I would much prefer to have a cord on it, so thank you.


    5 years ago on Introduction

    If you do this mod properly you can power your drill off of anything that supplies 18 volts of power. I modded my drill's dead battery pack to accept power from anything, whether it be wall power, or a car battery for when you are on the road, to solar power when you are just away from normal power sources. TNKs, and it's a great job! About more informations

    1 reply

    Reply 5 years ago on Introduction

    By "properly" do you mean putting a voltage regulator in? Otherwise, it's probably not a good idea to feed 18 volts to a device that's designed for 12.

    I would keep the temperature sensor as long as it's not inside the cells or something. Just remove the cells from the battery pack and leave the temperature sensor in there.


    Reply 6 years ago on Introduction

    Good question. But this one was a NiCad drill and the third contact is only for charging. The drill itself only has two contacts.
    Someone familiar with LIon devices might know.


    6 years ago on Introduction

    This is a good idea - I hadn't thought of using a battery jumper box.


    6 years ago on Introduction

    I came up with an Instructable with the same idea ( It's true!). I stumbled with your 'ible after I published mine. Great minds think alike!


    6 years ago on Introduction

    I have adapted a ridgid jobmax multitool....(add smiley here)
    the samsung lithium batteries are notoriously poor quality and can die after 6 charge cycles!!
    I used a laptop charger!
    Straightforward procedure and it appears to work well.


    7 years ago on Introduction

    I am interested in doing this to as i have a good 12v drill and 2 Batteries just sometimes when i down my allotment and the Batteries go flat i have no way to charge them.

    But I do have lots of car 12v Batteries whic i us as a power source for lights and stuff.

    just need a old Battery to play with now lol as i dont wont to f up a good one.


    Nice idea Great idea but turn a perfectly good cordless into a corded one well i would not do this unless it was totaly screwed

    3 replies

    Reply 7 years ago on Introduction

    Ok it's pretty simple. I have a 12 volt battery charger. I BARED the wires and clamped the teeth on them. Works fine. What's the problem???? Just take the battery apart and yank the terminals away.
    I have the charger set on 12 volt. Amps can differ, I just get more rpms. I used this set-up to power a grain mill for 23 pounds of , malted barley for a beer that I'm brewing tomorrow. In the bag quit whining