Cordless/Corded Drill




Introduction: Cordless/Corded Drill

About: I am an automation engineer but I will give anything a go. I don't know if you call if pessimism or just being an engineer, but I look for problems everywhere, then I look for some weird, left field way to s...

This instructable may seem a little counter-intuitive, why would you take a cordless drill and put a cord on it?

Well I bought this ROK 14.4V cordless drill to use as a cheap screw gun about a year ago (I use my good 18V cordless to drill the holes). The drill came with 2 batteries and I have obviously favored one as it now only holds a charge for about 10 mins. The drill cost about 70 euro and I do like using it as its well balanced, however, I could not track down a replacement and a local tool center quoted 110 euro to rebuild so it would be cheaper to buy a new drill.

I have seen some tutorials on fully converting to corded but I still have one good battery and I also have a good corded drill so I came up with this. I use a mains voltage to DC converter and adapt the failed battery housing to supply the drill from the mains and I can still swap to the battery and go cordless when needed.



Step 1: What I Used

For this instructable I used:

  • Cordless drill with dead battery
  • 230AC -> 24DC power supply (10A)
  • 2 pole MCB (6A)
  • gG fuse holder and fuse (6A)
  • Fibox enclosure
  • DIN rail
  • 16mm cable glands x3
  • 4m 3 core 1.5mm sq cable
  • Assorted ferrals and barrel crimps

Step 2: Power Box

As I said earlier, the drill is 14.4V. After measurement, I found that the drill draws 6A at full speed and no load.

This results in 14.4V x 6A = 86.4W

I had a spare 24V 10A power supply, using the adjustment I could dial this down to 22V, not really caring about the drill that much and knowing that they are usually fairly tolerant I tried it and there was no excessive heat or burning of the motor. I did not test the drill running continuously, this is used as a screw gun and is used in short bursts, there is no hammer action so I do not use with masonry. If you plan on running continuously then you need to better match the power supply to the drill.

The resultant current requirement is 86.4W/22V = 3.92A

I started by fitting 2 cable glands on the side of the box.

I cut and mounted some DIN rail inside and mounted the 6A MCB, power supply, and the fuse holder.

I wired the 230V AC supply through the MCB for mains protection and to provide isolation if needed.

From the 24V output, I wired the + though the fuse. In an ideal world, I would have used red/black 2 core for the DC, but all I had to hand was regular 3 core.

Step 3: Battery Pack Modification

I started by removing the casing of the battery.

I noted that the battery holder retains the spring on the battery pack clip so I needed to keep that.

I removed the lithium cells and disposed of them in my companies battery recycling.

Be careful not to short batteries when removing them, wrap the terminals with tape before disposing to prevent fire risk.

The + and - terminals are clearly identified on the battery casing.

I drilled out the case and fitted a gland, then ran the cable through and connected on using barrel crimps.

I then tightened the gland and closed up the battery.

Step 4: Test

I happened to have a nice clear cover already fitted with a warning label to isolate the supply before opening the box.

I inserted a 6A fuse into the holder and closed it up, then put the lid in place.

Check out the video to see the drill in action.

I can now swap between mains and battery in a matter of second.

The drill is portable when required and when I'm near a mains outlet I never need to worry about running out of battery!

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    48 Discussions

    did I see that right? you replaced a 14,4V battery with a 24V/10 Amp power supply?

    3 replies

    yes, the motor is more than capable of accepting this step up in voltage. it's obviously not drawing the full 10A. As I stated, I wouldn't want to do this with a drill that would be running constantly but some screw running or light drilling (it's a pretty low quality drill to be fair) is fine.

    I think I can reasonably guess the answer to this: if as I think it is, the drill has speed (torque) control and is therefore applying Pulse Width Modulated voltage (current) pulses to the motor in order to control the torque, so (within reason) the battery voltage is not the determining factor. The pulses meter out the current to what the drill requires.

    To be honest, I don't know. It sounds like a very reasonable theory. The current draw is lower on the mains than the battery. Another commentator spoke about an increased current demand when voltage increases on a motor but PWM would seem to explain my findings. Thanks for your input.

    I already have a corded drill. So this conversion seems somewhat pointless or am I missing something?

    1 reply

    It's not so much a conversion as there is still the option to run cordless. The point is that if you are within reach of mains you won't run out of power but you can switch and go cordless without a second tool


    1 year ago

    You also can do this with a Computer PSU (for ATX you have to connect some wires to turn it on, info on the net), if you have a 12 Volt tool like I did once :)

    I like it! I'm planning a similar thing myself.

    One thing though: your calculation of the current at the higher voltage appears to assume the power will remain constant, why would that be? Surely a higher voltage will cause in increase in current and therefore power...

    4 replies

    No, power is calculated using P = V * I (Power = Voltage * Current) so I = P/V. The power required by the motor would only vary with load (higher load = higher current draw) I just held the chuck in my hand while testing to provide a simulation of load.

    I worked the example for calculating the new current requirement in the steps. The only downside is that the increased voltage will cause the motor to heat but again as I said I am not going to be drilling concrete walls, this is really just for small item drilling or as a screw gun.

    Increasing the voltage to the motor will increase the current taken by it.

    Putting a load on the motor increases the current taken by it.

    So when the motor is put under load with a higher voltage supply, the current drawn will be massively increased. (If the power supply has the capacity.)

    But if the power supply is then being overloaded, you can expect to blow a fuse or burn it out.

    You need to do your power calculations on the basis of the maximum current being taken under load. (Ideally the power supply should be able to provide (or almost provide) the motor's stall current.

    You may get away with a higher voltage on a motor for short periods, but if the drill has an electronic speed control system, you may burn that out.

    Thanks ElectroFrank & GarethR5, I was not aware that this was the case (goes to show every day is a school day and why instructables is cool). I have studied this further and think I have a grasp of the concept.

    For clarity, I tested the current draw on the battery while retarding the chuck by hand, the drill was close to but not stalled.

    The Power supply is rated for 10A. I have used the drill several times now with the last time running in several 5X100mm screws into timber, the drill did not flinch, no heating, overloading or stalling.

    Thanks for your comments.

    No, the power dissipated in the motor, P = V * I, that is not a constant, the constant is the resistance of the motor coils, I = V / R, so the current will increase with voltage.

    It is pretty obvious that the current must increase with increasing voltage, not decrease as you have it.

    You say, "The only downside is the increased voltage will cause the motor to heat", the reason for that is that it is driving more current through it! Another formula for the power dissipated in a resistive load: P = I^2 * R


    1 year ago

    Follow-up to the above: Unfortunately that neighbor moved away and I now find myself in the same fix with the battery pack for my drill.

    would it have been cheaper and easier to just replace the lithium cells and continue to use the drill cordless?

    3 replies

    Certainly would but there is an added advantage to a tool that can switch from mains (continuous running) to battery (mobile applications). Also there was an element of experimentation and learning too. All of the parts were in my workshop anyway, waiting for a purpose, and there is still a second output on the power supply to all additional accessories.

    fair enough, have you got any other tools that take the same battery?

    Ive replaced nicad cells in a 12v drill with 4 x 18650 li-ion cells to make it a 14.8V drill, relatively simple transplant job.

    Not in this battery type, as this was a cheap drill and a bit of an experiment I wasn't too worried if I damaged it.

    My "Good" tools are a set of Metabo LTX tools, in this set I have an 18V hammer drill, a 600nm 1/2 impact gun, a 100mm angle grinder and a worklight, all using the same battery type. I may adapt one of the older batteries and put it on the other power supply outlet. This would be great especially for the grinder as it can drain a full 5.2Ah battery in 25mins under load


    1 year ago

    Shouldn't it be possible to open the battery pack and replace the individual cells? A few years ago a neighbor did exactly that, saving his Sony Saio notebook by ordering the cells off internet, because he couldn't get a replacement pack except at an outrageous price.

    Can't you use the charger as the power supply instead of formulas and calculations!

    1 reply

    No, the charger is not designed to put out the kind of current required while in operation. Batteries are charged at a much lower rate, hence a three or four hour charging time to get 45-60 mins run time.