Converting an electric screwdriver to 12v lithium batteries

Components needed for rework

converting, electric, screwdriver, lithium

Beforehand, it is necessary to select the components that will help to transform the electric screwdriver. The composition is determined by the specifics of the process, namely by soldering, using special cassettes or spot welding. Cassettes are not recommended due to their vulnerability to current. The rest of the list includes:

  • rechargeable batteries Li-ion18650;
  • Protective plate or module that provides a uniform load during charging;
  • contact welding machine. It is preferable to soldering because lithium batteries are sensitive to heat and can fail;
  • wires with a cross section of 0.75 mm², 1.5 mm², 2.5 mm²;
  • heat shrink;
  • screwdriver;
  • disc cutter.

The battery must match the wattage of the old components in the ratio of 1/3. Т.е. Lithium cell is a full-fledged replacement for 3 nickel-cadmium batteries. Usually use 3. Li-ion instead of 10 Ni-Mh, which will slightly reduce the power of the unit. You can install 4 batteries, but this will reduce the life of the electric motor.

The key factor is the current value listed on the data sheet of the electric screwdriver. It varies in the range of 15-40 A, respectively selected elements with similar output parameters. This applies to both batteries and protection boards. Universal option BMS module for 25A or 30A. Batteries from old notebook computers are not desirable, since they are not designed for a high load.

Choice of controller

For all their merits, lithium-ion cells are sensitive to:

To control these parameters on their own for a few hours, which will be needed to replenish the battery power, is difficult. Therefore, these functions are entrusted to the PCB (Power Control Board) or SOF (function support system). It is a small board which is often built into the battery case (because of that the length of 18650 cell is a little bit longer than promised 65 mm). This system stops charging when the correct voltage is reached and disconnects the battery when discharged to a set level. Such units are marked Protected on the casing. If there is no marking or it is directly written “Unprotected”, it means that the battery is not equipped with such a system and we will have to control the charging parameters manually or we will have to entrust this function to an external device.

PCB should not be confused with BMS. Battery Management System or PCM. Power Charge Module. This system is designed for element-by-element charge control of batteries in a battery in series. Cells, which make up the battery, have a certain spread of parameters, so it is possible that some of the elements are already charged, and the other part still needs to be charged. It is obvious that this mode is unfavorable for the batteries. This problem is solved by BMS (“balancer”). And in this case we can not do without this system.

Typical BMS connection diagram is shown on the picture. When reaching the nominal parameters, the cell is shunted by the internal key, the remaining batteries continue to charge.

The marking may differ slightly from board to board (instead of “B-” there is “0V”, instead of the serial number of the battery. total voltage at the connection point). You can buy ready-made device on the Internet at well-known marketplaces. It is necessary to choose by the following parameters:

And, of course, it is necessary to commensurate the size of the board with the available installation space.

Disassembling the battery case

Each user is able to disassemble the case consisting of two parts connected with screws and glue by himself. The screws are unscrewed, the glue layer is broken by a thin object that is pushed all the way around.

After the repair the screws are put back in their original place and the glue layer is renewed.

The safest way to connect the cans is by spot welding. Its essence is the following: the electrodes are pressed to the welding point. A large current is passed through them for a short period of time. During this time the metal of the plate has time to melt and weld to the battery. In this case, the heat does not have time to penetrate the battery and damage it.

  • On a flat surface set the banks to be connected, for convenience, you can wrap them with electrical tape or tape, so they are located as in the finished assembly;
  • We put a connecting strip on top of the battery;
  • Press the electrodes to the strip and turn on the current.

Spot-welding apparatus can be purchased or you can make your own hands.

Rebuilding an electric screwdriver with a lithium battery

Many models, including Makita, Hitachi, Interskol, are equipped with universal mechanisms, which means the charger is designed to power different types of batteries: Li-Ion and Ni-Mh.

The characteristics of the elements to be replaced and the new ones must match each other. If this is not adhered to, there will be a glitch or a break in the chain.

An indicator light will let you know when this has happened. In the event of a break or overload, the green and red lights will immediately start flashing.

Non-universal charger, like the power supply, must be reworked. The process depends on the manufacturer and type of charger, will have to:

There is a universal way to rebuild the charger when BMS board (DC-DC StepDown) is used. It stabilizes the input voltage and current. There are trimmer resistors on the board. In the circuit of the charger solder the module, using the old charging terminals, and on the board connection P and P-.

If you convert an electric screwdriver to lithium, you can extend its life

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Screwdriver battery conversion to Li-Ion

I will not say anything new in this article, but I just want to share my experience with upgrading batteries of my old Makita screwdriver. This tool was originally designed for nickel-cadmium batteries (which are long dead, as dead as bought to replace them). Disadvantages of Ni-Cd are known: low capacity, short life span, high price. That is why cordless tool manufacturers have long switched to lithium-ion batteries.

Well, what about those who have an old tool? Yes, everything is very simple: throw out the Ni-Cd banks and replace them with Li-Ion batteries of the popular format 18650 (marking indicates a diameter of 18 mm and length of 65 mm).

What board and items are needed to convert the screwdriver to lithium-ion

So, here is my battery at 9.6 V and a capacity of 1.3 Ah. At maximum charge it has a voltage of 10.8 volts. Li-Ion cells have a nominal voltage of 3.6 volts and a maximum voltage of 4.2 volts. Therefore, to replace the old nickel-cadmium cells with lithium-ion cells I need 3 cells, their operating voltage will be 10.8 volts, the maximum. 12.6 volts. Exceeding the rated voltage will not damage the motor in any way, it will not burn out and with a larger difference, no need to worry.

Lithium-ion cells, as it has long been known, categorically do not like overcharge (voltage above 4.2 V) and excessive discharge (below 2.5 V). At such excesses of the operating range the cell degrades very quickly. Therefore, lithium-ion cells always work together with an electronic circuit board (BMS. Battery Management System) which controls the cell and monitors both the upper and lower voltage limits. It is a protection board that simply disconnects the can from the circuit when the voltage is outside the operating range. So in addition to the cells themselves, you will need such a BMS board.

Now two important points, with which I experimented a few times unsuccessfully, until I came to the right choice. This is the maximum allowable working current of Li-Ion cells themselves and the maximum working current of BMS-board.

In a screwdriver operating currents at high load are 10-20 A. That is why you should buy the cells that are able to deliver high currents. Personally I successfully use 30-amp 18650 cells manufactured by Sony VTC4 (2100 mAh) and 20-amp Sanyo UR18650NSX (2600 mAh). They work fine in my electric screwdrivers. And, for example, Chinese TrustFire 2500 mAh and Japanese light green Panasonic NCR18650B 3400 mAh are not suitable, they are not designed for such currents. So it is not necessary to be overly concerned with the capacity of cells. even 2100 mAh is more than enough; the main thing when choosing is not to miscalculate the maximum allowable discharge current.

And similarly, the BMS board must be designed for high operating currents. I saw on YouTube, how people build batteries on the 5 or 10 amp boards. I don’t know, but when I turn on the screwdriver, the boards get deflected at once. Sounds like a waste of money to me. I will say that Makita itself puts 30 amp boards in its batteries. So I use a 25 amp BMS bought on Aliexpress. They cost about 6-7 dollars and are searched by “BMS 25A”. Since you need a board for a 3-piece assembly, you should look for one with “3S” in its name.

One more important point: some boards have different contacts for charge (marked “C”) and load (marked “P”). For example, the board can have three pins: “P-“, “P” and “C-“, like on a native Makita lithium-ion board. This board will not work for us. Charging and discharging (charge/discharge) should be done through one contact! That is, the board should have 2 working contacts: just “plus” and just “minus”. Because our old charger also has only two contacts.

All in all, as you might have guessed by now, I threw a lot of money away with my experiments on both the wrong parts and the wrong boards, making all the mistakes that could be made. But it was an invaluable experience.

How to Disassemble a Screwdriver Battery

How to Disassemble an Old Battery? There are batteries where the halves of the body are attached with screws, but there are also glued. My batteries are just the latter and for a long time I thought it was impossible to disassemble them. It turned out that it is possible, if you have a hammer.

In general, with the help of intensive blows to the perimeter of the edge of the bottom case (hammer with a nylon head, the battery must be held in the hand in the weight) the gluing place is successfully disconnected. The housing is not damaged in any way, I have already disassembled 4 pieces.

Only the contact plates are needed from the old circuit. They are firmly welded to the top two elements by spot welding. You can unscrew the welding with a screwdriver or pliers, but pick as carefully as possible not to break the plastic.

Everything is almost ready for further work. By the way, I kept the thermosensor and the circuit breaker, although they are not really relevant anymore.

But it is very likely that the presence of these elements is necessary for normal operation of the regular charger. So I strongly recommend to keep them.

Assemble the lithium-ion battery

Here are new cells Sanyo UR18650NSX (you can find them on Aliexpress by this part number) with the capacity of 2600 mAh. For comparison, the old battery had a capacity of only 1300 mAh, half as much.

You need to solder the wires to the cells. The wire cross section should not be less than 0.75, because we’re going to have a lot of currents. A wire with such a cross-section works well with currents over 20 A at 12 V. You can solder lithium-ion battery banks, short-term overheating will not hurt them, it’s proven. But you need a good fast flux. I use TAGS glycerine flux. Half a second and it’s done.

Solder other ends of the wires to the board according to the diagram.

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At the battery terminals I always let even thicker wires of 1.5 because space allows. Before soldering them to the mating pins, I put a piece of heat shrink tubing on the board. It is needed for additional insulation of the board from the battery cells. Otherwise, the sharp edges of the solder can easily rub or puncture the thin film of the lithium-ion cell and cause a short circuit. It is not necessary to use a heat shrink, but at least something insulating to put between the board and the cells is absolutely necessary.

The contact part can be attached to the battery by a couple of drops of superglue.

It’s good when the body is screwed, but this is not my case, so I just glue the halves together again with “MoMoment”.

The battery is charged with the regular charger. True, the algorithm changes.

I have two chargers, a DC9710 and a DC1414 T. And they work differently now, so I’ll tell you how.

A Makita DC9710 charger and a Li-Ion battery

It used to be that the charger itself controlled the battery charge. When it reached full level, it would stop the process and signal when it was done charging with the green LED. But now the level control and the power disconnection is performed by the BMS circuit that we have installed. So when the charger has finished charging, the red LED on the charger will simply turn off.

If you have an old device like this, you’re in luck. Because it’s so simple. The diode is on. charging. Off. charging is complete, battery is fully charged.

Makita DC1414 T battery charger and lithium-ion battery

Here’s a little something to be aware of. This charger is newer and designed to charge a wider range of batteries from 7.2 to 14.4V. It was charging as usual with the red LED on:

But when the battery (which in the case of NiMH-cells should have a maximum voltage of 10.8 volts) reaches 12 volts (we have Li-Ion cells, in which the maximum total voltage can be 12.6 volts), the charger will go crazy. Because it doesn’t know if it is charging a 9.6 volt or a 14.4 volt battery. And at this point, the Makita DC1414 will enter the error mode, alternately flashing red and green LEDs.

It’s OK! Your new battery will still recharge. but not to the end. The voltage would be about 12 volts.

So you will miss some capacity with this charger, but I think you can live with that.

Total battery upgrade cost about 1000. A new Makita Makita PA09 costs twice as much. And we ended up with twice the capacity, and further repair (in the case of an early failure) will consist only of replacing the lithium-ion cells.

Note: This article and the images in it are copyright. Reproduction in part or in full on other resources without permission is prohibited.

For the beginning it is necessary to reflect, whether I need this alteration? Because it is a blatant “homemade” and in some cases can lead to failure of both the battery and the screwdriver. So let’s take a look at the pros and cons of this procedure. It is possible that after this some of you may decide not to convert the Ni─Cd battery pack for your screwdriver to lithium cells.


  • The energy density of lithium─ion cells is much higher than the nickel─cadmium cells that are used by default in electric screwdrivers. That is, a lithium bank battery will have less weight than a cadmium bank battery for the same capacity and output voltage;
  • Lithium battery cells charge much faster than Ni─Cd. It takes about an hour to charge them safely;
  • Lithium─ion batteries have no “memory effect. This means that they don’t have to be fully discharged before putting them on charge.

Black & Decker cordless screwdriver conversion to Lithium Ion.

The arguments “against”

  • Lithium battery cells cannot be charged above 4.2 volts and discharged below 2.7 volts. In the real world, this range is even narrower. If you go beyond these limits, the battery can be destroyed. Therefore, in addition to the lithium battery cells themselves, you need to connect and install a charge/discharge controller in the screwdriver;
  • The voltage of one Li─Ion cell is 3,6─3,7 volt, and for Ni─Cd and Ni─MH it is 1,2 volt. That is, problems arise with the assembly of a battery for screwdrivers with a voltage rating of 12 volts. You can make a battery with a rating of 11.1 volts from three lithium cells connected in series. From four ─ 14.8 volts, from five ─ 18.5 volts and so on. Naturally, the charge-discharge voltage limits will also be different. That means that there may be compatibility issues between the converted battery and the screwdriver;
  • In most cases the lithium cells used for conversion are standard 18650 cans. They differ in size from Ni─Cd and Ni─MH cans. Plus, you’ll need room for a charge-discharge controller and wiring. All of this will need to fit into a standard screwdriver battery pack. Otherwise, they will be extremely uncomfortable to work with;
  • The cadmium battery charger may not be suitable for charging the battery after it has been rebuilt. It may be necessary to modify the charger or use universal chargers;
  • Lithium batteries become unusable at subzero temperatures. This is critical for those who use the screwdriver outdoors;
  • Lithium batteries are more expensive than cadmium batteries.

Nickel-cadmium and nickel-metal hydride regulations require that the battery must be fully discharged before recharging, or its capacity will rapidly drop. If you do not follow these rules, the battery will not last long. And a full charge takes about 10 hours, which is not very fast.

Lithium batteries do not have this disadvantage. They can be charged at any level. And charging is possible many times faster. A full charge cycle from 0 to 100% with the right charger can take about an hour and a half. And for rechargeable batteries with a fast charge capability of less than one hour.

With the same capacity and weight as NiCd or Ni MH, a lithium battery will have twice the capacity, which means it will last for more work. In addition lithium batteries have a low self-discharge, longer life and lighter nickel cadmium and nickel metal hydride batteries.

See also  How to Charge a Lithium Screwdriver Battery

Not only an electric screwdriver, but also other battery-powered gadgets and battery-powered devices can be converted in a similar way.

Converting an electric screwdriver to lithium batteries

Over time, the electric screwdriver’s native nickel-cadmium batteries lose their capacity, the charge is enough for a couple of screws, and it takes a couple of minutes to charge. If faced with such a problem, the first thing that comes to mind is to buy a new battery or electric screwdriver. But you can give a screwdriver a second life and convert it to a lithium battery (of course, if the electric screwdriver is not killed and appropriate). As an example, I will use an electric screwdriver Soyuzmash ASH-14M with a voltage of 12 V.

Necessary parts: Electric screwdriver Soyuzmash AS-14M x 1 pc; Battery LiitoKala HG2, 18650, 3000 mAh x 3 pcs; BMS 3S, 40A, 12.6V balancer x 1 pc; XL4015 step-down converter x 1 pc; 1.5 mm wire (black, red) 20 cm.

Disassembly of the case:In my case, the battery case is fastened with screws, also there is a variant with latches or glue. The most difficult thing to disassemble with a glued block, for disassembly use a special hammer with a plastic base. Everything is removed from the inside of the battery block, we only need the contact plates, to connect to the screwdriver and charging station.

Battery choice: The Ash-14M electric screwdriver is designed to run on a 14-volt battery, so I will use three lithium-ion batteries with a total voltage of 12.6 V, of course you can use and four batteries and raise the voltage to 16.8, but then you will need to use a separate power supply, as well as high voltage reduce the life of an electric screwdriver. Not all batteries are suitable for battery conversion, so there are several factors to consider:

It is not recommended to use batteries with different capacities; Batteries should not be selected only by capacity, the main parameter is the discharge current. Some people recommend using lithium batteries from old laptops, this is not correct, they are designed to work with a lower discharge current.

In this article I use batteries LiitoKala HG2, type 18650, capacity 3000 mAh and current discharge 30A, come already with or without soldered tails, in my case without, for convenience, I advise to buy with tails

Choice of BMS board: The lithium-ion battery can not be used without a protection board BMS. There are different quantities on the market with different parameters. The BMS 3S marking shows that the board is designed for three batteries. Marking BMS 3S suggests, for example, that the board is designed for 3 cells. What you need to pay attention to:

The presence of a balancer ensures that the batteries are evenly charged. Maximum long term operating current.

In the article I use BMS 3S, 40A, 12.6V with balancing, it is well proven.

Rework the battery (assembling): battery using without soldered tails, so the wire will be soldered directly to the contacts, for this better use soldering iron 60W or high power, so as not to overheat the battery.

Note! Do not overheat the battery in any case.

We take acid, solder and tin both sides of the battery contacts and solder wires, instead of wires you can use the lithium nickel tape that you can buy or take from an old battery. In my case I use a wire, 1 square meter thick, because the space does not allow to place the battery evenly and the tape will not reach. After all the wires are soldered, take and bind all the batteries with duct tape. Various battery holders are now available.

Now according to the scheme, in series solder each battery output from 0 to 12.6, so at first we solder to 0, then 4,2, then 8,4, then 12,6 to the BMS 3S card

Further we solder the wires with cross section not less than 1,5 squared to the contact plates and with the help of hot melt glue fix them in the battery case. Also, some people leave two old batteries, so the contact group does not fly out.

We solder the wires from the contact plates to the BMS board, respecting the polarity and assemble the battery case in the reverse order and everything is ready.

Reworking the charger: Included with an electric screwdriver Soyuzmash ASh-14M, is the charger, but it is designed for charging nickel-cadmium batteries to charge the lithium-ion battery needs to finalize it. Of course some people use chargers without modification but this is not correct.

Revision is to add a board to reduce the voltage and current limit, well-proven board on the chip XL4015.

I don’t see the point in describing the rework because it is different for each charger, but the essence is that you need to cut a couple of tracks on the charger board and solder from the output circuit transformer to the input with XL4015. Next, you need to set the voltage 12.If you put more current, charging will be faster, but the batteries will fail quickly.

Who does not want to deal with rework, you can buy a ready-made charger with charging indication.

Optional: optional indicator can be added to indicate the level of battery charging. Of course it was possible to convert the electric screwdriver to 16.8V (4S), but in my case, I had to keep within the budget.

Buy on Aliexpress Battery LiitoKala HG2, 18650, 3000 mAh BMS 3S, 40A, 12.6V balanced surge voltage converter XL4015

Buy in Samara and the region LiitoKala HG2 Battery, 18650, 3000 mAh BMS 3S, 40A, 12.6V balanced XL4015 step-down converter