Lithium ion battery charge balancer for screwdriver. How to convert a screwdriver battery to lithium-ion: step-by-step instructions. Selecting the nominal voltage

Many craftsmen have a cordless screwdriver in their service. Over time, the battery degrades and holds a charge less and less. Battery wear greatly affects battery life. Constant recharging doesn't help. In this situation, “repacking” the battery with the same elements helps. The most commonly used elements in screwdriver batteries are the “SC” size type. But the most valuable thing a master has is repairing things with his own hands.
Let's remake a screwdriver with a 14.4 volt battery. Screwdrivers often use a motor for a wide range of supply voltage. So in this case, you can use only three Li-ion cells of the 18650 format. I will not use control boards. The discharge of elements will be visible in operation. As soon as the self-tapping screw does not tighten, for example, it’s time to put it on charge.

Converting a screwdriver to Li-ion without a BMS board

First, let's disassemble our battery. There are 12 elements inside it. 10 pieces in one row and 2 in the second row. A contact group is welded to the second row of elements. We leave a couple of elements with a contact group, and dispose of the rest.

Now you need to solder the wires for further work. The contacts turned out to be made of a material that cannot be tinned, so we soldered the wires to the elements. Minus to the body of the element, and plus directly to the positive patch. The old elements act as a support and do not participate in the work.

I will use lithium-ion batteries of the 18650 format. The elements are used. High-current elements are needed for modification. I “changed” my elements into heat-shrink from Sanyo, the old one was pretty shabby. I checked the residual capacity Imax.
We connect the batteries in series and solder the head elements. The battery is almost ready.

Now let's ensure comfortable charging. You need to install a four-pin connector. I used a connector from an old motherboard for the number of pins I needed. I took the mating part from an old computer power supply.

Cut a hole for the connector. Fill the connector with epoxy glue or super glue with soda. We also solder the wires.

Solder the wires to the elements. Wire from the first contact of the connector to the battery positive. A wire from the second contact of the connector to the plus of the second element, which is also the minus of the first element, and so on. Since I will be charging with a “smart” charger, I need to make a balancing wire.

As a connector for connecting to the charger, I will use the wire from the computer's power supply. The wire through which the floppy drive was powered. We cut off all the keys from the connector and it fits perfectly into the charger. It unsolders easily. Red wire to the first contact of the battery connector. Black wire to the second pin of the battery connector, etc.

“How much will it cost to replace the old nickel batteries with lithium-ion batteries in my screwdriver” is perhaps one of the most popular questions we hear from our customers.
And indeed, the problem is quite common. Many people have an old cordless screwdriver (wrench, hammer drill, jigsaw, trimmer, etc.) in which the standard batteries are out of order, and there is either no way to buy new ones, since they may be discontinued or you simply don’t want to spend money on outdated technology, but I want to immediately replace Ni-Mh batteries with Li-Ion and give, often, expensive and high-quality power tools a second life.

There are indeed many reasons for such a desire:
- the first and main thing is that Li-Ion batteries have a much higher electrical density than Ni-Mh batteries.
Simply put, with the same weight, a Li-Ion battery will have a higher electrical capacity than a Ni-Mh battery. Accordingly, by installing Li-ion batteries in the old case, we get a much longer operating time of the tool.

The charge current for high-power Li-ion batteries, especially for new models, can reach values ​​of 1C - 2C (single or double capacity value).
Those. such a battery can be charged in 1 - 0.5 hours, without exceeding the parameters recommended by the manufacturer and, accordingly, without reducing the battery life.

But there are enough stopping factors to implement such an idea:
- Due to technological limitations, Li-ion batteries cannot be charged above 4.25-4.35V and discharged below 2.5-2.7V (indicated in the technical specifications for each specific battery). Exceeding these values ​​may damage the battery and render it inoperable. To protect the Li-Ion battery, special charge-discharge controllers are used that keep the voltage on the Li-Ion cell within the permitted limits. That is, in addition to the batteries themselves, you will also need a charge-discharge controller.
- The voltage of Li-ion batteries is always a multiple of 3.7V (3.6V), while for Ni-Mh batteries it is a multiple of 1.2V. This is due to the rated voltage (the voltage value that is maintained on the Li-Ion battery for a sufficiently long time in the middle of the current-voltage characteristic of the discharge curve) on an individual cell. For Li-ion batteries this voltage is 3.7V, for Ni-Mh batteries it is 1.2V. Therefore, you will never be able to assemble a 12V battery from Li-Ion batteries. In nominal terms, it can be 11.1V (3 in series) or 14.8V (4 in series). Moreover, the voltage of the Li-Ion cell changes during operation from fully charged - 4.25V to completely discharged -2.5V. Thus, the voltage of the 3S (3 serial - 3 serial connections) battery will change during operation from 12.6V (4.2x3) to 7.5V (2.5x3). For 4S batteries - from 16.8V to 10V.
- Li-Ion battery size 18650, and 99 percent of all Li-Ion batteries consist of cells size 18650, has different overall dimensions from Ni-Mh cells. The 18650 cell measures 18mm in diameter and 65mm in height. It is important to “estimate” how many Li-Ion cells will fit into your case. At the same time, you need to understand that for an 11.1V battery you will need a number of Li-ion cells that is a multiple of 3. For a 14.8V battery - four. In this case, there should be space left for placing the charge-discharge controller and switching wires.
- The charger for Li-ion batteries differs from the charger for Ni-Mh batteries. To be fair, it should be noted that the chargers supplied with many screwdrivers are universal chargers and can charge both NI-Cd, Ni-Mh and Li-ion batteries. Make sure your memory has this capability.
- Cost of Li-ion batteries. and it, compared to Ni-Mh batteries, can differ significantly.

If all of the above does not scare you away, then consider an example of the process of manufacturing a Li-Ion battery to replace the Ni-Mh battery we have from a DEWALT DC840 impact wrench.

This impact wrench is equipped with two Ni-Mh rechargeable batteries with a voltage of 12V and a capacity of 2.6Ah.

To begin with, we will decide on the choice of nominal voltage for our Li-ion battery.

The choice is between a 3S Li-ion battery with a voltage range of 12.6V - 7.5V and a 4S Li-Ion battery with a voltage range of 16.8V - 10V.
We will focus on the second option, because:
a) The voltage on the battery drops quite quickly from maximum to nominal, i.e. from 16.8V to 14.8V, and for an electric motor, which is what a wrench actually is, an excess of 2.8V is not critical.
b) The minimum voltage of a 3S Li-Ion battery will be 7.5V, which is extremely low for normal operation of the power tool. And the efficiency of a 4S battery in this case will be higher than the efficiency of a 3S Li-Ion battery.
c) By installing 4 Li-ion cells, we will thereby increase the electrical capacity of our battery.

So, we’ve sorted out point 1: we’re making a 4S (14.8V) Li-Ion battery.

Second. We decide on the choice of Li-ion cells.

To do this, we need to identify the limiting factors.
In the case of the manufacture of Li-Ion batteries for power tools, the main limitation is the maximum load current. Currently, there are Li-Ion batteries with a permissible rated (long-term) load current of 20-25A. Pulse (short-term, up to 1-2 seconds) load current values ​​can reach 30-35A. In this case, you will not damage the structure of the battery.

Up to 6 Li-Ion 18650 cells can comfortably fit into our case from an old Ni-Mh battery. Accordingly, we cannot assemble a 4S2P (4 serial connections and 2 parallel) Li-ion battery, which will require 8 cells but must fit into 4 cells . Naturally, in this case, each of the cells must “hold” a single value of the maximum load current throughout the entire range of operating modes of the power tool.

We determine the maximum current flowing in the battery during operation of the impact wrench.
The video below shows that we connected the impact wrench to a laboratory power supply (PS) with a maximum current of 30A. We set the maximum current limiter regulator to the maximum possible value. Having set the IP voltage close to the nominal voltage of our future battery, we begin to smoothly pull the trigger. Current consumed by the impact wrench. rises to 5A.

Now we pull the trigger very sharply - thereby we practically “short-circuit” the power circuit. The current pulses up to 20 - 30A. Maybe he would have flown higher, but the power of the IP does not allow him to see this. You must understand that this will be a short-term load current in the event of a very sharp pull on the trigger of the impact wrench. And any screwdriver/anything with an electric motor will behave exactly this way. That’s why it’s funny to hear buyers’ statements, saying that you have non-working controllers and bad batteries, because, you see, my screwdriver consumes only 4A - I measured it - and I took Samsung 22F batteries with a capacity of 2200 mAh (the cheapest with the maximum current of 3A) and a controller of 8A and nothing works for me... And unprotected Li-ion batteries and controllers are not subject to exchange/return. Here, I think, everything is clear... Ignorance of the laws does not exempt you from responsibility...
Now let’s clamp the tip of the impact wrench into a fixed vice and see to what value the current consumption will increase under operating modes when the ratchet in the impact wrench is activated. The current value jumps to 10-12A.

At this stage, we have decided on the load current value. In our case, it will be: at idle 5A, with a sharp start 30A, at maximum load - 12A. Respectively. we choose Li-ion cells with a rated load current of 10-20A and a pulse current of 25-30A.

Li-ion battery models are suitable for us (in stock at the time of writing): 18650 2000mAh LG INR18650HD2 3.7V 25A, 18650 2500mAh LG ICR18650HE4 3.7V 20A, 18650 2600mAh SONY US18650VTC5 3.6V 30A, 18650 3000mAh LG INR18650HG2 3, 7V 20A.

We settled on the 18650 3000mAh LG INR18650HG2 3.7V 20A for maximum capacity.

Selecting a controller (overdischarge-overcharge protection board).

The controller must satisfy two parameters:

Rated operating voltage (in our case 14.8V)
rated operating current.

With voltage, everything is clear: if the battery is 14.8V, then the controller should be 14.8V, if the battery is 11.1V, then the controller should be selected with a nominal voltage of 11.1V.

The "rated operating current" parameter determines the "throughput" of the protection board. Those. The 4A controller is designed for a current of 4A and at 8A it will have overload protection. A controller with a 16A rated load will “go into protection” at 30±10A. All these parameters are indicated on the "Characteristics" tab for each specific controller model.

In this case, for one controller instance the limiting current may be 30A and for another 50A. And both of these controllers will be formally operational. But we are also limited in size, so the controller should be chosen in such a way that it fits into your case from an old battery.

Based on the conditions described above, we chose a protection board for a 14.8V battery model HCX-D177 with a rated operating current of 16A and a maximum current threshold of 30±10A.

So, we have decided on the components for our Li-ion battery. There were no problems with the charger, since it is designed to work with both Ni-Mh and Li-ion batteries.

Plus, provided that we install a charge-discharge controller, we are insured against overcharging our battery.

Let's begin the disassembly and assembly process.

We open the old battery by unscrewing 5 screws.

We take out the old Ni-Mh battery

It can be seen that the contact pad, which engages with the contact group of the impact wrench, is welded to the plane of the negative contact of one of the Ni-Mh cells.

We cut off the weld points using a DREMEL 4000 multi-tool with a cutting stone installed. As a result, we are left with a direct contact group from the battery.

We solder wires with a cross-section of at least 2mm2 for power terminals and 0.2mm2 for connecting the thermistor to the contacts and glue the contact pad into the battery case using hot-melt adhesive.

We select 4 LG INR18650HG2 3000mAh cells based on internal resistance using a battery internal resistance meter. Its value should be the same for all four batteries in our battery.

We glue the Li-Ion cells of LG INR18650HG2 with hot glue in such a way as to ensure the most convenient location in the case.

We weld the cells on a resistance welding machine using nickel welding tape with a cross-section of 2x10mm.

Install the protection board.

At this stage, we can already estimate how much we have lightened the weight of our battery.

The weight of old Ni-Mh batteries was 536 g. The weight of the new Li-Ion battery is 199g. Thus, the weight gain is 337 grams, which is quite noticeable during operation. At the same time, our energy capacity increases from 31.2Wh (12V * 2.6Ah) in the original Ni-Mh battery to 44.4Wh (14.8V * 3Ah)

Install the battery into the case. We fill the voids with soft packaging material.

Battery ready

We connect it to our impact wrench.

The video demonstrates that when the trigger is pulled sharply, the current protection on our protection board is triggered. But in real conditions, this mode will most likely not be used. If you do not specifically try to force the protection to operate, the impact wrench behaves absolutely predictably.
We clamp the tip into the jaws of the vice. As expected, the battery power is more than enough to activate the ratchet, which limits the torsional force.

We discharge the Li-ion battery of our impact wrench on an electronic load. The discharge current is set to 5A. The discharge graph is shown in the illustration below.

We insert the battery into the standard charger. The charge current, when measured, was 3A, which fits within the permissible charge current values ​​for these Li-ion cells (for LG INR18650HG2 the maximum charge current is 4A, which is indicated on the Characteristics tab).

In terms of time, the work of replacing Ni-Mh batteries with Li-Ion batteries took about 2 hours (with checking all parameters on the equipment - about 4 hours). In principle, all this can be done on your own, but resistance welding and selection of batteries cannot be done without special equipment.

The cost of replacing a Ni-Mh battery with Li-Ion.

Let's see what we get in terms of cost:
- the cost of 4 Li-ion batteries 18650 3000mAh LG INR18650HG2 3.7V 20A, at the time of writing, is 4 x 550 rubles = 2200 rubles
- the cost of a charge-discharge controller with a balancer HCX-D177 is 1240 rubles
- the cost of welding and assembly work is 800 rubles

In total, it turns out that a homemade Li-ion battery 14.8V 3Ah costs 4240 rubles

Let's find a similar factory-made Li-Ion battery for some other screwdriver. The Makita 194065-3 battery has absolutely identical parameters.

At the time of writing, such a battery cost from 5,500 rubles to 6,500 rubles.

It turns out that direct savings amount to 1300 to 2300 rubles. And, at the same time, we should not forget that the battery we made is impossible to buy in principle!

The company Reserve Power carries out work on converting Ni-Mh batteries from screwdrivers to Li-Ion. You can calculate the cost yourself in the same way as we did above, i.e. the total cost of batteries, controller and cost of work.

The warranty for the services provided is 6 months. The guarantee is provided only if the work was carried out using our components

PS. Special thanks for providing the experimental impact wrench and moral support :) to the company

A friend has a BOSCH GSR 12-2 Professional screwdriver, he’s had it for a long time, but it rarely works, and the batteries began to die intensively, back in the fall, let me tell you, I’ll revive it over the winter, there’s plenty of time and options, restore old cans by pouring distilled water into them water and after training them, replace the dead cans, if there are few of them, convert them to lithium. But no, I say they don’t work enough for me, the capacity is enough, as a result, both batteries died at zero volts by spring, I started the battery with a charger, but there is still no capacity, buying new ones is like buying a new screwdriver, changing nickel-cadmium banks too not cheap and not for long, as a result I get the go-ahead to convert to lithium. The owner is a pensioner, so we try to save money, and he uses it occasionally. I am ordering a BMS 4S 15A from ALI, so that I can later convert it into a 3S according to the scheme.

Oddly enough, the 4S costs less than the 3S, the vision is certainly not the same, but it was still redone, and 100-150 rubles. saved. I also ordered 6 high-current folk batteries. Samsung inr1865025rm 20a is just for two battery packs. They arrived and checked the capacity at 1A current.

It seems good, and the reviews from the seller are quite good.

There is a lot of information on the network about modifications, but the boards for three and four batteries are slightly different; if the board has 4 batteries, then you need to put 4 or convert it according to the scheme for 3 batteries. I did it according to this scheme, because the screwdriver itself is 12 volt.

The capacity of each assembly is like two new Ni-Ca (the old ones in theory 1.3 Ah), the old and new batteries were secured with hot glue, the battery was soldered and not welded, I know that it’s not feng shui, but I didn’t overheat, it will work like that;) and I didn’t redo the charging ( it works in normal mode, all the indications correctly show both charging and the end of the charge), it turns like new and better, I didn’t install a balancer on the battery, it’s at least another 300 rubles, better in a year or two I’ll take it apart and balance it manually. This is how the screwdriver got its “second wind”.

GVGVLG, Volgograd, Russia
https://www.drive2.com/users/gvgvlg/

Video selection. The best videos about converting screwdrivers.

1. Converting a screwdriver to a Li-Ion battery.

Converting a screwdriver to a Lithium-ion battery

How to convert a screwdriver to lithium batteries (welding batteries into a battery)

How to convert a nickel-cadmium battery to a lithium-ion battery yourself using a screwdriver

Converting a screwdriver to lithium-ion batteries standard 18650

Converting a screwdriver to lithium 18650

2. Converting the screwdriver to a network one.

Converting a screwdriver to a network one. Test of different power supplies

Converting a screwdriver to a network one

When the batteries do not hold a charge and have exhausted their service life, and the screwdriver is still in good condition, it can be connected to a 220V network through a power supply with sufficient power.

For several decades, screwdrivers have been used for various jobs. These devices are powered by nickel or cadmium batteries. But progress does not stand still; scientists have found a replacement for such outdated batteries. They were replaced by lithium analogues. To use such a battery, the screwdriver must be modified. A lithium battery will improve the performance of an old tool. Moreover, it is possible to carry out such alterations independently, without resorting to the services of special companies.

The lithium battery of the screwdriver has a number of advantages that were absent in cadmium analogues.

The energy density of a Li ion screwdriver battery is much higher. The battery with lithium banks is lightweight, and the voltage of 12 volts, as well as the battery capacity, remains unchanged. Lithium batteries charge faster than ion batteries. Safe charging lasts approximately 60 minutes.

Lithium-ion batteries do not have a “memory effect”. In other words, they do not need to be completely discharged to be charged. Among the positive qualities of a lithium battery, there are also a number of disadvantages that need to be taken into account:

• Charging lithium batteries should not be higher than 4.2 volts, and discharging should not be higher than 2.7 volts. But this is theoretical data. In real life, the interval gets even worse. If the set values ​​are not observed, the battery will simply stop functioning. To avoid this situation, after converting the screwdriver to lithium, you need to install a special discharge controller in the screwdriver, as well as its charging.
• One Li ion has a voltage of 3.63.7 V. For a nickel battery it is no more than 1.2 volts. In other words, converting a screwdriver to li ion material causes problems associated with the assembly process of the battery, whose nominal voltage is 12 volts. Three lithium banks connected in series give a voltage of 11.1 volts, four 14.8 V. The charge voltage limits will change. In other words, reworking a battery for a screwdriver is associated with solving the problem of compatibility of the new battery with the tool.
• To remake the cadmium battery of a screwdriver, craftsmen use 18650 lithium cans. Their dimensions differ from nickel cans. Remaking the battery for a screwdriver also requires the installation of a controller, which will require additional space.
• After the modification, the charger for nickel batteries will have to be modified, or use a universal charger.
• Sub-zero temperatures negatively affect the operation of ion batteries. Therefore, such a converted screwdriver cannot always be used outdoors.
• The cost of lithium batteries is much higher than their cadmium counterparts.

Algorithm for converting a battery to a lithium-ion battery

How to modify a screwdriver to get the best performance? To do this, it is necessary to strictly follow a certain technological sequence.

Selecting the right battery

The batteries are connected in series, so the voltage rating of each element is added to the next one. That is, to get 14.4 volts, you will need four elements with a voltage of 3.3 V.

To convert a cordless screwdriver, you need to buy miniature batteries only from a well-known manufacturer. For example, LiFePO4 batteries manufactured by Sistem A123. The cell capacity reaches 2,300 mAh. This value is sufficient for the efficient operation of the electric tool. Cheap batteries made in China will not have much effect. They will quickly fail.

When choosing a battery for conversion, you need to have copper strips on the terminals. Soldering such elements is much easier.

Selection of tools and materials

Soldering technology is distinguished by its specifics. The temperature of the soldering iron tip is constantly high. If the battery is exposed to such heat for a long time, it will quickly deteriorate. Therefore, the heating of the soldering iron should be minimal.

For this to happen, it is necessary to replace ordinary rosin with soldering acid. It can be purchased at a radio parts store. For such a process, you will also have to purchase a soldering iron with enough power to melt solder in the shortest possible time. The most suitable would be a household soldering iron with a power of 65 watts. At 100 watts the battery will overheat all the time.

Soldering work requires a lot of experience. For example, a 40-watt soldering iron will take a long time to heat up; you can simply “overdo it.” To start converting ion batteries, you need to purchase the following parts:

• 18650 battery.
• BMS board CF-4S30A-A/
• Wires, cross section 2.5 sq. mm.
• Soldering iron.
• Old battery housing.

A few words about the BMS board

It is designed to control the charge or discharge of the battery. The CF-4S30A-A is designed for four banks of 18650 batteries, giving a discharge current of 30A. The board is equipped with a special “balancer”. It performs charge control functions for each element separately. This completely eliminates the possibility of uneven charging. For the board to function properly, the batteries in the assembly must have the same capacity. It is desirable that they be taken from the same block.

The industry produces a large number of BMS boards, differing in their technological characteristics. For converting a screwdriver battery, a board operating at a current value of less than 30A is not very suitable. It will constantly turn on the protection mode.

To restore operation, some boards require a short-term supply of charging current. To do this, you will have to remove the battery from the case and connect the charger to it again. The CF-4S30A-A board does not have this drawback. It is enough to release the trigger of the screwdriver; if there is no current causing a short circuit, the board will turn on automatically.

The converted battery on this board can be charged with a universal charger. The latest models from the Interskol company are equipped with multifunctional chargers.

Lithium-ion battery installation

Of course, any installation requires preliminary preparation. It includes several very important points. Before you start soldering parts, you need to determine how the battery mounting compartment will be arranged. All the necessary elements should easily fit in it.
The new lithium batteries are then held together with tape. Since the contacts oxidize over time, they are cleaned with fine-grained sandpaper before soldering.

Nuances of the soldering process

First, the contact part of the battery is thoroughly degreased. Tinning is then carried out by heating the applied solder. POS-40 solder is most suitable for tinning.

The contact of the soldering iron with the battery contact should not exceed 2 seconds. The process of soldering the battery plus requires special attention. The most suitable are jumpers made of copper wires with a cross-section of more than 2.5 mm. sq. All wires are covered with a cambric, which acts as a good insulator.

The connection of mini-batteries must be carried out with special jumpers according to the developed diagram. Jumpers can be metal strips or thin wires.

At the final stage, the wires are connected to the compartment terminals intended for the battery. If installation of the prefabricated block is difficult, it is necessary to remove the stiffeners. Since they are made of plastic, they are easy to bite with ordinary side cutters.

Contact wiring diagram

To connect to the charger, you need to select connectors that correspond to a specific model. Soldering of connecting cables is carried out according to the electrical diagram:

Connectors for connecting to the charger are selected depending on its model. Both connecting cables are soldered according to the diagram.

• “+” – 5 and 9.
• “–” – 1 and 6.
• Balancing contacts (ascending) – 2, 7, 3, 8 and 4.

Of course, installing lithium-ion batteries has a large number of positive qualities:

• Lack of "memory".
• Minimum self-charging.
• You can operate the tool at sub-zero temperatures.
• Long service life (8 years).

However, these batteries are highly sensitive to the charging process. The voltage must always be at a minimum value, otherwise the Li-ion battery will quickly become unusable. To fulfill such conditions, you need another memory device, the cost of which is an order of magnitude higher. The screwdriver's native charger will not be able to charge the lithium-ion battery.

It is impossible to say unequivocally which battery is better for a screwdriver. Their service life depends on careful handling and strict adherence to the instructions supplied by the manufacturer.

Popular models

Today, batteries are produced by many manufacturers. Among such a large assortment of lithium-ion systems, the most popular are: “Bosh” 10.8, with technical characteristics:

• Capacity – 1.3 A/hour.
• Voltage – 10.8 V.
• Dimensions -110 x 54 x 52mm.
• Warranty - 1 year.
• Power – average.

If we talk about nickel-cadmium batteries, the most popular brands remain:

• "Bort".
• Hitachi.

Russian batteries are designed for low voltage; they differ from imported models only in price. They are much cheaper, but at the same time they are not inferior in their technical indicators. The most famous models are:

• "Kraton".
• "ZAKB".

Conclusion

Lithium batteries have always been considered the most technologically advanced devices. But a tool with such batteries costs much more. You can, of course, remake your device and get rid of the cadmium batteries. However, this will cause other problems. Therefore, everyone makes the decision to convert a screwdriver to lithium himself, depending on the circumstances.

Interesting videos about converting a screwdriver battery

The cordless tool is more mobile and easier to use compared to its networked counterparts. But we must not forget about the significant disadvantage of cordless tools; as you yourself understand, the fragility of batteries. Buying new batteries separately is comparable in price to purchasing a new tool.

After four years of service, my first screwdriver, or rather the batteries, began to lose capacity. To begin with, I assembled one from two batteries by choosing working “banks,” but this modernization did not last long. I converted my screwdriver to a corded one - it turned out to be very inconvenient. I had to buy the same, but new 12 volt “Interskol DA-12ER”. The batteries in the new screwdriver lasted even less. As a result, two working screwdrivers and more than one working battery.

There is a lot written on the Internet about how to solve this problem. It is proposed to convert old Ni-Cd batteries to Li-ion batteries of size 18650. At first glance, there is nothing complicated about this. You remove the old Ni-Cd batteries from the case and install new Li-ion ones. But it turned out that not everything is so simple. The following describes what you should pay attention to when upgrading your cordless tool.

For the remodel you will need:

I'll start with 18650 lithium-ion batteries. Purchased at.

The nominal voltage of the elements is 18650 - 3.7 V. According to the seller, the capacity is 2600 mAh, marking ICR18650 26F, dimensions 18 by 65 mm.

The advantages of Li-ion batteries over Ni-Cd are smaller dimensions and weight, with a higher capacity, as well as the absence of the so-called “memory effect”. But lithium-ion batteries have serious disadvantages, namely:

1. Negative temperatures sharply reduce capacity, which cannot be said about nickel-cadmium batteries. Hence the conclusion - if the tool is often used at subzero temperatures, then replacing it with Li-ion will not solve the problem.

2. Discharge below 2.9 - 2.5V and overcharge above 4.2V can be critical, and complete failure is possible. Therefore, a BMS board is needed to control charge and discharge; if it is not installed, the new batteries will quickly fail.

The Internet mainly describes how to convert a 14-volt screwdriver - it is ideal for modernization. With four 18650 cells connected in series and a nominal voltage of 3.7V. we get 14.8V. - just what you need, even with a full charge plus another 2V, this is not dangerous for the electric motor. What about a 12V instrument? There are two options: install 3 or 4 18650 elements, if three then seem to be not enough, especially with partial discharge, and if four - a bit too much. I chose four and in my opinion I made the right choice.

And now about the BMS board, it is also from AliExpress.

This is the so-called battery charge and discharge control board, specifically in my case CF-4S30A-A. As you can see from the markings, it is designed for a battery of four 18650 “cans” and a discharge current of up to 30A. It also has a built-in so-called “balancer”, which controls the charge of each element separately and eliminates uneven charging. For proper operation of the board, batteries for assembly are taken from the same capacity and preferably from the same batch.

In general, there are a great variety of BMS boards on sale with different characteristics. I don’t recommend taking it for a current lower than 30A - the board will constantly go into protection and to restore operation, some boards need to be briefly supplied with charging current, and to do this you need to remove the battery and connect it to a charger. The board we are considering does not have such a drawback; you just release the trigger of the screwdriver and in the absence of short circuit currents, the board will turn on itself.

The original universal charger was perfect for charging the converted battery. In recent years, Interskol has begun to equip its tools with universal chargers.

The photo shows to what voltage the BMS board charges my battery together with the standard charger. The voltage on the battery after charging is 14.95V, slightly higher than that required for a 12-volt screwdriver, but this is probably even better. My old screwdriver became faster and more powerful, and the fears that it would burn out gradually dissipated after four months of use. That seems to be all the main nuances, you can start remaking.

We disassemble the old battery.

We solder the old cans and leave the terminals along with the temperature sensor. If you also remove the sensor, it will not turn on when using the standard charger.

According to the diagram in the photo, we solder 18650 cells into one battery. The jumpers between the “banks” must be made with a thick wire of at least 2.5 square meters. mm, since the currents when operating a screwdriver are large, and with a small cross-section, the power of the tool will sharply drop. They write online that Li-ion batteries cannot be soldered because they are afraid of overheating, and they recommend connecting them using spot welding. You can only solder by needing a soldering iron with at least 60 watts of power. The most important thing is to solder quickly so as not to overheat the element itself.

It should be approximately so that it fits into the battery case.