Has the meaning. The advantage is that they have a high electrical density. As a result, by installing such a device in the screwdriver body, we can achieve an increase in the operating time of the tool many times over. The charging current for high-power lithium batteries, especially for new modifications, can reach 1-2 C. Such a device can be recharged in 1 hour, without exceeding the parameters recommended by the manufacturer and without spoiling the quality of the product.
What do lithium batteries look like?
Most lithium devices are housed in a prismatic body, but some models are cylindrical. These batteries use roll electrodes and separators. The body is made of aluminum or steel. The positive pole goes to the housing cover.
In prismatic configurations, the electrodes are in the form of rectangular plates. To ensure safety, the battery is equipped with a device that acts as a regulator of all processes and opens the electrical circuit in critical situations. Increased sealing of the housing prevents electrolyte from leaking out and oxygen and moisture from penetrating inside.
What precautions should be taken to avoid damaging the lithium battery?
- Due to technology limitations, the charge level of lithium batteries should not be higher than 4.25-4.35 V. The discharge should not reach 2.5-2.7. This condition is indicated in the technical data sheet for each specific model. If these values are too high, you may damage the device. Special charge and discharge controllers are used that keep the voltage on the lithium cell within normal limits. Converting the screwdriver to a lithium battery with a controller will protect the device from malfunction.
- The voltage of lithium batteries is a multiple of 3.7 V (3.6 V). For Ni-Mh models this figure is 1.2 V. This phenomenon is understandable. in lithium devices it is stored in a separate cell. The 12 volt lithium battery will never be assembled. The rating will be 11.1V (three cells in series) or 14.8V (four cells in series). In addition, the voltage indicator of the lithium cell changes when operating when fully charged by 4.25 V, and when fully discharged - by 2.5 V. The voltage indicator 3S (3 serial - three serial connections) will change when the device is operating from 12.6 V (4.2x3) to 7.5 V (2.5x3). For the 4S configuration, this figure ranges from 16.8 to 10 V.
- Converting a screwdriver to 18650 lithium batteries (the vast majority of products have this exact size) requires taking into account the difference in dimensions with Ni-Mh cells. The cell diameter 18650 is 18 mm and the height is 65 mm. It is very important to calculate how many cells will fit in the case. It should be remembered that for a model with a power of 11.1 V you will need a number of cells that is a multiple of three. For a model with a power of 14.8 V - four. The controller and patching wires must also fit.
- The charging device for a lithium-based battery differs from the device for Ni-Mh modifications.
The article will discuss how to convert a screwdriver to lithium. The tool is equipped with a pair of Ni-Mh rechargeable batteries with a voltage of 12 V and a capacity of 2.6 Ah. Hitachi screwdriver conversion will be considered. Lithium batteries will provide the device with long-term service.
Selecting the nominal voltage
First of all, you should decide on the choice of voltage rating for a lithium-based device. The choice should be made between the 3S model (its voltage range is from 12.6 to 7.5 V) and the 4S-Li-Ion battery (voltage range is from 16.8 to 10 V).
Advantages of the second option
The second option is more suitable because the voltage in the battery drops quite quickly from maximum to minimum (from 16.8 to 14.8 V). For an electric motor, which, strictly speaking, is a screwdriver, exceeding 2.8 V is not a critical level.
The lowest voltage indicator is for the 3S-Li-Ion modification. It is equal to 7.5 V, which is insufficient for the normal functioning of the electrical device. By mounting four configurations, we will increase the battery capacity.
How to decide on the choice of lithium cells?
To select lithium-based cells, limiting factors must be identified. Currently, lithium devices are produced with a permissible current load value of 20-25 A.
Pulse current values (short, up to 1-2 seconds) reach 30-35 A. The battery configuration will not be damaged.
How many cells will fit in the case?
It will not be possible to assemble 4S2P (four serial connections and two parallel ones). Converting a screwdriver to 18650 lithium batteries assumes the presence of eight cells. How can they make it to four? Each cell will bear the maximum current load.
How to determine the maximum current in a screwdriver?
Converting a 12V screwdriver to lithium batteries involves connecting the device to a laboratory power source with a maximum current of 30 A. The limiter regulator is set to the maximum value. Having created the voltage level of the power source close to the nominal value of the future battery, we begin to smoothly pull the trigger. The current consumed by the screwdriver will rise to 5 A. Now you should sharply pull the trigger. This will short out the power circuit. The current will reach a power of 20-30 A. Perhaps its indicator would be much higher, but the power of the power source will not allow this to be recorded. This will be a short-term load current when you sharply press the trigger of the screwdriver. Any model of such a device will react similarly.
Next, you should clamp the tip of the screwdriver with a vice and observe to what value the current consumption will increase during the operating mode when the ratchet in the screwdriver is activated. The current indicator in this case increases to 10-12 A.
This way you can determine the value of the load current. In this case, it will be equal to 5 A at idle and 30 A at a sharp start, and at maximum load it will be 12 A. The manufacturer must select lithium cells whose nominal load current will be 10-20 A, and the pulse current - 25-30 A.
How to choose a controller?
So, the screwdriver is being converted to lithium batteries. Regular charging for the device is required. When choosing a controller, please note that the device must meet two parameters:
- rated operating voltage indicator;
- rated operating current.
With voltage, everything is very clear: if the battery is 11.1 V, then the controller will have the same voltage.
The term “rated operating current” refers to the protection capacity of the board. Thus, a 4 A controller is designed for a current mark of 4 A, and at 8 A an additional load is placed on it. In this case, the protective device will operate. All these technical data are presented in the passport of each controller modification. In this case, one modification may have a limiting current indicator of 30 A, and another - 50 A. And both of these devices will formally be suitable for operation. Also, when creating a lithium battery, there is a limitation in size. Therefore, you should purchase a controller that will fit in the body of an old battery.
Disassembly and assembly
Converting a screwdriver to lithium batteries includes the following steps:
- You should open the old battery by unscrewing five screws.
- Remove the Ni-Mh battery from the housing. It will be noticeable that the contact pad that engages with the contact group of the screwdriver is welded to the negative contact of one of the Ni-Mh cells. Welding points should be cut using a tool with a cutting stone built into it
- Wires are soldered to the contacts, the cross-section of which is at least 2 mm 2 for power terminals and 0.2 mm 2 for the thermistor. The contact pad is glued into the battery case using hot-melt adhesive.
- Based on the internal resistance indicator, four cells are selected on the meter. The value must be the same for all four devices.
- Lithium cells are glued together with hot glue so that they are compactly located in the housing.
- Welding of cells is carried out on a resistance welding machine using a nickel welding tape (its cross-section should be 2X10 mm).
Installing the protection board
This stage can show how lightweight the lithium battery design is. The weight of the Ni-Mh device was 536 g. The weight of the new lithium device is 199 g, which will be quite noticeable. We managed to win 337 g in weight. At the same time, an increase in energy capacity is observed.
The battery is mounted in the housing. The voids are filled with soft material from the packaging.
Connection to a screwdriver
- A sharp pull on the trigger triggers the current protection mechanism. But in reality, such a protective mode is unlikely to be needed when using the tool. If you do not specifically provoke the defense, the operation of the screwdriver will be stable.
- The tip should be clamped in a vice. The battery power freely activates the ratchet, which limits the increase in rotation speed.
- The screwdriver is discharged by The discharge current indicator should be 5 A.
- The battery is inserted into the standard charger. The measured charge current is 3 A, which is acceptable for lithium cells. For the LG INR18650HG2 configuration, the maximum charge current will be 4 A, which is indicated in the technical specifications.
How long does it take to replace batteries?
Converting a screwdriver to lithium batteries will take approximately 2 hours. If all parameters are checked, then it will take 4 hours.
You can do everything yourself, without the help of another person. But resistance welding and selection of batteries cannot be carried out without specialized equipment.
How else can you test the degree of charge besides the controller?
The screwdriver has been converted to use lithium batteries. The standard charger built into the case is an ideal option. But the cost of the controller is quite high. The device will cost $30, which is the same as the cost of the battery itself.
To test the charge level of a lithium battery on the go, without using a charger, you can use a special indicator RC helicopter lipo battery AKKU portable voltage meter tester alarm 2-6S AOK. The cost of the device is very low. It has a balancing and charging connector similar to the iMax6 device. The device is connected to the battery using an adapter. This voltage level control device is very convenient. It can measure from two to six lithium cells connected in series, and also give the total indicator or voltage of each element separately with extreme accuracy.
How much will it cost to replace a Ni-Mh with a lithium device?
What financial costs will it require to convert a screwdriver to a lithium battery?
The price of such a device consists of the cost of several components:
- the lithium-based 4S battery configuration costs RUB 2,200;
- purchasing a controller for charging and discharging plus a balancer costs 1,240 rubles;
- the cost of welding and assembly is 800 rubles.
It turns out that a do-it-yourself lithium battery costs 4,240 rubles.
For comparison, let's take a similar configuration from factory-produced lithium. For example, the Makita 194065-3 device is designed for a screwdriver. It has similar parameters. The cost of such a device is 6500 rubles. It turns out that converting a screwdriver to lithium batteries saves 2,300 rubles.
“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. Deciding 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 3 0A, 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
There hasn't been a review of converting a screwdriver to lithium for a long time :)
The review is mainly devoted to the BMS board, but there will be links to some other little things involved in converting my old screwdriver to 18650 lithium batteries.
In short, you can take this board; after a little finishing, it works quite well in a screwdriver.
PS: a lot of text, pictures without spoilers.
P.S. The review is almost an anniversary on the site - the 58000th, according to the address bar of the browser;)
What is this all for
I have been using a nameless two-speed 14.4 volt screwdriver, bought cheaply at a construction store for several years now. More precisely, not just completely nameless - it bears the brand of this construction store, but not some famous one either. Surprisingly durable, it hasn’t broken yet and does everything I ask of it - drilling, tightening and unscrewing screws, and working like a winder :)
But his native NiMH batteries did not want to work for so long. One of the two complete ones finally died a year ago after 3 years of operation, the second recently no longer lived, but existed - a full charge was enough for 15-20 minutes of operation of the screwdriver with interruptions.
At first I wanted to do it with little effort and simply replace the old cans with the same new ones. I bought these from this seller -
They worked great (albeit a little worse than their original counterparts) for two or three months, after which they died quickly and completely - after a full charge they were not even enough to tighten a dozen screws. I don’t recommend taking batteries from him - although the capacity initially corresponded to what was promised, they did not last long.
And I realized that I would still have to bother.
Well, now about the main thing :)
Having chosen Ali from the offered BMS boards, I settled on the one under review, based on its dimensions and parameters:- Model: 548604
- Overcharge cutoff at voltage: 4.28+ 0.05 V (per cell)
- Recovery after overcharge shutdown at voltage: 4.095-4.195V (per cell)
- Over-discharge voltage cut-off: 2.55±0.08 (per cell)
- Overcharge shutdown delay: 0.1s
- Temperature range: -30-80
- Short circuit shutdown delay: 100ms
- Overcurrent shutdown delay: 500 ms
- Cell balancing current: 60mA
- Working current: 30A
- Maximum current (protection trip): 60A
- Short circuit protection operation: self-healing after load disconnection
- Dimensions: 45x56mm
- Main functions: overcharge protection, overdischarge protection, short circuit protection, overcurrent protection, balancing.
All board components are placed on one side: 
The second side is empty and covered with a white mask: 
The part responsible for balancing during charging: 
This part is responsible for protecting cells from overcharge/overdischarge and it is also responsible for general protection against short circuit: 
Mosfets: 
It is assembled neatly, there are no obvious flux stains, the appearance is quite decent. The kit included a tail with a connector, which was immediately plugged into the board. The length of the wires in this connector is about 20-25 cm. Unfortunately, I didn’t take a picture of it right away.
What else did I order specifically for this alteration:
Batteries -
Nickel strips for soldering batteries: (yes, I know that you can solder with wires, but the strips will take up less space and will be more aesthetically pleasing :)) And initially I even wanted to assemble contact welding (not only for this alteration, of course), that’s why I ordered the strips, but laziness prevailed and I had to solder them.
Having chosen a free day (or rather, having blatantly sent all other matters away), I set about redoing it. To begin with, I disassembled the battery with dead Chinese batteries, threw out the batteries and carefully measured the space inside. Then I sat down to draw the battery holder and circuit board in a 3D editor. I also had to draw the board (without details) in order to try on everything assembled. It turned out something like this: 
According to the idea, the board is attached from above, one side into the grooves, the other side is clamped with an overlay, the board itself lies in the middle on a protruding plane so that when it is pressed it does not bend. The holder itself is made of such a size that it fits tightly inside the battery case and does not dangle there.
At first I thought about making spring contacts for batteries, but abandoned this idea. This is not the best option for high currents, so I left cutouts in the holder for nickel strips with which the batteries will be soldered. I also left vertical cutouts for the wires that should extend from the inter-can connections beyond the lid.
I set it to be printed on a 3D printer from ABS and after a few hours everything was ready :) 
When screwing everything on, I decided not to trust screws and fused these M2.5 plug-in nuts into the body: 
Got it here -
Great item for this type of use! It is fused slowly with a soldering iron. To prevent the plastic from packing inside when melting into blind holes, I screwed a bolt of suitable length into this nut and heated its head with a soldering iron tip with a large drop of tin for better heat transfer. The holes in the plastic for these nuts are left slightly smaller (0.1-0.2 mm) than the diameter of the outer smooth (middle) part of the nut. They hold very tightly, you can screw in and unscrew the bolts as much as you like and don’t be too shy with the tightening force.
In order to have the possibility of cell-by-cell monitoring and, if necessary, charging with external balancing, a 5-pin connector will stick out in the back wall of the battery, for which I quickly threw on a scarf and made it on the machine: 
The holder has a platform for this scarf.
As I already wrote, I soldered the batteries with nickel strips. Alas, this method is not without its drawbacks, and one of the batteries was so outraged by this treatment that it left only 0.2 volts on its contacts. I had to desolder it and solder another one, fortunately I took them with a reserve. Otherwise there were no difficulties. Using acid, we tin the battery contacts and nickel strips cut to the required length, then thoroughly wipe everything tinned and around it with cotton wool and alcohol (but you can also use water), and solder it. The soldering iron must be powerful and either be able to react very quickly to the tip cooling, or simply have a massive tip that will not cool instantly upon contact with a massive piece of iron.
Very important: during soldering and during all subsequent operations with the soldered battery pack, you must be very careful not to short-circuit any battery contacts! In addition, as indicated in the comments ybxtuj
, it is very advisable to solder them discharged, and I absolutely agree with him, this way the consequences will be easier if something does short out. A short circuit of such a battery, even a discharged one, can lead to big troubles. 
By the way, I used silicone insulated wires everywhere - they do not react to heat at all and are very flexible. I bought several sections on Ebay, but I don’t remember the exact link... I really like them, but there is a minus - silicone insulation is not very mechanically strong and is easily damaged by sharp objects.
I tried on the batteries and the board in the holder - everything is excellent: 
I tried on a handkerchief with a connector, used a Dremel to cut out a hole in the battery case for the connector... and missed the height and took the size from the wrong plane. The result was a decent gap like this: 
Now all that remains is to solder everything together.
I soldered the included tail onto my scarf, cutting it to the required length: 
I also soldered the wires from the inter-can connections there. Although, as I already wrote, it was possible to solder them to the corresponding contacts of the BMS board, there is also an inconvenience - in order to remove the batteries, you will need to unsolder not only the plus and minus wires from the BMS, but also three more wires, but now you can simply pull out the connector.
I had to tinker a little with the battery contacts: in the original version, the plastic part (holding the contacts) inside the battery leg is pressed by one battery standing directly under it, but now I had to think about how to fix this part, so as not to be tight. Here's the detail: 
In the end, I took a piece of silicone (left over from pouring some form), cut off a roughly suitable piece from it and inserted it into the leg, pressing that part. At the same time, the same piece of silicone presses the holder with the board, nothing will dangle.
Just in case, I laid Kapton insulating tape over the contacts, and grabbed the wires with a few snot drops of hot glue so that they would not get between the halves of the case when assembling it. 
Charging and balancing
I left the original charger from the screwdriver, it just produces about 17 volts at idle. True, charging is stupid and there is no current or voltage stabilization in it, there is only a timer that turns it off about an hour after the start of charging. The current output is about 1.7A, which, although a bit too much, is acceptable for these batteries. But this is until I complete it to normal, with stabilization of current and voltage. Because now the board refuses to balance one of the cells, which initially had a charge of 0.2 volts more. The BMS turns off the charge when the voltage on this cell reaches 4.3 volts, respectively, on the rest it remains within 4.1 volts.I read somewhere a statement that this BMS normally balances only with CV/CC charging, when the current gradually decreases at the end of the charge. Perhaps this is true, so charging upgrades await me ahead :)
I haven’t tried to discharge it completely, but I’m sure that the discharge protection will work. There are videos on YouTube with tests of this board, everything works as expected.
And now about the rake
All banks are charged to 3.6 volts, everything is ready to start. I insert the battery into the screwdriver, pull the trigger and... I’m sure that more than one person familiar with this rake now thought, “And the hell started your screwdriver” :) Absolutely right, the screwdriver twitched slightly and that’s it. I release the trigger, press again - the same thing. I press it smoothly - it starts and accelerates, but if you start it a little faster - it fails.“Well...,” I thought. The Chinese probably indicated Chinese amps in the specification. Well, okay, I have an excellent thick nichrome wire, now I’ll solder a piece of it on top of the shunt resistors (there are two 0.004 Ohm in parallel) and I will, if not happiness, then at least some improvement in the situation. There was no improvement. Even when I completely eliminated the shunt from the work, simply soldering the minus of the battery after it. That is, it’s not that there has been no improvement, but that there have been no changes at all.
And then I went online and discovered that there was no copyright for this rake - they had long been trodden by others. But somehow there was no solution in sight, except for the cardinal one - buy a board suitable specifically for screwdrivers.
And I decided to try to get to the root of the problem.
I dismissed the assumption that the overload protection was triggered during inrush currents, since even without the shunt nothing changed.
But still I looked with an oscilloscope at a homemade 0.077 ohm shunt between the batteries and the board - yes, PWM is visible, sharp consumption peaks with a frequency of approximately 4 kHz, 10-15 ms after the start of the peaks the board cuts off the load. But these peaks showed less than 15 amperes (based on the shunt resistance), so it’s definitely not a matter of current overload (as it turned out later, this is not entirely true). And the ceramic resistance of 1 Ohm did not cause a shutdown, but the current was also 15 amperes.
There was also the option of a short-term drawdown on the banks during startup, which triggered the overdischarge protection, and I went to see what was happening on the banks. Well, yes, horror is happening there - the peak drawdown is up to 2.3 volts on all banks, but it is very short - less than a millisecond, while the board promises to wait a hundred milliseconds before turning on the overdischarge protection. “The Chinese indicated Chinese milliseconds,” I thought and went to look at the voltage control circuit of the cans. It turned out that it contains RC filters that smooth out sudden changes (R=100 Ohm, C=3.3 uF). After these filters, already at the input of the microcircuits that control the banks, the drawdown was smaller - only up to 2.8 volts. By the way, here is the datasheet for the can control chips on this DW01B board -
According to the datasheet, the response time to overdischarge is also considerable - from 40 to 100 ms, which does not fit into the picture. But okay, there’s nothing more to assume, so I’ll change the resistance in the RC filters from 100 Ohms to 1 kOhm. This radically improved the picture at the input of the microcircuits; there were no more drawdowns of less than 3.2 volts. But it didn’t change the behavior of the screwdriver at all - a slightly sharper start - and then shut up.
“Let’s go with a simple logical move”©. Only these DW01B microcircuits, which control all discharge parameters, can cut off the load. And I looked at the control outputs of all four microcircuits with an oscilloscope. All four microcircuits do not make any attempts to disconnect the load when the screwdriver starts. And the control voltage disappears from the mosfets gates. Either mysticism or the Chinese have screwed up something in a simple circuit that should be between microcircuits and mosfets.
And I started reverse engineering this part of the board. With swearing and running from the microscope to the computer. 
Here's what we ended up with: 
In the green rectangle are the batteries themselves. In blue - the keys from the outputs of the protection chips, also nothing interesting, in a normal situation their outputs to R2, R10 are simply “hanging in the air”. The most interesting part is in the red square, which is where, as it turned out, the dog rummaged. I drew the mosfets one at a time for simplicity, the left one is responsible for discharging to the load, the right one is for the charge.
As far as I understand, the reason for the shutdown is in resistor R6. Through it, “iron” protection against current overload is organized due to the voltage drop on the mosfet itself. Moreover, this protection works like a trigger - as soon as the voltage at the base of VT1 begins to increase, it begins to reduce the voltage at the gate of VT4, from which it begins to reduce conductivity, the voltage drop across it increases, which leads to an even greater increase in the voltage at the base of VT1 and an avalanche-like a process leading to the complete opening of VT1 and, accordingly, the closing of VT4. Why does this happen when starting a screwdriver, when the current peaks do not even reach 15A, while a constant load of 15A works - I don’t know. Perhaps the capacitance of the circuit elements or the inductance of the load plays a role here.
To check, I first simulated this part of the circuit: 
And this is what I got from the results of her work: 
The X axis is time in milliseconds, the Y axis is voltage in volts.
On the bottom graph - the load is turned on (you don’t have to look at the numbers on Y, they are arbitrary, just up - the load is on, down - off). The load is a resistance of 1 ohm.
In the top graph, red is the load current, blue is the voltage at the mosfet gate. As you can see, the gate voltage (blue) decreases with each pulse of load current and eventually drops to zero, which means the load is turned off. And it is not restored even when the load stops trying to consume something (after 2 milliseconds). And although other mosfets with different parameters are used here, the picture is the same as in the BMS board - an attempt to start and shutdown after a few milliseconds.
Well, let’s take this as a working hypothesis and, armed with new knowledge, let’s try to chew on this piece of Chinese science :)
There are two options here:
1. Place a small capacitor in parallel with resistor R1, this is: 
The capacitor is 0.1 uF, according to the simulation it is possible even less, up to 1 nf.
The result of the simulation in this version: 
2. Remove resistor R6 altogether: 
The result of the simulation of this option: 
I tried both options - both work. In the second option, the screwdriver does not turn off under any circumstances - start, rotation is blocked - it turns (or tries with all its might). But somehow it’s not entirely peaceful to live with the protection turned off, although there is still protection against short circuits on the microcircuits.
With the first option, the screwdriver starts confidently with any pressure. I was able to achieve shutdown only when I started it at second speed (increased for drilling) with the chuck blocked. But even then it jerks quite strongly before turning off. At first speed I could not get it to turn off. I left this option for myself; I am completely satisfied with it.
There are even empty spaces for components on the board, and one of them seems to be specially designed for this capacitor. It was designed for the size of SMD 0603, so I soldered 0.1 uF here (circled it in red): 
RESULT
The board fully met expectations, although it was a surprise :)I don’t see the point in describing the pros and cons, it’s all in its parameters, I’ll point out only one advantage: a completely minor modification turns this board into a fully functional one with screwdrivers :)
PS: damn, it took me less time to remodel the screwdriver than it took me to write this review :)
ZZY: perhaps my comrades who are more experienced in power and analogue circuitry will correct me on something, I myself am a digital and analogue person through the roof :)
The industry has been making screwdrivers for a long time, and many people have older models with nickel-cadmium and nickel-metal hydride batteries. Converting a screwdriver to lithium will improve the performance characteristics of the device without buying a new tool. Now many companies offer services for converting screwdriver batteries, but you can do it yourself.
Benefits of lithium-ion batteries
Nickel-cadmium batteries have a low price, withstand many charging cycles, and are not afraid of low temperatures. But the battery capacity will decrease if you charge it before it is completely discharged (memory effect).
Lithium-ion batteries have the following advantages:
- high capacity, which will ensure longer operating time of the screwdriver;
- smaller size and weight;
- Retains charge well when not in use.
But a lithium battery for a screwdriver does not withstand full discharge well, so factory tools on such batteries are equipped with additional circuit boards that protect the battery from overheating, short circuit, and overcharging to avoid explosion or complete discharge. When the microcircuit is installed directly into the battery, the circuit opens if the unused battery is located separately from the tool.
Difficulties in reworking
Li-Ion batteries have objective disadvantages, such as poor performance at low temperatures. In addition, when converting a screwdriver to 18650 lithium batteries, you may encounter a number of difficulties:
- The 18650 standard means that the diameter of one battery cell is 18 mm with a length of 65 mm. These dimensions do not coincide with the dimensions of the nickel-cadmium or nickel-metal hydride elements previously installed in the screwdriver. Replacing batteries will require placing them in a standard battery case, plus installing a protective microcircuit and connecting wires;
- The output voltage of lithium cells is 3.6 V, and for nickel-cadmium cells it is 1.2 V. Let’s say the nominal voltage of an old battery is 12 V. Such a voltage cannot be provided when connecting Li-Ion cells in series. The scope of voltage fluctuations during charge-discharge cycles of an ion battery also changes. Accordingly, converted batteries may not be compatible with the screwdriver;
- Ion batteries differ in the specifics of their operation. They do not withstand overcharge voltages greater than 4.2 V and discharge voltages less than 2.7 V until they fail. Therefore, when the battery is rebuilt, a protective board must be installed in the screwdriver;
- The existing charger may not be able to be used for a screwdriver with a Li-Ion battery. You will also need to remake it or purchase another one.
Important! If a drill or screwdriver is cheap and not of very high quality, then it is better not to remodel it. This may cost more than the cost of the tool itself.
Battery selection
Screwdrivers often use 12 V batteries. Factors to consider when choosing a Li-Ion battery for a screwdriver:
- Such instruments use elements with high discharge current values;
- In many cases, the capacity of the element is inversely related to the discharge current, so you cannot select it based on capacity alone. The main indicator is current. The value of the operating current of the screwdriver can be found in the tool passport. Usually it is from 15 to 30-40 A;
- When replacing a screwdriver battery with a Li-Ion 18650, it is not recommended to use cells with different capacity values;
- Sometimes there are tips to use a lithium battery from an old laptop. This is absolutely unacceptable. They are designed for a much lower discharge current and have unsuitable technical characteristics;
- The number of elements is calculated based on the approximate ratio - 1 Li-Ion to 3 Ni-Cd. For a 12-volt battery, you will need to replace 10 old cans with 3 new ones. The voltage level will be slightly reduced, but if 4 elements are installed, the increased voltage will shorten the life of the motor.
Important! Before assembly, it is necessary to fully charge all elements for equalization.
Disassembling the battery case
The case is often assembled using self-tapping screws, other options are assembled using latches or glue. The glued block is the most difficult to disassemble; you have to use a special hammer with a plastic head so as not to damage parts of the body. Everything from inside is removed. You can reuse only the contact plates or the entire terminal assembly for connecting to a tool or charger.
Battery Cell Connection
CompoundLi– Ionbatteries for screwdriverperformed in several ways:
- The use of special cassettes. The method is fast, but the contacts have a high transition resistance and can quickly be destroyed by relatively high currents;
- Soldering. A method suitable for those who know how to solder, since you need to have certain skills. Soldering must be done quickly, because the solder cools quickly, and prolonged heating can damage the battery;
- Spot welding. Is the preferred method. Not everyone has a welding machine; such services can be provided by specialists.
Important! The elements must be connected in series, then the battery voltage is added, but the capacity does not change.
At the second stage, the wires are soldered to the contacts of the assembled battery and to the protective board according to the connection diagram. Wires with a cross-sectional area of 1.5 mm² are soldered to the contacts of the battery itself for power circuits. For other circuits, you can take thinner wires - 0.75 mm²;
A piece of heat shrink tubing is then placed over the battery, but this is not necessary. You can also put heat shrink on the protective microcircuit to isolate it from contact with the batteries, otherwise sharp solder protrusions can damage the shell of the element and cause a short circuit.
Further battery replacement consists of the following steps:
- The disassembled parts of the body are well cleaned;
- Since the dimensions of the new battery cells will be smaller, they need to be securely fixed: glued to the inner wall of the case with Moment glue or sealant;
- The positive and negative wires are soldered to the old terminal block, it is placed in its original place in the case and fixed. The protective board is laid, the parts of the battery pack are connected. If they were previously glued, then “Moment” is used again.
The lithium-ion battery of the screwdriver will not function properly without the BMS protection board. The copies sold have different parameters. The BMS 3S marking assumes, for example, that the board is designed for 3 elements.
What you need to pay attention to in order to choose a suitable microcircuit:
- The presence of balancing to ensure uniform charge of the elements. If it is present, the description of the technical data should include the value of the balancing current;
- The maximum value of operating current that can be withstood for a long time. On average, you need to focus on 20-30 A. But this depends on the power of the screwdriver. Low-power ones need 20 A, high-power ones – from 30 A;
- Voltage at which the batteries are switched off when overcharging (about 4.3 V);
- The voltage at which the screwdriver turns off. This value must be selected based on the technical parameters of the battery cell (minimum voltage - about 2.6 V);
- Overload protection current;
- Resistance of transistor elements (select the minimum value).
Important! The magnitude of the trip current during overload is not very important. This value is adjusted to the operating load current. In case of short-term overloads, even if the tool has turned off, you must release the start button, and then you can continue to work.
Whether the controller has an autostart function can be determined by the presence of the “Automatic recovery” entry in the technical data. If there is no such function, then in order to start the screwdriver again after the protection has tripped, you will need to remove the battery and connect it to the charger.
Charger
The lithium-ion battery of the screwdriver cannot be charged by connecting it to a conventional power supply. A charger is used for this. The power supply simply produces a stable charge voltage within specified limits. And in the charger, the determining parameter is the charge current, which affects the voltage level. Its meaning is limited. The charger circuit contains nodes responsible for stopping the charging process and other protective functions, for example, shutdown in case of incorrect polarity.
The simplest charger is a power supply with a resistance included in the circuit to reduce the charging current. Sometimes they also connect a timer that fires after a set time period has passed. All of these options are not conducive to long battery life.
Charging methodsLI Ionbatteries for screwdriver:
- Using a factory charger. Often it is also suitable for charging a new battery;
- Reworking the charger circuit, with the installation of additional circuit elements;
- Purchase of a ready-made memory. A good option is IMax.
Let's say there is an old Makita DC9710 charger for charging a 12 V Ni-Cd battery, which has an indication in the form of a green LED signaling the end of the process. The presence of a BMS board will allow you to stop the charge when the specified voltage limits per element are reached. The green LED will not light up, but the red one will simply go out. The charge is complete.
The Makita DC1414 T charger is designed to charge a wide range of 7.2-14.4 V batteries. In it, when the protective shutdown is triggered at the end of the charge, the indication will not work correctly. The red and green lights flash, which also signals the end of the charge.
The cost of replacing screwdriver batteries with lithium-ion ones depends on the power of the tool, the need to buy a charger, etc. But if the drill/driver is in good functional condition and the charger does not require major alteration or replacement, then for a couple of thousand rubles you can get an improved power tool with increased battery life.
Video
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.
