BMS lithium battery protection controller for screwdriver. We transfer a cordless screwdriver from ni-cad batteries to li-ion batteries, with BMS and dc-dc down converter. Connecting battery cells
Greetings to all who looked at the light. The review will focus, as you probably already guessed, on two simple handkerchiefs designed to control the assembly of Li-Ion batteries, called BMS. The review will be testing, as well as several options for converting a screwdriver for lithium based on these boards or similar. Who cares, you are welcome under the cat.
General form:
Brief performance characteristics of the boards:
Note:
I want to warn you right away - with a balancer, only a blue board, red without a balancer, i.e. this is purely an overcharge/overdischarge/short circuit/high load current protection board. And also, contrary to some beliefs, none of them has a charge controller (CC / CV), therefore, a special scarf with a fixed voltage and current limitation is required for their work.
Board dimensions:
The dimensions of the boards are quite small, only 56mm * 21mm for blue and 50mm * 22mm for red: 
Here is a comparison with AA and 18650 batteries: 
Appearance:
Let's start with blue protection board :
On closer examination, you can see the protection controller - S8254AA and balancing components for the 3S assembly: 
Unfortunately, the operating current, according to the seller, is only 8A, but judging by the datasheets, one AO4407A mosfet is designed for 12A (peak 60A), and we have two of them: 
I also note that the balancing current is quite small (about 40mA) and balancing is activated as soon as all cells / banks go into CV mode (second phase of charge).
Connection: 
simpler, because it does not have a balancer: 
It is also made on the basis of the protection controller - S8254AA, but is designed for a higher operating current of 15A (again, according to the manufacturer): 
According to the datasheets on the used power mosfets, the operating current is declared 70A, and the peak 200A, even one mosfet is enough, and we have two of them: 
Connection similar: 
In total, as we can see, on both boards there is a protection controller with the necessary decoupling, power mosfets and shunts for controlling the passing current, but the blue one also has a built-in balan. I didn't really go into the circuit, but it looks like the power mosfets are paralleled, so the operating currents can be multiplied by two. These handkerchiefs do not know about the charge algorithm (CC / CV). In confirmation that these are protection boards, one can judge by the datasheet for the S8254AA controller, in which there is not a word about the charging module: 
The controller itself is designed for a 4S connection, therefore, with some refinement (according to the datasheet) - soldering the capacitor and resistor, it is possible that the red scarf will work: 
It is not so easy to modify the blue scarf to 4S, you will have to solder the elements of the balancer.
Board testing:
So, let's move on to the most important thing, namely, to what extent they are suitable for real use. For testing, the following devices will help us:
- assembly module (three three / four register voltmeters and a holder for three 18650 batteries), which flashed in my review of the charger, however, already without a balancer: 
- two-register amvoltmeter for current control (lower readings of the device): 
- step-down DC / DC converter with current limiting and the ability to charge lithium: 
- charging and balancing device iCharger 208B for discharging the entire assembly
The stand is simple - the converter board supplies a fixed constant voltage of 12.6V and limits the charging current. By voltmeters, we look at what voltage the boards operate and how the banks are balanced.
To begin with, let's look at the main feature of the blue board, namely balancing. There are 3 cans in the photo, charged at 4.15V / 4.18V / 4.08V. As you can see - imbalance. We apply voltage, the charging current gradually drops (lower device): 
Since the handkerchief does not have any indicators, the end of balancing can only be assessed by eye. The ammeter for more than an hour before the end already showed zero. For those who are interested, here is a short video about how the balancer works in this board:
As a result, the banks are balanced at the level of 4.210V / 4.212V / 4.206V, which is very good: 
When a voltage is applied a little more than 12.6V, as I understand it, the balancer is inactive and as soon as the voltage on one of the cans reaches 4.25V, then the S8254AA protection controller turns off the charge: 
The same situation with the red board, the S8254AA protection controller turns off the charge also at the level of 4.25V: 
Now let's go through the load cutoff. I will discharge, as already mentioned above, with the iCharger 208B charging and balancing device in 3S mode with a current of 0.5A (for more accurate measurements). Since I don’t really want to wait for the discharge of the entire battery, so I took one discharged battery (pictured green Samson INR18650-25R).
The blue board disconnects the load as soon as the voltage on one of the cans reaches 2.7V. In the photo (no load->before shutdown->end): 
As you can see, exactly at 2.7V the board turns off the load (the seller stated 2.8V). It seems to me that it is a bit high, especially if you take into account the fact that in the same screwdrivers the loads are huge, therefore, and the voltage drop is large. Nevertheless, it is desirable in such devices to have a cut-off under 2.4-2.5V.
The red board, on the contrary, turns off the load as soon as the voltage on one of the cans reaches 2.5V. In the photo (no load->before shutdown->end): 
Here, in general, everything is excellent, but there is no balancer.
Conclusion: my personal opinion is that for a power tool, a regular protection board without a balancer (red) is perfect. It has high operating currents, the optimum cutoff voltage is 2.5V, and it can be easily upgraded to a 4S configuration (14.4V / 16.8V). I think this is the most optimal choice for converting a budget shurika to lithium.
Now for the blue scarf. Of the pluses - the presence of balancing, but the operating currents are still small, 12A (24A) this is for Shurik with a torque of 15-25Nm a little small, especially when the cartridge is already almost heavy Yes and napryazhenie otcechki vcego 2,7V, a znachit IT'S chto at cilnoy nagruzke chact emkocti batarei octanetcya nevoctrebovannoy, pockolku nA vycokix tokax procadka napryazheniya bankax prilichnaya nA, and they are normally yes raccchitany nA 2,5V. It is better to use a blue scarf in some homemade products, but again, this is my personal opinion.
Possible application schemes or how to convert Shurik's power to lithium:
So, how can you change the power of your favorite Shurik from NiCd to Li-Ion / Li-Pol? This topic has already been sufficiently hackneyed and solutions, in principle, have been found, but I will briefly repeat myself.
To begin with, I’ll say only one thing - in budget shuriks there is only a protection board from overcharging / overdischarging / short circuit / high load current (analogue of the observed red board). There is no balancing there. Moreover, even in branded power tools there is no balancing. The same applies to all tools, where there are proud inscriptions "Charging in 30 minutes." Yes, they charge in half an hour, but the shutdown occurs as soon as the voltage on one of the cans reaches the nominal value or the protection board works. It is not difficult to guess that the banks will not be fully charged, but the difference is only 5-10%, so it is not so important. The main thing to remember is that the charge with balancing goes on for at least a few hours. Therefore, the question arises, do you need it?
So, the most common option looks like this:
Network charger with stabilized output 12.6V and current limit (1-2A) -> protection board ->
As a result: cheap, fast, acceptable, reliable. Balancing varies depending on the state of the cans (capacitance and internal resistance). Quite a working option, but after some time, the imbalance will let you know about itself by the time of work.
More correct option:
Network charger with stabilized output 12.6V, current limiting (1-2A) -> protection board with balancing -> 3 connected batteries in series
As a result: expensive, fast / slow, high quality, reliable. Balancing is normal, battery capacity is maximum
In total, we will try to make it look like the second option, here's how you can do it:
1) Li-Ion / Li-Pol batteries, protection boards and a specialized charger and balancing device (iCharger, iMax). Additionally, you will have to remove the balancing connector. There are only two minuses - model chargers are not cheap, and it’s not very convenient to maintain. Pluses - high current charge, high current balancing cans
2) Li-Ion / Li-Pol batteries, protection board with balancing, DC converter with current limiting, PSU
3) Li-Ion / Li-Pol batteries, protection board without balancing (red), DC converter with current limiting, PSU. Of the minuses, only that over time, an imbalance of cans will appear. To minimize the imbalance, before altering the shura, it is necessary to adjust the voltage to one level and it is advisable to take cans from one batch
The first option is suitable only for those who have a model memory, but it seems to me that if they needed it, then they already changed their Shurik a long time ago. The second and third options are practically the same and have the right to life. You just need to choose what is more important - speed or capacity. I believe that the most optimal option is the last one, but only once every few months you need to balance the banks.
So, enough chatter, let's move on to the alteration. Since I don’t have a Shurik on NiCd batteries, therefore, about the alteration only in words. We will need:
1) Power supply:
First option. Power supply unit (PSU), at least 14V or more. The output current is desirable not less than 1A (ideally about 2-3A). We will need a power supply from laptops / netbooks, from chargers (output more than 14V), power supplies for LED tapes, video recording equipment (DIY PSU), for example or: 
- Step-down DC / DC converter with current limiting and the possibility of charging lithium, for example or: 
- The second option. Ready-made power supplies for shurikov with current limiting and 12.6V output. They are not cheap, as an example from my review of the MNT screwdriver -: 
- The third option. : 
2) Protection board with or without a balancer. It is advisable to take the current with a margin: 
If the option without a balancer is used, then it is necessary to solder the balancing connector. This is necessary to control the voltage on the banks, i.e. to evaluate the imbalance. And as you understand, it will be necessary to periodically recharge the battery with a simple TP4056 charging module if the imbalance has begun. i.e. once in several months, we take a TP4056 scarf and charge in turn all the banks, which, at the end of the charge, have a voltage below 4.18V. This module correctly cuts off the charge at a fixed voltage of 4.2V. This procedure will take an hour and a half, but the banks will be more or less balanced.
Written a little chaotically, but for those who are in the tank:
After a couple of months, we put the screwdriver battery on charge. At the end of the charge, we take out the balancing tail and measure the voltage on the banks. If you get something like this - 4.20V / 4.18V / 4.19V, then balancing is, in principle, not needed. But if the picture is as follows - 4.20V / 4.06V / 4.14V, then we take the TP4056 module and charge two banks in turn to 4.2V. I don’t see any other option, except for specialized balancer chargers.
3) High current batteries: 
I have previously written a couple of small reviews about some of them - and. Here are the main models of high current 18650 Li-Ion batteries:
- Sanyo UR18650W2 1500mah (20A max.)
- Sanyo UR18650RX 2000mah (20A max.)
- Sanyo UR18650NSX 2500mah (20A max.)
- Samsung INR18650-15L 1500mah (18A max.)
- Samsung INR18650-20R 2000mah (22A max.)
- Samsung INR18650-25R 2500mah (20A max)
- Samsung INR18650-30Q 3000mah (15A max)
- LG INR18650HB6 1500mah (30A max.)
- LG INR18650HD2 2000mah (25A max.)
- LG INR18650HD2C 2100mah (20A max)
- LG INR18650HE2 2500mah (20A max.)
- LG INR18650HE4 2500mah (20A max.)
- LG INR18650HG2 3000mah (20A max.)
- SONY US18650VTC3 1600mah (30A max.)
- SONY US18650VTC4 2100mah (30A max.)
- SONY US18650VTC5 2600mah (30A max)
I recommend the tried and tested cheap Samsung INR18650-25R 2500mah (20A max.), Samsung INR18650-30Q 3000mah (15A max.) or LG INR18650HG2 3000mah (20A max.). I didn’t particularly encounter other jars, but my personal choice is Samsung INR18650-30Q 3000mah. Skis had a small technological defect and fakes with low current output began to appear. I can throw off an article on how to distinguish a fake from the original, but a little later, you need to look for it.
How to connect all this economy:
Well, a couple of words about the connection. We use high-quality copper stranded wires of decent cross section. These are high-quality acoustic or conventional ball screw screws / PVC with a cross section of 0.5 or 0.75 mm2 from the home (we rip off the insulation and get high-quality wires of different colors). The length of the connecting conductors must be kept to a minimum. Batteries, preferably from one batch. Before connecting them, it is advisable to charge them up to one voltage so that there is no unbalancing as long as possible. Soldering batteries is not difficult. The main thing is to have a powerful soldering iron (60-80W) and an active flux (soldering acid, for example). Soldered with a bang. The main thing then is to wipe the place of soldering with alcohol or acetone. The batteries themselves are placed in the battery compartment from old NiCd cans. It is better to have a triangle, minus to plus or, as the people say, “valt”, by analogy with this (one battery will be located the other way around): 
So, the wires connecting the batteries will turn out to be short, therefore, the drop in the precious voltage in them under load will be minimal. I do not recommend using holders for 3-4 batteries, they are not intended for such currents. Side and balancing conductors are not so important and may be of a smaller cross section. Ideally, it is better to put the batteries and the protection board in the battery compartment, and the DC-down converter separately in the docking station. The charge / charged LED indicators can be replaced with your own and brought to the docking station case. If desired, you can add a minivoltmeter to the battery module, but this is extra money, because the total voltage on the battery will only indirectly tell about the residual capacity. But if there is a desire, why not. Here: 
Now let's estimate the prices:
1) BP - from 5 to 7 dollars
2) DC / DC converter - from 2 to 4 dollars
3) Protection boards - from 5 to 6 dollars
4) Batteries - from 9 to 12 dollars (3-4 $ thing)
In total, an average of $15-20 for a remake (with discounts / coupons), or $25 without them.
Benefits:
I have previously mentioned the advantages of lithium power supplies (Li-Ion / Li-Pol) over nickel (NiCd). In our case, a face-to-face comparison is a typical Shurik battery from NiCd batteries versus lithium:
+ high energy density. A typical nickel battery 12S 14.4V 1300mah has a stored energy of 14.4 * 1.3 = 18.72Wh, and a lithium battery 4S 18650 14.4V 3000mah - 10.8 * 3 = 43.2Wh
+ no memory effect, i.e. you can charge them at any time without waiting for a full discharge
+ smaller dimensions and weight with the same parameters with NiCd
+ fast charge time (not afraid of high charge currents) and clear indication
+ low self-discharge
Of the minuses of Li-Ion, only:
- low frost resistance of batteries (afraid of negative temperatures)
- requires balancing of cans when charging and the presence of protection against overdischarge
As you can see, the advantages of lithium are obvious, so it often makes sense to change the power supply ...
Conclusion: The reviewed handkerchiefs are not bad, they should be suitable for any task. If I had a Shurik on NiCd banks, I would choose a red handkerchief for alteration, :-) ...
The product was provided for writing a review by the store. The review is published in accordance with clause 18 of the Site Rules.
For a long time there was no review of the conversion of a screwdriver to lithium :)
The review focuses on the main BMS board, but there will be links to some other little things involved in the transfer of my old screwdriver to 18650 lithium batteries.
In short - you can take this board, after a little finishing, it works quite normally in a screwdriver.
PS: a lot of text, pictures without spoilers.
P.S. The review is almost anniversary on the site - the 58000th, according to the address bar of the browser;)
What is this all for
I have been working for several years, bought cheaply in a construction store, an unnamed two-speed screwdriver for 14.4 volts. More precisely, not completely nameless - it bears the mark of this construction worker, but not some eminent one either. Surprisingly tenacious, still hasn't broken down and does everything that I demand from it - drilling, screwing and unwinding, and how the winder works :)
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 one has 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 with small forces and just replace the old cans with the same new ones. Bought these from this seller
They worked perfectly (although a little worse than relatives) 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 do not recommend taking batteries from him - although the capacity initially corresponded to the promised one, they did not last long.
And I realized that I still have to be confused.
Well, now about the main thing :)
Having chosen Ali from the offered BMS boards, I settled on the monitored one, in terms of its size and parameters:- Model: 548604
- Voltage overcharge shutdown: 4.28+ 0.05 V (per cell)
- Recovery after overcharge shutdown at voltage: 4.095-4.195V (per cell)
- Over-discharge shutdown at voltage: 2.55±0.08 (per cell)
- Disable overcharge delay: 0.1s
- Temperature range: -30-80
- Short circuit trip delay: 100ms
- Overcurrent trip delay: 500ms
- Cell balancing current: 60mA
- Working current: 30A
- Maximum current (protection operation): 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 blank and covered with a white mask: 
The part responsible for balancing when charging: 
This part is responsible for protecting cells from overcharging / overdischarging, and it is also responsible for general short circuit protection: 
Mosfets: 
Assembled neatly, there are no frank streaks of flux, the view is quite decent. The kit included a tail with a connector, it was immediately plugged into the board. The length of the wires in this connector is about 20-25 cm. Unfortunately, I did not take a picture of it right away.
What else I ordered 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 turn out to be more aesthetically pleasing :)) Yes, and initially I even wanted to assemble contact welding (not only for this alteration, of course), and therefore I ordered strips, but laziness won and I had to solder.
Having chosen a free day (more precisely, brazenly sending all other cases away), I took up the alteration. To begin with, I dismantled the battery with dead Chinese batteries, threw out the batteries and carefully measured the space inside. Then I sat down to draw a battery holder and boards in a 3D editor. The board also had to be drawn (without details) in order to try on everything assembled. It turned out something like this: 
As planned, the board is attached from above, with one side into the grooves, the second 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 sits tightly inside the battery case and does not hang out there.
At first I thought about making spring contacts for batteries, but abandoned this idea. For high currents, this is not the best option, so I left cutouts for nickel strips in the holder, with which the batteries will be soldered. I also left vertical cutouts for wires that should go from the inter-jar connections outside the lid.
I set it to be printed on an ABS 3D printer and after a few hours everything was ready :) 
I decided not to trust the screws when screwing everything attached and fused these M2.5 nuts into the body: 
Take it here -
Great product for this kind of use! Melted slowly with a soldering iron. To prevent the plastic from stuffing inside when fused into blind holes, I screwed a bolt of a suitable length into this nut and heated its cap 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 (by 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 not be particularly shy with the tightening force.
In order to be able to control per jar and, if necessary, charge 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 provides a platform for this scarf.
As I already wrote, I soldered the batteries with nickel strips. Alas, this method is not without drawbacks, and one of the batteries was so indignant at such treatment that it left only 0.2 volts on its contacts. I had to solder it and solder another one, since I took them with a margin. Otherwise, there were no difficulties. With the help of acid, we tin the battery contacts and nickel strips cut to the desired length, then carefully wipe everything tinned and around it with cotton wool and alcohol (but it is also possible with water), and solder. The soldering iron must be powerful and either be able to react very briskly to the cooling of the tip, or simply have a massive tip that will not cool down instantly upon contact with a massive piece of iron.
Very important: during soldering and during all subsequent operations with a soldered battery pack, you must be very careful not to close any battery contacts! Also, as pointed out in the comments ybxtuj, it is very desirable to solder them discharged, and I absolutely agree with him, so the consequences will be easier if something still closes. A short circuit of such a battery, even a discharged one, can lead to big troubles.
I soldered wires to the three intermediate connections between the batteries - they will go to the BMS board connector for controlling banks and to the external connector. Looking ahead, I want to say that I did a little extra work with these wires - they can not be led to the board connector, but soldered to the corresponding pins B1, B2 and B3. These pins on the board itself are connected to the connector pins. 
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 Ebee, but I don’t remember the exact link ... I like them very much, but there is a minus - the silicone insulation is not very strong mechanically 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 scarf with a connector, cut a hole for the connector in the battery case with a dremel ... and missed the height, took the size from the wrong plane. It turned out a decent gap like this: 
Now it remains to solder everything together.
I soldered the tail that came with the kit to my scarf, cutting it to the desired length: 
I also soldered the wires from the interbank connections there. Although, as I already wrote, it was possible to solder them to the corresponding contacts of the BMS board, but there is also an inconvenience - in order to pull out the batteries, you will need to solder not only plus and minus from the BMS, but also three more wires, and now you can just pull out the connector.
I had to tinker with the battery contacts a little: in the native version, the plastic part (holding the contacts) inside the battery leg is pressed by one battery standing right under it, and now I had to think about how to fix this part, so as not to be tight. Here is that detail: 
In the end, he took a piece of silicone (left over from pouring some form), cut off an approximately 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 hang out.
Just in case, I laid Kapton electrical tape over the contacts, grabbed the wires with several snots and drops of hot melt adhesive so that they would not get between the halves of the case during its assembly. 
Charging and balancing
I left the charge from my screwdriver, it just gives out about 17 volts at idle. True, charging is stupid and there is no stabilization of current or voltage in it, there is only a timer that turns it off about an hour after the start of charging. The current gives out about 1.7A, which, although a bit much, is acceptable for these batteries. But this is until I finish it to normal, with current and voltage stabilization. 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 the 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 the case, so ahead of me is the modernization of charging :)
I did not try to discharge to the end, but I am 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 run. 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, “Damn, your screwdriver started!” :) Absolutely, 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 I start it a little sharper - it's a failure."That's it..." I thought. The Chinese probably indicated Chinese amps in the specification. Well, okay, I have an excellent thick nichrome wire, now I will solder a piece of it over shunt resistors (there are two of 0.004 Ohm in parallel) and if not happiness, then at least some improvement in the situation will come to me. There has been no improvement. Even when I completely excluded the shunt from work, simply soldering the minus of the battery after it. That is, not that there were no improvements, but no changes at all.
And then I got into the Internet and found that the copyright for this rake does not shine for me - they have long been trodden by others. But somehow the solution was not visible, except for the cardinal one - to buy a board that is suitable specifically for screwdrivers.
And I decided to try to get to the root of the problem.
I dismissed the assumptions that overload protection is triggered at inrush currents, since even without a shunt nothing changed.
But still I looked with an oscilloscope on a homemade 0.077 ohm shunt between the batteries and the board - yes, PWM is visible, sharp peaks in consumption with a frequency of about 4 kHz, 10-15 ms after the start of the peaks, the board cuts off the load. But these peaks showed less than 15 amps (based on the resistance of the shunt), so it's definitely not a current overload (as it turned out later, this is not entirely true). Yes, and a ceramic resistance of 1 ohm did not cause a shutdown, but the current is also under 15 amperes.
There was another option for a short-term drawdown on the banks at startup, from which the overdischarge protection is triggered, and I climbed to see what was happening on the banks. Well, yes, horror is happening there - a peak drawdown of 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 climbed to look at the voltage control circuit of the cans. It turned out that it has RC filters that smooth out sharp changes (R=100 Om, 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 microcircuits 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 suggest, so I’ll change the resistances in the RC filters from 100 Ohm to 1 kOhm. This radically improved the picture at the input of microcircuits, there were no more drawdowns of less than 3.2 volts. But the behavior of the screwdriver did not change at all - a slightly sharper start - and plugging.
"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 turn off the load when starting the screwdriver. And from the gates of the mosfets, the control voltage disappears. Either the mystic or the Chinese screwed up something in a simple circuit, which should be between microcircuits and mosfets.
And I started reverse engineering this part of the board. With obscenities and running from the microscope to the computer. 
Here is what emerged as a result: 
In the green rectangle are the batteries themselves. In blue - the keys from the outputs of the protection microcircuits, also nothing interesting, in a normal situation, their outputs to R2, R10 simply “hang in the air”. The most interesting part is in the red square, that's where, as it turned out, the dog rummaged. I drew mosfets one at a time for simplicity, the left one is responsible for the discharge into the load, the right one for the charge.
As far as I understand, the reason for the shutdown is in the resistor R6. Through it, an “iron” protection against current overload is organized due to the voltage drop on the mosfet itself. Moreover, this protection works as a trigger - as soon as the voltage at the base of VT1 starts to rise, it starts to reduce the voltage at the gate of VT4, from which it begins to reduce conductivity, the voltage drop on it increases, which leads to an even greater increase in the voltage at the base of VT1 and went avalanche a process leading to the full opening of VT1 and, accordingly, the closure of VT4. Why this happens when starting the screwdriver, when the current peaks do not reach even 15A, while a constant load of 15A works - I do not know. Perhaps the capacitance of the circuit elements or the load inductance plays a role here.
To test, I first made a simulation of this part of the circuit: 
And this is what I got as a result of her work: 
On the X axis - time in milliseconds, on the Y - voltage in volts.
On the lower graph - the load is turned on (you can not look at the numbers along Y, they are conditional, just up - the load is on, down - off). The load is a resistance of 1 ohm.
On the upper 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 load current pulse and eventually drops to zero, which means the load is turned off. And it does not recover 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 one to one as in the BMS board - an attempt to start and turn off in a matter of milliseconds.
Well, let's take this as a working hypothesis and, armed with new knowledge, let's try to crack this piece of Chinese science :)
There are two options here:
1. Put a small capacitor in parallel with resistor R1, this is: 
Capacitor 0.1 microfarad, according to the simulation it is possible and less, up to 1 nf.
The simulation result is as follows: 
2. Remove resistor R6 altogether: 
Simulation result of this option: 
I tried both options - both work. In the second option, the screwdriver does not turn off under any circumstances - start, rotation lock - turns (or tries hard). But somehow it’s not quite easy to live with disabled protection, although there is still protection against short circuits on microcircuits.
With the first option, the screwdriver starts confidently with any pressure. I was able to achieve a shutdown only when I started it at second speed (high for drilling) with a locked chuck. But even then it pulls quite strongly before shutting down. At the first speed, I could not get it off. I left this option to myself, it completely suits me.
There are even empty places for components on the board, and one of them seems to be specially designed for this capacitor. It is calculated for the size of SMD 0603, here I soldered 0.1 microfarads (circled it in red): 
TOTAL
The board fully lived up to expectations, although it brought 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 revision turns this board into a fully functional one with screwdrivers :)
PS: damn it, I redid the screwdriver in less time than I wrote this review :)
ZZY: perhaps my comrades, more experienced in power and analog circuitry, will correct me in something, I myself am a digital and analog perceive a deck through a stump :)
Cordless tools are more mobile and easier to use than their corded counterparts. But we must not forget about the significant drawback of the cordless tool, as you yourself understand the fragility of the 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 network one - it turned out to be very inconvenient. I had to buy the same, but a new 12 volt Interskol DA-12ER. The batteries in the new screwdriver lasted even less. As a result, two serviceable screwdrivers and not one working battery.
There is a lot of writing on the Internet about how to solve this problem. It is proposed to convert used 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 not to be so simple. The following describes what to pay attention to when upgrading a cordless tool.
For conversion you will need:
I'll start with 18650 lithium-ion batteries. Purchased at.
The nominal voltage of the 18650 elements is 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 larger capacity, as well as the absence of the so-called "memory effect". But lithium-ion batteries have serious disadvantages, namely:
1. Negative temperatures drastically reduce capacity, which cannot be said about nickel-cadmium batteries. Hence the conclusion - if the tool is often used at low temperatures, then replacing with Li-ion will not solve the problem.
2. A discharge below 2.9 - 2.5V and overcharging above 4.2V can be critical, complete failure is possible. Therefore, a BMS board is needed to control charge and discharge, if it is not installed, then new batteries will quickly fail.
On the Internet, they mainly describe how to convert a 14 volt screwdriver - it is ideal for retrofitting. With a series connection of four 18650 cells and a nominal voltage of 3.7V. we get 14.8V. - just what you need, even when fully charged, plus another 2V, this is not scary for the electric motor. And what about the 12V tool. There are two options, install 3 or 4 18650 elements, if three then it seems to be not enough, especially with partial discharge, and if four - a bit too much. I chose four and in my opinion made the right choice.
And now about the BMS board, it is also from AliExpress.
This is the so-called charge control board, battery discharge, specifically in my case CF-4S30A-A. As can be seen from the marking, it is calculated for a battery of four "cans" of 18650 and a discharge current of up to 30A. It also has a so-called “balancer” built into it, which controls the charge of each element separately and eliminates uneven charging. For the correct operation of the board, the batteries for the assembly are taken from the same capacity and preferably from the same batch.
In general, there are a great many BMS boards with different characteristics on sale. I don’t advise you to take it for a current below 30A - the board will constantly go into protection and to restore work on some boards you need to briefly apply charging current, and for this you need to remove the battery and connect it to the charger. There is no such drawback on the board that we are considering, just release the trigger of the screwdriver and in the absence of short circuit currents, the board will turn on by itself.
To charge the converted battery, the native universal charger was perfect. In recent years, Interskol began to equip its tools with universal chargers.
The photo shows to what voltage the BMS board charges my battery together with a standard charger. The voltage on the battery after charging 14.95V is slightly higher than what is needed for a 12 volt screwdriver, but it is rather even better. My old screwdriver became faster and more powerful, and fears that it would burn out after four months of use gradually dissipated. That seems to be all the main nuances, you can start reworking.
We disassemble the old battery.
We solder the old cans and leave the terminals together with the temperature sensor. If you remove the sensor as well, then when using a standard charger, it will not turn on.
According to the diagram in the photo, we solder 18650 cells into one battery. Jumpers between the "banks" must be made with a thick wire of at least 2.5 kv. mm, since the currents during the operation of the screwdriver are large, and with a small section, the power of the tool will drop sharply. The network writes that it is impossible to solder Li-ion batteries because they are afraid of overheating, and they recommend connecting using spot welding. You can only solder a soldering iron with a power of at least 60 watts. The most important thing is to solder quickly so as not to overheat the element itself.
It should look like it fits into the battery case.
Greetings to all who looked at the light. The review will focus, as you probably already guessed, on two simple scarves designed to control the assembly of Li-Ion batteries, called BMS. The review will include testing, as well as several options for converting a screwdriver to lithium based on these boards or similar ones. Who cares, you are welcome under the cat.
Update 1, Added a test of the working current of the boards and a short video on the red board
Update 2, Since the topic has aroused little interest, so I will try to supplement the review with several more ways to remake Shurik to get some simple FAQ
General form:
Brief performance characteristics of the boards:
Note:
I want to warn you right away - there is only a blue board with a balancer, a red one without a balancer, i.e. This is purely an overcharge/overdischarge/short/high load current protection board. And also, contrary to some beliefs, none of them has a charge controller (CC / CV), so they need a special scarf with a fixed voltage and current limit to work.
Board dimensions:
The dimensions of the boards are quite small, only 56mm * 21mm for the blue one and 50mm * 22mm for the red one:
Here is a comparison with AA and 18650 batteries:
Appearance:
Let's start with: 
On closer inspection, you can see the protection controller - S8254AA and balancing components for the 3S assembly: 
Unfortunately, according to the seller, the operating current is only 8A, but judging by the datasheets, one AO4407A mosfet is rated for 12A (peak 60A), and we have two of them:
I also note that the balancing current is quite small (about 40mA) and balancing is activated as soon as all cells / banks switch to CV mode (second charge phase).
Connection: 
simpler, because it does not have a balancer: 
It is also based on the protection controller - S8254AA, but is designed for a higher operating current of 15A (again, according to the manufacturer): 
According to the datasheets for the power mosfets used, the operating current is declared 70A, and the peak current is 200A, even one mosfet is enough, and we have two of them: 
Connection is similar: 
In total, as we can see, on both boards there is a protection controller with the necessary decoupling, power mosfets and shunts to control the passing current, but the blue one also has a built-in balancer. I haven't looked into the circuit too much, but it looks like the power mosfets are in parallel, so the operating currents can be multiplied by two. Important note - maximum operating currents are limited by current shunts! These scarves do not know about the charge algorithm (CC / CV). In confirmation that these are protection boards, one can judge by the datasheet for the S8254AA controller, in which there is not a word about the charging module: 
The controller itself is designed for a 4S connection, so with some refinement (judging by the datasheet) - soldering the conder and the resistor, the red scarf may work: 
It is not so easy to modify the blue scarf to 4S, you will have to solder the elements of the balancer.
Board testing:
So, let's move on to the most important thing, namely, how suitable they are for real use. For testing, the following devices will help us:
- a prefabricated module (three three / four register voltmeters and a holder for three 18650 batteries), which flashed in my review of the charger, however, already without a balancing tail: 
- two-register ampervoltmeter for current control (lower instrument readings): 
- step-down DC / DC converter with current limiting and the ability to charge lithium: 
- charger and balancer iCharger 208B to discharge the entire assembly
The stand is simple - the converter board supplies a fixed constant voltage of 12.6V and limits the charging current. Using voltmeters, we look at what voltage the boards work and how the banks are balanced.
To begin with, let's look at the main feature of the blue board, namely balancing. In the photo there are 3 cans charged at 4.15V / 4.18V / 4.08V. As you can see, imbalance. We apply voltage, the charging current gradually drops (lower device): 
Since the handkerchief does not have any indicators, the end of balancing can only be assessed by eye. The ammeter for more than an hour before the end was already showing zeros. For those who are interested, here is a short video about how the balancer works in this board:
As a result, the banks are balanced at the level of 4.210V/4.212V/4.206V, which is quite good:
When a voltage of a little more than 12.6V is applied, as I understand it, the balancer is inactive and as soon as the voltage on one of the cans reaches 4.25V, the S8254AA protection controller turns off the charge:
The situation is the same with the red board, the S8254AA protection controller also turns off the charge at the level of 4.25V:
Now let's go through the cutoff under load. I will discharge, as I mentioned above, with the iCharger 208B charging and balancing device in 3S mode with a current of 0.5A (for more accurate measurements). Since I don’t really want to wait for the discharge of the entire battery, so I took one discharged battery (pictured is a green Samson INR18650-25R).
The blue board disconnects the load as soon as the voltage on one of the cans reaches 2.7V. In the photo (no load->before shutdown->end):
As you can see, the board disconnects the load exactly at 2.7V (the seller stated 2.8V). It seems to me that it is a bit high, especially considering the fact that in the same screwdrivers the loads are huge, therefore, the voltage drop is also large. Nevertheless, it is desirable in such devices to have a cut-off under 2.4-2.5V.
The red board, on the contrary, turns off the load as soon as the voltage on one of the cans reaches 2.5V. In the photo (no load->before shutdown->end):
Here, in general, everything is fine, but there is no balancer.
Update 1: Load test:
The following stand will help us with the recoil current:
- all the same holder / holder for three 18650 batteries
- 4-register voltmeter (total voltage control)
- automotive incandescent lamps as a load (unfortunately, I only have 4 incandescent lamps of 65W each, I don’t have any more)
- multimeter HoldPeak HP-890CN for measuring currents (max 20A)
- high-quality copper stranded acoustic wires of large cross section
A few words about the stand: the batteries are connected with a “jack”, i.e. as if one after another, to reduce the length of the connecting wires, and therefore the voltage drop across them under load will be minimal: 
Connection of cans on the holder ("valtom"): 
The probes for the multimeter were high-quality wires with crocodiles from the iCharger 208B charging and balancing device, because HoldPeak's ones do not inspire confidence, and extra connections will introduce additional distortion.
First, let's test the red protection board, as the most interesting in terms of current load. Solder the power and side wires: 
It turns out something like this (load connections turned out to be of a minimum length): 
I already mentioned in the section on Shurik's alteration that such holders are not very suitable for such currents, but they will do for tests.
So, a stand based on a red scarf (according to measurements, no more than 15A): 
Briefly explain: the board holds 15A, but I do not have a suitable load to fit into this current, since the fourth lamp adds about 4.5-5A more, and this is already outside the handkerchief. At 12.6A, the power mosfets are warm, but not hot, just right for continuous operation. At currents over 15A, the board goes into protection. I measured with resistors, they added a couple of amps, but the stand has already been dismantled.
A huge plus of the red board is that there is no protection blocking. Those. when the protection is triggered, it does not need to be activated by applying voltage to the output contacts. Here is a short video:
I'll explain a little. Since incandescent lamps in cold form have low resistance, and besides, they are also connected in parallel, the scarf thinks that a short circuit has occurred and protection is triggered. But due to the fact that the board has no blocking, you can warm up the coils a little, making a “softer” start.
The blue scarf holds more current, but at currents of more than 10A, the power mosfets get very hot. At 15A, the handkerchief can withstand no more than a minute, because after 10-15 seconds the finger no longer holds the temperature. Fortunately, they cool down quickly, so for a short-term load they are quite suitable. Everything would be fine, but when the protection is triggered, the board is blocked and to unlock it is necessary to apply voltage to the output contacts. This option is clearly not for a screwdriver. In total, it holds a current of 16A, but the mosfets get very hot: 
Conclusion: my personal opinion is that a regular protection board without a balancer (red) is perfect for a power tool. It has high operating currents, an optimal cutoff voltage of 2.5V, and can be easily upgraded to a 4S configuration (14.4V / 16.8V). I think this is the best choice for converting a budget shura to lithium.
Now for the blue scarf. Of the pluses - the presence of balancing, but the operating currents are still small, 12A (24A) is somewhat not enough for a Shurik with a torque of 15-25Nm, especially when the cartridge almost stops when the screw is tightened. Yes, and the cut-off voltage is only 2.7V, which means that with a heavy load, part of the battery capacity will remain unclaimed, since at high currents the voltage drop on the banks is decent, and they are also designed for 2.5V. And the biggest disadvantage is that the board is blocked when the protection is triggered, so it is undesirable to use it in a screwdriver. It is better to use a blue scarf in some homemade products, but again, this is my personal opinion.
Possible application schemes or how to convert Shurik's power to lithium:
So, how can you change the power of your favorite Shurik from NiCd to Li-Ion / Li-Pol? This topic is already quite hackneyed and solutions, in principle, have been found, but I will briefly repeat myself.
To begin with, I’ll just say one thing - in budget shuriks there is only an overcharge / overdischarge / short circuit / high load current protection board (similar to the monitored red board). There is no balance there. Moreover, even in some branded power tools there is no balancing. The same applies to all tools where there are proud inscriptions “Charging in 30 minutes”. Yes, they charge in half an hour, but the shutdown occurs as soon as the voltage on one of the cans reaches the nominal value or the protection board trips. It is not difficult to guess that the banks will not be fully charged, but the difference is only 5-10%, so it is not so important. The main thing to remember is that the charge with balancing takes at least several hours. So the question is, do you need it?
So, the most common option looks like this:
Network charger with stabilized output 12.6V and current limit (1-2A) -> protection board ->
As a result: cheap, fast, acceptable, reliable. Balancing walks depending on the state of the cans (capacity and internal resistance). Quite a working option, but after a while the imbalance will make itself felt by the time of work.
More correct option:
Network charger with stabilized output 12.6V, current limit (1-2A) -> protection board with balancing -> 3 batteries connected in series
As a result: expensive, fast / slow, high quality, reliable. Balance is normal, battery capacity is maximum
In total, we will try to do something like the second option, here's how you can do it:
1) Li-Ion / Li-Pol batteries, protection boards and a specialized charging and balancing device (iCharger, iMax). Additionally, you will have to remove the balancing connector. There are only two minuses - model chargers are not cheap, and it’s not very convenient to maintain. Pros – high charge current, high jar balancing current
2) Li-Ion / Li-Pol batteries, protection board with balancing, current-limiting DC converter, PSU
3) Li-Ion/Li-Pol batteries, protection board without balancing (red), DC converter with current limiting, PSU. Of the minuses, only that over time, an imbalance of cans will appear. To minimize imbalance, before altering the Shurik, it is necessary to adjust the voltage to the same level and it is advisable to take cans from the same batch
The first option is only suitable for those who have a model memory, but it seems to me that if they needed it, then they remade their Shurik a long time ago. The second and third options are almost the same and have the right to life. You just need to choose what is more important - speed or capacity. I think that the last option is the best, but only once every few months you need to balance the banks.
So, enough chatter, let's move on to the alteration. Since I do not have a Shurik on NiCd batteries, therefore, about the alteration only in words. We will need:
1) Power supply:
First option. Power supply unit (PSU), at least 14V or more. The recoil current is desirable at least 1A (ideally about 2-3A). A power supply from laptops / netbooks, from chargers (output more than 14V), power supplies for LED strips, video recording equipment (DIY PSU), for example, or: 
- Step-down DC / DC converter with current limiting and the ability to charge lithium, for example or: 
- The second option. Ready-made power supplies for shurikov with current limiting and 12.6V output. They are not cheap, as an example from my review of the MNT screwdriver -:
- The third option. : 
2) Protection board with or without a balancer. It is advisable to take the current with a margin: 
If the option without a balancer is used, then it is necessary to solder the balancing connector. This is necessary to control the voltage on the banks, i.e. to assess imbalance. And as you understand, it will be necessary to periodically recharge the battery by the cell with a simple TP4056 charging module if an imbalance has begun. Those. once every few months, we take a TP4056 scarf and charge all the banks in turn, which, at the end of the charge, have a voltage below 4.18V. This module correctly cuts off the charge at a fixed voltage of 4.2V. This procedure will take an hour and a half, but the banks will be more or less balanced.
Written a little chaotically, but for those who are in the tank:
After a couple of months, we put the screwdriver battery on charge. At the end of the charge, we take out the balancing tail and measure the voltage on the banks. If it turns out something like this - 4.20V / 4.18V / 4.19V, then balancing is, in principle, not needed. But if the picture is as follows - 4.20V / 4.06V / 4.14V, then we take the TP4056 module and recharge two banks in turn to 4.2V. I don’t see any other option, except for specialized balancer chargers.
3) High current batteries: 
I have previously written a couple of small reviews about some of them - and. Here are the main models of high-current 18650 Li-Ion batteries:
- Sanyo UR18650W2 1500mah (20A max.)
- Sanyo UR18650RX 2000mah (20A max.)
- Sanyo UR18650NSX 2500mah (20A max.)
- Samsung INR18650-15L 1500mah (18A max.)
- Samsung INR18650-20R 2000mah (22A max.)
- Samsung INR18650-25R 2500mah (20A max.)
- Samsung INR18650-30Q 3000mah (15A max.)
- LG INR18650HB6 1500mah (30A max.)
- LG INR18650HD2 2000mah (25A max.)
- LG INR18650HD2C 2100mah (20A max.)
- LG INR18650HE2 2500mah (20A max.)
- LG INR18650HE4 2500mah (20A max.)
- LG INR18650HG2 3000mah (20A max.)
- SONY US18650VTC3 1600mah (30A max.)
- SONY US18650VTC4 2100mah (30A max.)
- SONY US18650VTC5 2600mah (30A max.)
I recommend the time-tested cheap Samsung INR18650-25R 2500mah (20A max.), Samsung INR18650-30Q 3000mah (15A max.) or LG INR18650HG2 3000mah (20A max.). I didn’t particularly come across other jars, but my personal choice is Samsung INR18650-30Q 3000mah. Skis had a small technological defect and fakes with low current output began to appear. I can throw off an article on how to distinguish a fake from the original, but a little later, you need to look for it.
How to connect all this economy:
Well, a few words about the connection. We use high-quality copper stranded wires of a decent section. These are high-quality acoustic or conventional ShVVP / PVS with a section of 0.5 or 0.75 mm2 from a household store (we rip open the insulation and get high-quality wires of different colors). The length of the connecting conductors must be kept to a minimum. Batteries, preferably from the same batch. Before connecting them, it is advisable to charge them to one voltage so that there is no imbalance for as long as possible. Soldering batteries is not difficult. The main thing is to have a powerful soldering iron (60-80W) and an active flux (soldering acid, for example). Soldered with a bang. The main thing then is to wipe the place of soldering with alcohol or acetone. The batteries themselves are placed in the battery compartment from old NiCd cans. It is better to have a triangle, minus to plus, or, as the people say, “valt”, by analogy with this (one battery will be located the other way around), or a little higher a good explanation (in the testing section):
So, the wires connecting the batteries will turn out to be short, therefore, the drop in the precious voltage in them under load will be minimal. I do not recommend using holders for 3-4 batteries, they are not intended for such currents. Side and balance conductors are not so important and can be of a smaller cross section. Ideally, it is better to stuff the batteries and the protection board into the battery compartment, and the DC-down converter separately into the docking station. Charge / charged LED indicators can be replaced with your own and displayed on the docking station case. If desired, you can add a minivoltmeter to the battery module, but this is extra money, because the total voltage on the battery will only indirectly tell about the residual capacity. But if there is a desire, why not. Here :
Now let's look at prices:
1) BP - from 5 to 7 dollars
2) DC / DC converter - from 2 to 4 dollars
3) Protection boards - from 5 to 6 dollars
4) Batteries - from 9 to 12 dollars ($ 3-4 thing)
Total, an average of $15-20 per remake (with discounts / coupons), or $25 without them.
Update 2, a few more ways to remake Shurik:
The next option (suggested by the comments, thanks I_R_O and cartmannn):
Use inexpensive 2S-3S type chargers (this is the manufacturer of the same iMax B6) or all kinds of copies of B3 / B3 AC / imax RC B3 () or ()
The original SkyRC e3 has a charging current per cell of 1.2A versus 0.8A for copies, should be accurate and reliable, but twice the price of copies. You can buy quite inexpensively on the same. As I understood from the description, it has 3 independent charging modules, something akin to 3 TP4056 modules. Those. SkyRC e3 and its copies do not have balancing as such, but simply charge the banks to one voltage value (4.2V) at the same time, since they do not have power connectors. There are really charging and balancing devices in the SkyRC assortment, for example, but the balancing current is only 200mA and already costs around $ 15-20, but it can charge life pads (LiFeP04) and charge currents up to 3A. Those who are interested can get acquainted with the model range.
In total, for this option, you need any of the above 2S-3S chargers, a red or similar (without balancing) protection board and high-current batteries: 
As for me, a very good and economical option, I would probably stop at it.
Another option proposed by the comrade Volosaty:
Use the so-called "Czech balancer": 
Where it is for sale is better to ask him, I heard about him for the first time :-). I won’t tell you anything about the currents, but judging by the description, it needs a power source, so the option is not so budgetary, but it seems to be interesting in terms of charging current. Here is a link to . In total, this option requires: a power source, a red or similar (without balancing) protection board, a "Czech balancer" and high-current batteries.
Advantages:
I have previously mentioned the advantages of lithium power supplies (Li-Ion / Li-Pol) over nickel (NiCd). In our case, a face-to-face comparison is a typical Shurik battery from NiCd batteries versus lithium:
+ high energy density. A typical 12S 14.4V 1300mah nickel battery has a stored energy of 14.4*1.3=18.72Wh, while a 4S 18650 14.4V 3000mah lithium battery has 14.4*3=43.2Wh
+ no memory effect, i.e. you can charge them at any time without waiting for a full discharge
+ smaller dimensions and weight with the same parameters as NiCd
+ fast charge time (not afraid of high charge currents) and clear indication
+ low self-discharge
Of the minuses of Li-Ion, only:
- low frost resistance of batteries (they are afraid of negative temperatures)
- balancing of cans during charging and protection against overdischarge is required
As you can see, the advantages of lithium are obvious, so it often makes sense to remake the power supply ...
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