Protection circuit for li ion battery in a screwdriver. Do-it-yourself conversion of a screwdriver using Li-Ion batteries and mains power

I welcome everyone who stopped by. The review will focus, as you probably already guessed, on two simple headsets designed to monitor Li-Ion battery assemblies, called BMS. The review will include testing, as well as several options for converting a screwdriver for lithium based on these boards or similar ones. For anyone interested, you are welcome under cat.
Update 1, Added a test of the operating current of the boards and a short video on the red board
Update 2, Since the topic has aroused little interest, I will try to supplement the review with several more ways to remake Shurik to make a kind of simple FAQ

General form:


Brief performance characteristics of the boards:


Note:

I want to warn you right away - only the blue board has a balancer, the red one does not have 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 have a charge controller (CC/CV), so for their operation a special board with a fixed voltage and current limitation is required.

Board dimensions:

The dimensions of the boards are very 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:


Upon closer examination, 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 designed for 12A (peak 60A), and we have two of them:

I will also note that the balancing current is very 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):


Looking at the datasheets for the power mosfets used, the operating current is stated to be 70A, and the peak current is 200A, even one mosfette is enough, and we have two of them:

The connection is similar:


So, as we can see, both boards have a protection controller with the necessary isolation, 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 paralleled, so the operating currents can be multiplied by two. Important note - maximum operating currents are limited by the current shunts! These scarves do not know about the charging algorithm (CC/CV). To confirm that these are precisely 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 modification (judging by the datasheet) - soldering the connector and resistor, perhaps the red scarf will work:


It’s not so easy to upgrade the blue scarf to 4S; you’ll have to solder on the balancer elements.

Board testing:

So, let's move on to the most important thing, namely how suitable they are for real use. The following devices will help us for testing:
- a prefabricated module (three three/four-register voltmeters and a holder for three 18650 batteries), which appeared in my review of the charger, although without a balancing tail:


- two-register ampere-voltmeter for current monitoring (lower readings of the device):


- step-down DC/DC converter with current limiting and lithium charging capability:


- 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. Using voltmeters, we look at what voltage the boards operate at and how the banks are balanced.
First, 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 we can see, there is an imbalance. We apply voltage, the charging current gradually drops (lower gauge):


Since the scarf does not have any indicators, the completion of balancing can only be assessed by eye. The ammeter was already showing zeros more than an hour before the end. For those interested, here is a short video about how the balancer works in this board:

Update 1: Load test:
The following stand will help us with the output current:
- the same holder/holder for three 18650 batteries
- 4-register voltmeter (control of total voltage)
- car incandescent lamps as a load (unfortunately, I only have 4 incandescent lamps of 65W each, I don’t have any more)
- HoldPeak HP-890CN multimeter for measuring currents (max 20A)
- high-quality copper stranded speaker wires large section

A few words about the stand: the batteries are connected by 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:


Connecting cans on a holder (“jack”):


The probes for the multimeter were high-quality wires with crocodile clips from the iCharger 208B charger and balancing device, because HoldPeak’s do not inspire confidence, and unnecessary connections will introduce additional distortions.
First, let's test the red protection board, as it is the most interesting in terms of current load. Solder the power and can wires:


It turns out something like this (the load connections turned out to be of minimal length):


I already mentioned in the section on remaking Shurik that such holders are not really designed for such currents, but they will do for tests.
So, a stand based on a red scarf (according to measurements, no more than 15A):


Let me briefly explain: the board holds 15A, but I don’t have a suitable load to fit into this current, since the fourth lamp adds about 4.5-5A more, and this is already beyond the limits of the board. At 12.6A, the power mosfets are warm, but not hot, just right for long-term operation. At currents of more than 15A, the board goes into protection. I measured with resistors, they added a couple of amperes, but the stand was already disassembled.
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's a short video:

The blue scarf holds more current, but at currents of more than 10A, the power mosfets get very hot. At 15A the scarf will last no more than a minute, because after 10-15 seconds the finger no longer holds the temperature. Fortunately, they cool down quickly, so they are quite suitable for short-term loads. Everything would be fine, but when the protection is triggered, the board is blocked and to unlock it you need to apply voltage to the output contacts. This option is clearly not for a screwdriver. In total, the current is 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 cut-off voltage of 2.5V, and is easily upgraded to a 4S configuration (14.4V/16.8V). I think this is the most optimal choice for converting a budget Shurik for lithium.
Now for the blue scarf. One of the advantages is 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 tightening the screw. And the cutoff voltage is only 2.7V, which means that under heavy load, part of the battery capacity will remain unclaimed, since at high currents the voltage drop on the banks is significant, and they are designed for 2.5V. And the biggest disadvantage is that the board is blocked when the protection is triggered, so use in a screwdriver is undesirable. It is better to use a blue scarf in some homemade projects, but again, this is my personal opinion.

Possible application schemes or how to convert Shurik’s power supply to lithium:

So, how can you change the power supply 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 a protection board against overcharge/overdischarge/short circuit/high load current (analogous to the red board under review). There is no balancing there. Moreover, even some branded power tools do not have balancing. The same applies to all tools that proudly say “Charge in 30 minutes.” Yes, they charge in half an hour, but the shutdown occurs as soon as the voltage on one of the banks reaches the nominal value or the protection board is triggered. 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 a balanced charge lasts for at least several hours. So the question arises, do you need it?

So, the most common option looks like this:
Network charger with stabilized output 12.6V and current limitation (1-2A) -> protection board ->
The bottom line: cheap, fast, acceptable, reliable. Balancing varies depending on the condition of the cans (capacity and internal resistance). This is a completely working option, but after a while the imbalance will make itself felt in the operating time.

More correct option:
Network charger with stabilized output 12.6V, current limitation (1-2A) -> protection board with balancing -> 3 batteries connected in series
In summary: expensive, fast/slow, high quality, reliable. Balancing is normal, battery capacity is maximum

So, we’ll try to do something similar to 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 disadvantages - model chargers are not cheap, and they are not very convenient to service. Pros – high charging current, high can balancing current
2) Li-Ion/Li-Pol batteries, protection board with balancing, DC converter with current limiting, power supply
3) Li-Ion/Li-Pol batteries, protection board without balancing (red), DC converter with current limiting, power supply. The only downside is that over time the cans will become unbalanced. 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 will only work 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 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 last option is the best option, but only once every few months you need to balance the banks.

So, enough chatter, let's get to the remodeling. Since I don’t have experience with NiCd batteries, I’m talking about the conversion only in words. We will need:

1) Power supply:

First option. Power supply (PSU) at least 14V or more. The output current is desirable to be at least 1A (ideally about 2-3A). We will use a power supply from laptops/netbooks, from chargers (output more than 14V), units for powering LED strips, video recording equipment (DIY power supply), for example, or:


- Step-down DC/DC converter with current limiting and the ability to charge lithium, for example or:


- Second option. Ready-made power supplies for Shuriks with current limiting and 12.6V output. They are not cheap, as an example from my review of the MNT screwdriver -:


- Third option. :


2) Protection board with or without balancer. It is advisable to take the current with a reserve:


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, you will need to periodically recharge the battery one by one with a simple TP4056 charging module if imbalance begins. Those. Once every few months, we take the TP4056 scarf and charge one by one all the banks that, 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.
It’s written a little chaotically, but for those in the tank:
After a couple of months, we charge the screwdriver battery. 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 basically 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 other than specialized chargers-balancers.

3) High current batteries:


I have previously written a couple of short 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 haven’t had much experience with other jars, but my personal choice is Samsung INR18650-30Q 3000mah. The Skis had a small technological defect and fakes with low current output began to appear. I can post an article on how to distinguish a fake from an original, but a little later, you need to look for it.

How to put all this together:


Well, a few words about the connection. We use high-quality copper stranded wires with a decent cross-section. These are high-quality acoustic or ordinary SHVVP/PVS with a cross-section of 0.5 or 0.75 mm2 from a hardware store (we rip the insulation and get high-quality wires of different colors). The length of the connecting conductors should be kept to a minimum. Batteries preferably from the same batch. Before connecting them, it is advisable to charge them to the same 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). Solders with a bang. The main thing is to then wipe the soldering area with alcohol or acetone. The batteries themselves are placed in the battery compartment from old NiCd cans. It is better to arrange it in a triangle, minus to plus, or as popularly called “jack”, by analogy with this (one battery will be located in reverse), or there is a good explanation a little higher (in the testing section):


Thus, the wires connecting the batteries will be short, therefore, the drop in 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-by-side and balancing conductors are not so important and can be of smaller cross-section. Ideally, it is better to stuff the batteries and the protection board into the battery compartment, and the step-down DC converter separately into the docking station. LED indicators charge/charged can be replaced with your own and displayed on the docking station body. If you wish, you can add a minivoltmeter to the battery module, but this is extra money, because the total voltage on the battery will only indirectly indicate the residual capacity. But if you want, 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 per item)

Total, on average, $15-20 for a remodel (with discounts/coupons), or $25 without them.

Update 2, a few more ways to remake Shurik:

The next option (suggested from the comments, thanks I_R_O And cartmann):
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 as expensive as copies. You can buy it very inexpensively at the same place. As I understand 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. SkyRC's assortment actually includes charging and balancing devices, for example, but the balancing current is only 200mA and costs around $15-20, but it can charge life-changing devices (LiFeP04) and charge currents up to 3A. Anyone interested can check out model range.
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, it’s a very good and economical option, I’d probably stick with it.

Another option suggested by comrade Volosaty:
Use the so-called “Czech balancer”:

It’s better to ask him where it’s sold, it’s the first time I’ve heard about it :-). I can’t tell you anything about the currents, but judging by the description, it needs a power source, so the option is not so budget-friendly, but seems to be interesting in terms of charging current. Here is the link to. In total, for this option you need: a power supply, a red or similar (without balancing) protection board, a “Czech balancer” and high-current batteries.

Advantages:
I have already mentioned the advantages of lithium power supplies (Li-Ion/Li-Pol) over nickel ones (NiCd). In our case, a head-to-head comparison – a typical Shurik battery made of 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, and lithium battery 4S 18650 14.4V 3000mah - 14.4*3=43.2Wh
+ no memory effect, i.e. you can charge them at any time without waiting for complete discharge
+ smaller dimensions and weight with the same parameters as NiCd
+ fast charging time (not afraid of high charge currents) and clear indication
+ low self-discharge

The only disadvantages of Li-Ion are:
- low frost resistance of batteries (they are afraid of negative temperatures)
- balancing of the cans during charging and the presence of overdischarge protection is required
As you can see, the advantages of lithium are obvious, so it often makes sense to rework the power supply...

Conclusion: The scarves under review are not bad, they should be suitable for any task. If I had a shurik on NiCd cans, I would choose a red scarf for conversion, :-)…

The product was provided for writing a review by the store. The review was published in accordance with clause 18 of the Site Rules.

As you know, any battery sooner or later exhausts its life and needs either partial replacement of the batteries, or it should be changed completely. When it comes to a screwdriver, it can be much easier for someone to buy a new one than to replace the batteries in it, because this requires both time and a certain skill. However, if you have the skill and knowledge, replacing batteries in a screwdriver can be a good alternative to buying a new one. In many cases it is cheaper.

Nickel-cadmium or lithium-ion cells are usually used as batteries in screwdrivers. more unpretentious and, if a partial replacement of elements in such a block is carried out, it will still work for a long time. Partial replacement lithium batteries It can also be done, but it is a little more difficult to implement. It should be borne in mind that not only the elements themselves will have to be soldered, but also the balancing board. also in Lately electronics enthusiasts often change screwdriver batteries with their own hands, with nicd batteries to lithium. This is a good way out if the screwdriver has to work frequently and intensively. The capacity is much higher and the number of cycles is greater.

How to repair a nickel-cadmium battery in a screwdriver

The specificity of nickel-cadmium jars is that at the end of their service life, the contents of their electrolyte can dry out. In this case, refilling with distilled water sometimes helps.

But if you think about what is better and obviously more efficient, you should still decide to replace the screwdriver batteries. Filling does not always help. There is a much higher probability that the tool will work well with a battery in which the cans will be partially replaced. Of course, provided that everything is done correctly.

Finally, the filling process itself is no less labor-intensive than the battery repair process. And if it turns out to be ineffective because the batteries are simply dry, it will be very annoying.

We disassemble the block and look for the “weak link”

Before you start with your own hands, you should keep in mind that the battery pack itself should be handled as carefully as possible. Sometimes this requires a lot of patience, because block manufacturers always strive to make it as difficult as possible to get to the batteries. This is understandable. Most manufacturers are interested in ensuring that craftsmen do not repair the screwdriver battery themselves and do not tinker with cans, but, without hesitation, purchase a new tool, often at a fairly high price.

After opening the battery, remove all batteries from its plastic case. Important point: do not forget to pre-charge the battery before carrying out this manipulation . You can charge for no more than three hours. Then, after removing the cans, you will need to use a multimeter to measure the voltage readings on each of them.

• After measuring the U of each jar, write down the results. Most likely, the elements with the lowest voltage reading will have to be removed later.
• Now the battery pack. You can connect a load in the form of a light bulb to it.
• Repeat the charging process again , measure the voltage on each battery and unsolder those with the weakest performance .

Of course, before replacing the batteries in a screwdriver, you should purchase new elements similar to the old ones, preferably with a small margin. Buy batteries with the same capacity.

Installing new banks

Before installing new batteries in the battery pack, it is important to take into account certain subtleties, without which it will be impossible to do everything correctly. First of all, It is important to remember to maintain polarity when soldering . And also understand the difference between conventional soldering and the principle of spot welding. Because it is not recommended to solder the plates connecting the batteries to each other in the usual way.

If you don't have a spot welder, try using a regular soldering iron. But everything should be done clearly, carefully and as quickly as possible. The main thing is to prevent critical overheating of the batteries. Use only high quality lead solder.

By the way, it is in such cases that one of the main advantages of nickel-cadmium batteries manifests itself. Being exposed to a certain risk during repairs, they have a fairly high chance of “withstanding” high temperatures due to the strong metal body and composition, which does not have an increased explosion hazard. Lithium cells are much less resistant to flashing and are more capricious.

Place each battery in the same order as in the old bundle and reassemble the battery pack. After the battery is reassembled, you need to “swing” it properly in order to balance the potential of all elements and remove what is called the “memory effect”. Give the new battery at least two or three charge-discharge cycles. As you know, it is not recommended to constantly “recharge” nickel-cadmium batteries without first completely discharging them, which is not always possible during operation.

In the future, when using the repaired battery it is necessary to completely discharge it from time to time and then fully charged - to prevent the frequent occurrence of the “memory effect”. It is recommended to do this at least once every six months. This way you can extend the life of nickel-cadmium cells with optimal utilization of their resources, without them accumulating unnecessary information about previous recharges.

Replacing nickel-cadmium batteries in a screwdriver with lithium ones

Recently, on forums dedicated to electrical tools, the process of replacing nickel-cadmium screwdriver batteries with Li Ion batteries is often described. And this is no coincidence. More modern Lithium based cells have much higher capacity . A they have more work cycles at least one and a half to two times.

Very often, cadmium batteries are replaced with the popular lithium 18650, so named based on their size. You can change batteries to lithium if the tool is used daily or very often. Large number of cycles lithium-ion batteries Ideal for professional craftsmen who use the tool every day.

In order to convert a screwdriver from “cadmium to lithium”, you will need 18650 batteries and a special charging module. This module allows you to charge the battery and transfer the load on the same terminals (the same protective board that was mentioned at the beginning). Such modules have protection against short circuits between elements.

How to solder elements

Soldering is strongly recommended to be carried out exactly apparatus contact welding - due to the fact that lithium batteries are even more sensitive to heat than cadmium batteries. If nickel-cadmium batteries can withstand manipulation with a soldering iron, then for lithium it is still better to use the resistance welding method.

To connect the batteries to each other you will need a thin metal strip. The strips themselves can be cut from soft tin cans. All surfaces to be joined must first be wiped with alcohol, and then begin spot welding using the device. The pulse duration is selected experimentally so that there is no burning and the connection is reliable. To ensure a reliable connection between the plate and the contact surface of the battery, it is better to make several point connections.

The excess part of the strip is cut off, and its free edge is connected to another battery. Next, all the elements are connected to each other according to the same principle. Of course, observing polarity.

The entire finished assembly is fixed to each other using electrical tape. It is better to make two turns of electrical tape on one side and two turns on the other - for greater reliability. After this, the battery contacts are connected again with a metal strip. It turns out ready new battery, to which you now need to attach the board (module).

The module can be soldered to the new battery with a regular soldering iron.

The negative wire of the battery assembly is connected to the B- terminal on the board, and the positive wire to the B+ terminal. Contact terminals are connected to terminals P- and P+, balancing taps are connected to terminals B1, B2 and B3. For solder, it is better to use high-quality flux, which spreads very well over the entire surface. The positive wire is soldered directly, and a thick wire with a cross-section of at least 0.5 mm 2 is soldered to the negative contact, since a current of at least 10 amperes will flow through it.

After this, balancing wires with a small cross-section are soldered.

• to contact B3 connect the connection point third And fourth batteries;
• to contact B2- connection point second And third;
• to contact B1- connection point first And second(we start counting from the positive contact).

After charging the battery, check the voltage on all its elements. U on each of them should not exceed 4.2 volts.

After the new battery pack is ready, we disassemble the old nickel-cadmium battery. We only remove the old batteries, and leave the old temperature sensors in place, because the screwdriver charger will not work without them. We solder a new block inside the plastic case, and fill the space remaining inside with foam plastic.

Thus, if there is a need to replace the battery in a screwdriver, you can do it yourself. In the case of old but reliable cadmium batteries, you can use the method partial replacement for new ones. And if you want to build yourself a “professional and powerful screwdriver” yourself, you can successfully completely replace the battery pack with lithium-ion cells.

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 performance characteristics 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

IN Li-Ion batteries There are 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:

1. 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;
2. 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 the old battery is 12 V. This is the voltage when connected in series Li-Ion cells cannot be provided. 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;
3. 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;
4. 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:

1. Such instruments use elements with high discharge current values;
2. 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;
3. When replacing a screwdriver battery with a Li-Ion 18650, it is not recommended to use cells with different capacity values;
4. 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;
5. 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 you install 4 elements, then increased voltage will shorten the life of the electric 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:

1. 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;
2. 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;
3. Spot welding. Is the preferred method. Not everyone has 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:

1. The disassembled parts of the body are well cleaned;
2. 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;
3. The positive and negative wire, 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 be able to 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:

1. 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;
2. 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;
3. Voltage at which the batteries are switched off when overcharging (about 4.3 V);
4. The voltage at which the screwdriver turns off. This value must be selected based on technical parameters battery cell ( minimum voltage- about 2.6 V);
5. Overload protection current;
6. Resistance of transistor elements (select the minimum value).

Important! The magnitude of the operating current during overload does not have of great importance. 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:

1. Using a factory charger. Often it is also suitable for charging a new battery;
2. Redesign of the charger circuit, with installation additional elements scheme;
3. Purchase of a ready-made memory. A good option– IMax.

Let's say there is an old Makita DC9710 charger for charging Ni-Cd 12 V batteries, with 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 batteries 7.2-14.4 V. 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.

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