Rebuilding a 12 volt electric screwdriver for lithium 18650 batteries

High current 18650 with GB and another conversion of the screwdriver to lithium

Hi all. A review not so much of the batteries (which, by the way, came out, thanks to PlusPda), but rather a variant of the screwdriver conversion. Batteries are quality, capacity is appropriate, implanting them instead of the nickel-cadmium ones was successful

LG HE4 High Current Batteries from Gearbest: The batteries are good, I had their capacity tested by my friend with the Opus charger, the capacity is correct. No other special tests were done.

Imax B3 three-channel charger: This is my second attempt to buy such charger, the first time order did not come, I got my money back. The charger ordered from the seller at the link above arrived, it works, it comes with a 40cm long power cord, the cord in the picture is clearly different. There was no cable to connect the charger somewhere in the package.

Holder for three 18650 batteries: In the seller’s picture this variant of holder for three 18650 had pins for soldering into PCB, but I received another variant, not only not for printing, but with soldered in kolhozno jumpers, connecting all the three batteries in parallel.

rebuilding, volt, electric, screwdriver

Got a partial refund. I soldered the jumpers and used them, but not in the way they were supposed to be used.

History. My screwdriver Interskol DA-12ER-01 is almost 10 years old. The most he “got” during a repair in the apartment 6 years ago, but usually most of the year he had a rest, a little work in the summer in the country, and performed small tasks: crafts, assembling furniture, etc.д. Problems with the batteries began a couple of years ago, one battery stopped holding a charge, the second is working fine. I then disassembled the defective battery, found the two most tortured elements, and tried to replace them with similar ones, bought on eBay. But when I put new cells, I found out that the other cells, which I thought were still alive, were also candidates for the trash garbage can: under load, their voltage reversed polarity. There was no point in changing all the cells, so I converted this battery into a kind of adapter to connect the screwdriver to the cigarette lighter of the car.

But I was not going to connect it to the car onboard network, but to an old lead battery 12v 7 Ah from a halogen camcorder light, the socket which was similar to the car cigarette lighter socket. My camcorder light has long had a LED light powered by lithium batteries, but the 12v battery came in handy for a screwdriver, though I’ve only used it a couple of times. Here is this super-mega adapter:

But since the 12v 7ah battery was more than 8 years old, it stopped holding a charge, it could not be restored, and I was forced to sell it for scrap. So most likely the “adapter” for the cigarette lighter will disassemble, to connect the “screwdriver” to the car makes no sense.

Bosch 12v battery Restoration| diy li-ion battery

This summer I finally gave up and the second battery screwdriver, it began to run out so quickly that it was impossible to perform serious work. In spring it was working at least somehow, but by fall a dozen medium-sized self-tapping screws on a single charge was its limit.

But nevertheless, I think that the original batteries of the screwdriver worked very well. I had them for 8 and 10 years, while my friends died in the 3rd and 5th year, with approximately the same non-professional mode of use.

To buy even one new nickel-cadmium battery is a formidable savagery, it is 50-60% of the price of such a screwdriver (yes, they still sell those) with two such batteries in the set. I also rejected the option of buying an already assembled battery of nickel-cadmium batteries from ali or ebay, ready to be installed in a battery case: it is cheaper, but the quality of these batteries is questionable, for example, two cells I bought on ebay had a decent variation of capacity, and how long it all works, nobody knows. In addition, the nickel-cadmium I have decided to give up completely and irrevocably: the conversion to lithium cordless screwdriver, which I did six months ago, my impressions are very positive.

Actually, of course, my screwdriver is old and shabby, so I was thinking to buy a new one, modern, with a lithium battery to replace it. But the mechanical part is still in good order, and the mechanics of modern inexpensive screwdrivers is extremely weak: those that I had the chance to hold in my hands, had just an obscene backlash in the chuck bearing after an obscenely short period of time. And buying a professional expensive screwdriver makes no sense, most of the year it will lie in the closet.

But the most important thing is that I was itching to remake my screwdriver for lithium by myself. There were certain doubts: the cost of batteries, protection and charge leveling board was close to a simple lithium-powered screwdriver from Leroy-Merlin, with a one-year warranty. But the desire to solder and tinker with it outweighed the doubts that some unknown batteries would be sent, that something would go wrong, etc.п.

At first I wanted to do everything classical i.e. to take three high-current 18650 batteries, add to them protection and equalization board 3S, respectively remake the charger for lithium batteries. But then I decided to make it simpler and, in my opinion, much more convenient.

VOTO 12 Volt Lithium-ion Battery Cordless Screwdriver. Battery Replacement

By experience with batteries for camcorders VBG6, F550, F770 etc., where two batteries 18650 connected in series, I have long ago concluded that the batteries die mainly because the circuit charge equalization does not cope with its task. As a result, one battery is constantly overcharged, the other undercharged, and very soon the battery goes in the trash. Even the replacement of dead cells with the original Sanyo, which has much more stable parameters, did not give the effect as long as I would like, a couple of years and that’s all.

But in a screwdriver the battery will be of three cells, current loads are much higher, the unbalance of the capacity of the cells will manifest itself faster, so I doubt very much that the charge equalization/balancing board will help batteries not to die prematurely. That’s why I decided not to charge all batteries from one source, in favor of charging each battery separately. Three-channel charger I decided to take a ready, well-known Imax B3, in my opinion it is more effective in any case than the balancer card, besides it is very compact and lightweight.

I decided not to use the overdischarge/overdischarge protection card at all, the screwdriver has a battery voltage indicator, it is enough to find out how low the battery is. Well, if any battery out of the three “fails” and will suffer along with all (protection against voltage drop would have long knocked out the whole battery) know, it is his fate, he can not help, but the battery will not turn off before time.

I figured that after installing the battery in the battery three cells 18650 it still has a lot of free space, I decided to shove the charger Imax B3 itself there. You simply plug in the 220-volt cord to the screwdriver to charge the batteries. And it’s really comfortable: no external charging, the screwdriver comes with only one 220v cable, and the cable is universal, even from the receiver / printer / music is okay.

Said and done. The first GB batteries came to me, at first I tried to test them myself, putting one into my existing vverbank, giving a load of 1A, and calculating the capacity based on the time of operation until shutdown. Even though I was recalculating the capacity from 5v to 3.7v, I got very low results, about 1.5 Ah, so I asked my friend to test these batteries with a fully functional Opus test charger, I don’t remember the model, and he calmed me down, the capacity of all batteries was normal, but not 2.5 Ah, but 2.3 Ah, which I was quite happy with.

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Originally I wanted to connect the batteries by spot welding, even bought for this purpose nickel strip, but the unit for spot welding has not yet been completed. That’s why I decided to use a ready made holder for three 18650 cells, ordered for a completely different project. It did not fit the seller’s description, but after small modifications it fit perfectly, especially as the batteries are very tightly seated in it, contacts are thick and stiff enough. Even with a very dynamic shaking the batteries did not jump out of the holder.

The charger Imax B3 came to me at the very last. Tested it. it works, and then started the process of converting the screwdriver to lithium.

The original battery was gutted, I soldered the wires to the contact group, screwed the battery compartment to the base of the case, and soldered the wires to it. I put a 10A fuse, but I hung it on the terminals: the car holder didn’t fit into the case. By the way, one of the nickel-cadmium elements is supporting the contact group, it’s just the right length. I ran the screwdriver through the lithium batteries and was surprised at how much torque it got.

Next, I installed the battery charger Imax B3 in the battery cover, put on the side of the cover connector for charging (not native). With indicator LEDs I removed the stands and put them into the holes in the case, so now you can watch the whole process of charging by three shining “eyes”. Naturally, red light. charging, green light. charged.

Then I connected the charger to the batteries, drove the screwdriver for a while, and put it on the charger. And that’s where the problem came out, which I’d already read about, and which couldn’t be avoided in principle. The TP4056 charge controller chips began to heat up wildly. But they won’t get warm. Charging current (judging by the current-retaining resistor 1.8k) is about 600 mA, the input is about 6v. And I had almost fully charged batteries with a voltage of about 4,15V at the time of charging and about 1,1W of power dissipated by each chip. It’s enough for three microcircuits on a small board and in a confined space to get burnt. If the batteries had to be charged from zero, more power would be dissipated on the microcircuits.

So I replaced the current drivers by increasing them from 1.8k to 4.7k, thus reducing the charging current to about 270 mA. Even so, the chips burned my fingers. Of course there was nothing to worry about in this mode, the batteries were charging normally and the green LEDs lit up almost at the same time. But still, in a strong heat charger can overheat, the case I have during the test was not covered. And the charging current is a little low.

That’s why I put a small heat sink on microcircuits (through Nomakon), again changing the current charge resistors to 2,2k. charging current is about 500 mA. After running the charger in this mode I didn’t notice any serious heating of the heatsink and I’m sure that even on a hot day with the battery enclosure closed the temperature will be ok.

The only thing that bothers me is the maximum voltage of the batteries at the end of the charge: 4,20 4,23 4,21v. Isn’t that too much? But it’s impossible to influence this voltage except to change the microcircuits.

In general, assembled a new battery finally. Instead of the former 1.5Ah it has a capacity of 2.3Ah, and without memory effect. The disadvantage is that you can not leave it in extreme cold, but no one is forced to do so.

I like the way the screwdriver works with the new battery.

Now a little about the original screwdriver charger:

The battery charger worked fine for 10 years, in spite of the fact that it was warm as an iron. Surprisingly, after 10 years the pungent smell of plastic and burnt gethinax has never disappeared from it. Now I have no place to use it, so I decided to gut it:

All Interskol products I have encountered, raised great doubt that they were made in our country, as Interskol itself says. Everything is too “Chinese”, both printing and assembly, and only imported components. Also with the charger, “its” just zero. I’m familiar with the domestic production, as consumer goods, as well as military equipment, and I think that in this case made everything “not our way”. I think Interskol was just putting their labels.

But now that the charger was being scrapped I decided to borrow from it the contact group that connected to the battery. The board disassembled and sawed off, leaving a piece with contacts:

The question is why? Yes, to be able to connect to the battery instead of a screwdriver external load. I used to have a 12 volt 7 Ah battery as a power source for the car, but it died, so it was reasonable to use a screwdriver battery instead. So I made a special adapter out of a piece of charger and other handy materials.

The purpose of this adapter with the cigarette lighter plug on the wire is to power the car’s on-board power supply when removing the starter battery to recharge or replace it with another battery (I have two). I really don’t want to restore the settings of the radio and other devices after disconnecting the onboard power grid. You just plug it into the cigarette lighter and do your job, and you can turn on and off your parking lights and emergency lights, and all the settings will be saved. Only a pity there is no lamp under the hood It is not recommended to start the engine with the external battery connected, the battery current limiter is absent, but in case of a fuse burns out at 5A in the plug.

The plan is to make the adapter universal to connect different devices, but I have not found a suitable connector, later will remake.

All in all, I’m happy with the conversion of the screwdriver. It cost me about 1100, plus three evenings after work for alteration. In my opinion it is convenient, but of course not without flaws. Battery discharge must be monitored to avoid battery damage, and it is better not to give the converted screwdriver in the wrong hands. But for myself I still don’t know exactly how the screwdriver will behave when the battery is completely discharged, how much its power will drop, and what the indicator will say about it. So I’ll have to watch the screwdriver while I’m working with it.

The advantages of the second option

The 2nd variant is more suitable because the battery voltage is fast enough the voltage drops from the highest to the lowest (from 16.8V to 14.8V). For an electronic motor, which is, in fact, what an electric screwdriver is, an excess of 2.4.8V is not the critical point.

The 3S-Li-Ion modification has the smallest voltage. It is equal to 7.5 V, which is insufficient for the productive activity of the electronic device. By assembling four configurations, we increase the electronic capacity of the battery.

Scheme of connecting the batteries

To get the cherished 12 or 18 V, the elements must be connected in series. That’s it, no tricks, just the polarity. The minus of each battery is connected to the plus of the next one, the two outermost wires are connected to the terminal block.

If you double the capacity, do not connect individual batteries in series, but assemblies of 2 cells. In each assembly, the positive contact is connected to the positive neighbor, the same is true for the negative.

To ensure that the jumpers between the batteries are not eventually spliced into an incongruous web, think through the connection diagram in advance. It is most convenient to solder the batteries when they are already rolled up into a tight pack, choose the minimum length of jumpers.

The contacts of each battery should be well tinned for soldering. First remove the nickel layer by scraping them with a chisel or fine emery cloth. As the flux, use orthophosphoric acid, solder the most common POS-61 with rosin. The soldering iron must be powerful, 60 Watt or more. Do not overheat lithium batteries categorically, the contact time with the stinger should not exceed 2 seconds. So first tin, let cool, then solder.

Also pre-characterize with 2.5 mm 2 stranded wire jumpers and supplement them with balancing wires so that one wire per node between the batteries or groups of batteries connected in parallel. The length of the wire to reach the balancing connector in the case, cross section of about 0.5 mm 2.

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When soldering, the tinned core of the jumper is heated first, then it is brought close to the battery contact until the solder is melted on it. During the cooling period you can press the soldering point with a wooden chip. And don’t spare the tin, the connection should be very secure. Also do not forget to rinse off the flux residue, otherwise after six months to a year of operation all efforts will go in vain. Especially carefully wash the intricately shaped plus contact, you can use medical alcohol or acetone to wash it off.

If you try to solder the battery terminals to the nickel pins of the battery pack, you will most likely ruin it by overheating the plastic. It is much better to drill two Ø34 mm holes each and tighten the cores to the plates with a couple of small screws. It is convenient to use double hole plates, which were forged en masse from old soviet plugs.

Screw in a couple more balancing wires along with the outermost strands of the battery bundle. The resulting balancing stub must be soldered in a certain order. From the datasheet on the connector identify its contact, numbered one, and solder the wire from the positive terminal to it. Next, follow the chain of batteries and solder the wires in series, one after the other, completing the connection of the last contact with the common minus conductor.


Most people with an electric screwdriver on Ni-Cd or Ni-Mn, are familiar with such a situation, when after a long time the batteries lose their capacity. And not only because of the lifetime of the battery, but also because of the memory effect. The point of it is that a long-lost discharged battery remembers the level of charge and subsequently no longer charges to its nominal capacity. And to keep the battery permanently charged is unlikely anyone. Some people try to rebuild old batteries or combine two bad batteries into a good one.

I did it the other way around. Nowadays Li-Ion batteries are quite widespread. They don’t have that memory effect and for those who don’t use an electric screwdriver every day, they’re ideal for storing in a not fully charged state. Another plus is that they have more capacity compared to nickel batteries for the same size. For comparison, the standard battery was 1.3 Ah, and the handmade 5.2 Ah. About it we will talk further.

First you need batteries. And not simple, but high current. They are capable of delivering high currents up to about 30A. All items were purchased from aliexpress. Next we need a battery control board. It monitors many parameters, which are shown in the table. And also let’s not forget about the charger board. Picked the LM2596. This is a really good charger. Used it to charge an assembly of 6 x Li-Ion batteries (25.2V; 2800mAh).

Replacing the batteries

A lithium electric screwdriver battery has a number of advantages that cadmium counterparts do not have.

The energy density of the battery of an electric screwdriver Li-ion is much higher. The battery with lithium banks is lightweight, and the voltage of 12 volts, as well as the battery capacity remains the same. Lithium batteries charge faster than ionic units. Safe charging takes about 60 minutes.

Li-ion batteries have no “memory effect. In other words, they do not need to be completely discharged to put them on charge. Among the positive qualities of the lithium battery, there are also a number of disadvantages that need to be considered:

  • Charging lithium batteries should not be above 4.2 volts and discharging above 2.7 volts. But this is theoretical data. In real life, the interval gets even worse. If the set values are not met, the battery will simply cease to function. To avoid this situation, after converting an electric screwdriver to lithium, you need to install a special discharge controller in the screwdriver, as well as its charging.
  • One Li-ion battery has a voltage of 3.63.7 volts. The nickel battery has no more than 1.2 volts. In other words, converting an electric screwdriver to the Li-ion material causes problems associated with the assembly process of the battery, which has a rated voltage of 12 volts. Three lithium cans in series produce 11.1 volts, four 14.8 volts.Charge voltage limits will change. In other words, converting the battery for an electric screwdriver involves solving the problem of compatibility between the new battery and the tool.
  • To remake the cadmium battery of an electric screwdriver, craftsmen use lithium 18650 batteries. Their dimensions are different from the nickel cans. Rebuilding a battery for an electric screwdriver, also requires the installation of a controller, which requires additional space.
  • After conversion, the battery charger for nickel batteries will have to be modified or a universal battery charger can be used.
  • Ion batteries are exposed to subzero temperatures. Therefore, this converted electric screwdriver may not always work outdoors.
  • The cost of lithium batteries is much higher than their cadmium counterparts.

Converting an electric screwdriver to lithium 18650 batteries

In this article you will learn how to inexpensively remake a battery electric screwdriver with Ni Cd on Li-ion batteries 18650, thereby upgrading the battery electric screwdriver, making it more powerful and increasing battery life. All the stages of remaking are described in detail, so you should not have any problems, all the necessary components are listed and available.

Necessary parts for making adjustments

High-current 18650 batteries with a capacity of 2500 mA/h were used for overkill. These batteries have a soldered on lead, which is very convenient and also saves a lot of money on battery compartments. You can order them online, they come in batches of 4 or 6. You can buy them at the links below:

You will also need two BMS 12 boards for the conversion.6V 40A, bought them here:

The charger also needs to be redesigned and you will need a voltage and current regulator.

You can buy a stabilizer at the link below:

At the time of the modification all the components (two batteries) cost only 1100, which is a lot cheaper than buying a new battery for an electric screwdriver with the same Ni Cd batteries. Looking at the on the internet I found out that one battery costs 1200 and for remaking DU battery I spent only 1100! All links to the components can also be found at the end of the article!

Rebuilding a battery

The first thing to do is to carefully disassemble the battery and throw out the old Ni Cd batteries.

Then it is necessary to disconnect the power terminal of the battery.

To it you need to solder two wires, preferably with a large cross section, in this modification were used wire cross section of 4 mm² and a length of about 100 mm. In the photo above you can see the red wire, it was left in order not to mix up the polarity, to this wire preferably soldered red wire, too, to avoid trouble and you will know exactly what it is

You need to solder the minus wire to the shiny contact:

Then you need to put the battery terminal with soldered wires back in the case in its place, making sure that the polarity is correct!

To fix the terminal you can pour hot melt glue inside the battery jar, it is the best way to fix the terminal, especially as it works very well!

Now you can start soldering the batteries. We take off a heat shrink tubing from batteries and bend them in a way that it would be possible to solder them in series.

Next, apply thermal adhesive to the side of the battery where the contacts stick out and glue the BMS board as shown in the photo below. Note that the plus and minus of the board and the battery, are opposite each other.

Then bend the contacts of the battery to the contacts of the board and solder them, starting with the minus!

We solder a short wire to the contact of the board B1, and solder its other end to the point of battery connection!

To the contact B2 as well solder a short wire, the other end of which, solder to the connection point of the battery on the opposite side!

And finally, solder the last positive contact.

Now it is left to connect the housing terminals with the resulting battery, for this we solder the red wire to terminal P, and the blue, negative wire, to terminal P-.

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This completes the battery modification! It remains to fix the fabricated battery and put the second part of the body in place. For the conversion of two batteries was spent no more than an hour of time and as mentioned above, 1100 bucks. After the tests, the screwdriver works no worse than with the factory battery and I would say a lot better, in terms of power and the charge lasts longer. I advise everyone to change their old batteries! ))

Buy BMS board 12.6V 40A Buy Samsung 18650 2500 mah batteries 6 pcs.Buy Batteries Samsung 18650 2500 mah 4pcs.Buy Voltage and Current Stabilization Module Buy 3 S 25A Li-Ion 18650 BMS Boards Buy Charger Socket

For those who have no desire to remake the charger, the link below, you can buy a ready-made.

Rebuild Electric Screwdriver for Lithium Batteries 18650

The industry has been making screwdrivers for a long time, and many people have older models with nickel-cadmium and nickel-metal hydride batteries. The modification of an electric screwdriver to lithium batteries allows you to improve the performance of the machine without buying a new tool. Now a lot of companies offer services to remake the batteries of an electric screwdriver, but you can also do it with your own hands.

Electric Screwdriver Conversion for Lithium Batteries

Reverting Electric Screwdriver to Lithium Batteries

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

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

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

Battery choice: Electric screwdriver ASh-14M is designed to work with a 14 V battery, so I will use three lithium ion batteries with a total voltage of 12.6 V, of course you can use and four batteries and raise the voltage to 16.8, but then you will need to use a separate power supply, as well as high voltage reduce the life of an electric screwdriver. Not all batteries will be suitable for battery conversion, so several factors must be taken into account:

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

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

Choosing a BMS board:A lithium-ion battery cannot be used without a BMS protection board. On the market there are different numbers with different parameters. The BMS 3S designation indicates that the card is designed for three batteries. BMS 3S, for example, implies that the card is designed for 3 cells. What you need to pay attention to:

The presence of a balancer ensures an even charge of the batteries. Maximum long-term working current.


In this article I use a BMS 3S, 40A, 12.6V balanced, it is well-proven.

Battery modification (mounting):I use a battery without soldered tails so I will solder the wires directly to the pins and I use a 60W soldering iron or a big one to avoid overheating the battery.

Note! Do not overheat battery in any way.

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

Now according to the diagram, in series solder each battery output from 0 to 12.6, that is, first solder to the 0, then 4.2, then 8.4, then 12.6 to the board BMS 3S

Then we solder the wires with cross section not less than 1.5 square centimeters to the contact pads and fix them in the battery case with hot melt. Some people also leave the two old batteries, so the contact group does not fly out.

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

Adaptation of the charger:A charger is included with an electric screwdriver Soyuzmash ASh-14M, but it is designed for charging nickel-cadmium batteries to charge the lithium-ion battery needs to finalize it. Of course, some people use chargers without modification, but it’s not right.

Reworking is that you need to add a board to reduce the voltage and current limit, well proven board on the chip XL4015.

Describe the modification makes no sense because for each charger is different, but the essence is that you need to cut a couple of tracks on the board the charger and the output circuit transformer soldered to the input with XL4015. Next, you need to set the voltage 12.6V, in my case 3S or 16.8V for 4S and set the current to 1A, if you put more current, charging will go faster, but the batteries will fail quickly, if less, charging will be longer.

Who does not want to deal with the redesign, you can buy a ready-made battery charger with charging indicator.

Optional: optional indicator can be added to show battery charge level. Of course it was possible to convert the electric screwdriver to 16.8 volts (4S), but in my case it was necessary to keep within budget.

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

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

What kind of BMS board is necessary and how to connect it

Lithium batteries 18650 are afraid of overcharge and deep discharge. When cells are connected in series, it is impossible to guarantee the synchronous operation of the cells. If one jar has a lower capacity, then when charging it will replenish the energy faster than the others, and further charging will overcharge. A lower capacity battery will discharge faster than others during operation, which can lead to a deep discharge.

All these problems can be solved by the protection board with balancing. BMS boards:

  • protect against short circuits;
  • They recover after the protection has tripped;
  • monitor the voltage of each bank and disconnect the load when at least one of the cells is completely discharged (deep discharge protection);
  • carry out balancing (overcharge protection).

BMS board for an electric screwdriver must be able to withstand a maximum peak current of at least 30A. In addition, when choosing, it is necessary to be guided by the number of banks connected in series. For an electric 12 volt screwdriver, 3 batteries are needed, choose the 3S board. If you need 14V supply, buy 4S, and for 18V buy 5S.

How to connect 2, 3 or 4 banks in series to the BMS board is shown in the picture.

You can also use a mixed, series-parallel connection. In that case, connect the same number of batteries in parallel to the banks connected in series.

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