How to charge a screwdriver converted to lithium. Converting a screwdriver to lithium batteries. There is a solution - converting the screwdriver into a network one

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

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

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

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

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

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

Video selection. Best videos about remaking screwdrivers.

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

Converting a screwdriver to a Lithium-ion battery

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

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

Converting a screwdriver to lithium ion batteries 18650 standard

Converting a screwdriver to lithium 18650

2. Converting the screwdriver to a network one.

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

Converting a screwdriver to a network one

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

Well, what should those who have an old instrument do? Yes, everything is very simple: throw away the Ni-Cd cans and replace them with Li-Ion of the popular 18650 format (the marking indicates a diameter of 18 mm and a length of 65 mm).

What board is needed and what elements are needed to convert a screwdriver to lithium-ion

So, here is my 9.6 V battery with a capacity of 1.3 Ah. At maximum charge level it has a voltage of 10.8 volts. Lithium-ion cells have a nominal voltage of 3.6 volts, a maximum voltage of 4.2. Therefore, to replace the old nickel-cadmium cells with lithium-ion ones, I will need 3 elements, their operating voltage will be 10.8 volts, maximum – 12.6 volts. Exceeding the rated voltage will not harm the motor in any way, it will not burn out, and with a larger difference, there is no need to worry.

Lithium-ion cells, as everyone has long known, categorically do not like overcharging (voltage above 4.2 V) and excessive discharge (below 2.5 V). When the operating range is exceeded in this way, the element degrades very quickly. Therefore, lithium-ion cells are always paired with an electronic board (BMS - Battery Management System), control element and controlling both the upper and lower voltage limits. This is a protection board that simply disconnects the can from electrical circuit when the voltage goes beyond the operating range. Therefore, in addition to the elements themselves, such a BMS board will be required.

Now there are two important points that I unsuccessfully experimented with several times until I came to the right choice. This is the maximum permissible operating current of the Li-Ion elements themselves and the maximum operating current of the BMS board.

In a screwdriver, the operating currents at high loads reach 10-20 A. Therefore, you need to buy elements that are capable of delivering high currents. Personally, I successfully use 30-amp 18650 cells manufactured by Sony VTC4 (capacity 2100 mAh) and 20-amp Sanyo UR18650NSX (capacity 2600 mAh). They work fine in my screwdrivers. But, for example, the Chinese TrustFire 2500 mAh and the Japanese light green Panasonic NCR18650B 3400 mAh are not suitable, they are not designed for such currents. Therefore, there is no need to chase the capacity of the elements - even 2100 mAh is more than enough; The main thing when choosing is not to miscalculate the maximum permissible discharge current.

And in the same way, the BMS board must be designed for high operating currents. I saw on Youtube how people assemble batteries on 5 or 10-amp boards - I don’t know, personally, such boards immediately went into protection when I turned on the screwdriver. In my opinion, this is a waste of money. I will say this, that Makita itself puts 30-amp circuit boards in its batteries. That's why I use 25 amp BMS purchased from Aliexpress. They cost about 6-7 dollars and are searched for “BMS 25A”. Since you need a board for an assembly of 3 elements, you need to look for a board with “3S” in its name.

Another important point: some boards may have different contacts for charging (designated “C”) and load (designated “P”). For example, the board may have three contacts: “P-”, “P+” and “C-”, like on a native Makita lithium-ion board. Such a fee will not suit us. Charging and discharging (charge/discharge) must be carried out through one contact! That is, there should be 2 working contacts on the board: just “plus” and just “minus”. Because our old charger also only has two pins.

In general, as you might have guessed, with my experiments I wasted a lot of money on both the wrong elements and the wrong boards, making all the mistakes that could be made. But I gained invaluable experience.

How to disassemble a screwdriver battery

How to disassemble an old battery? There are batteries where the case halves are attached with screws, but there are also ones with glue. My batteries are just one of the last ones, and I generally for a long time believed that they were impossible to disassemble. It turns out it's possible if you have a hammer.

In general, with the help of intensive blows to the perimeter of the edge of the lower part of the case (a hammer with a nylon head, the battery must be held suspended in your hand), the gluing area is successfully separated. The case is not damaged in any way, I have already disassembled 4 pieces like this.

The part that interests us.

From the old circuit, only contact plates are needed. They are firmly spot welded to the top two elements. You can pick out the weld with a screwdriver or pliers, but you need to pick as carefully as possible so as not to break the plastic.

Everything is almost ready for further work. By the way, I left the standard temperature sensor and circuit breaker, although they are no longer particularly relevant.

But it is very likely that the presence of these elements is necessary for the normal operation of the standard charger. Therefore, I strongly recommend saving them.

Assembling a lithium-ion battery

Here are the new Sanyo UR18650NSX cells (you can find them on Aliexpress using this article number) with a capacity of 2600 mAh. For comparison, the old battery had a capacity of only 1300 mAh, half as much.

You need to solder the wires to the elements. Wires must be taken with a cross-section of at least 0.75 sq. mm, because we will have considerable currents. A wire with this cross-section works normally with currents of more than 20 A at a voltage of 12 V. Lithium-ion cans can be soldered; short-term overheating will not harm them in any way, this has been verified. But you need a good fast-acting flux. I use TAGS glycerin flux. Half a second - and everything is ready.

Solder the other ends of the wires to the board according to the diagram.

I always use even thicker wires of 1.5 sq. mm for the battery contact connectors - because space allows. Before soldering them to the mating contacts, I put a piece of heat-shrink tubing on the board. It is necessary for additional isolation of the board from the battery cells. Otherwise, the sharp solder edges can easily rub or pierce the thin film of the lithium-ion cell and cause a short circuit. You don’t have to use heat shrink, but at least laying something insulating between the board and the elements is absolutely necessary.

Now everything is insulated as it should.

The contact part can be strengthened in the battery case with a couple of drops of super glue.

The battery is ready for assembly.

It’s good when the case is on screws, but this is not my case, so I just glue the halves together again with “Moment”.

The battery is charged using a standard charger. True, the operating algorithm is changing.

I have two chargers: DC9710 and DC1414 T. And they work differently now, so I'll tell you exactly how.

Makita DC9710 charger and lithium-ion battery

Previously, the battery charge was controlled by the device itself. When the full level was reached, it stopped the process and signaled the completion of charging with a green indicator. But now the BMS circuit we installed is responsible for level control and power shutdown. Therefore, when charging is complete, the red LED on the charger will simply turn off.

If you have such an old device, you are in luck. Because everything is simple with him. The diode is on - charging is in progress. Goes off – charging is complete, the battery is fully charged.

Makita DC1414 T charger and lithium-ion battery

There is a small nuance here that you need to know. This charger is newer and is designed to charge a wider range of batteries from 7.2 to 14.4 V. The charging process on it proceeds as usual, the red LED is on:

But when the battery (which in the case of NiMH cells is supposed to have a maximum voltage of 10.8 V) reaches 12 volts (we have Li-Ion cells, for which the maximum total voltage can be 12.6 V), the charger will go crazy. Because he will not understand which battery he is charging: either a 9.6-volt one or a 14.4-volt one. And at this moment, the Makita DC1414 will enter error mode, flashing the red and green LED alternately.

This is fine! Your new battery will still charge - although not completely. The voltage will be approximately 12 volts.

That is, you will miss some part of the capacity with this charger, but it seems to me that this can be survived.

In total, upgrading the battery cost about 1000 rubles. The new Makita PA09 costs twice as much. Moreover, we ended up with twice the capacity, and further repairs (in the event of a short-term failure) will only consist of replacing lithium-ion elements.

Every master encounters the problem of reduced tool performance, or complete failure due to the battery. Manufacturers use batteries made from nickel-cadmium batteries in 12, 14, 18-volt screwdrivers. The sequential assembly of several elements creates the required voltage. Replacing nickel-cadmium batteries with lithium ones increases battery life by making the design lighter. Mandatory installation of a BMS board adds reliability. Therefore, converting the screwdriver to lithium batteries, mainly to the 18650 form factor, is justified.

Why do nickel-cadmium batteries fail quickly? In a garland of cans connected in series, each one is special. The chemical process is individual, the charge in closed systems different. If there is a malfunction in one bank, the design does not provide the required voltage. A charge control and balancing system is not provided in individual components.

1. Each Ni-Cd bank provides 1.2 V, and li-ion 18650 - 3.6 V.
2. The capacity of a lithium battery is 2 times larger than a nickel-cadmium battery, which is similar in size.
3. An overheated li-ion battery threatens to explode and catch fire, so installing charge uniformity control in the banks is mandatory. BMS is not installed in nickel-cadmium batteries - the manufacturer is not interested.
4. Lithium cells do not have a memory effect, unlike Ni-Cd, they can be charged at any time and within an hour.
5. The screwdriver becomes much lighter after converting the battery to li-ion, using 18650 cans.

There are only two obstacles to converting a screwdriver for lithium batteries - it is impossible to work with it at minus. The capacity of the cans decreases, starting from a decrease already from +10 0 C. Lithium batteries are expensive.

Knowing what input voltage is required for the screwdriver, the charger is redesigned, taking into account the placement of lithium battery cans and control elements in the factory container. You can do the same with a flashlight by upgrading the socket for a block of 18650 elements.

Let's say you need to rework a 12 V screwdriver using Ni-Cd cans on li-ion. If you use 3 banks, the output voltage is not enough: 3.6 x 3 = 10.8 V. With 4 components, the power of the device will be higher: 3.6 x 4 = 14.4 V. At the same time, the tool will become 182 g lighter , its power and capacity will increase slightly - all pluses. But when dismantling it is necessary to leave the terminals and the original temperature sensor.

Conversion of a screwdriver to lithium batteries 18650 14 V

When converting screwdrivers of different power and flashlights from Ni-Cd to Li-ion, 18650 form factor batteries are more often used. They easily fit into a container or socket, since instead of two or three original ones they install one lithium one. The modification of the screwdriver battery should be carried out taking into account the features of 18650 lithium batteries.

This type of energy source does not tolerate deep discharge and excessive charge. This means that it is necessary to use voltage control boards. Since each battery has its own character, their charge is adjusted by a balancer. The point of converting a screwdriver with a voltage of 14.4 V is to create a device using lithium batteries to make a hand tool lighter and improve its performance. 18650 lithium batteries are most suitable for these purposes.

When selecting components, it should be taken into account that the starting current of the screwdriver is high; you must select the appropriate BMS for the required number of cans and at least 30 A. To convert the charging of the screwdriver to a lithium battery, you need to stock up on a good soldering iron, non-acid flux and thick wires for making jumpers.

Equipment:

• Lithium-ion cans in the amount of 4 pcs.
• Li-ion battery controller for 4 banks, CF-4S30A-A fits well. It has a built-in balancer that controls the charge of each element.
• Hot melt adhesive, TAGS soldering flux, solder.
• Heat-resistant tape;
• Connecting jumpers or thick insulated wire with a cross-section of at least 0.75 square, cut for bridges.

The procedure for converting a screwdriver for 18650:

• Disassemble the case and remove a bundle of 12 Ni-Cd elements from the container.
• Remove the garland, leaving the connector with the “+” and “-” terminals. Instead of a temperature sensor, a thermocouple from the controller will be installed.
• Solder the assembly, taking into account that you cannot use acid, only neutral flux and clean solder. During the connection period, the lids must not be heated. Work precisely.
• Connect balancing points to the controller according to the diagram. There are connectors on the board.
• Connect the assembly to the plus and minus terminals.
• Check the functionality of the circuit. If everything works, place the assembled battery, place the controller in the socket, and secure it with sealant.

If the memory is not universal, additional rework will be required. 12 V screwdrivers with a universal charger are assembled in the same way, but a protective circuit for connecting 3x18650 3.7 V to lithium batteries is used. A screwdriver is converted in the same way using a 18650 battery kit consisting of 2 elements.

Converting a Makita screwdriver to a lithium battery

There is a Makita screwdriver with a battery capacity of 1.3 A/h and a voltage of 9.6 V. To change the power source on it to lithium-ion, you will need 3 18650 components. The conversion will give the old tool new capabilities: it will increase the operating time on a single charge , will add power as the operating voltage rises to 10.8 V.

The design will require the use of a BMS, a control controller that maintains the operation of lithium cells within operating limits. With this breaker, the charging of each bank will be uniform without exceeding 4.2 V, the lower voltage is 2.7 V. A built-in balancer is used here.

The controller parameters must accompany the operation of the tool when the operating current increases to 10-20 A. A 30 A Sony VTC4 board, designed for a capacity of 2100 A/h, can ensure operation without shutdown. Of the 20 amperes, the Sanyo UR18650NSX is suitable, receiving energy 2600A/h. The board is needed for 3 elements, which is marked in the 3S classification. In this case, the board should have 2 contacts, plus and minus. If the terminals are designated with the letters “P-”, “P+”, “C-”, they are intended for later models of screwdrivers.

Step-by-step instructions for converting a Makita screwdriver to lithium batteries look like this.

1. You can disassemble the battery with glue by tapping the joint while holding it with a soft-headed hammer. The direction of the blow is downward, into the joint along the lower part of the body.
2. Take only the contact plates from the old assembly, carefully disconnecting them from the battery. The sensor and breaker must be left.
3. Solder 3 elements in series using TAGS flux and insulated jumpers. The wire cross-section must be greater than 0.75 mm2.
4. Assemble the circuit with the controller, and connect the power supply to the contact connectors with 1.5 square wires.
5. Check the functionality of the circuit and reassemble the body, placing it back on the glue.

In a screwdriver with an old DC9710 charger, after the 18650 lithium battery has finished charging, the red LED on the panel will turn off. The charge level is monitored by a built-in controller.

The Makita DC1414 T charger is used to charge 7.2-14.4 V power supplies. While charging is in progress, the red light is on. But when charging a lithium battery, its voltage does not fit into the standards of salt products, and after 12 V the charger will start flashing red and green. But the necessary charging is already there. The screwdriver is ready for use.

Converting a 12V Hitachi screwdriver to 18640 lithium batteries

Features of converting a 12 V Hitachi screwdriver to lithium batteries. The very compact battery cell socket is designed for finger-type cells. Therefore, you should prepare space for 18650 elements. It is necessary to cut one side of the partition in order to tightly place 1 element.

You need to get flux, flat metal connecting tape, hot glue. It is necessary to install lithium batteries in a screwdriver during remodeling through a protective controller. It should handle 3 18650 cells, 3.7V and rated at 20-30 amps.

Extract old battery from the socket, carefully disconnect the contacts in the assembly with the temperature sensor and power indicator. Clear and sign contacts. They should be brought out in one direction, connected with solder to the leads from thick wires, and the assembly should be filled with hot glue.

Assemble an energy source with one of the controllers designed for 3 elements. Assemble a sequential circuit of 3 Li-ion elements. Connect the controller. The 12-volt lithium battery conversion is complete when the structure is installed in the block, secured, and the charging indicator lights up. After full charging, measurements show 12.17 volts in the external network. But this is enough for trouble-free long-term operation of the device.

Converting the Interskol screwdriver to 18650 lithium batteries

Sooner or later, the nickel-cadmium assembly of 15 cans fails. One or two elements have become lazy, and it is no longer possible to obtain output voltage. Modern Interskol DS with lithium batteries serve much better. Craftsmen have mastered converting a screwdriver to 18-volt lithium batteries.

You need to purchase a protection board for 5S, 3.7 V and 40-50 A. You will need a balancing board and the energy sources themselves - 5 lithium 18650 batteries, you can leave them with factory thermistors by lengthening the wires. During installation, create a contact pad, insert the assembly, check functionality, and secure it. Assembly features and expert advice are given in detail in the video. Here full information about converting an 18-volt lithium screwdriver

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

Converting a screwdriver to Li-ion without a BMS board

There hasn't been a review of converting a screwdriver to lithium for a long time :)
The review is mainly devoted to the BMS board, but there will be links to some other little things involved in converting my old screwdriver to lithium batteries 18650 format.
In short, you can take this board; after a little finishing, it works quite well in a screwdriver.
PS: a lot of text, pictures without spoilers.

P.S. The review is almost an anniversary on the site - the 58,000th, if you believe it address bar browser;)

What is this all for

Well, now about the main thing :)

• Model: 548604
• Overcharge cutoff at voltage: 4.28+ 0.05 V (per cell)
• Recovery after overcharge shutdown at voltage: 4.095-4.195V (per cell)
• Over-discharge voltage cut-off: 2.55±0.08 (per cell)
• Overcharge shutdown delay: 0.1s
• Temperature range: -30-80
• Short circuit shutdown delay: 100ms
• Overcurrent shutdown delay: 500 ms
• Cell balancing current: 60mA
• Working current: 30A
• Maximum current (protection trip): 60A
• Short circuit protection operation: self-healing after load disconnection
• Dimensions: 45x56mm
• Main functions: overcharge protection, overdischarge protection, short circuit protection, overcurrent protection, balancing.

All board components are placed on one side:

The second side is empty and covered with a white mask:

The part responsible for balancing during charging:

This part is responsible for protecting cells from overcharge/overdischarge and it is also responsible for general protection against short circuit:

Mosfets:

It is assembled neatly, there are no obvious flux stains, the appearance is quite decent. The kit included a tail with a connector, which was immediately plugged into the board. The length of the wires in this connector is about 20-25 cm. Unfortunately, I didn’t take a picture of it right away.

What else did I order specifically for this alteration:
Batteries -
Nickel strips for soldering batteries: (yes, I know that you can solder with wires, but the strips will take up less space and will be more aesthetically pleasing :)) And initially I even wanted to assemble contact welding (not only for this alteration, of course), that’s why I ordered the strips, but laziness prevailed and I had to solder them.

Having chosen a free day (or rather, having blatantly sent all other matters away), I set about redoing it. To begin with, I disassembled the battery with dead Chinese batteries, threw out the batteries and carefully measured the space inside. Then I sat down to draw the battery holder and circuit board in a 3D editor. I also had to draw the board (without details) in order to try on everything assembled. It turned out something like this:


According to the idea, the board is attached from above, one side into the grooves, the other side is clamped with an overlay, the board itself lies in the middle on a protruding plane so that when it is pressed it does not bend. The holder itself is made of such a size that it fits tightly inside the battery case and does not dangle there.
At first I thought about making spring contacts for batteries, but abandoned this idea. This is not the best option for high currents, so I left cutouts in the holder for nickel strips with which the batteries will be soldered. I also left vertical cutouts for the wires, which should extend from the inter-can connections beyond the lid.
I set it to be printed on a 3D printer from ABS and after a few hours everything was ready :)


When screwing everything on, I decided not to trust screws and fused these M2.5 plug-in nuts into the body:


Got it here -
Great item for this type of use! It is fused slowly with a soldering iron. To prevent the plastic from packing inside when melting into blind holes, I screwed a bolt of suitable length into this nut and heated its head with a soldering iron tip with a large drop of tin for better heat transfer. The holes in the plastic for these nuts are left slightly smaller (0.1-0.2 mm) than the diameter of the outer smooth (middle) part of the nut. They hold very tightly, you can screw in and unscrew the bolts as much as you like and don’t be too shy with the tightening force.

In order to have the possibility of cell-by-can control and, if necessary, charging with external balancing, a 5-pin connector will stick out in the back wall of the battery, for which I quickly threw on a scarf and made it on the machine:




The holder has a platform for this scarf.

As I already wrote, I soldered the batteries with nickel strips. Alas, this method is not without its drawbacks, and one of the batteries was so outraged by this treatment that it left only 0.2 volts on its contacts. I had to desolder it and solder another one, fortunately I took them with a reserve. Otherwise there were no difficulties. Using acid, we tin the battery contacts and nickel strips cut to the required length, then thoroughly wipe everything tinned and around it with cotton wool and alcohol (but you can also use water), and solder it. The soldering iron must be powerful and either be able to react very quickly to the tip cooling, or simply have a massive tip that will not cool instantly upon contact with a massive piece of iron.
Very important: during soldering and during all subsequent operations with the soldered battery pack, you must be very careful not to short-circuit any battery contacts! In addition, as indicated in the comments ybxtuj, it is very advisable to solder them discharged, and I absolutely agree with him, this way the consequences will be easier if something does short out. A short circuit of such a battery, even a discharged one, can lead to big troubles.
I soldered wires to three intermediate connections between the batteries - they will go to the BMS board connector for monitoring the 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 Ebay, but I don’t remember the exact link... I really like them, but there is a minus - silicone insulation is not very mechanically strong and is easily damaged by sharp objects.

I tried on the batteries and the board in the holder - everything is excellent:

I tried on a handkerchief with a connector, used a Dremel to cut out a hole in the battery case for the connector... and missed the height and took the size from the wrong plane. The result was a decent gap like this:

Now all that remains is to solder everything together.
I soldered the included tail onto my scarf, cutting it to the required length:


I also soldered the wires from the inter-can connections there. Although, as I already wrote, it was possible to solder them to the corresponding contacts of the BMS board, there is also an inconvenience - in order to remove the batteries, you will need to unsolder not only the plus and minus from the BMS, but also three more wires, but now you can simply pull out the connector.
I had to tinker a little with the battery contacts: in the original version, the plastic part (holding the contacts) inside the battery leg is pressed by one battery standing directly under it, but now I had to think about how to fix this part, so as not to be tight. Here's the detail:


In the end, I took a piece of silicone (left over from pouring some form), cut off a roughly suitable piece from it and inserted it into the leg, pressing that part. At the same time, the same piece of silicone presses the holder with the board, nothing will dangle.
Just in case, I laid Kapton insulating tape over the contacts, and grabbed the wires with a few snot drops of hot glue so that they would not get between the halves of the case when assembling it.

Charging and balancing

And now about the rake

And I decided to try to get to the root of the problem.

I dismissed the assumption that the overload protection was triggered during inrush currents, since even without the shunt nothing changed.
But still I looked with an oscilloscope at a homemade 0.077 ohm shunt between the batteries and the board - yes, PWM is visible, sharp consumption peaks with a frequency of approximately 4 kHz, 10-15 ms after the start of the peaks the board cuts off the load. But these peaks showed less than 15 amperes (based on the shunt resistance), so it’s definitely not a matter of current overload (as it turned out later, this is not entirely true). And the ceramic resistance of 1 Ohm did not cause a shutdown, but the current was also 15 amperes.
There was also the option of a short-term drawdown on the banks during startup, which triggered the overdischarge protection, and I went to see what was happening on the banks. Well, yes, horror is happening there - the peak drawdown is up to 2.3 volts on all banks, but it is very short - less than a millisecond, while the board promises to wait a hundred milliseconds before turning on the overdischarge protection. “The Chinese indicated Chinese milliseconds,” I thought and went to look at the voltage control circuit of the cans. It turned out that it contains RC filters that smooth out sudden changes (R=100 Ohm, C=3.3 uF). After these filters, already at the input of the microcircuits that control the banks, the drawdown was smaller - only up to 2.8 volts. By the way, here is the datasheet for the can control chips on this DW01B board -
According to the datasheet, the response time to overdischarge is also considerable - from 40 to 100 ms, which does not fit into the picture. But okay, there’s nothing more to assume, so I’ll change the resistance in the RC filters from 100 Ohms to 1 kOhm. This radically improved the picture at the input of the microcircuits; there were no more drawdowns of less than 3.2 volts. But it didn’t change the behavior of the screwdriver at all - a slightly sharper start - and then shut up.
“Let’s go with a simple logical move”©. Only these DW01B microcircuits, which control all discharge parameters, can cut off the load. And I looked at the control outputs of all four microcircuits with an oscilloscope. All four microcircuits do not make any attempts to disconnect the load when the screwdriver starts. And the control voltage disappears from the mosfets gates. Either mysticism or the Chinese have screwed up something in a simple circuit that should be between microcircuits and mosfets.
And I started reverse engineering this part of the board. With swearing and running from the microscope to the computer.

Here's what we ended up with:


In the green rectangle are the batteries themselves. In blue - the keys from the outputs of the protection chips, also nothing interesting, in a normal situation their outputs to R2, R10 are simply “hanging in the air”. The most interesting part is in the red square, which is where, as it turned out, the dog rummaged. I drew the mosfets one at a time for simplicity, the left one is responsible for discharging to the load, the right one is for the charge.
As far as I understand, the reason for the shutdown is in resistor R6. Through it, “iron” protection against current overload is organized due to the voltage drop on the mosfet itself. Moreover, this protection works like a trigger - as soon as the voltage at the base of VT1 begins to increase, it begins to reduce the voltage at the gate of VT4, from which it begins to reduce conductivity, the voltage drop across it increases, which leads to an even greater increase in the voltage at the base of VT1 and an avalanche-like a process leading to the complete opening of VT1 and, accordingly, the closing of VT4. Why does this happen when starting a screwdriver, when the current peaks do not even reach 15A, while a constant load of 15A works - I don’t know. Perhaps the capacitance of the circuit elements or the inductance of the load plays a role here.
To check, I first simulated this part of the circuit:


And this is what I got from the results of her work:


The X axis is time in milliseconds, the Y axis is voltage in volts.
On the bottom graph - the load is turned on (you don’t have to look at the numbers on Y, they are arbitrary, just up - the load is on, down - off). The load is a resistance of 1 ohm.
In the top graph, red is the load current, blue is the voltage at the mosfet gate. As you can see, the gate voltage (blue) decreases with each pulse of load current and eventually drops to zero, which means the load is turned off. And it is not restored even when the load stops trying to consume something (after 2 milliseconds). And although other mosfets with different parameters are used here, the picture is the same as in the BMS board - an attempt to start and shutdown in a matter of milliseconds.
Well, let’s take this as a working hypothesis and, armed with new knowledge, let’s try to chew on this piece of Chinese science :)
There are two options here:
1. Place a small capacitor in parallel with resistor R1, this is:


The capacitor is 0.1 uF, according to the simulation it is possible even less, up to 1 nf.
The result of the simulation in this version:


2. Remove resistor R6 altogether:


The result of the simulation of this option:

I tried both options - both work. In the second option, the screwdriver does not turn off under any circumstances - start, rotation is blocked - it turns (or tries with all its might). But somehow it’s not entirely peaceful to live with the protection turned off, although there is still protection against short circuits on the microcircuits.
With the first option, the screwdriver starts confidently with any pressure. I was able to achieve shutdown only when I started it at second speed (increased for drilling) with the chuck blocked. But even then it jerks quite strongly before turning off. At first speed I could not get it to turn off. I left this option for myself; I am completely satisfied with it.

There are even empty spaces for components on the board, and one of them seems to be specially designed for this capacitor. It was designed for the size of SMD 0603, so I soldered 0.1 uF here (circled it in red):

RESULT

PS: damn, it took me less time to remodel the screwdriver than it took me to write this review :)
ZZY: perhaps my comrades who are more experienced in power and analogue circuitry will correct me on something, I myself am a digital and analogue person through the roof :)