What Lithium Batteries Are Needed For A Screwdriver
I will not say anything new in this article, but I just want to share the experience of upgrading the batteries of my old Makita screwdriver. Initially, this tool was designed for nickel-cadmium batteries (which had already died long ago, as they had died, and those bought in replacement were the same). The disadvantages of Ni-Cd are known: low capacity, short life, high price. Therefore, manufacturers of cordless tools have long switched to lithium-ion batteries.
Well, what about those who have an old instrument? Yes, everything is very simple: throw out Ni-Cd cans and replace them with Li-Ion in the popular 18650 format (marking indicates a diameter of 18 mm and a length of 65 mm).
What kind of board do you need and what elements are needed to convert a lithium-ion screwdriver
So, here is my 9.6 V battery with a capacity of 1.3 Ah. At maximum charge, it has a voltage of 10.8 volts. Lithium-ion cells have a nominal voltage of 3.6 volts, maximum. 4.2. Therefore, to replace the old nickel-cadmium cells with lithium-ion cells, I need 3 cells, their operating voltage will be 10.8 volts, the 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, strongly dislike recharging (voltage above 4.2 V) and excessive discharge (below 2.5 V). With such excesses of the operating range, the element degrades very quickly. Therefore, lithium-ion cells always work in tandem with the electronic board (BMS. Battery Management System), which controls the cell and controls both the upper and lower voltage limits. This is a protection board that simply disconnects the jar from the 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 with which I experimented several times unsuccessfully, until I came to the right choice. This is the maximum allowable working current of the Li-Ion elements themselves and the maximum working current of the BMS board.
In a screwdriver, operating currents at high load reach 10-20 A. Therefore, you need to buy elements that are capable of delivering high currents. Personally, I successfully use 30-ampere 18650 cells manufactured by Sony VTC4 (with a capacity of 2100 mAh) and 20-ampere Sanyo UR18650NSX (with a capacity of 2600 mAh). They work fine in my screwdrivers. But, for example, Chinese TrustFire 2500 mAh and Japanese light green Panasonic NCR18650B at 3400 mAh are not suitable, they are not designed for such currents. Therefore, do not chase the capacity of the elements. Even 2100 mAh is more than enough; the main thing when choosing is not to miscalculate with the maximum permissible discharge current.
And in exactly the same way, the BMS board must be rated for high operating currents. I saw on Youtube how people collect batteries on 5 or 10-amp boards. I don’t know, personally, when I turned on the screwdriver, such boards immediately went to defense. In my opinion, this is a waste of money. I will say that Makita itself puts 30-ampere boards in its batteries. Therefore, I use 25-amp BMS purchased on Aliexpress. They cost about 6-7 dollars and are searched for by request “BMS 25A”. Since you need a board for an assembly of 3 elements, you need to look for a board in the name of which will be “3S”.
Another important point: some boards may have different contacts for charging (designation “C”) and load (designation “P”). For example, a board can have three pins: “P-”, “P”, and “C-”, as on a native Makita lithium-ion board. Such a board will not suit us. Charging and discharging (charge / discharge) must be done through one contact! That is, the board should have 2 working contacts: just “plus” and just “minus”. Because our old charger also has only two pins.
In general, as you might have guessed, with my experiments I threw a ton of money both on the wrong elements and on the wrong boards, having made all the mistakes that could have been made. But got invaluable experience.
How to disassemble a screwdriver battery
How to disassemble an old battery? There are batteries where the halves of the case are screwed, but there is also glue. My batteries are just the last, and I generally thought for a long time that they could not be taken apart. It turned out that 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 body (a hammer with a nylon head, the battery must be kept in hand in weight), the gluing place is successfully disconnected. The case is not damaged in any way, I have already disassembled 4 pieces.
Part of interest to us.
What Lithium Batteries Are Needed For A Screwdriver
From the old circuit, only contact plates are needed. They are firmly welded to the upper two elements by spot welding. You can pick out the welding with a screwdriver or pliers, but you need to pick it 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 a standard charger. Therefore, I strongly recommend that you save them.
Putting a lithium-ion battery
Here are the new elements of the Sanyo UR18650NSX (you can find them on this article on Aliexpress) with a capacity of 2600 mAh. For comparison, the old battery had a capacity of only 1300 mAh, half as much.
It is necessary to solder the wires to the elements. Wires must be taken with a cross-section of at least 0.75 sq. Mm, because the currents we have will be considerable. A wire with such a cross section normally works with currents of more than 20 A at a voltage of 12 V. It is possible to solder lithium-ion banks, short-term overheating will not harm them in any way, this has been checked. But you need a good high-speed flux. I use TAGS glycerin flux. Half a second. And you’re done.
Solder the other ends of the wires to the board according to the diagram.
On the battery connectors, I always run even thicker wires of 1.5 sq. Mm. Because the place allows. Before soldering them to the mating contacts, I put on 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 edges of the solder can easily rub or pierce a thin film of the lithium-ion cell and cause a short circuit. You can not apply heat shrinkage, but at least something insulating to lay between the board and the elements is absolutely necessary.
Now everything is insulated as it should.
The contact part can be fixed in the battery case with a couple of droplets of super-glue.
The battery is ready for assembly.
It’s good when the case is screwed, but this is not my case, so I just glue the halves together with the “Moment” again.
The battery is charged with a standard charger. True, the algorithm of work is changing.
I have two chargers: DC9710 and DC1414 T. And they now work differently, so I’ll tell you exactly how.
Makita DC9710 Battery Charger and Li-ion Battery
Previously, the battery charge was controlled by the device itself. Upon reaching the full level, it stopped the process and signaled the completion of charging with a green indicator. But now level control and power off are handled by the BMS circuit we have installed. Therefore, when charging is complete, the red LED on the charger will simply turn off.
If you have just such an old device. You’re in luck. Because everything is simple with him. The diode is on. Charging. Off. Charging is complete, the battery is fully charged.
Makita DC1414 T Battery Charger and Li-ion Battery
There is a small nuance that you need to know. This memory is newer and it is designed to charge a wider range of batteries from 7.2 to 14.4 V. The charging process on it goes as usual, the red LED is on:
But when the battery (which is supposed to have a maximum voltage of 10.8 V in the case of NiMH cells) reaches 12 volts (we have Li-Ion cells with a maximum total voltage of 12.6 V), the roof will be blown down by the charger. Because he will not understand what kind of battery he is charging: either 9.6-volt, or 14.4-volt. And at that moment, the Makita DC1414 will enter error mode, alternately blinking red and green LEDs.
This is normal! Your new battery will still charge. Though not completely. The voltage will be approximately 12 volts.
That is, you miss some part of the capacity with this charger, but it seems to me that you can survive it.
Total modernization of the Bosch battery cost about 1,000 rubles. The new Makita Makita PA09 costs twice as much. Over, in the end, we got twice the capacity, and further repairs (in the event of a failure several times) will consist only in the replacement of lithium-ion cells.
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