Accumulators and batteries What is the difference between a lithium battery and a nickel-cadmium battery. Calculation of t component schemes of alteration. Operating conditions of the lithium battery. Features of alteration of batteries and chargers from different manufacturers.
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Conversion of a screwdriver to lithium batteries 18650 14 V
When converting screwdrivers of different power and flashlights from Ni-Cd to Li-ion, batteries of the form factor 18650 are often used. They easily fit into a container or a nest, since instead of two or three relatives, one lithium is installed. Alteration of the screwdriver battery should be carried out taking into account the peculiarities of lithium 18650 batteries.
This type of energy source does not tolerate deep discharge and excessive charge. Hence, 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 reworking a screwdriver with a voltage of 14.4 V lies in creating a device using lithium batteries to facilitate a hand tool and increase its performance. Lithium 18650 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, it is necessary to choose the appropriate BMS for the required number of cans and at least 30 A.
- Lithium-ion cans in the amount of 4 pcs.
- 4-cell li-ion battery controller, CF-4S30A-A works well. It has a built-in balancer that controls the charge of each element.
- Hot glue, TAGS soldering flux, solder.
- Heat-resistant adhesive tape;
- Jumpers or thick insulated wire with a cross section of at least 0.75 squares, cut for bridges.
The procedure for converting a screwdriver for 18650:
- Disassemble the case and remove a bundle of 12 Ni-Cd cells from the container.
- Remove the garland, leaving the connector with pins and -. Instead of a temperature sensor, a thermocouple from the controller will be installed.
- Solder the assembly, considering that you cannot use acid, only neutral flux and pure solder. During the connection period, do not warm up the covers. Work pointwise.
- Connect balancing points to the controller according to the diagram. The connectors are provided on the board.
- Connect the assembly to the plus and minus terminals.
- Check the functionality of the circuit. If everything works, the assembled battery, place the controller in the socket, secure with sealant.
If the charger is not universal, additional alteration will be required. Screwdrivers for 12 V with a universal charger are assembled in the same way, but a protective connection circuit 3×18650 3.7 V for lithium batteries is used. In the same way, a screwdriver is reworked using a set of 18650 batteries in the amount of 2 cells.
Conversion of a screwdriver to lithium batteries 18650
Every craftsman is faced with the problem of reduced tool performance, or complete failure due to the battery. Manufacturers use 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 batteries extends battery life, making the design easier. Mandatory BMS board installation adds reliability. Therefore, the conversion of a screwdriver to lithium batteries, mainly to the 18650 form factor, is justified.
Converting the battery of the screwdriver to Li-Ion
I will not say anything new in this article, but I just want to share my experience of upgrading the batteries of my old Makita screwdriver. Initially, this tool was designed for nickel-cadmium batteries (which have long since died, just as those bought for replacement have died). The disadvantages of Ni-Cd are well known: low capacity, short lifespan, high price. Therefore, cordless tool manufacturers have long since switched to lithium-ion batteries.
Well, what about those who have an old instrument? Everything is very simple: throw away the Ni-Cd cans and replace them with Li-Ion of the popular 18650 format (the marking indicates the diameter of 18 mm and the length of 65 mm).
What board is needed and what elements are needed to convert a screwdriver to lithium-ion
So, here is my 9.6V 1.3 Ah battery. At the maximum charge level, it has a voltage of 10.8 volts. Lithium-ion cells have a nominal voltage of 3.6 volts, with a maximum of 4.2. Therefore, to replace the old nickel-cadmium cells with lithium-ion ones, I need 3 cells, their operating voltage will be 10.8 volts, the maximum is 12.6 volts. Exceeding the rated voltage will not damage 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 known for a long time, categorically do not like overcharging (voltage above 4.2 V) and excessive discharge (below 2.5 V). When the operating range is exceeded, the element degrades very quickly. Therefore, lithium-ion cells are always paired with an electronic board (BMS Battery Management System), which controls the cell and monitors both the upper and lower voltage limits. This is a protection board that simply disconnects the can from the electrical circuit when the voltage goes out of the operating range. Therefore, in addition to the elements themselves, such a BMS board is required.
Now there are two important points that I experimented with unsuccessfully several times until I came to the right choice. These are the maximum allowable operating current of the Li-Ion cells themselves and the maximum operating current of the BMS board.
In a screwdriver, operating currents at a high load reach 10-20 A. Therefore, you need to buy elements that are capable of delivering high currents. Personally, I successfully use Sony VTC4 30-amp 18650 cells (2100 mAh capacity) and 20-amp Sanyo UR18650NSX (2600 mAh capacity). They work fine in my screwdrivers. But, for example, Chinese TrustFire 2500 mAh and 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 cell capacity, even 2100 mAh is more than enough; the main thing when choosing is not to miscalculate with the maximum permissible discharge current.
Likewise, the BMS board must be rated for high operating currents. I saw on Youtube how people assemble batteries on 5 or 10-ampere boards, I do not know, personally, when I turned on the screwdriver, such boards immediately went into defense. In my opinion, this is a waste of money. I will say that Makita itself puts 30-amp boards in its batteries. Therefore, I use 25-amp BMS purchased from Aliexpress. They cost around 6-7 and are searched for by BMS 25A. Since you need a board for an assembly of 3 elements, you need to look for such a board with 3S in its name.
Another important point: some boards for charging (designation C) and load (designation P) may have different contacts. For example, a board may have three pins: P-, P and C-, as on the native Makitov lithium-ion board. Such a fee will not work for us. Charging and discharging (charge / discharge) must be done through one contact! That is, there should be 2 working contacts on the board: just a plus and just a minus. Because our old charger also only has two contacts.
In general, as you might have guessed, with my experiments I threw out a lot of money both on the wrong elements and on the wrong boards, having made all the mistakes that could be made. But I got invaluable experience.
Makita DC9710 charger and lithium-ion battery
In the past, the battery 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 have installed is engaged in level control and power off. Therefore, when charging is complete, the red LED on the charger will simply turn off.
If you have just such an old device you are in luck. Because everything is simple with him. The diode is on, charging is in progress. Extinguished charging is complete, the battery is fully charged.
Difficulties in rework
There are objective disadvantages in Li-Ion batteries, such as poor performance at low temperatures. In addition, when converting a screwdriver to lithium 18650 batteries, a number of difficulties can be encountered:
- The 18650 standard means that a single cell has a diameter of 18 mm and a length of 65 mm. These dimensions do not match 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;
- The voltage at the output of the lithium cells is 3.6 V, and at the nickel-cadmium cells it is 1.2 V. Let us assume that the nominal voltage of the old battery is 12 V. Such a voltage cannot be ensured when Li-Ion cells are connected in series. The range of voltage fluctuations during the charge-discharge cycles of the ion battery also changes. Accordingly, converted batteries may not be compatible with the screwdriver;
- Ionic batteries differ in the specifics of their work. They do not withstand overcharging voltage more than 4.2 V and discharge less than 2.7 V until they fail. Therefore, when a battery is being reworked, a protective board must be installed in a screwdriver;
- The existing charger can sometimes not be used for a screwdriver with a Li-Ion battery. You will also need to redo it or purchase another.
Important! If the drill or screwdriver is cheap and not of very high quality, then it is better not to rework. This can cost more than the cost of the tool itself.
The advantages of lithium-ion batteries
Nickel-cadmium batteries have a low price, withstand many charging cycles, and are not afraid of low temperatures. But the capacity of the battery will decrease if you put it on charge without waiting for a full discharge (memory effect).
Lithium-ion batteries offer the following benefits:
- High capacity, which will provide longer operating time of the screwdriver;
- Smaller size and weight;
- Keeps charge well when inoperative.
But the lithium battery for a screwdriver does not withstand a full discharge, therefore, factory tools on such batteries are equipped with additional boards that protect the battery from overheating, short-circuit, overcharge in order to avoid an explosion, a complete discharge. Placing the microcircuit directly into the battery will open the circuit if the unused battery is separated from the tool.
Battery cell connection
Compound LiIon batteries for screwdriver performed in several ways:
- The use of special cassettes. The method is fast, but the contacts have a large transition resistance, they can quickly collapse from relatively high currents;
- Soldering. A method suitable for those who know how to solder, since you need to have certain skills. Soldering should be done quickly, because the solder cools quickly, and prolonged heating can damage the battery;
- Spot welding. Is the preferred method. Not everyone has a welding machine, such services can be provided by specialists.
Important! The cells must be connected in series, then the battery voltage is added up, and the capacity does not change.
At the second stage, wires are soldered to the contacts of the assembled battery and to the protective board according to the connection diagram. To the contacts of the battery itself for power circuits, wires with a cross-sectional area of 1.5 mm² are soldered. For other circuits, you can take wires thinner than 0.75 mm²;
A piece of heat shrink tubing is then placed over the battery, but this is not required. A heat shrinkage can also be put on the protective microcircuit to isolate it from contact with the batteries, otherwise the sharp soldering projections can damage the cell shell and provoke a short circuit.