Battery assembly
Further battery replacement consists of the following steps:
- The disassembled parts of the case are well cleaned;
- Since the dimensions of the new battery cells will be smaller, they must be securely fixed: glued to the inner wall of the case with Moment glue or sealant;
- The positive and negative wires are soldered to the old terminal blocks, it is placed in the same 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.
Conversion of a screwdriver to 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. Converting a screwdriver to a cast one will improve the performance of the device, rather than buying a new tool. Now many companies offer services for altering screwdriver batteries, but you can do it yourself.
Converting a screwdriver to lithium batteries
Battery selection
12V batteries are often used for screwdrivers. Factors to consider when choosing a Li-Ion battery for a screwdriver:
- In such instruments, elements with high discharge currents are used;
- In many cases, the cell capacity is inversely related to the discharge current, so it cannot be selected based on capacity alone. The main indicator is the 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;
- It is not recommended to use cells with different capacities when replacing a screwdriver battery with a Li-Ion 18650;
- Sometimes there are tips to use a lithium battery from an old laptop. This is absolutely unacceptable. They are designed for much lower discharge currents and have inappropriate technical characteristics;
- 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 and supply 3 new ones. The voltage level will be slightly reduced, but if 4 cells are installed, the overvoltage will shorten the life of the motor.
Important! Before assembly, it is necessary to fully charge all elements to equalize.
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, and not wait until it is completely discharged (memory effect).
Lithium-ion batteries have the following benefits:
- High capacity, which will provide longer operating time of the screwdriver;
- Smaller size and weight;
- Keeps charge well when inoperative.
But a 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, full discharge. When the microcircuit is inserted directly into the battery, the circuit is opened if the unused battery is separated from the tool.
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 may arise:
- The 18650 standard means that a single cell has a diameter of 18 mm and a length of 65 mm. These dimensions are NOT the same as 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 the installation of a protective microcircuit and connecting wires;
- The voltage at the output of the lithium cells is 3.6 V, and on the nickel-cadmium cells. 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 overcharge voltages of more than 4.2 V and a discharge of less than 2.7 V until they fail. Therefore, when the battery is being reworked, a protective board must be installed in the screwdriver;
- The existing charger can 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.
Tips for choosing a security chip
The lithium-ion battery of the screwdriver will NOT function properly without the BMS protection board. The copies on sale have different characteristics. BMS 3S marking assumes, for example, that the board is designed for 3 elements.
What you need Pay attention to choose a suitable microcircuit:
- The presence of balancing to ensure uniformity of the charge of the cells. If it is present, the value of the balancing current should be in the description of the technical data;
- Maximum long-term operating current. On average, you need to focus on 20-30 A. But this depends on the power of the screwdriver. Low-power enough 20 A, powerful. that’s 30 A;
- Voltage, upon reaching which the batteries are disconnected when overcharging (about 4.3 V);
- Voltage at which the screwdriver turns off. It is necessary to select this value, Based on the technical characteristics of the battery cell (the minimum voltage is about 2.6 V);
- Overload protection current;
- Resistance of transistor elements (minimum value selected).
Important! The magnitude of the overload tripping current is not very important. This value is offset from the workload 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.
Connection diagram of the elements with the protective board
Whether the controller has an autorun function can be determined by the presence of an “Automatic recovery” entry in the technical data. If there is such a function, then in order to restart the screwdriver after the protection is triggered, it will be necessary to remove the battery and connect it to the charger.
Battery cell connection
The connection of Li-Ion batteries for the screwdriver is performed in several ways:
- Application of Special Cassettes. The method is fast, but the contacts have a large transition resistance, they can quickly collapse from relatively high currents;
- Soldering. The method is suitable for those who know how to solder, since you need to have certain skills. Soldering should be done at an accelerated rate, because the solder cools quickly, and prolonged heating can damage the battery;
- Spot welding. This is the preferred method. But not everyone has a welding machine, such services can be provided by specialists.
Soldering elements
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 the second circuits, you can take thinner wires. 0.75 mm²;
Then a piece of heat shrink tubing is put on the battery, but this is not necessary. You can also put on heat shrinkage on the protective microcircuit to isolate it from contact with the batteries, otherwise sharp soldering projections can damage the cell shell and provoke a short circuit.
Disassembling the battery case
The body is often assembled with self-tapping screws, other options are assembled with 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 the parts of the case. Everything is removed from the inside. You can only reapply the contact plates or the entire terminal assembly for connecting to the tool, charger.
Charger
The lithium-ion battery of the screwdriver cannot be charged by connecting it to the usual power supply. A charger is used for this. The power supply simply delivers a stable charge voltage within specified limits. And in the charger, the determining parameter is the charge current, which affects the voltage level. Its value is limited. There are nodes in the memory circuit that are responsible for stopping the charging process and other protective functions, for example, shutdown when the polarity is incorrect.
The simplest charger is a power supply with a resistor included in the circuit to reduce the charging current. Sometimes they also connect a timer, which is triggered after a set time interval. All of these options do NOT contribute to long battery life.
Charging methods for LI Ion screwdriver batteries:
- Factory charger application. It is often also suitable for charging a new battery;
- Alteration of the charger circuit, with the installation of additional circuit elements;
- Purchase of a ready-made storage device. A good option is IMax.
Let’s say there is an old Makita DC9710 charger for charging a 12V Ni-Cd battery, which has an indication in the form of a green LED indicating the end of the process. The presence of the BMS board will allow you to stop charging when the specified voltage limits per cell are reached. The green LED will NOT light up, but the red LED will just go out. Charge over.
Makita DC9710 charger
The Makita DC1414 T charger is designed to charge a wide range of 7.2-14.4 V rechargeable batteries. In it, when the protective shutdown is triggered at the end of the charge, the indication will not work correctly. There is a blinking red and green light, which also signals the end of the charge.
You can get an improved power tool with extended battery life.
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