Alteration Of A 12v Screwdriver For Lithium Batteries 18650
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 lithium will improve the performance of the device without 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
Disassembling the battery case
The body is often assembled with self-tapping screws, other options 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 reapply only the contact plates or the entire terminal assembly for connection to the tool, charger.
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 18650 lithium 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 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 the installation of 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 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.
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. This is the preferred method. Not everyone has a welding machine, such services can be provided by specialists.
Important! The elements 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 mm are soldered². 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. 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.
12 V batteries are often used for screwdrivers. Factors to consider when choosing a Li-Ion battery for a screwdriver:
- In such instruments, elements with high values of the discharge current 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 of 1 Li-Ion to 3 Ni-Cd. For a 12-volt battery, you will need to install 3 new ones to replace 10 old cans. 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.
Tips for choosing a security chip
The lithium-ion battery of the screwdriver cannot function normally without the BMS protection board. Instances on sale have different parameters. BMS 3S marking assumes, for example, that the board is designed for 3 elements.
What you need to pay attention to in order 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 from 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 parameters of the battery cell (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 no such 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.
The Li-Ion batteries installed in the old compartment can be connected in the following ways:
- Use of special adapter cassettes;
- Soldering elements with a soldering iron;
- Spot welding.
The fastest of them is the first, however, when using it, contact zones with transitional resistances are formed, which are palpable at high operating currents. In addition, the dimensions of the compartment in this case increase significantly, which is not always convenient from the point of view of ergonomics.
Connecting elements for soldering is suitable for those who have mastered the techniques of working with a soldering iron well, which is very important in this case. The fact is that when soldering a battery, this operation must be done as quickly as possible so as not to overheat the contact zones of its poles.
The so-called spot welding is the most convenient and reliable method of all those considered earlier. But since the presence of a welding machine in a personal household is very rare, you will have to contact specialists, which is also not very cheap. Let’s consider the most accessible of all these approaches (soldering) in more detail.
Before you disassemble the case of the old battery compartment with your own hands, you should pay attention to the fact that it can be made using the following technologies:
- The individual parts are fastened together by means of small self-tapping screws;
- These elements are fixed on the base of a screwdriver using technical glue or special latches (the photo below shows the appearance of such a block).
To disassemble the glued block located on the screwdriver, it is most convenient to use a mallet with a plastic head, which excludes possible damage to the device case. Before dismantling, all unnecessary parts of the structure should be removed from the compartment, leaving only the contact plates (their assembly) necessary for connection to the tool itself and an external charger.
Features of lithium ion battery
Before converting a screwdriver for a lithium-ion battery, you must carefully familiarize yourself with the intended modes of its operation as part of this tool. In this case, the following factors should be taken into account:
- The main operating parameter of these products is the load current (its nominal value can be found in the instrument’s passport);
- When choosing a suitable type of Li-Ion 18650, you should focus on a model that provides significant discharge (or load) currents, reaching values from 15 to 30-40 Amperes;
- In this case, it is not necessary to take into account the declared capacity of the selected battery, which can always be restored by additional charging of the li ion screwdriver.
Note! These features explain the inadmissibility of using a lithium battery from an old laptop, which is often mentioned on the Internet. Such batteries are not designed for high discharge current and do not have the required technical parameters.
Note also that when choosing several 18650 cells inserted into one battery compartment, it is not allowed to use cells with very different capacities.
Based on the operating voltages of old and new batteries (1.2 and 3.7 Volts) indicated in the technical characteristics, the proportion of 1 to 3 should be adhered to when selecting their quantitative ratio. So, for a 12-volt battery compartment of nickel-cadmium cells (10 pieces), it is remade in such a way that 3 lithium batteries can fit in it (this results in a small voltage shortfall).
We also recall that before assembly, it is necessary to fully charge each of the installed elements, which will ensure the equalization of their potentials.
The bases and difficulties of the alteration. Modification of the compartment
To realize the above advantages, it will be necessary to solve a number of issues that arise when converting a screwdriver battery to li-ion, namely:
- The working dimensions of the new product, determined from its designation (diameter 18 mm, length 65 mm), do not coincide with the dimensions of the elements being replaced;
- A full replacement of the batteries is possible only if the battery compartment is modified to accommodate the controller board and the wiring harness;
- When reworking, the voltage difference of each of the elements of the prefabricated source, consisting of several batteries (1.2 Volts for nickel-cadmium versus 3.7 Volts for LI Ion) must also be taken into account.
Important! Taking this circumstance into account, it is necessary to try in advance to adjust the total voltage of several new elements to its old value (the figure below shows nickel-cadmium batteries).
In some cases, it is not possible to achieve the coincidence of the supply voltages at all, which makes it necessary to abandon the alteration or look for other products that are suitable for this parameter. At the same time, it is important to observe the measure and calculate the economic feasibility of switching to a li ion 18650 (otherwise, the upgrade may be more expensive than the tool itself).
What you need to estimate before starting work?
Also, more lithium cells will give more capacity. This means longer operating time of the screwdriver.
Lithium battery cells 18650
Next, you need to choose the right lithium cells themselves. Form factor without 18650 options. The main things to look at are discharge current and capacity. According to statistics, during normal operation of the screwdriver, the current consumption is in the range of 5-10 amperes. If you suddenly press the start button, then the current can jump to 25 amperes for a few seconds. That is, you need to choose 18650 lithium batteries with a maximum discharge current of 20-30 amperes. Then, with a short-term increase in current to these values, the battery will not be damaged.
The nominal voltage of lithium cells is 3.6-3.7 volts, and the capacity in most cases is 2000-3000 mAh. If the battery case allows, you can take not 4, but 8 cells. Connect them two by two into 4 parallel assemblies, and then connect them in series. As a result, you will be able to increase the battery capacity. But not every case will be able to pack 8 cans of 18650.
And the last preparatory stage is choosing a controller. According to its characteristics, it must correspond to the rated voltage and discharge current. That is, if you decide to assemble a 14.4 volt battery, then choose a controller with this voltage. The working discharge current is usually chosen half of the maximum permissible current.
Charge-Discharge Controller Board
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Choosing the rated voltage
First of all, you should decide on the choice of the voltage rating indicator for a lithium-based device. The choice should be made between the 3S model (its voltage range is from 12.6 to 7.5 V) and the 4S-Li-Ion battery (voltage range is from 16.8 to 10 V).
Connecting to a screwdriver
- A sharp pull on the trigger provokes the activation of the protective current mechanism. But in fact, such a protective mode is unlikely to be needed when using the tool. If you do not specifically provoke protection, then the work of the screwdriver will be stable.
- The tip should be clamped in a vice. The battery power freely triggers the ratchet, which limits the increase in the number of torsion revolutions.
- The screwdriver’s lithium battery is discharged electronically. The discharge current should be 5 A.
- The battery is inserted into the standard charger. Conversion of a screwdriver to lithium batteries :. The charge current indicator when measured is 3 A, which is acceptable for lithium cells. For the LG INR18650HG2 configuration, the maximum charge current will be 4 A, which is indicated in the technical specification.
How long does it take to replace batteries?
Rework screwdriver on lithium batteries will take approximately 2 hours. If all parameters are checked, then it will take 4 hours.
Everything can be done independently, without the help of another person. Conversion of a screwdriver to lithium batteries :. But contact welding and selection of batteries cannot be carried out without specialized equipment.
- Lithium battery cells cannot be charged above 4.4.5 volts and discharged below 2.4.7 volts. In real terms This interval is even narrower. If you go beyond these limits, the battery will of course be damaged. Therefore, apart from the lithium cans themselves, you will need to connect and install a charge-discharge controller in the screwdriver;
- The voltage of the textbook of the Li─Ion cell is 3.6─3.7 volts, for Ni─Cd and Ni─MH this value is 1.3.5 volts. In other words, there are difficulties with assembling a battery for screwdrivers with a voltage rating of 12 volts. From three lithium cans connected in turn, there is an option to assemble a battery with a nominal value of 11.1 volts. Out of four ─ 14.8, out of 5 ─ 18.5 volts, etc. Than that the voltage limits during charge-discharge will also be different. In other words, there are problems of comparability of a converted battery with a screwdriver;
- Almost always, in the role of lithium parts for alteration, cans of the standard 18650 are used. They differ in size from Ni─Cd and Ni─MH cans. Today, space will be needed for a charge-discharge controller and wires. All this will need to fit in a standard battery case of a screwdriver. Otherwise it will be very awkward for them to work;
- A cadmium battery charger may not be suitable for recharging the battery after a redesign. Maybe it will be necessary to revise the charger or introduce universal chargers;
- Lithium batteries lose their functionality at low temperatures. This is critical for those who simply use a screwdriver on the street;
- The cost of lithium batteries is higher than cadmium.
This step can show how lightweight the lithium battery is. The weight of the Ni-Mh device was 536 g. The weight of the new lithium device is 199 g, which will be quite noticeable. We managed to win 337 g in weight. At the same time, an increase in energy capacity is observed.
The battery is mounted in the case. The voids are filled with soft material from the packaging.