How To Convert A Screwdriver Battery To Lithium
Converting a screwdriver battery to lithium cells Converting a screwdriver to lithium batteries has its pros and cons. Before proceeding with the rework, you need to think through some important points.
Converting the battery of a screwdriver to lithium cells
Many screwdriver owners want to convert their batteries to lithium battery cells. Many articles have been written on this topic and in this material I would like to summarize information on this issue. First of all, we will consider the arguments in favor of converting a screwdriver to lithium batteries and against it. And also we will consider certain moments of the process of replacing batteries itself.
Let’s start with the benefits:
- The energy density of lithium-ion cells is much higher than that of nickel-cadmium, which are used by default in screwdrivers. That is, the battery on lithium cans will have less weight than on cadmium with the same capacity and output voltage;
- Lithium battery cells are charged significantly faster than Ni-Cd. It will take about an hour to charge them safely;
- Lithium Ion batteries have no memory effect. This means that they do not need to be fully discharged before charging..
Now about the disadvantages and difficulties of lithium batteries.
The arguments against
- Lithium battery cells cannot be charged above 4.2 volts and discharged below 2.7 volts. In real conditions, this interval is even narrower. If you go beyond these limits, the battery can be damaged. Therefore, in addition to the lithium cans themselves, you will need to connect and install a charge-discharge controller in the screwdriver;
- The voltage of one Li─Ion cell is 3.6─3.7 volts, and for Ni─Cd and Ni─MH this value is 1.2 volts. That is, there are problems with assembling a battery for screwdrivers with a voltage rating of 12 volts. From three lithium cans connected in series, you can assemble a battery with a nominal value of 11.1 volts. Out of four ─ 14.8, out of five ─ 18.5 volts, and so on. Naturally, the voltage limits during charge-discharge will also be different. That is, there may be problems with the compatibility of the converted battery with a screwdriver;
- In most cases, 18650 standard cans are used in the role of lithium cells for conversion. They differ in size from Ni─Cd and Ni─MH cans. In addition, you will need space 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 extremely inconvenient for them to work;
- A cadmium battery charger may not be suitable for recharging a battery after a redesign. You may need to revise the charger or use universal chargers;
- Lithium batteries lose their performance at low temperatures. This is critical for those who use a screwdriver outdoors;
- The price of lithium batteries is higher than cadmium batteries.
All pros and cons of converting a screwdriver battery to lithium cells
First you should think about whether I need this alteration? After all, it will be a frank self-propeller and in some cases can lead to failure of both the battery and the screwdriver itself. Therefore, let’s consider all the pros and cons of this procedure. It is possible that after that some of you will decide to abandon the conversion of the Ni─Cd battery for a screwdriver to lithium cells.
Replacing batteries in a screwdriver with lithium
Also, more lithium cells will give more capacity. This means more operating time of the screwdriver.
Lithium battery cells 18650
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 in 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 to be two times less than the maximum permissible current.
Charge-Discharge Controller Board
The nuances of the soldering process
First, the contact part of the battery is thoroughly degreased. Then, tinning is carried out by heating the applied solder. POS-40 solder is most suitable for tinning.
The contact of the soldering iron with the battery contact should not exceed 2 seconds. The process of soldering the battery plus requires special attention. The most suitable jumpers are made of copper wires with a cross section of more than 2.5 mm. Sq. All wires are covered with cambric, which plays the role of a good insulator.
The connection of mini-batteries should be carried out with special jumpers according to the developed scheme. Metal strips or thin wires can become the jumpers.
The final step is to connect the wires to the battery terminals made in the compartment. If the assembly of the prefabricated block is difficult, it is necessary to remove the stiffeners. Since they are made of plastic, it is easy to bite into them with ordinary side cutters.
Installing the lithium-ion battery
Of course, any installation requires preliminary preparation. It includes several very important points. Before you start soldering the parts, you need to determine how the battery mounting compartment will be arranged. All the necessary elements should easily fit in it.
Then new lithium batteries are held together with tape. Since the contacts oxidize over time, they are cleaned with fine-grained sandpaper before soldering.
Some helpful tips
Of course, installing lithium-ion batteries has a large number of positive qualities:
- Lack of memory.
- Minimum self-loading.
- You can operate the tool at sub-zero temperatures.
- Long service life (8 years).
However, these batteries are highly sensitive to the charging process. The voltage must always have a minimum value, otherwise the Li-ion battery will quickly become unusable. To fulfill such conditions, you need another memory, the cost of which is an order of magnitude higher. The native charger of the screwdriver will not be able to charge the lithium-ion battery.
It is impossible to say unequivocally which battery for a screwdriver is better. Their service life depends on careful handling, on strict adherence to the instructions supplied by the manufacturer.
DIY li-ion lithium screwdriver conversion
For several decades, screwdrivers have been used in various works. These devices are powered by nickel or cadmium batteries. But progress does not stand still, scientists have found a replacement for such outdated batteries. They were replaced by lithium counterparts. To use such a battery, you need to rework the screwdriver. A lithium battery will enhance the performance of your old instrument. Over, it is possible to carry out such an alteration independently, without resorting to the services of special firms.
A few words about BMS board
It is designed to control the charge or discharge of the battery. CF-4S30A-A is designed for four banks of 18650 rechargeable batteries, giving a discharge current of 30A. The board is equipped with a special balancer. It performs the functions of controlling the charge of each element separately. This completely eliminates the possibility of uneven charging. For the board to function properly, the batteries for assembly must have the same capacity. It is desirable that they are taken from the same block.
The industry produces a large number of BMS boards that differ in their technological characteristics. For reworking a screwdriver battery, a board operating on a current value of less than 30A is not very suitable. It will constantly turn on the protection mode.
Some boards require a short supply of charging current to recover. To do this, you will have to remove the battery from the case, reconnect the charger to it. The CF-4S30A-A board has no such drawback. It is enough to release the trigger of the screwdriver, if there is no current causing a short circuit, the board will turn on automatically.
The redesigned battery on this board can be charged with a universal charger. The latest models are supplied by Interskol with multifunctional chargers.
Finding the right battery
The connection of the batteries is made in series, therefore, the voltage rating of each cell is summed up with the subsequent one. That is, to get 14.4 volts, you need four cells with a voltage of 3.3 V.
To convert a cordless screwdriver, you only need to buy miniature batteries from a well-known manufacturer. For example, LiFePO4 batteries manufactured by Sistem A123. The cell capacity reaches 2,300 mAh. This value is sufficient for the efficient operation of the electric tool. Cheap batteries made in China won’t do much. They will quickly fail.
When choosing a battery for rework, copper strips are required on the terminals. It is much easier to solder such elements.
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 operation current;
- Resistance of transistor elements (minimum value is selected).
Important! The magnitude of the overload tripping current is of little importance. 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.
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.
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.
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 current 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, all elements must be fully charged for equalization.
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 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 on 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.