Features of the
The design of a lithium rechargeable battery is not too different from the design of batteries based on other chemistry. But a fundamental feature is the use of anhydrous electrolyte, which prevents the release of free hydrogen during operation. This was a significant disadvantage of the batteries of the previous designs and led to a high probability of fire.
The anode is made of a cobalt oxide film deposited on an aluminum base-current collector. The cathode is the electrolyte itself, which contains lithium salts in liquid form. The electrolyte impregnates a porous mass of electrically conductive chemically neutral material. Loose graphite or coke is suitable for it. Current collection is carried out from a copper plate superimposed on the back of the cathode.
For normal battery operation, the porous cathode must be pressed tightly enough to the anode. Therefore, in the design of lithium batteries, there is always a spring that compresses the “sandwich” from the anode, cathode and negative current collector. The ingress of ambient air can upset the carefully balanced chemical balance. And the ingress of moisture and does threaten the danger of fire and even explosion. Therefore, the finished battery cell must be carefully sealed.
A flat battery is simpler in design. All other things being equal, a flat lithium battery will be lighter, much more compact, and provide significant current (that is, more power). But it is necessary to design a device with flat-shaped lithium batteries, which means that the battery will have a narrow, specialized application. Such batteries are more expensive than their counterparts.
To make the sales market wider, manufacturers produce battery cells with universal shapes and standard sizes.
Among lithium batteries, the 18650 version actually dominates today. Such batteries have a form similar to the cylindrical finger batteries familiar in everyday life. But the 18650 standard specifically provides for a slightly larger size. This avoids confusion and prevents such a power supply unit from being mistakenly replaced in place of a conventional saline battery. But this would be very dangerous, since the lithium battery has two and a half times the standard voltage (3.6 volts versus 1.5 volts for a salt battery).
For an electric screwdriver, lithium cells are sequentially collected into a battery. This allows the voltage to the motor to be increased to provide the power and torque required by the tool.
The rechargeable battery necessarily contains in its design temperature sensors and a specialized electronic device. a controller.
- monitors the uniformity of the charge of individual elements;
- controls the charge current;
- does not allow excessive discharge of elements;
- prevents overheating of the battery.
Features, advantages and disadvantages of lithium batteries for screwdriver
- Features of the
- Advantages and disadvantages
- Difference from nickel cadmium batteries
- How to choose?
- How to remake and assemble?
- How to charge correctly?
- How to store?
If a hand-held power tool powered by a household power supply is tied to an outlet with a wire, limiting the movement of a person holding the device in his hands, then battery-operated counterparts of the units “on a leash” provide much more freedom of action in work. Battery is essential when it comes to using screwdrivers.
Depending on the type of battery used, they can be conditionally divided into two groups. with nickel and lithium batteries, and the features of the latter make this power tool the most interesting for the user.
How to choose?
When it comes to choosing a battery for a screwdriver, the task comes down to the selection of the electrical device itself, which will include a battery of a specific model.
The rating of inexpensive cordless screwdrivers this season looks like this:
- Makita HP331DZ, 10.8 volts, 1.5 Ah, lithium;
- Bosch PSR 1080 LI, 10.8 volts, 1.5 Ah, lithium;
- Bort BAB-12-P, 12 volt, 1.3 Ah, nickel;
- Interskol DA-12ER-01, 12 volts 1.3 Ah, nickel;
- Kolner KCD 12M, 12 volt, 1.3 Ah, nickel.
The best professional models are:
- Makita DHP481RTE, 18 volts, 5 Ah, lithium;
- Hitachi DS14DSAL, 14.4 volts, 1.5 Ah, lithium;
- Metabo BS 18 LTX Impuls 201, 18 volt, 4 Ah, lithium;
- Bosch GSR 18 V-EC 2016, 18 volts, 4 Ah, lithium;
- Dewalt DCD780M2, 18 Volt 1.5 Ah, lithium.
The best cordless screwdrivers in terms of reliability:
- Bosch GSR 1440, 14.4 volts, 1.5 Ah, lithium;
- Hitachi DS18DFL, 18 Volt, 1.5 Ah, Lithium
- Dewalt DCD790D2, 18 Volt, 2 Ah, Lithium.
You can see that the best screwdrivers in the semi-professional and professional segments have 18 volt rechargeable batteries.
This voltage is considered the industry professional standard for lithium batteries. Since a professional tool is designed for long-term active work, and also implies an additional level of comfort, a significant part of the produced 18-volt screwdriver batteries are fully compatible with each other, and sometimes even interchangeable between tools from different manufacturers.
In addition, the 10.8 volt and 14.4 volt standards are widely used. The first option is found only among the most inexpensive models. The second is traditionally a “middle peasant” and can be found both among professional models of screwdrivers and in models of the middle (intermediate) class.
But the designations of 220 volts in the characteristics of the best models cannot be seen, since this indicates that the screwdriver is connected with a wire to a household power outlet.
How to charge correctly?
Lithium batteries are quite finicky about charger specifications. Such batteries can be charged fairly quickly with a significant current, but excessive charging current leads to severe heating and fire hazard.
To charge a lithium battery, it is imperative to use a special charger with electronic control of the charge current and temperature control.
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It should also be borne in mind that when cells are connected in series in a battery, lithium sources are very prone to uneven charging of individual cells. This leads to the fact that it is not possible to charge the battery to its full capacity, and the cell, which regularly works in undercharged mode, simply wears out faster. Therefore, chargers are usually built according to the “charge balancer” scheme.
Fortunately, all modern factory-made lithium batteries (except for outright fakes) have built-in protection and balancing circuits. However, the charger for these batteries must be specialized.
Difference from nickel cadmium batteries
Historically, the first truly mass-produced rechargeable batteries for handheld power tools were nickel-cadmium batteries. At a low price, they are quite capable of relatively large loads and have a satisfactory electrical capacity with reasonable dimensions and weight. Batteries of this type are still widespread today, especially in the inexpensive sector of handheld appliances.
The main difference between lithium batteries and nickel-cadmium batteries is low weight with high electrical capacity and very good load capacity.
In addition, a very important difference between lithium batteries is the significantly shorter charging time. This battery can be charged in a couple of hours. But the full charge cycle of nickel-cadmium batteries takes at least twelve hours.
There is another peculiarity associated with this: while lithium batteries tolerate both storage and operation in an incompletely charged state quite calmly, nickel-cadmium batteries have an extremely unpleasant “memory effect”. In practice, this means that in order to extend the service life, as well as to prevent a rapid loss of capacity, it is advisable to use nickel-cadmium batteries until they are completely discharged. After that, be sure to charge to full capacity, which takes a considerable time.
Lithium batteries do not have this disadvantage.
How to remake and assemble?
Often, the master already has an old cordless screwdriver that suits him completely. But the device is equipped with outdated nickel-cadmium batteries. Since the battery will still have to be changed, there is a desire to replace the old battery with something newer. This will not only provide more comfortable work, but also eliminate the need to look for batteries of an outdated model on the market.
The simplest thing that comes to mind is to assemble a power supply from an electronic transformer in an old battery case. Now you can use the screwdriver by connecting it to the household power supply.
14.4 volt models can be connected to car batteries. Having assembled an extension adapter with terminals or a cigarette lighter plug from the body of an old battery, you get an indispensable device for a garage or work “in the field”.
Unfortunately, when converting an old battery into a wired adapter, the main advantage of the cordless screwdriver is lost. mobility.
If we are converting an old battery to lithium, we can take into account that 18650 lithium cells are extremely widespread in the market. Thus, we can make screwdriver batteries based on readily available parts. over, the prevalence of the 18650 standard allows you to choose batteries from any manufacturer.
It will not be difficult to open the case of an old battery and remove the old filling from it. It is important not to forget to mark the contact on the case to which the “plus” of the old battery assembly was previously connected.
Depending on the voltage for which the old battery was designed, it is necessary to select the number of lithium cells connected in series. The standard voltage of a lithium cell is exactly three times that of a nickel cell (3.6 V instead of 1.2 V). Thus, each “lithium” replaces three series-connected “nickels”.
By providing for the design of the battery, in which three lithium cells are connected one after the other, it is possible to obtain a battery with a voltage of 10.8 volts. Among nickel batteries, these are found, but not often. When four lithium cells are connected to a garland, we already get 14.4 volts. This will replace both 12 volt and 14.4 volt nickel batteries. these are very common standards for nickel cadmium and nickel metal hydride batteries. It all depends on the specific model of the screwdriver.
After it was possible to determine the number of successive stages, it will probably turn out that there is still free space in the old building. This will allow two cells to be connected in each stage in parallel, which will double the battery capacity. To connect lithium batteries to each other in production, a nickel strip is used. Sections of the tape are connected to each other and to lithium elements by resistance welding. But in everyday life, soldering is quite acceptable.
Soldering lithium cells should be done with great care. The joint must be thoroughly cleaned beforehand and a good flux applied. Tinning is done very quickly, with a well-heated soldering iron of sufficiently high power.
The soldering itself is performed by quickly and confidently warming up the place where the wire is connected to the lithium cell. To avoid dangerous overheating of the element, the soldering time should not exceed three to five seconds.
When designing a homemade lithium battery, you should take into account that it is charged in a special way. It is imperative to provide an electronic circuit for monitoring and balancing the charge in the design of the battery. In addition, such a circuit should prevent possible overheating of the battery and excessive discharge. Without such a device, a lithium battery is simply explosive.
It is good that now there are ready-made electronic control and balancing modules on sale at fairly low prices. It is enough to choose the solution that suits your particular case. Basically, these controllers differ in the number of series-connected “steps”, the voltage between which is subject to equalization (balancing). In addition, they differ in their permissible load current and temperature control method.
In any case, it is no longer possible to charge a homemade lithium battery with an old nickel battery charger. They have fundamentally different charging algorithms and control voltages. You will need a dedicated charger.
Advantages and disadvantages
- The main advantage of lithium batteries is their high electrical capacity. This allows you to create a lightweight and compact hand tool. On the other hand, if the user is ready to work with a heavier device, he will receive a very powerful battery that allows the screwdriver to work for a long time.
- Another advantage is the ability to fill lithium batteries with energy relatively quickly. A typical full charge time is approximately two hours, and some batteries can be charged in half an hour with a special charger! This advantage can be an exceptional reason for equipping a screwdriver with a lithium battery.
Lithium batteries also have some specific disadvantages.
- The most noticeable is the significant drop in practical capacity when operating in cold weather. At subzero temperatures, an instrument equipped with lithium batteries has to be warmed up from time to time, while the electrical capacity is fully restored.
- The second noticeable drawback is not too long service life. Despite the assurances of the manufacturers, the best samples, with the most careful use, withstand no more than three to five years. Within a year after the purchase, a lithium battery of any common brand, with the most careful use, can lose up to a third of its capacity. After two years, hardly half of the original capacity will remain. Average life of normal operation is two to three years.
- And another notable drawback: the price of lithium batteries is much higher than the cost of nickel-cadmium batteries that are still widely used in handheld power tools.
12 V batteries are often used for screwdrivers. Factors to consider when choosing a Li-Ion battery for a screwdriver:
- Elements with high discharge currents are used in such instruments;
- 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 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.
Converting 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.
Conversion of a screwdriver to lithium batteries
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 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’s say the nominal voltage of the old battery is 12 V. This 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 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
The connection of Li-Ion batteries for a screwdriver is 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.
Soldering the elements
Important! The elements must be connected in series, then the voltage of the batteries 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 thinner wires. 0.75 mm²;
A piece of heat shrink tubing is then placed over the battery, but this is not required. Heat shrinkage can also be put 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.
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 block, 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.
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.
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What you need to pay attention to in order to choose a suitable microcircuit:
- The presence of balancing to ensure the 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 (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 elements with a 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 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 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, a complete discharge. When the microcircuit is inserted directly into the battery, the circuit is opened if the unused battery is separated from the tool.