If a hand-held power tool powered by a household power supply is tied to a power outlet by a wire, restricting the movement of the person holding the device in his hands, then the cordless assemblies of the units “on a leash” provide much greater freedom of action. Having a battery is very important when it comes to using screwdrivers.
Depending on the type of battery used, they can be 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.
The device of a lithium battery is not too different from the design of batteries based on different chemistry. But a fundamental feature is the use of anhydrous electrolyte, which prevents the release of free hydrogen during operation. This was a significant drawback of the batteries of previous designs and led to a high probability of fire.
The anode is made of a cobalt oxide film deposited on an aluminum current collector base. The cathode is the electrolyte itself, containing lithium salts in liquid form. The electrolyte is impregnated with a porous mass of 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 needs to be pressed firmly against the anode. Therefore, a spring is necessarily present in the design of lithium batteries, compressing a “sandwich” of the anode, cathode and negative current collector. Exposure to atmospheric air can upset the carefully balanced balance of chemical processes. And moisture penetration poses a danger of fire and even explosion. therefore the ready-made battery cell must be carefully sealed.
The flat battery is structurally simpler. Ceteris paribus, 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 lithium batteries in a complex, which means that the battery will have a narrow, specialized application. Such batteries are more expensive than their counterparts.
To make the market wider, manufacturers produce battery cells of a universal shape and standard sizes.
Among the lithium batteries, the 18650 variant actually actually dominates today. Such batteries have a look similar to cylindrical finger batteries familiar in everyday life. But standard 18650 specifically provides for a few large dimensions. This helps to avoid confusion and prevents the erroneous insertion of such a power supply in place of a conventional salt battery. But this would be very dangerous, since a lithium battery has a two and a half times higher standard voltage (3.6 volts versus 1.5 volts for a salt battery).
For an electric screwdriver, lithium cells are sequentially assembled into a battery. This allows you to increase the voltage supplied to the engine, which provides the necessary power and torque for the tool.
The battery necessarily contains in its design temperature sensors and a specialized electronic device. the controller.
Video: Redo Screwdriver Battery For 18 V Lithium
- monitors the uniformity of the charge of individual elements;
- controls the charge current;
- does not allow excessive discharge of elements;
- prevents battery overheating.
Batteries of the type described are called ionic. There are also lithium-polymer elements, this is a modification of lithium-ion. Their design fundamentally differs only in material and structural design of the electrolyte.
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 you to work with a screwdriver for a long time.
- Another advantage is the ability to relatively quickly energize lithium batteries. The typical full charge time is approximately two hours, and some batteries can be charged even in half an hour if you have a special charger! This advantage can be an exceptional argument in favor of a lithium battery screwdriver.
Lithium batteries also have some specific disadvantages.
- The most noticeable is a significant drop in practical capacity when working in the cold. At low temperatures, a tool equipped with lithium batteries has to be heated from time to time, while the electric capacity is completely restored.
- The second noticeable drawback is the not too long service life. Despite the assurances of manufacturers, the best samples with the most accurate operation can withstand no more than three to five years. A year after purchase, a lithium battery of any common brand, with the most careful use, can lose up to a third of the capacity. Two years from the original capacity, hardly half will remain. The average normal life is two to three years.
- And one more noticeable drawback: the price of lithium batteries is much higher than the cost of nickel-cadmium batteries, which are still widely used in hand-held power tools.
Unlike Nickel Cadmium Batteries
Historically, the first truly massive batteries for hand-held power tools were nickel-cadmium batteries. At a low price, they quite allow relatively large loads and have a satisfactory electrical capacity with reasonable dimensions and weight. Batteries of this type are still widespread, especially in the inexpensive sector of hand-held electrical appliances.
The main difference between lithium batteries and nickel-cadmium batteries is their low weight with high electric capacity and very good load capacity.
Also very An important difference between lithium batteries is the significantly shorter charging time.. Such a battery can be charged in a couple of hours. But the full charge cycle of nickel-cadmium batteries takes at least twelve hours.
One more peculiarity is connected with this: while lithium batteries quite safely transfer both storage and operation in an incompletely charged state, nickel cadmium have an extremely unpleasant "memory effect". In practice, this means that to extend the service life, as well as to prevent rapid loss of capacity, It is advisable to use nickel-cadmium batteries until they are completely discharged. Then it is necessary to charge to full capacity, which takes a considerable time.
Lithium batteries do not have this drawback.
How to choose?
When it comes to choosing a battery for a screwdriver, the task boils down to the selection of the electrical device itself, complete with which will be a battery of a specific model.
The rating of inexpensive cordless screwdrivers this season is as follows:
- 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 volts, 1.3 Ah, nickel;