Not Charged Metabo Screwdriver Battery
Often, the native charger included in the screwdriver’s kit works slowly, charging the battery for a long time. For those who use the screwdriver intensively, this is a hindrance in their work. Despite the fact that usually two batteries are included in the kit (one is installed in the handle of the instrument and in operation, and the other is connected to the charger and is in the process of charging), often the owners cannot adapt to the working cycle of the batteries. Then it makes sense to make a charger yourself and charging will become more convenient.
Types of batteries
Batteries are not the same in type and charge modes may vary. Nickel-cadmium (Ni-Cd) batteries are a very good source of energy, capable of delivering more power. However, for environmental reasons, their production has been discontinued and they will be found less and less. Now everywhere they have been replaced by lithium-ion batteries.
Sulfuric acid (Pb) lead gel batteries have good characteristics, but make the instrument heavier and therefore not very popular, despite the relative cheapness. Since they are gel (the solution of sulfuric acid is thickened with sodium silicate), there are no plugs in them, the electrolyte does not leak from them and they can be used in any position. (By the way, nickel-cadmium batteries for screwdrivers also belong to the gel class.)
Lithium-ion batteries (Li-ion) are now the most promising and advanced in technology and on the market. Their feature is the complete tightness of the cell. They have a very high specific power, are safe to use (thanks to the built-in charge controller!), Are disposed of favorably, are the most environmentally friendly, and light in weight. In screwdrivers are currently used very often.
The nominal voltage of the Ni-Cd cell is 1.2 V. The nickel-cadmium battery is charged with a current of 0.1 to 1.0 of the nominal capacity. This means that a battery with a capacity of 5 ampere hours can be charged with a current of 0.5 to 5 A.
The charge of sulfuric acid batteries is well known to all people holding a screwdriver, because almost every one of them is also a car enthusiast. The nominal voltage of the Pb-PbO2 cell is 2.0 V, and the charging current of the lead sulfuric acid battery is always 0.1 C (current fraction of the rated capacity, see above).
Video: Not Charged Metabo Screwdriver Battery
The lithium-ion cell has a nominal voltage of 3.3 V. The charge current of a lithium-ion battery is 0.1 C. At room temperature, this current can be gradually increased to 1.0 C. this is a fast charge. However, this is only suitable for batteries that have not been recharged. When charging lithium-ion batteries, the voltage must be strictly observed. Charge up to 4.2 V for sure. Exceeding sharply reduces the service life, lowering. reduces capacity. When charging, you should monitor the temperature. A warm battery should either be limited to a current of 0.1 C or disconnected before cooling.
ATTENTION! If the lithium-ion battery overheats when charging over 60 degrees Celsius, it may explode and catch fire! Do not rely too much on the built-in safety electronics (charge controller).
When a lithium battery is charged, the control voltage (voltage at the end of charge) forms an approximate series (the exact voltages depend on the specific technology and are indicated in the passport for the battery and its housing):
The charge voltage should be monitored with a multimeter or circuit with a voltage comparator tuned exactly to the battery used. But for “entry-level electronics engineers” it is really possible to offer only a simple and reliable circuit described in the next section.
The charger, which is proposed below, provides the desired charging current for any of the listed batteries. Screwdrivers are powered by batteries with different voltages of 12 volts or 18 volts. It doesn’t matter, the main parameter of the battery charger is the charge current. The voltage of the charger when the load is off is always higher than the rated voltage, it drops to normal when the battery is connected when charging. During charging, it corresponds to the current state of the battery and is usually slightly higher than the nominal at the end of charging.
The charger is a current generator using a powerful composite transistor VT2, which is powered by a rectifier bridge connected to a step-down transformer with sufficient output voltage (see the table in the previous section).
This transformer must also have sufficient power to provide the necessary current during continuous operation without overheating of the windings. Otherwise, it may burn out. The charge current is set by adjusting the resistor R1 with the battery connected. It remains constant during the charging process (the more constant, the higher the voltage from the transformer. Note: the voltage from the transformer should not exceed 27 V).
Resistor R3 (at least 2 W 1 Ohm) limits the maximum current, and the VD6 LED lights up while charging. By the end of the charge, the LED glow decreases and it goes out. Nevertheless, do not forget about the precise control of the voltage of lithium-ion batteries and their temperature!
All parts in the described circuit are mounted on a printed circuit board made of foil textolite. Instead of the diodes indicated in the circuit, you can take Russian diodes KD202 or D242, they are quite available in the old electronic scrap. It is necessary to arrange the details so that the board has as few intersections as possible, ideally not a single one. You should not get carried away by the high density of installation, because you are not collecting a smartphone. It will be much easier for you to solder parts if 3-5 mm remain between them.
The transistor should be installed on a heat sink of sufficient area (20-50 cm2). All parts of the charger are best mounted in a convenient home-made housing. This will be the most practical solution; nothing will interfere with your work. But there can be great difficulties with the terminals and connecting to the battery. Therefore, it is better to do this: take an old or faulty charger from friends that is suitable for your model of battery, and subject it to alteration.
- Open the case of the old charger.
- Remove all former filling from it.
- Choose the following radio elements: