Start Machine From Cordless Screwdriver
The screwdriver is not the last in the line of cordless power tools. Unlike cord devices, it is indispensable when working at heights or in places not equipped with a power supply network. It does not differ from cord screwdrivers in terms of torque, cartridge diameter and functionality. Its only drawback is its limited time. To know how to charge the screwdriver battery correctly, you need to study the device and the principle of operation of the power source.
Screwdriver battery device
The battery of the instrument is a set of series-connected nickel-cadmium elements. They are located in a special removable plastic box, located at the fifth of the case, and serve as its support. The removable energy source has 2 built-in plate contacts intended for connection to an electric motor and terminals of a charger (charger).
A Ni-Cd battery is a chemical current source in which the anode is made of nickel oxide hydrate and the cathode is made of cadmium. Potassium hydroxide with a density of 1.19-1.21 g / cm³ is used as an electrolyte. The voltage of a charged cell is about 1.37 V, and that of a discharged one is 1 V. The service life is from 100 to 900 charge-discharge cycles, and self-discharge is 10% per month.
Due to the low internal resistance, the battery does not heat up even when charged with high current. When the battery is recharged, its temperature rises, which is a sign of the end of the charge. The battery can be operated in the range of 50. 40 ° С without loss of capacity.
NiCd systems are subject to a “memory effect." It manifests itself when the battery is charged before it is completely discharged. The capacity lost as a result of this is restored after a deep discharge with a subsequent charge.
The total battery voltage is 18 V and consists of the sum of the voltages of the individual batteries. The block of elements is assembled using tires that are soldered to the electrodes. This improves contact and reduces the transient resistance at the attachment points. To protect against overheating, the unit is equipped with thermal protection (thermistor).
Some power tool models are equipped with lithium cells. However, they increase the price of the product. In addition, lithium sources are sensitive to charge quality and should be equipped with special charging units.
General charging rules
Fully discharged batteries must be charged. To replenish the capacity, standard chargers are used, which are included in the set of a screwdriver. Due to the fact that the charge increases the temperature of the elements, it is not recommended to leave the kit in the sun or in closed rooms with a temperature of more than 30 ° C. Complete charging units do not have parameter adjustment. The process of recharging the battery capacity is monitored by LED indication.
Charging time depends on the type of power source used and can last from 0.5 to 5-6 hours. It is not recommended to leave a charged product in the charger. After cooling, the battery is ready for use.
The nuances of charging various types of batteries
For the normal operation of power supplies of any type, they are recommended:
- do not overheat;
- do not recharge;
- do not redistribute.
To recharge the battery capacity, use pulsed or standard unregulated charging units. The initial charge is carried out by a pre-discharged battery. New NiCd cells are recommended to do a 3x discharge-charge mode. In the future, only a full charge will be needed. An indicator of the end of the replenishment of the capacity will be a noticeable heating of the battery case.
Nickel-metal hydride batteries, unlike cadmium batteries, should be stored with a small (30-40%) capacity level. These batteries are more sensitive to heat, so they should not be overloaded during operation. To do this, there is a torque ring on the screwdriver. Due to the fact that the Ni-MH battery is subject to the “memory effect", to restore the capacity you need to periodically conduct 4-6-fold modes of "training".
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After charging the battery, allow time to cool. Otherwise, this will affect the magnitude of the current output. If during the discharge a voltage of 0.9 V or less was reached, some memory devices will not “see” the inserted element. On any memory with low currents, it will be necessary to achieve the required value, and then continue charging with a standard device.
Lithium-ion batteries can be charged without waiting for their full discharge. The delivered capacity is highly dependent on the ambient temperature. Optimum parameters are achieved in room conditions. Li-ion batteries are sensitive to the magnitude of the charging current, especially at the end of the process. The permitted tolerance is 0.05 V. The middle element charges about 3 hours. Time may vary depending on capacity.
Protected lithium batteries do not suffer from over or undercharging. The built-in protection board cuts off excessive voltage (more than 3.7 V per can) when charging and turns off the battery if the charge level drops to the minimum, about 2.4 V. The presence of the device significantly prolongs the life time of the cell.
Custom methods for charging a screwdriver battery
In the absence of a complete memory device or its failure, you can replenish the battery capacity without it. To do this, fit:
- automobile memory;
- external sources of electricity;
- homemade devices.
The best way out of this situation is to purchase a charge compatible with the existing model or to repair a regular one. Using a screwdriver without a charger will lead to a quick battery failure.
Using a charging module for a car battery
To recharge the battery of a screwdriver, you can use the charger for the car. Due to the fact that the battery voltage of the instrument is 18 V, and the charger used is not more than 16.5 V, this process is not a danger to the power source. It is advisable to use a device with a current regulator. In the process of charging, it is necessary to periodically monitor the temperature and voltage of the battery. All conditions for the onset of charge must be observed for any power supply.
To control the charging current, you can use a multimeter or tester, connected in series to the low voltage circuit. Its value should not exceed 0.1-0.3 parts of the battery capacity. Signs of the end of the charge is the heating of the block body.
Making a homemade charging block
Homemade memories are used not only in the absence of a standard device. The latter has a small capacity, which increases the time of replenishment of the tank. The charger is a current generator using a powerful composite transistor KT829, which is powered by a rectifier bridge connected to a step-down transformer with a sufficient output voltage.
The charge current is regulated by a variable resistor of 10 kOhm. Ballast resistance (2 W, 1 Ω) limits the maximum current. The charger is assembled in a separate housing with terminal ends for connecting the battery.
If there is a non-working memory suitable in design for this type of battery, then the device is best placed in it.
Then there will be no problem with connecting the battery. To protect the circuit, a 0.5 A fuse is installed in the transformer circuit. Measurements of the parameters during the charging process are controlled by a multimeter.
USB Battery Equipment
The battery can be charged through the USB connector if you change the cadmium batteries to Li-ion. The new battery has the same capacity, but about 2 times smaller in size. For management, the AB protection and control board is used. The load current should not exceed 1 A. Otherwise, the board will heat up.
Charging through external sources of electricity
Charging in this way can be done from a working car battery, either directly connected to the battery with constant monitoring of the charging current, or from a USB charge through the cigarette lighter socket. The control board will allow to replenish the capacity to the nominal. However, lithium power supplies can be charged in this way. If the battery fails, you can work with a screwdriver by connecting it directly to any 12 V battery.
Checking the battery status with a multimeter
The device checks the voltage and current strength of the power supply under load. The first parameter must be measured while the device is running, because a disconnected battery will show the emf of the source. To measure the voltage under load, it is necessary to output 2 wires from the battery terminals, connect a multimeter to them and turn on the screwdriver.
If 10 cadmium elements are installed in the box, then the value should not be lower than 10 V. Otherwise, either the source is discharged or there are damaged elements. To find them, you need to measure the voltage of each can.
To control the current, the device is connected in series with the load. The mode switch is set to 10 A. In the same way, you can measure the current of the charger. Its value should not differ from the passport.
For long-term storage, sources must be disconnected from the instrument and placed in a dry room at room temperature. Ni-MH batteries charge to full capacity, while NiCd and Li-ion charge up to 30-50%. With proper care and storage, lithium cells will last 3-5 years from the date of manufacture, and nickel cells 2-3 years.
How to start a car from a screwdriver battery
Some motorists started the car with a screwdriver battery. To do this, they connected a fully charged source to a discharged battery for 15-20 minutes. Sometimes this gave a positive result. This cannot be done with an automotive source that has exhausted an installed resource. In winter, such attempts do not lead to anything. It is incorrect to say that starting the engine from the battery of a screwdriver is incorrect, since this is about charging a dead car battery.