Screwdriver - this is a necessary and useful tool in the economy. When a person gets used to such an instrument, it is difficult to do without it. What to do if a screwdriver fails? How do you not want to go to the workshop if you only need to repair the batteries of the screwdriver!
Scheme of the device cordless screwdriver.
With all the reliability of modern designs, batteries are often the cause of instrument malfunction. In order to repair the batteries of the screwdriver did not bring many difficulties, it is necessary to get acquainted with the design, principles of testing and repair.
The battery of the screwdriver is a source of direct current, which is produced in the process of electrolysis. Each element has two electrodes (cathode and anode). The voltage generated by it is determined by the potential difference between the electrodes (poles). The main characteristic (along with the voltage) of the cells and the battery as a whole is capacity. When connecting elements in series, the voltage of each is added. As a result, the voltage at the battery output is defined as the sum of the voltages of all the components. A voltage of 12 V is reached by a battery of 10 cells, each of which has 1.2 V.
Diagram of lithium battery screwdriver.
Many screwdriver batteries have nickel-cadmium cells. The anode is made of a nickel compound, and the cathode is based on cadmium or its compound. The electrolyte used is a solution of potassium and lithium hydroxides. Nickel-cadmium elements have a high capacity with small sizes and an increased lifetime (over 3000 cycles). The voltage can reach 1.37 V.
Nickel-metal hydride elements that consist of the same anode and cathode of nickel alloy are used. They are environmentally friendly, but have a tendency to self-discharge in a non-operating state. Most imported screwdrivers are equipped with batteries with lithium-ion and lithium-polymer components. They possess high values of capacity in small-sized execution. In both types, the cathode is made of coal, and the anode is made of lithium and cobalt compounds. Saline composition saturated with lithium ions and liquefied polymer composition are used as electrolytes, respectively.Back to table of contents
Conducting a battery screwdriver check is aimed at clarifying performance in order to determine the need for repair or to identify the cause of the malfunction. The most accurate performance of the elements and the battery as a whole can be determined by the capacity, which can be measured with a special pendant tester. However, this professional device is not available to everyone.
Diagram of the device for testing batteries.
It remains to assess the state and capacitance by indirect indicators, namely, the current and voltage at the output terminals, which can be measured by a direct path (with an ammeter and a voltmeter).
Is a screwdriver really necessary to repair the battery? This can only be installed after fully charging it. Already at the stage of charging the battery, you can conduct a preliminary assessment of its state. To do this, with the charger on, the rate of recovery of the current and voltage at the output of the battery is determined.
This check is carried out in the following order. After 30 minutes of charging the cells, the voltage at the output terminals of the battery is measured. It is normal to reach a value of 13 V. Measurements continue every 30 minutes. If the second measurement shows 13.5 V, and after another 2 hours the voltage reaches 14 V and no longer rises, then charging has reached a maximum. The nominal voltage value is 17 V. In this case, you need to think about how to repair the screwdriver battery. At the same time, it is too early to make a final conclusion, since a “memory effect” is possible. This phenomenon is characteristic of nickel-cadmium cells and is explained by residual processes with incomplete discharges and battery charging before.
Similarly, you can assess the state of the battery on the current value. Good elements show a constant increase in current during the first 60 minutes of charging to a value of at least 1 A. Such a process is characteristic of intact elements.Back to table of contents
Measurements under load
Screwdriver battery connection diagram.
If there are no obvious manifestations of failure of the battery when charging, then it is too early to talk about its normal operation. It is possible to determine more precisely whether repair of the battery of a screwdriver is necessary when carrying out measurements under load. Such tests of the instrument can be performed independently by connecting the artificial load to the battery. Such a load should be about 35-40 watts. As a load, you can use a car lamp for a headlamp of 35 W or a spot lamp of 35-40 W for a voltage of 12 V.
For testing, an elementary electric circuit is assembled in which the elements are discharged to the load. In this case, the current and voltage are measured by appropriate devices. Discharge time - 3-5 minutes. Using the lamp as a load allows you to visually assess the battery status: if the brightness of the lamp has not changed, then the battery capacity is normal. This conclusion is, of course, preliminary. Another thing, if the light dimmed, then this is a clear manifestation of a malfunction of the elements. This means battery repair is required. The result is better clarified by measuring the voltage at the output terminals. After discharge for 5 minutes, the voltage should be in the range of 12-12.4 V (at nominal 12.4 V). If the voltage fell below 12 V, then we can talk about the need for repair.Back to table of contents
Check individual items
If preliminary measurements indicate the need to repair the screwdriver battery, open the tool body and remove the battery. As a rule, 10-12 cells (cans) with a nominal voltage of 12-14 V are included in the rechargeable battery. Do-it-yourself repair of the screwdriver battery is to find and replace the faulty part.
Table of types of battery.
After removing the battery, inspection is carried out, first of all, the places of the rations. Vibration of the instrument during operation could lead to contact disturbance. Therefore, the first repair of batteries for screwdrivers is done by the method of soldering damaged contacts.
If everything is fine with the contacts, then each bank is disconnected in turn, the voltage across the electrodes is measured. The voltage value should not be lower than 1.2 V. During measurements, all additional elements should be disconnected, in particular, charging control sensors. Measurements are carried out with a DC voltmeter with a scale of up to 1.5-2 V. If the voltage value does not correspond to the nominal value, the screwdriver's battery is repaired by replacing an unusable can with a new element of the same rating.
The new bank should correspond to the former at the nominal capacity (the value is indicated on the case).
A situation may arise when all banks show normal voltage, and a preliminary assessment indicated a malfunction of the screwdriver battery. In this case, it is necessary to take measurements of the parameters of each can under load. Tests are made similar to the tests of the battery, but the load will serve as a light bulb from a flashlight.Back to table of contents
Quality assessment by resistance
The accuracy of the evaluation of the performance of elements increases with the evaluation of internal resistance. This value is obtained from the calculation (quotient of dividing the voltage by the current minus the resistance of the load). Voltage and current are measured under load. A 10-ohm resistor of 25 watts is recommended as a load. Evaluation of the calculated resistance is carried out taking into account that the resistance of the new bank reaches 0.1 Ohm. A significant (more than 20%) excess of resistance indicates that the bank must be replaced.
Repair of the screwdriver battery by replacing the elements should be carried out if a significant self-discharge of the battery without working load is noticed. This assessment is carried out by measuring the voltage at the output terminals every 24 hours for 30 days. For nickel-cadmium elements, self-discharge during this time should not exceed 20%, and for lithium-ion elements - no more than 8%.Back to table of contents
To repair the battery screwdriver do it yourself to have the tools:
- voltmeter at 2 and 15 volts;
- ammeter to 2 A;
Repairing a battery of screwdrivers do-it-yourself is usually about finding and replacing a battery cell. To do this, you need to know the order and sequence of testing and analyzing parameters.