In recent years, the screwdriver has become quite popular tool. For convenience, many tend to buy a screwdriver, powered by a charging battery. Over time, of course, the question arises: how can I check the battery of the screwdriver?
Diagram of a nickel-cadmium battery screwdriver.
The main types of batteries
The most common type of drive used in screwdrivers is a nickel-cadmium battery. The main advantages of such elements are high capacity with small dimensions and weight, as well as a sufficiently long service life (up to 3500 cycles). The electromotive force of the element reaches 1.37 V, and the specific electric energy - up to 65 Wh / kg. Restricts the use of such elements (especially in imported tools) harmful production.
Nickel-metal hydride batteries for the screwdriver become the main competitor of nickel-cadmium copies. The main advantage of such elements is safety and environmental cleanliness. It is recommended to store the elements in a charged state, since if they are not used within a month, they can be discharged to a state where their charging becomes impossible.
In the latest models of screwdrivers modern advanced types of batteries are used: lithium-ion and lithium-polymer. They have a very high capacity with small dimensions, but their cost is still quite large.Back to table of contents
General information about the battery
Table of types of battery.
In the general case, an electrical accumulator is a source of constant electric current, due to the conversion of a chemical reaction into electrical energy. When working, he gives the accumulated electricity to the electrical circuit. When charging the battery of the screwdriver, the current is passed in the opposite direction and the process of energy accumulation proceeds.
The main parameter of any battery is the energy storage capacity, which indicates how much current the battery is capable of delivering in one hour. Therefore, battery capacity is usually measured in ampere hours.
The principle of operation of any battery is based on electrolysis. Consequently, the battery consists of two electrodes - an anode and a cathode, located in the electrolyte. The chemical reaction causes the creation of an electric charge on the electrodes (poles). The potential difference between the electrodes determines the battery voltage, which is considered one of the most important characteristics of the battery. Consistent connection of individual batteries leads to the addition of their electrical voltages.
The main parameters of storage devices depend on the materials of the electrodes and the composition of the electrolyte. In nickel-cadmium batteries, the anode is made of a mixture of nickel hydroxide and graphite, and the cathode is cadmium oxide hydrate or metallic cadmium. As the electrolyte used potassium hydroxide with the addition of lithium hydroxide. A similar anode is used in a nickel-metal hydride battery, but the cathode is made of an alloy of nickel with rare earth metals. In lithium-ion batteries, the cathode is made of coal, and the anode consists of lithium dioxide and cobalt. The electrolyte is a salt solution with lithium ions. The difference between the lithium-polymer version is only a change in the composition of the electrolyte - it is a gel-like polymer substance.Back to table of contents
Principles check drive
Diagram of the device for testing batteries.
To check the screwdriver's battery means to determine its real main parameters. A battery check is usually carried out to determine its quality or the cause of a failure. In the first case, it is aimed at clarifying the quality of the new battery, and in the second, it includes measurements of parameters on the battery that do not power the screwdriver in the right amount. The check is performed only when the battery is fully charged.
When testing the batteries for the screwdriver, be aware of the effect of the “memory effect”. This phenomenon is based on the fact that frequent charging of a fully discharged battery can change the capacity of the cell due to the residual charges from the previous charge. Nickel-cadmium specimens are particularly susceptible to the memory effect. This property causes a complete "training cycle" before the test. It consists in completely discharging the battery and then fully charging it.
The most important parameter of a screwdriver battery is its capacity. To determine it, there is a special device - a “pendant” type battery tester, but it is mainly used by professionals, and for most users it is not available. Therefore, this parameter is usually analyzed by evaluating other parameters. Direct measurement of the current and voltage at the output of the battery.Back to table of contents
The first stage of verification
Checking the battery only makes sense when it is fully charged. The first stage of testing is carried out at the stage of charging the battery. At this stage, measured voltage and current, as well as the speed of their recovery. In other words, these parameters are measured periodically after a certain period of time.
Circuit check battery voltage.
Monitoring voltage is as follows. After 0.5 hours of charging, the voltage on the battery is measured. For example, it reached 13 V, which is normal. The voltage increase gradually decreases and after another 0.5 hour of charging reaches 13.5 V. The last measurement after 2 hours of charging shows a voltage of 14 V, and the last 0.5 hours does not show an increase. Charging reached the maximum possible. The drives in fully working condition have a voltage value of 17 V. The conclusion of such a test is that there are non-working elements in the battery. In the given example, there are probably two such elements.
The quality of the battery can be assessed by measuring the current during charging. A normal battery is characterized by a steady increase in accumulated current in the first hour of charging. If the current reaches a force above 1 A, then we can talk about the performance of the battery.
If the battery is already installed in a screwdriver in a charged state (for example, a new one), then the first measurement of the voltage on it is made without disassembling the tool. Using a simple tester or a voltmeter, the voltage between the poles is measured. It should be remembered that the measured voltage without load corresponds to the no-load voltage, which is slightly higher than the nominal operating voltage. For example, with 12 cells at 1.2 V, each operating voltage will be 14.4 V, and the open circuit voltage is set at 17 V. If the measurement shows a voltage value lower than the required one, this means that there are non-working cells or the battery is not fully charged.
Thus, the first conclusions about the health of the battery can be made at the first stage of testing, by using a simple tester. According to the results of such a check, the need for disassembly of the screwdriver and battery is established.
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Circuit test battery ammeter.
Preliminary check does not allow to estimate the battery capacity, i.e. time during which it will be discharged. To estimate the parameter, it is necessary to conduct a battery test under load. If the power is indicated on the accumulator, then the load power is selected by this value. If the battery power is unknown, the load can be approximately chosen from the calculation that its power is half the product of the current strength given by the battery during operation to the battery voltage. Usually enough to use a load capacity of 35-40 watts. As such a load, you can use a lamp for a car headlight with a power of 35 W or a spot-lamp of 12 V of the same power.
A circuit is assembled where the battery, as a source of electricity, is discharged to the load through an ammeter. Voltage is measured by a voltmeter. The battery turns on for 2-3 minutes. If during this time the brightness of the load lamp has not decreased, then the battery capacity can be pre-estimated as normal. Such a conclusion should be supported by measuring the voltage (it should be more than 12.4 V). When the voltage is from 12 to 12.4 V, you should look for a possible damaged element. Voltage below 23 V indicates insufficient battery capacity.
If the brightness decreases markedly, this indicates the presence of non-working elements. And really bad if the lamp goes out. This means that the battery is discharged very quickly and its capacity is very small.Back to table of contents
Battery cell check
After the preliminary check has established the presence of faults in the drive, it is necessary to open the screwdriver and remove the battery, i.e. battery cells connected in series with each other. The battery includes from 10 to 12 cells (cans), each of them has a working voltage of 1.2 V. Usually, a screwdriver of a battery of 10 such cans is installed in screwdrivers.
Inspection of elements begins with a visual inspection of attachment points. Failure to mount (solder, weld) can cause underestimation of parameters. Then the voltage is measured at each bank. The voltage should not be less than 1.2 V. It should be noted that in modern designs of screwdrivers are placed thermal sensors to monitor the charging of the battery. When measuring, they should be disconnected, and the device should be connected to the main terminals (banks poles). Revealed banks with low operating voltage are disconnected from the battery and must be replaced. If a simple measurement of the voltage did not reveal the presence of non-working elements, then measurements should be made under load according to a method similar to a preliminary test of the drive.Back to table of contents
Check for resistance
Diagram of the device multimeter.
The performance of each battery bank can be assessed more likely by comparing the cans for their internal electrical resistance. This parameter clearly indicates the reliability of the battery. The resistance value is determined by calculation as the result of dividing the operating voltage by the operating current strength minus the load resistance.
The operating voltage is necessarily measured under load, and as a load, a resistor with a precisely defined value of its own electrical resistance should be used. Can be recommended to create a load resistor with a resistance of 10 Ohms and a power of 25 watts. The check is carried out on each bank separately. Measured working voltage and current.
For example, consider the average test. For a new battery bank, the internal resistance is 0.1 ohms. In general, the lower the internal resistance of the banks, the better it is. Under actual conditions, the operating voltage under load of 1.19 V and current of 112 mA in one canister and 1.18 V and 70 mA in the second canister were obtained. Resistance will be, respectively, 0.63 ohms and 5.71 ohms.
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Significant excess of resistance indicates the unsuitability of such a battery.
Check other parameters
All batteries have a certain amount of self-discharge, i.e. discharge without load in storage conditions. Thus, self-discharge of nickel-cadmium batteries can reach 20% during a month of storage, nickel-metal hydride - up to 30%, lithium-ion - up to 8%. It is recommended to check the self-discharge by measuring the voltage every day during the month.
Checking for the presence of a “memory effect” is advisable, since it helps to eliminate its harmful effects. It is carried out by carrying out several (3-4 times) cycles: full discharge-full charge of the battery. You can discharge the battery through the load, which is used as a 12-volt light bulb. Measured residual operating voltage and open circuit voltage. With repeated such training "memory effect" should disappear.Back to table of contents
When conducting a battery screwdriver check, you will need the following tools and instruments:
- DC voltmeter at 15 V;
- ammeter and milliammeter DC;
- soldering iron.
To determine the battery failure, it is necessary to conduct a full check of its elements. Such a test is under the power of any user with a screwdriver.