How to check cans on a screwdriver battery
General information about the battery
Battery type table.
In the general case, an electric storage device is source of constant electric current by converting a chemical reaction into electrical energy. During operation, it transfers the accumulated electricity into the electrical circuit. When charging the battery of a screwdriver, the current is passed in the opposite direction and the process of energy storage takes place.
The main parameter of any battery is the capacity of stored energy, which indicates how much current the battery can deliver in one hour. Therefore, the capacity of the battery is usually measured in ampere-hours.
The principle of operation of any battery is based on electrolysis. Consequently, the battery consists of two electrodes. the anode and the cathode, which are in the electrolyte. A chemical reaction creates an electrical 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. Serial connection of individual batteries leads to the addition of their electrical voltages.
The main parameters of the storage devices depend on the materials of the electrodes and the composition of the electrolyte. In nickel-cadmium batteries, the anode is made from a mixture of nickel hydroxide and graphite, and the cathode is cadmium hydroxide or metallic cadmium. Potassium hydroxide with the addition of lithium hydroxide was used as an electrolyte. The nickel metal hydride battery uses a similar anode, but the cathode is made of a rare earth nickel alloy. In lithium-ion batteries, the cathode is made of carbon and the anode is made of lithium dioxide and cobalt. The electrolyte is a saline 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.
How to quickly check the battery of a screwdriver?
Recently, the screwdriver has become a fairly popular tool. For convenience, many tend to purchase a screwdriver powered by a charging battery. Over time, of course, the question arises: how can you check the battery of a screwdriver?
Diagram of a nickel-cadmium battery for a screwdriver.
Battery Cell Test
After a 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 has an operating voltage of 1.2 V. Usually, a battery of 10 such cans is installed in screwdrivers.
Checking the elements begins with a visual inspection of the attachment points. Failure in fastening (soldering, welding) can lead to underestimated parameters. Then the voltage on each bank is measured. The voltage should not be less than 1.2 V. It should be borne in mind that thermal sensors are placed in modern screwdriver designs to monitor battery charging. When measuring, they should be disconnected, and the device should be connected to the main terminals (poles of the jar). Identified banks with an underestimated value of the operating voltage are disconnected from the battery and must be replaced. If a simple voltage measurement did not reveal the presence of non-working elements, then measurements should be made under load using a method similar to the preliminary check of the drive.
Drive test principles
Battery tester circuit.
Checking the screwdriver battery means determining its real basic parameters. A battery test is usually done to determine the quality of the battery or the cause of the inoperability. 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 required volume. The test is carried out only when the battery is fully charged.
When testing batteries for a screwdriver, remember about the influence of the “memory effect”. This phenomenon is based on the fact that frequent charging of an incompletely discharged battery can change the cell’s capacity due to residual charges from the previous charge. Nickel-cadmium specimens are especially susceptible to the “memory effect”. This property causes a complete “training cycle” to be carried out before testing. 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 battery tester of the “pendant” type, 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. The current and voltage at the battery output are directly measured.
The main types of batteries
The most common type of drive used in screwdrivers is the nickel-cadmium battery. The main advantages of such elements are recognized as high capacity with small dimensions and weight, as well as a fairly long service life (up to 3500 cycles). The electromotive force of the cell reaches 1.37 V, and the specific electrical energy. up to 65 Wh / kg. Limits the use of such elements (especially in imported tools) harmful production.
Nickel-metal hydride batteries for the screwdriver are becoming the main competitor to nickel-cadmium copies. The main advantage of such elements is safety and environmental friendliness. It is recommended to store the cells in a charged state, since if they are not used for a month, they may be discharged to such a state that they cannot be charged.
In the latest models of screwdrivers, modern promising 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 high.
Checking under load
Battery test circuit with an ammeter.
The preliminary check does not allow us to estimate the capacity of the battery, i.e. the time during which it will be discharged. To estimate the parameter, it is necessary to test the battery under load. If the power is indicated on the drive, then the load power is selected according to this value. If the power of the battery is unknown, the load can be approximately selected on the basis that its power is half the product of the current given by the battery during operation and the voltage of the battery. Usually it is sufficient to use a 35-40 W load. As such a load, you can use a 35 W car headlight lamp or a 12 V spot lamp of the same power.
A circuit is being assembled, where the battery, as source of electricity, is discharged to the load through an ammeter. The voltage is measured with a voltmeter. The battery turns on for 2-3 minutes. If during this time the brightness of the loading lamp has not decreased, then the battery capacity can be preliminary estimated as normal. This conclusion should be supported by measuring the voltage (it must be more than 12.4 V). At voltages between 12 and 12.4 V, look for a possible damaged element. Voltage below 23 V indicates insufficient battery capacity.
If the brightness decreases noticeably, then this indicates the presence of non-working elements. And it’s really bad if the lamp goes out. This means the battery is discharging very quickly and its capacity is very low.
The first stage of verification
Checking the battery only makes sense when it is fully charged. The first stage of verification is carried out at the stage of battery charging. At this stage, the voltage and current are measured, as well as the rate of their recovery. In other words, these parameters are measured periodically after a certain period of time.
Battery voltage test circuit.
Voltage control is performed as follows. After 0.5 hours of charging, the battery voltage is measured. For example, it reached 13 V, which is normal. The increase in voltage gradually decreases and after another 0.5 hours of charging reaches 13.5 V. The last measurement after 2 hours of charging shows a voltage of 14 V, and for the last 0.5 hours its growth is not noted. Charging has reached the maximum possible. The drives in fully working condition have a voltage value of 17 V. The conclusion of such a check is that there are non-working cells in the battery. In the given example, there are most likely two such elements.
The quality of the battery can also be assessed by measuring the current during the charging process. A normal battery is characterized by a stable increase in the accumulated current in the first hour of charging. If the current reaches a strength above 1 A, then we can talk about the performance of the battery.
If the battery is already installed in the screwdriver in a charged state (for example, a new one), then the first voltage measurement on it is made without disassembling the tool. Using a simple tester or voltmeter, the voltage between the poles is measured. It should be remembered that the measured no-load voltage corresponds to an open-circuit voltage that is slightly higher than the rated 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 to 17 V. If the measurement shows a voltage value lower than the required one, then 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 already at the first stage of testing, by using a simple tester. Based on the results of such a check, it is established that it is necessary to disassemble the screwdriver and the battery.
Checking by resistance value
The normal functioning of each battery can be checked by comparing the “banks” by internal resistance. The value is determined by dividing the operating parameters voltage by current and deducting the load resistance.
The operating voltage is measured without fail under load. As a load, you should take a resistor with a resistance of 10 ohms and a power of 25 watts. Each battery is tested. Measure the working amperage and voltage.
For a better understanding, here are some approximate calculations. Let’s say, during the measurement under load, data were obtained for one “can”: operating voltage. 1.19 V and operating current. 112 mA. Before making the calculation, do not forget to convert the current value from mA to A. 0.112 A. We perform the appropriate actions (1.19 / 0.112). 10 = 0.63 Ohm. Recall that the subtracted in our expression is the load resistance of the resistor (10 Ohm).
Checking the Drive Batteries
So, let it turn out that with the help of preliminary checks, the presence of faulty elements in the drive was established. Then it is necessary to disassemble the battery and remove the batteries connected in series. “banks”. As mentioned above, the battery consists of 10-12 such cells with a voltage of 1.2 V.
First, a visual inspection of the joints of the elements is carried out for violations. They can degrade the overall battery performance.
After inspection, you should measure the voltage of each of the “cans“. The voltage of one cell should not be less than 1.2 V. During measurements, the battery cells should be disconnected from the connections with any kind of sensors. The measuring device is connected to the battery poles. Reduced voltage “banks” must be replaced. If during a simple measurement no faulty elements were found, you should try on the “banks” under load.
Screwdriver battery repair work
So, during the checks, non-working batteries were identified. What to do in this case? There are two ways out. an attempt to “reanimate” the elements or a simple replacement of non-working “cans”.
The electrical storage can be checked using:
- DC voltmeter 15 V;
- ammeter and DC voltmeter;
From the tools you should acquire:
The first stage of verification
Voltage and current measurements are carried out during the charging of the electric storage device. The readings are taken periodically after a certain period of time. With increasing time, the increase in voltage decreases.
So, half an hour after the start of charging, the voltage value will be 13 V. If you measure it after another half an hour, then the voltage will be 13.5 V. 2 hours after the start of charging, the voltage will already be about 14 V. This indicates that the maximum has been reached. A fully charged battery has a voltage of 17 V.
You can assess the quality of the drive by measuring the current during the charging process. If the battery is in good condition, then it is characterized by a steady rise in current of 1 hour during the charging process. The passage of the current value of the 1 A mark indicates the normal functioning of the drive.
The battery installed in the screwdriver can be checked with a tester or voltmeter by measuring the voltage between the poles. No load voltage will correspond to no-load voltage. So, if for 12 “cans” with a nominal value of 1.2 V, the operating voltage is 14.4 V, then the open circuit voltage will increase to 17 V. A decrease in this value means that some cells in the battery are inoperative or the drive is not fully charged.
Based on the results of the first check, you can get an initial impression of the health of the battery cells. This will help determine if the battery needs to be disassembled.
Checking under load
To answer the question for how long the battery will be discharged, you should check the drive under load. The load must be selected based on the capacity of the drive. If it is unknown, then it is considered that the load power is equal to half the product of the current that is given to the battery during operation by the voltage of the drive. As a rule, this value is taken equal to 35-40 watts. Thus, you can use a car headlight (35 W) as a load or use a 12 V spot lamp with the same power.
For battery measurements, the battery is connected to the load through an ammeter. Readings are taken with a voltmeter. “Banks” are connected for 2-3 minutes. The measured voltage must be greater than 12.4 V. If the readings fall within the range of 12 to 12.4 V, this means that the battery has a damaged cell. The presence of faulty batteries can also be indicated by a decrease in the brightness of the lamp used as a load. If the lamp goes out in the allotted time period, it means that the drive is discharging very quickly. it has a very small capacity.
Signs of a closed battery bank
Since there is a redistribution of charge inside, the battery case heats up, which is one of the signs of an internal short circuit. If the battery is serviced, you can identify the closed bank during charging. At the moment the voltage rises, the plugs on the cans are open, hydrogen is released from them, the cans are boiling. If one does not show signs of life, it is closed. You can check and find the reason for the undercharging of the battery in a ventilated room or on the street.
If a voltage drop occurs in a maintenance-free battery, the device does not charge up to the operating voltage, as determined by a closed bank, or another reason. Experts advise to close contacts for 1-3 seconds. An abundant discharge will begin from a non-working jar.
Even a maintenance-free battery allows you to see the electrolyte level in the cans through the translucent walls. Signs of a closed can there will be a low electrolyte level. it boils away, sometimes a color change to black is noticeable.
Replacing the “cans” in the screwdriver battery
The task itself is simple. It is good if you have experience in soldering. In the connection of the elements, the faulty battery is cut off, a good one is put in its place, then soldering is performed. As you can see, nothing complicated.
However, in this case, several important nuances should be taken into account:
- you need to solder quickly so that the “banks” do not heat up. this may affect their performance;
- to connect the elements, it is better to use native plates, or copper, but of the same dimensions;
- when attaching a new element to an old one, do not confuse plus and minus. When connected in series, the minus from the previous battery goes to the plus of the new battery.
After soldering, you should carry out a charge-discharge cycle, and then measure the voltage on the “banks”. It should be around 1.3V.
We check the screwdriver battery with a multimeter
Many home craftsmen have to deal with the need to check a drill or screwdriver for battery health. Over time, the battery sits down, and in order to assess the possibility of its further performance, you need to know how to check the battery of a screwdriver with a multimeter or tester. Multimeter. a device with voltmeter and ammeter functions.
Checking performance under load
This means that we will check how long the screwdriver battery will be fully discharged, provided that an additional load is connected to it. for example, an electric light bulb.
The load level must be selected based on the capacity of the battery. If it is not indicated in the operating instructions, it should be calculated independently. It will be equal to half the current delivered by the battery during operation, multiplied by the U of the current source. Usually this figure is from 35 to 40 watts, which means that the load can be a headlight from a car from 35 watts, or a 12-volt light bulb.
To take readings, the battery must be connected to the lamp through an ammeter, and the readings themselves must be taken with a voltmeter. Connection time is two to three minutes, after which we measure U. If it is less than 12.4 volts, some “bank” is definitely out of order. Also, a significant decrease in the brightness of the light bulb may indicate a battery malfunction. If it goes out quickly in two or three minutes, the battery is clearly out of order, and its capacity is very small.
What does the battery consist of?
The internal structure of the battery of any screwdriver, regardless of the country of origin, is absolutely identical. If you disassemble the plastic block, there are always “jars” inside, assembled in a certain sequence. The battery voltage indicator as a whole is added up based on the U level that each battery separately has. The battery also has four contacts, two of which provide charge-discharge cycles, the third is connected to a thermal sensor, and the fourth, which has a service purpose, is responsible for equalizing the charge potential in all batteries.
So, the interconnected “banks” of the battery of an electric tool are nothing more than source of current with a constant value, in which chemical reactions are constantly being converted into electricity. This is how the battery transfers the stored energy to the circuit. And when it is charging, the process occurs in the opposite direction: the battery simply takes energy from the network.
Express test method: measure U at the battery poles
This method is even simpler, but with its help you can get an initial idea of whether the battery is in order. If we measure U without connecting the load, we get an indicator equal to the “idle” of the tool.
For example, if we have 12 cells in the battery with a voltage of 1.2 volts each, and the working indicator U is 14.4 volts, the “idle” U will grow to 17 volts. If the “open” voltage is less than the specified one, it means that there are “banks” in the bundle that are out of order and need to be replaced. Also, a decrease in open-circuit voltage may mean that the battery is not fully charged.
General recommendations before testing the battery
Before you check the battery of a screwdriver with a multimeter for possible malfunctions, you should remind yourself that the nickel-cadmium batteries installed in most power tools have a so-called “memory effect”. Briefly, its essence lies in the fact that due to frequent and irregular recharging, the capacity of the “cans” of the battery decreases, and the battery does not use its resource in its entirety.
The battery should be fully charged before testing the battery to ensure the tester’s readings are as accurate as possible. Keep in mind that testing is optimally accurate if it is done under load. This is what the battery will need a sufficient amount of charge for.
The toolkit you’ll need is simple:
- tester (or multimeter);
- soldering iron;
First stage of testing
Checking the battery of a screwdriver at the first stage is the simplest, current and voltage indicators are taken from the battery while it is charging.
Readings are taken several times, at regular intervals:
- 30 minutes after charging has started, U will be about 13 volts;
- after another 30 minutes, U will increase to 13.5 volts;
- two hours after the start of the process. 14 volts;
- a fully charged battery will give a voltage of 17 volts.
As for the increase in current (amperage) during charging, if the operating state of the battery is in order, then the current strength increases steadily during the first hour. In addition to voltage, measure the current strength one hour after the start of the process. If the indicator passes the “mark” of 1 ampere, your battery is in good health and does not need to be disassembled and repaired.
Checking the elements in the disassembled battery
So, if preliminary testing has shown that there may be faulty elements in the screwdriver, the battery should be carefully disassembled and batteries that are unusable for work should be calculated. As already mentioned, the normal voltage of each battery individually should be 1.2 volts. If this figure is less, the “can” is carefully removed from the chain using pliers. It also does not hurt to carefully examine the entire bundle for external damage: rust, leakage of electrolyte.
Screwdriver battery maintenance
In the event that the voltage on all “banks individually is within the normal range, you must again use the test under load with a check on the level of internal resistance. This value is determined as follows: the voltage is divided by the current strength, and then the load resistance is subtracted from it.
To find out the voltage, we immediately connect the load. This time, you should use a resistor with a power of 25 watts and a resistance of 10 ohms. We check each battery, measuring the indicator of the working current and U.
The calculations should be something like this: for example, when measuring under load, we received the operating voltage of one element of 1.19 volts, and the current strength of 112 milliamperes. Before calculating, be sure to convert milliamps to amperes. It turns out 0.112 amperes, therefore: 1.19 is divided by 0.112 and we subtract the resistance of 10 ohms. It turns out the value of 0.63 Ohm. this means that the indicator is normal.
Self-checking the performance of a screwdriver battery using a multimeter is a useful skill to find out if the battery needs repair or a complete replacement of cans. Measurements of voltage indicators in general, without disassembling the battery pack, should be carried out from time to time. This will help to avoid a sudden failure of the tool and eliminate the malfunction in time. Also, to avoid the accumulation of “memory effect”, do not neglect to fully charge your battery. This will help to avoid premature drop in its capacity.