A device with which you can check the capacity of lithium-ion AA batteries. Quite often, laptop batteries become unusable due to the fact that one or more batteries lose their capacity. As a result, you have to buy a new battery when you can get by with a little bloodshed and replace these worthless batteries.
What you need for the device:
Arduino Uno or any other compatible one.
16x2 LCD display using Hitachi HD44780 driver
Solid State Relay OPTO 22
Resistor 10 MΩ at 0.25 W
18650 battery holder
Resistor 4 ohm 6W
One button and power supply from 6 to 10V at 600 mA
Theory and operation
The voltage on a fully charged Li-Ion battery at no load is 4.2V. When a load is connected, the voltage rapidly drops to 3.9V, and then slowly decreases as the battery works. A cell is considered discharged when the voltage across it drops below 3V.
In this device, the battery is connected to one of the analog outputs of the Arduino. The voltage on the battery without load is measured and the controller waits for the “Start” button to be pressed. If the battery voltage is above 3V. , pressing the button will start the test. To do this, a 4 ohm resistor is connected to the battery through a solid state relay, which will act as a load. The voltage is read by the controller every half a second. Using Ohm's law, you can find out the current given to the load. I=U/R, U is read by the analog input of the controller, R=4 Ohm. Since measurements are taken every half second, 7200 measurements are obtained in each hour. The author simply multiplies 1/7200 of an hour by the current value, and adds the resulting numbers until the battery is discharged below 3V. At this moment, the relay switches and the display shows the measurement result in mAh
LCD pinout
PIN Purpose
1 GND
2 +5V
3 GND
4 Digital PIN 2
5 Digital PIN 3
6,7,8,9,10 No connected
11 Digital PIN 5
12 Digital PIN 6
13 Digital PIN 7
14 Digital PIN 8
15 +5V
16 GND
The author did not use a potentiometer to adjust the brightness of the display, instead he connected pin 3 to ground. The battery holder is connected negatively to ground and positively connected to analog input 0. A 10 MΩ resistor is connected between the plus of the holder and the analog input, which acts as a pull-up resistor. The solid state relay is turned on with a minus to the ground, and a plus to digital output 1. One of the relay's contact outputs is connected to the positive of the holder, a 4 ohm resistor is placed between the second output and the ground, which acts as a load when the battery is discharged. Keep in mind that it will get pretty hot. The button and switch are connected according to the diagram in the photo.
Since PIN 0 and PIN 1 are used in the scheme, they must be disabled before downloading the program to the controller.
After you connect everything, fill in the firmware attached below, you can try to test the battery.
The photo shows the voltage value that the controller considered.
The voltage on it must be higher than 3V.
This design is connected as a prefix to the charger, a lot of various schemes of which have already been described on the Internet. It displays on the LCD the input voltage value, the battery charging current, the charging time and the charging current capacity (which can be either in Amp-hours or in milliamp-hours - it depends only on the controller firmware and the applied shunt). (Cm. Fig.1 And Fig.2)
Fig.1
Fig.2
The output voltage of the charger must not be less than 7 volts, otherwise this set-top box will require a separate power supply.
The device is based on a PIC16F676 microcontroller and a 2-line liquid crystal indicator SC 1602 ASLB-XH-HS-G.
The maximum charging capacity is 5500 mAh and 95.0 Ah respectively.
The circuit diagram is shown on Fig 3.
Fig.3. Schematic diagram of the attachment for measuring charging capacity
Charger connection - on Fig 4.
Fig.4 Scheme of connecting the set-top box to the charger
When turned on, the microcontroller first requests the required charging capacity.
Set with the SB1 button. Reset - button SB2.
Pin 2 (RA5) goes high, which turns on relay P1, which in turn turns on the charger ( Fig.5).
If the button is not pressed for more than 5 seconds, the controller automatically switches to the measurement mode.
The algorithm for calculating the capacity in this set-top box is as follows:
Once per second, the microcontroller measures the voltage at the input of the set-top box and the current, and if the current value is greater than one of the least significant digit, it increases the seconds counter by 1. Thus, the clock only shows the charging time.
Next, the microcontroller calculates the average current per minute. For this, the charging current readings are divided by 60. An integer is written to the counter, and the remainder of the division is then added to the next measured current value, and only then this sum is divided by 60. Having thus made 60 measurements in 1 minute, the counter will have a number average current per minute.
When the readings of seconds pass through zero, the average current value, in turn, is divided by 60 (according to the same algorithm). Thus, the capacity meter increases 1 time per minute by one sixtieth of the average current per minute. After that, the counter of the average current value is reset to zero and the counting starts again. Each time, after calculating the charging capacity, a comparison is made between the measured capacity and the specified one, and if they are equal, a message is displayed on the display - "Charging completed", and in the second line - the value of this charging capacity and voltage. Microcontroller pin 2 (RA5) goes low, which causes the relay to turn off. The charger will disconnect from the mains.
Fig.5
Device setup comes down only to setting the correct readings of the charging current (R1 R5) and input voltage (R4) using a reference ammeter and voltmeter.
Now about shunts.
For a charger for current up to 1000 mA, you can use a 15 V power supply, a 0.5-10 Ohm resistor with a power of 5 W as a shunt (a smaller resistance value will introduce a smaller measurement error, but will make it difficult to accurately adjust the current when calibrating the device), and in series with a rechargeable battery, a variable resistance of 20-100 ohms, which will set the value of the charging current.
For charging current up to 10A, it will be necessary to make a shunt from a high-resistance wire of a suitable cross section with a resistance of 0.1 Ohm. The tests performed have shown that even with a signal from the current shunt equal to 0.1 volts, the tuning resistors R1 and R3 can easily set the current reading to 10 A.
Printed circuit board for this device was developed under the indicator WH1602D. But you can use any suitable indicator by soldering the wires accordingly. The board is assembled in the same dimensions as the liquid crystal indicator and is fixed at the back. The microcontroller is installed on the socket and allows you to quickly change the firmware to switch to a different charger current.
Before first switching on, set the trimming resistors to the middle position.
As a shunt for the firmware option for low currents, you can use 2 MLT-2 1 Ohm resistors connected in parallel.
You can use the WH1602D indicator in the console, but you will have to swap pins 1 and 2. In general, it’s better to check the documentation for the indicator.
MELT indicators will not work, due to the incompatibility of working on a 4-bit interface.
If desired, you can connect the indicator backlight through a 100 Ohm current-limiting resistor
This prefix can be used to determine the capacity of a charged battery.
Fig.6.Determining the capacity of a charged battery
As a load, you can use any load (Light bulb, resistor ...), only when you turn it on, you need to set any obviously large battery capacity and at the same time monitor the battery voltage to prevent deep discharge.
(From the author) The prefix was tested with a modern pulse charger for car batteries,
These devices provide stable voltage and current with minimal ripple.
When connecting the set-top box to an old charger (step-down transformer and diode rectifier), I was unable to adjust the charging current readings due to large ripples.
Therefore, it was decided to change the algorithm for measuring the charging current by the controller.
In the new edition, the controller makes 255 current measurements in 25 milliseconds (at 50Hz, the period is 20 milliseconds). And from the measurements made, selects the largest value.
The input voltage is also measured, but the smallest value is selected.
(At zero charging current, the voltage should be equal to the battery emf.)
However, with such a scheme, it is necessary to put a diode and a smoothing capacitor (> 200 μF) in front of the 7805 stabilizer for a voltage not less than the output voltage of the charger
devices. Poorly smoothed microcontroller supply voltage led to malfunctions.
For accurate setting of the set-top box readings, it is recommended to use multi-turn trimmers.or put additional resistors in series with trimmers (choose experimentally).
As a shunt for a 10 A set-top box, I tried using a piece of aluminum wire with a cross section of 1.5 mmabout 20 cm long - works great.
The most important parameter of each battery is its battery capacity. It determines the amount of energy given to them for each period of time. This applies to all batteries from car to telephone. It is important to know about them and understand the device, because using the wrong capacity battery can cause serious problems when starting these devices.
The units of this value are Amps or Milliamps / hour. According to this parameter, a battery for equipment is selected, guided by the recommended values. If the recommendations are violated, for example, the car may not start in winter.
What is the capacity of a battery or accumulator
All batteries are usually decorated with inscriptions like 55, 70 Ah or 1800mAh. This designation indicates that the capacity of this battery is, respectively, 55 Amperes or fractions of Amperes per hour, only translated into English - A / hour. It must be distinguished from another parameter - voltage, which is written in Volts.
Standard battery
The Ah indicator shows how long the battery will last for an hour at a load of 60 Amps and a voltage of 12.7V. In other words, capacity is a store of energy that a battery can hold in itself.
And if there is less than 60A load, then the battery will last longer than 60 minutes.
How to quickly check the capacity of any battery
Most often, battery capacity is measured using a tester. This is a quick measurement device. It works automatically, no additional knowledge is needed to use it. The time spent is no more than 15 seconds. All that is required is to connect the tester to a power source and press a single button, after which it begins to determine the capacity of the connected batteries.
It is used when choosing a battery, comparing the residual and nominal capacity, which is officially indicated on the device. If the difference is more than 50%, then the battery cannot be operated.
Which instrument to use to accurately measure the capacity of any battery
The capacitance indicator determines the density of electrolytes, it is determined using a special device - a hydrometer. On new batteries, the main parameters are always indicated. However, this value is determined independently.
Small battery
The simplest way is the usual testers like "Coulomb". With this device, the capacity and voltage of the battery in the car are measured. This requires minimal effort and time to achieve reliable results.
To use the "Pendant", you need to connect it to the battery terminals, after which it will begin to determine the voltage and capacity.
There are many other ways to calculate these parameters. The classic is the measurement with a car battery multimeter. In order to do this, it must be fully charged and connected to the consumer (a regular 60W light bulb is enough). However, even this does not guarantee the absolute accuracy of the readings.
instrument multimeter
The first step after assembling the circuit from the battery itself, a multimeter, a light bulb is to apply voltage. If the light does not go out within 2 minutes (if this is not the case, the battery cannot be restored), take the “Coulomb” readings. As soon as the reading falls below the battery voltage standards, it begins to discharge. Having measured the time required for the final consumption of energy and the load current of the consumer, these readings must be multiplied by each other. The resulting number is the capacity of the battery.
If the result differs from the official value, the battery must be replaced. The multimeter allows you to calculate the capacity of any battery. The disadvantage of this method is that it is time consuming.
In the second measurement method, the battery is discharged using a resistor according to a special scheme. With the help of a stopwatch, the discharge time is determined. However, it is important not to discharge the battery completely, being protected from this by means of a relay.
How to make a device with your own hands
If the necessary equipment is not at hand, you can implement the device yourself. Load forks will fit. There are always a lot of them on sale, but they are also collected independently. Such an option is considered below.
Plug scheme
This fork has an expanded scale, which allows achieving the highest reading accuracy. Built in load resistance. The ranges of the scale are divided in half, thereby reducing the error of the readings. The device is equipped with a 3-volt scale. This makes it possible to test individual battery banks. Scales of 15V are achieved by lowering the voltage on diodes and zener diodes.
The current reading of the device will increase as soon as the voltage values \u200b\u200bbecome greater than the opening level of the zener diode. During the supply of voltage of the wrong polarity, the diodes provide protection. In the picture: SB1 is a toggle switch, R1 is a transmitter of the required current, R2 and R3 are resistors designed for the M3240, R4 are determinants of the width of narrow ranges of scales, R5 is a load resistance.
How to find out the capacity of a phone battery at home
When using a cell phone, its battery undergoes constant degradation. This process cannot be avoided, it is natural. This happens regardless of the model, price, phone features. To understand exactly how long the battery will last in the device, you need to measure its current capacity. This will allow you to replace the battery in time before it starts to turn off at the most inopportune time.
Swollen battery
First of all, you need to inspect the battery. Dangerous problems in a lithium battery are immediately visible: the case may swell, be full of traces of corrosion, greenish and white spots.
If signs of swelling are found, it is dangerous to continue using such a battery. This can cause a short circuit in the electrical circuits in the phone. Perhaps the beginning of swelling with a small bulge up to serious deformations. Another worrying factor is the rapid drop in the charge in the phone.
Today, there are many applications for measuring the current capacity of the phone.
To accurately determine battery capacity, use the advanced charger method. The battery is completely discharged, then connected to this device. It, in turn, calculates the capacity of the battery, taking into account the time and current value.
Load differences
The parameters of each car are different. Their volumes of engines, battery capacity differ. In a passenger car, usually a battery with a capacity of 40-45A, and in a large car about 60-75A.
The reasons for this lie in the starting current - the smaller the battery, the less electrolytes, lead, etc. in it. The larger it is, the greater the amount of energy that can be given at one moment. Based on this, large batteries are able to work successfully on a small car, and small batteries cannot be inserted into a large car.
Hull dependency
Batteries in different sizes
Capacity is directly related to the number of electrolytes and lead in the battery. Because of this, small capacity batteries will be much smaller in volume and weight than larger batteries. For these reasons, large batteries are never put on a small car, as this does not make sense - there is not enough space under the hood in these cars. And the small battery does a great job of starting the motor.
Capacity reduction
Any battery is subject to depreciation, its capacity decreases over time. Regular batteries last about 3-5 years. The highest quality specimens are stored in good condition up to 7 years.
As capacity drops, the battery loses its ability to supply enough starting current. Then it's time to replace it. The main reasons for the drop in capacity are:
- Accumulation of sulfuric acid on the positive plate. It can completely cover all surfaces, contact with electrolytes deteriorates, and capacity drops.
- The plate crumbles due to overcharges, then there is a lack of electrolytes. This leads to an instant decrease in battery capacity.
- When the can is closed and the negative and positive plates are connected to each other, the battery capacity decreases. However, it is being restored.
What determines the current capacity of the battery?
During the lifetime of a battery, its capacity changes. At the beginning of their work, they have the highest capacity, since the plates are actively developed. Then comes a period of stable operation, and the capacity is kept at the same level. Further, the capacity decline begins due to wear of the plates.
Battery test process
The battery capacity varies depending on the presence of active materials and the design of electrodes, electrolytes, their temperatures and concentration, discharge current, battery depreciation, concentration of additional deposits in electrolytes, and many other factors.
As the discharge current increases, the capacity of the battery decreases. With a fast, specially provoked discharge, the batteries lose less capacity than with smoother modes with low current values. Based on this, indicators for 4, 15, 100 hours of discharge are recorded on the case. The capacities of the same batteries at the same time change extremely strongly. The capacity is least at 4 hours of discharge, and most of all - at long periods of time.
Also, the capacitance indicators change with an increase in the temperature of the electrolytes, however, with an increase in the maximum permissible norms, the service life decreases. The reasons for this lie in the fact that at elevated temperatures, electrolytes penetrate into the active mass, because their viscosity decreases, while the resistance, on the contrary, increases. Because of this, in the reactions of discharging the active mass is greater than during the charge with a lower temperature.
At particularly low temperatures, the capacity of the battery is reduced in the same way as its useful effect.
With an increase in the concentration of electrolytes, the capacity of the battery also increases. However, the battery deteriorates faster, as the active mass of the battery is loosened.
Thus, checking the battery capacity is necessary at all stages of its life.
How to use the battery tester?
Very simple. You connect the Coulomb clamps to the battery, and in a second the device shows its voltage.
Why do I need a pendant? I have been working with batteries for a long time and can assess the health of the battery by measuring the voltage under load or even just by the glow of a light bulb connected to the battery.
Of course, you can get a qualitative picture of the battery. But it's like checking battery voltage with your tongue. 
- even an experienced person will not be able to name the number - voltage in volts (or, in our case, in ampere-hours). Also, imagine how many batteries it will take to transfer your experience to an employee. And Coulomb works even in inexperienced hands. Therefore, just as you use a multimeter to measure battery voltage, you will use a Coulomb for measuring battery voltage.
Can Coulomb be used to test nickel-cadmium or lithium batteries?
No. The Coulomb indicator is intended only for testing lead-acid batteries.
What is the measurement error of Coulomb?
K ulon is not a precision measuring device. It does not measure, but evaluates it by the response of the battery to the test signal. This is an indicator that serves to distinguish good batteries from batteries that have lost part as a result. The measurement error is not specified in the list of its technical characteristics and is not standardized. The pendant was tested on traditional several different companies with liquid (soaked into the plates and separator) electrolyte - AGM technology. For these batteries, the estimation error did not exceed 10-15%. But in recent years, some battery manufacturers have begun to produce batteries with markedly different electrical characteristics. These are, for example, batteries for short discharges (often positioned as) or numerous "noname" batteries, which are often installed in alarm systems for their cheapness (in the hope that a fire will not happen). Therefore, today on unknown batteries, even if they are made using AGM technology, the error may be greater. To reduce this error, the user can configure the tester to test a certain type, in fact, replacing the factory calibration of the device with his own, obtained with its batteries and in its conditions.
In all measurements and estimates are made relative to some standard. For example, a voltmeter compares the voltage of a battery with that of a reference primary cell. And Coulomb compares the tested battery with those lead batteries on which it was tested. By replacing the factory calibration with your own, you can make your battery a reference and all capacity estimates will become more accurate. In the operating instructions, several methods for calibrating the instrument are suggested. You just have to choose and use the method that suits you best.
How to use if it is not possible to independently calibrate?
For the most part, the error is small and the Coulomb can be used without any preparation. If this is not the case in your case, and there is no way to calibrate, you can use KULON as a device for relative measurements. For example, you have a dozen identical batteries with a nominal 10 Ah. On nine of them, the PENDANT shows 9 A * hour, and on the tenth - 3 A * hour. Conclusion - the tenth battery is defective and must be replaced immediately.
Even if there is only one battery of this type, you can test it with Coulomb before commissioning. In the process of further maintenance, you can record readings with a certain frequency (for example, once a quarter). When the Pendant shows that it has become less than 70% of the initial capacity (you can choose this limit yourself), the battery needs to be replaced.
Homemade measuring instruments
B. STEPANOV, Moscow
Radio, 2002, No. 7
Batteries gradually lose capacity during use. Assess the actual condition of the battery and to draw conclusions about the advisability of its further use allows the device, the description of which is given in the article.
To control the state of the battery, only a few parameters are available to the user: voltage at its terminals without load, internal resistance, voltage at the terminals at a certain load and its change over time. The last parameter is associated with the capacity of the battery (it is denoted by the Latin letter C). For batteries designed to power electronic devices, the capacity is usually estimated in ampere-hours (A \ h) or milliamp-hours (mAh) as the time during which the voltage on the Ni-Cd / Ni-MH battery when discharging it with a stable current decreases to 1 V. The choice of such a value is to some extent conditional, but not accidental. It is believed that by this moment the battery has time to give up about 90% of the energy stored in it, and the rate of decrease in the voltage on the battery increases markedly. It should be noted that the battery capacity determined in this way depends on the selected discharge current. This dependence noticeably weakens only at its values less than 0.5C.
It is convenient to measure the battery capacity in a device capable of discharging it with a stable current of up to 1 V. 1. Its basis is the integrated timer KR1006VI1 (DA1). It contains two comparators (upper and lower levels), a trigger, an output stage and a discharge transistor. Pins 5 and 6 are the inputs of the high-level comparator. The voltage on the first of them is set by the internal divider of the microcircuit and is equal to 2/3 of the supply voltage of the microcircuit, on the second - by a resistive divider R1 - R3, which is powered by a stabilized source of +9 V.
As you can see, power is supplied to the microcircuit through connector X1 from the battery being tested. If it consists of six elements, the comparator should work at a voltage of 6 V, and if out of seven (for example, the Nika battery and the like) - at 7 V. Therefore, the voltage at pin 6 of DA1, set by the divider R1 - R3, in in the first case it should be equal to 4, and in the second - 4.67 V. These values need to be clarified, since they depend on the parameters of the internal divider of a particular microcircuit instance. For definiteness, the variant of the device for the Nika storage battery is further considered.
As long as the battery voltage is above 7 V, the timer output (pin 3) is high (about 1.5 V below the current supply voltage). The discharge current is the sum of the load current (it is maintained unchanged by the current stabilizer on the field-effect transistor VT1) and the current consumed by the microcircuit itself (about 5 mA). Setting a total current of more than 30 mA is undesirable. In the author's version, it is chosen equal to 20 mA. This allows you to discharge the Nika battery with a current of 0.2C, which, on the one hand, reduces the discharge time by half (to about 5 hours), and on the other hand, does not significantly “reduce” the capacity of the tested battery (when discharged with a current of 1C, it may turn out to be 30% lower than low-current discharge).
The load is resistor R4 and LED HL1. The glow of the latter informs that the battery is being discharged and the level of 7 V has not yet been reached. Since the nominal current through the AL307BM LED is 10 mA, the "excess" of the stabilized current (5 mA) flows through the resistor R4.
If more discharge current is needed, the device is supplemented with a transistor VT2 with a resistor R6 (shown in dashed lines). The current through this circuit will be stable, since the voltage at the base of the transistor is almost constant (it is known that the forward voltage drop across the LED does not change much in the region of operating currents). The current in the emitter circuit (and hence the collector) is calculated by the formula I \u003d (U - 0.6) / R. Here U is the voltage at the base of the transistor, V; R is the resistance of the resistor R6, Ohm; I - collector current, A; 0.6 - approximate value of the voltage drop at the emitter junction of the transistor (0.6 V). This formula is estimated, so the value of the discharge current must be clarified when setting up the device by selecting the resistor R6.
To eliminate possible failures, pin 4 ("Reset") is connected to the positive power rail. The input of the low-level comparator (pin 2) is used to turn on the discharge mode by touching the touch contact E1. Capacitor C1 is connected to the second input of the high-level comparator in order to reduce the likelihood of false alarms from impulse noise penetrating the power circuits.
To pin 7 (the collector of the discharge transistor of the timer), a piezoelectric sound emitter HPM14AX from JL World (with a built-in generator) is connected, which gives a signal when the battery is discharged.
The details of the device are mounted on a printed circuit board, the drawing of which is shown in fig. 2. All parts are installed on it, except for the sound emitter HA1 and connector X1. The board is designed for the use of fixed MLT resistors, SP5-2 wire trimming resistor and KM capacitors. Resistors R2, R4, R5 are installed perpendicular to the board.
An additional regulated voltage source is required to establish the device. It is connected to the device instead of the battery and the voltage is set to 9.4 V. When touching the touch contact E1, the HL1 LED should light up. By selecting resistor R4, they ensure that the total current consumed by the device from an additional source becomes 20 mA. Then the voltage is lowered to 7 V and the voltage at pin 5 of the microcircuit is measured. The same voltage is set with a tuning resistor R3 at its output 6. After that, the device is ready for operation.
In a device with an additional transistor, resistor R6 is selected so that the total discharge current becomes equal to the required value (if VT2 is used without a heat sink, it should not exceed 150 mA). It should be noted that with a collector current of more than 100 mA, the transistor VT2 heats up noticeably. This leads to a change in the base-emitter voltage, and it affects the value of the stabilized current (the value of 0.6 changes in the above formula). Therefore, the discharge current should be set no earlier than 3 ... 4 minutes after the supply voltage is applied. This does not affect the operation of the device in the future, since the “run-out” of the collector current of the transistor VT2 during heating does not exceed a few milliamps and it lasts about 3 minutes.
Then a control experiment is carried out. Turning on the power and setting (according to the voltmeter) at the output of the additional source a voltage of 9 ... 10 V, touch the E1 contact. In this case, the HL1 LED lights up. Then, gradually reducing the output voltage of the additional source, register the value at which the LED went out and an audible signal appeared. If it differs from 7 V, adjust the voltage at the input of the upper level comparator with a tuning resistor R3. At the end of discharging, the device consumes a current of about 5 mA from the battery.
The change in voltage at pin 7 of the microcircuit can be used to disconnect the battery under test from the device at the end of the discharge, as well as to control the timer, which fixes the time of its discharge.
LITERATURE
Tenkov VV, Center BI Fundamentals of the theory and operation of sealed nickel-cadmium batteries. - Leningrad: Energoatomizdat, 1985.