Most of today's portable electronic devices draw power from the batteries, which have a limited life. Each charging and discharging cycle in small steps helps to demolition and battery "battery holds less". Presented device can measure the energy efficiency of the battery and to determine its consumption. With this device it is possible to measure the capacity of a new battery and compare the result with the parameters, declared by the manufacturer.
In recent years, batteries have large storage capacity entice thousands of milliamp hours. There is a desire to check, whether these small batteries can release as much energy. Using the device presented can also be measured “energy appetite” any consumer.
- calculation of measurement parameters based on the power supply capacity when the discharge,
- measuring DC voltage in the range 0 … 25 AT, with permission 25 mV,
- DC measurement range 0 … 5 BUT, with permission 10 mA,
- measuring the capacitance in the range of up to 100 with a resolution of Ah 1 mAh,
- measurement of consumed energy in the range of up 100 with a resolution of Wh 1 MWh,
- time measurement in the range of up 100 hours,
- suitable for almost any type of battery,
- the transfer of all the parameters in real time via the USB interface,
- automatic start of the measurement after connecting power test,
- completion of a manual or automatic measurement after exceeding the current values, voltage, time or capacity,
- automatic disconnection of the power supply after the test measurement,
- nutrition 8 … 15 DC battery or USB.
Battery capacity determines, how much charge the battery can give for a certain time. To determine this parameter, measured, how long the battery can provide the specific parameters of the current-voltage consumption. In this way, Testing requires a battery life cycle. It is not enough to "touch the meter", to immediately show the result. Result test performance depends on many parameters.
If the test is designed to check the nominal capacity of the battery, intended for a particular device, it should be provided with discharge conditions, for example caused by the device. If the test comes to a universal battery, the result should be considered as a value for said operating conditions. The battery capacity depends primarily on the discharge current – in practice, with a smaller discharge current of the battery will show a greater capacity, with vigorous than the discharge with high current. Therefore, the test should be conducted at a discharge current, close to the value, at which the battery will eventually run.
This scheme is not equipped with an adjustable load module. It must be connected to the output circuit. The best solution would be to connect the device, which will eventually be run from batteries. However, it should be remembered, that the output voltage decreases due to voltage drop at the measuring resistor. At low currents, the fall would be negligible, negligible, but at maximum current 5 A voltage drop will be up to 0,5 AND, which can lead to failure of the target device. In the simplest case, the output must be connected properly selected power resistor or bulb. Test at full capacity requires the full cycle. Therefore, the battery should be fully charged before beginning the test – here there is no doubt, that the special charger will ensure fulfillment of this condition. However, how to determine the end of the study? A commonly used method consists in determining the final voltage, for Ni-xx accumulators about 0,9 AT / element, for Li-xx batteries around 3 AT / and so element. d., Carefully check the characteristics of the battery. This scheme has the function of automatic test is completed, one of 5 embodiments which is to define the minimum voltage. When the battery voltage drops to this level, check will be completed, and the battery is disconnected from the load. Another variant – indicate the minimum current – helpful, if the device is connected to the output. When the battery is exhausted to the point, that the device can not be operated on and off, this will lead to a decrease in the current value, that will be the signal to end the test.
Schematic diagram of the battery capacity meter is shown in Figure 1, it can be divided into several blocks.
Microcontroller ATmega8 is the basis of the control unit. Considerate oscillator quartz resonator 32768 Hz operates one of the circuits of the microcontroller time – TIMER2. It is used for the precise measurement of time. Display and buttons – This user interface, FT232R chip works as a USB interface and relay K1. Other elements are the analog part. chip IC3 several passive elements forms a relatively complex power supply. Voltage is carefully filtered, a digital and analog are separated by mass to ensure accuracy of measurements. This was also applied to the precision voltage reference source MCP1525. Analog signals are digitized 10-bit converter,, contained in the peripherals of the microcontroller. Voltage measurement is carried out through the voltage dividers with potentiometers R18 and R21. One of the input voltage, the other for the output. The current is measured by measuring the voltage drop across resistor R9.
Due to the very low impedance voltage low, no more 0,5 AT, so the converter is supplied from two TLC272 chip voltage amplifiers with a gain of 5 and 50. Consequently, Current is measured in two ranges 0 … 0,5A and 0, 5 … 5BUT, program accordingly controls the process, using an appropriate hysteresis when changing ranges.
Assembly and adjustment
Author's printed circuit board has been designed mainly with SMD-components. Assembling be performed in accordance with the general principles. Do not place the display on the printed circuit board, because it will occupy a significant part of. An arrangement of elements shown in the picture 2.
After assembly, the device turn and adjust the contrast of the display by a suitable potentiometer (picture 3).
Power from the battery apparatus from 8 … 15AT, 0,2A or via USB. After the initial launch, prepare regulated power supply, multimeter and load, such as automotive lamp power of about 20 W, and align the, as described below. After this setting, the device is ready to work.
Operation and Maintenance
After connecting the power supply will “greeting” on the screen , and then the main menu (picture 4). This window displays the main parameters: the measured voltage, current, time and the estimated value of the permanent capacity.
The values are updated every second, but the actual measurement is performed several tens of times more often. The program performs a measurement of analog parameters about 30 times per second, and then calculates the average value and passes it for further calculations and displays. The designation «Vi» means a voltage value at, the voltage from the input circuit is measured, is displayed and transmitted to settlement. If a value of «Vo», it takes into account the voltage from the output of the system, ie taking into account the voltage drop across the sense resistor. Likewise, this applies to the criterion voltage check completion. time indicator determines, at what stage of the circuit works. If the time is increased, it means, that the scheme is in the process of testing, if the time is not changed, and indicates a constant value, it means, that test is completed. If the time indicates zero, circuit is ready to start the test. Verification can be started by pressing the "plus", when the main window is displayed, or the test will be started automatically, when the minimum voltage appears at the input connector 0,5 AT. Starting test activates the relay and connects the input and output circuits. end of the test can be forced to hold, holding down the "menu" for 3 seconds, or it may occur automatically, if this function has been set.
After completion of the automatic display backlight blinks, signaling system availability, Pressing any key will stop this effect. At this stage, the test result is displayed in the main window – the capacitance value, to prepare for the next test circuit, hold down the "menu" near 3 with – Results will be cleared. The menu structure contains four windows – four parameters and the main window, Switch to the next. After pressing the "menu" button, a window appears, parameter value is changed using buttons "plus" and "minus", as it shown on the picture 5.
In the first menu screen is selected complete test method "stop mode", in order, as shown in Figure 5, you can choose: 1- manual, 2- the minimum value of the current, 3- the minimum voltage, 4- the maximum voltage, 5- specific time, 6- permittivity.
In the case of the embodiment 1 the test will be stopped only after deduction of the "menu" button.
option 2 can be used, when the device is connected to the circuit, and after discharge of the battery unit is disconnected – current falls below the preset value, and completes the verification scheme.
option 3 It will be the best at discharge using the bulb or resistor, the battery is discharged to the set voltage, and then the test will be completed, and the battery is disconnected from the load.
option 4 It will be useful for testing the charging process, will disconnect the battery circuit, when it reaches the specified maximum voltage.
option 5 It allows to investigate energy consumption. If you try to assess the need for a simple receiver energy, Bulb e.g., It is sufficient to measure current consumption and easy to calculate the rest. The matter is complicated, when you want to explore more sophisticated electronic device. Power consumption is not constant, it is usually inactive, from time to time changes and consumes energy, depending on the task at hand. setting option 5, You can check, how many mAh would use such a device, For example, at a time. This information will allow to count, which battery should be used for the operation of the device, For example, to work on 24 o'clock.
Similarly applicable option 6 – it allows you to specify, how long the unit will operate, when it receives a specific capacity, For example, 500 mAh, second window. Meaning «Auto». PARAM “. selected in the previous window. Buttons "plus" and "minus" can be used to change the value of the parameter, current value increments 10 mA, voltage increments 100 mV, time increments 10 minutes and a container of step 100 mAh. In the case of manual control options is displayed «Auto stop dis», which means, that the automatic completion of the test is disabled.
Third window allows you to set, a voltage to be measured and transmitted to settlement. Setting «Input» selects the measurement of the input terminals, setting «Output» at the output terminals. The output voltage of the circuit is reduced compared with the input voltage drop across the measuring resistor. The circuit is so designed, the microcontroller senses the output voltage with respect to the bulk, that is, the mass at the entrance, and then subtracts the voltage drop at the measuring resistor, calculated based on the current and resistance. When testing the capacity of the battery should be set measurement of the input voltage, and when testing charging or power measuring receiver should set the output voltage. In the fourth «USB Period" menu, you can set the time period to send data through the USB interface. The possible range is 1 … 255 seconds increments 1 with. The value should be chosen with care, because it typically takes a few hours, and too much data will be difficult to handle. Besides, send a summary diagram – the last frame, when the test will end automatically, regardless of the sending time. scheme, connected to a computer, It will be installed as a virtual serial port, and can read data, using any terminal program, For example, BrayTerminal. communication Settings: 19200, 8, not, 1. Each frame begins with a new line, and then with an asterisk "*", then recorded in the following order: time [hh: mm: ss], capacity [Priority], energy [W], Power [W], voltage [AT] and current [BUT], each value ends with a semicolon. Such frame has the form:
* 0:00:01; 0.000Ah; 0.000Wh; 0.000W ; 0.00within; 0.00A;
BrayTerminal program also has a recording function in the file «Log to file». The stored data can be easily imported into a spreadsheet and build characteristics of parameters. On the picture 6 shows a graph of the test a brand new battery 2000 mAh.
On the picture 5 It shows another window with parameters, marked "Calibration". This window is used to calibrate the circuit, and is not available from the menu. To start the calibration process, before connecting power to the system, press the menu button, and then, holding down, connect the power supply. After a few seconds a window will appear, then you can release the menu button. The first step is to set the zero calibration compensation coefficients, ie storing voltage levels (results ADC) on the inputs without voltage connected. To do this, leave the input and output terminals unconnected and briefly press the "plus", a window will appear with the name of «Zero comp.». Four values determine compensation levels for the four analog channels, who uses the system – upper measuring range of the current band, lower range of current measurement, input voltage and the output voltage. first, third and fourth values should not exceed 3 points, second value should not exceed 40 … 50 points. After clicking the "plus" scheme will remember and apply the new settings. Next window, that appears, facilitate the setting of analog equipment. First, connect the steering power source and configured multimeter for measuring the DC voltage at the input circuits. Install the tension between 10 … 15 The respective potentiometers and (Picture 3), to set the correct display of the input and output voltage. Then, connect the load to the meter and DC measurements to yield. When adjusting the supply voltage set current of about 1 … 1,5 A and set the correct current value in the display via the upper range of the potentiometer. Then set the current about 0,25 A correct indication and set the current value in the display by the potentiometer lowband. After clicking the "plus" calibration will return to the first step, after pressing the "menu" calibration is completed and the settings will be saved.