How to use a multimeter to detect whether the battery of a mobile phone is good or bad?
Mobile phone batteries are generally lithium batteries, and the voltage is between 3.6 and 4.2. If the voltage is in this range, it proves that the battery can still be used. The closer the voltage is to or slightly higher than 4.2V, it proves that the charge is relatively full.
However, the multimeter can only measure the appearance, and the actual measurement. If you want to measure the capacity and 'bad' Chengdu, you need to use a professional instrument, and the multimeter will not work.
Or the battery is connected to a resistor of about 100 ohms (the power of the resistor is generally large, preferably a cement resistor). If the measured voltage of the mortgage is compared with that before discharge after one hour, if the voltage drops by more than 0.3v, the battery is generally inferior. The less the drop, the better the performance index of the battery.
Extended information
1. Working principle
The basic principle of the multimeter is to use a sensitive magnetoelectric DC ammeter (microampere meter) as the meter head. When a small current passes through the meter head, there will be a current indication. However, the meter head cannot pass a large current, so some resistors must be connected in parallel or in series on the meter head to shunt or lower the voltage, so as to measure the current, voltage and resistance in the circuit.
2. Design principle
(1) In the measurement process of the digital multimeter, the measured value is converted into a DC voltage signal by the conversion circuit, and then the analog voltage is converted into a digital value by the analog/digital (A/D) converter, and then counted by an electronic counter, and finally the measured The results are shown numerically directly on the display.
(2) The function of the multimeter to measure voltage, current and resistance is realized through the conversion circuit part, and the measurement of current and resistance is based on the measurement of voltage, that is to say, the digital multimeter is expanded on the basis of the digital DC voltmeter. .
(3) The A/D converter of the digital DC voltmeter converts the analog voltage that changes continuously with time into a digital quantity, and then counts the digital quantity by an electronic counter to obtain the measurement result, and then displays the measurement result by the decoding display circuit . The logic control circuit controls the coordinated work of the circuit, and completes the entire measurement process in sequence under the action of the clock.
Caution
1. Before using the multimeter, "mechanical zero adjustment" should be performed first, that is, when there is no electricity to be measured, make the pointer of the multimeter point to the position of zero voltage or zero current.
2. In the process of using the multimeter, do not touch the metal part of the test lead with your hands, so that on the one hand, it can ensure the accuracy of the measurement, and on the other hand, it can also ensure personal safety.
3. When measuring a certain amount of electricity, it is not possible to change gears while measuring, especially when measuring high voltage or high current, more attention should be paid. Otherwise, the multimeter will be destroyed. If you need to change gears, you should disconnect the test leads first, and then measure after changing gears.
4. When using the multimeter, it must be placed horizontally to avoid errors. At the same time, attention should be paid to avoid the influence of the external magnetic field on the multimeter.
5. After using the multimeter, the transfer switch should be placed in the maximum gear of the AC voltage. If it is not used for a long time, the battery inside the multimeter should also be taken out to prevent the battery from corroding other components in the meter.
