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Test method of battery charge point?

Time：

Oct 17,2022

There are usually two methods to check whether the electric capacity of common zinc-manganese dry batteries is sufficient. The first method is to estimate the internal resistance of the battery by measuring the instantaneous short-circuit current of the battery, and then judge whether the battery capacity is sufficient. The second method is to connect an ammeter in series with a resistor with an appropriate resistance, and calculate the internal resistance of the battery by measuring the discharge current of the battery, so as to judge whether the battery capacity is sufficient. The biggest advantage of the first method is that it is simple, and the power of the dry battery can be directly judged by using the high current gear of the multimeter. The disadvantage is that the test current is very large, far exceeding the limit value of the allowable discharge current of the dry battery, which affects the service life of the dry battery to a certain extent. The advantage of the second method is that the test current is small and safe, and generally it will not adversely affect the service life of the dry battery, but the disadvantage is that it is more troublesome. It is understood that a new No.2 dry battery and an old No.2 dry battery are tested and compared by MF47 multimeter with the above two methods. Assume that ro is the internal resistance of dry battery and RO is the internal resistance of ammeter. When using the second test method, RF is the additional series resistance with a resistance of 3Ω and a power of 2W. The measured results are as follows. The new No.2 battery E=1.58V (measured by 2.5V DC voltage level), and the internal resistance of voltmeter is 50kΩ, which is much larger than ro. Therefore, it can be approximately considered that 1.58V is the electromotive force of the battery, or the open circuit voltage. With the first method, the multimeter is set to 5A DC current, the internal resistance RO of the meter is 0.06Ω, and the measured current is 3.3A Therefore, ro+ro = ro+RO=1.58V÷3.3A≈0.48Ω, ro=0.48-0.06=0.42Ω. With the second method, the measured current is 0.395A, RF+ro+RO=1.58V÷0.395A=4Ω, and the internal resistance is 0.6Ω when the current is 500mA, so ro=4-3-0.6=0.4Ω. When the old No.2 battery is measured by the first method, the open-circuit voltage E=1.2V, the internal resistance RO=6Ω, the reading of 6.5mA, the multimeter setting 50mA DC current, ro+RO=1.2V÷0.0065A≈184.6Ω, ro=184.6-6=178.6Ω. With the second method, the measured current is 6.3mA, ro+RO+RF=1.2V÷0.0063A=190.5Ω, ro=190.5-6-3=181.5Ω. Obviously, the results of the two testing methods are basically the same. The slight difference of the final calculation results is caused by many factors, such as reading error, resistance RF error and contact resistance. This slight error will not affect the judgment of battery power. If the capacity of the battery to be tested is small and the voltage is high (for example, 15V, 9V laminated battery), the resistance value of RF should be increased.

There are usually two methods to check whether the electric capacity of common zinc-manganese dry batteries is sufficient.

The first method is to estimate the internal resistance of the battery by measuring the instantaneous short-circuit current of the battery, and then judge whether the battery capacity is sufficient. The second method is to connect an ammeter in series with a resistor with an appropriate resistance, and calculate the internal resistance of the battery by measuring the discharge current of the battery, so as to judge whether the battery capacity is sufficient.

The biggest advantage of the first method is that it is simple, and the power of the dry battery can be directly judged by using the high current gear of the multimeter. The disadvantage is that the test current is very large, far exceeding the limit value of the allowable discharge current of the dry battery, which affects the service life of the dry battery to a certain extent.

The advantage of the second method is that the test current is small and safe, and generally it will not adversely affect the service life of the dry battery, but the disadvantage is that it is more troublesome. It is understood that a new No.2 dry battery and an old No.2 dry battery are tested and compared by MF47 multimeter with the above two methods.

Assume that ro is the internal resistance of dry battery and RO is the internal resistance of ammeter. When using the second test method, RF is the additional series resistance with a resistance of 3Ω and a power of 2W. The measured results are as follows.

The new No.2 battery E=1.58V (measured by 2.5V DC voltage level), and the internal resistance of voltmeter is 50kΩ, which is much larger than ro. Therefore, it can be approximately considered that 1.58V is the electromotive force of the battery, or the open circuit voltage.

With the first method, the multimeter is set to 5A DC current, the internal resistance RO of the meter is 0.06Ω, and the measured current is 3.3A Therefore, ro+ro = ro+RO=1.58V÷3.3A≈0.48Ω, ro=0.48-0.06=0.42Ω. With the second method, the measured current is 0.395A, RF+ro+RO=1.58V÷0.395A=4Ω, and the internal resistance is 0.6Ω when the current is 500mA, so ro=4-3-0.6=0.4Ω. When the old No.2 battery is measured by the first method, the open-circuit voltage E=1.2V, the internal resistance RO=6Ω, the reading of 6.5mA, the multimeter setting 50mA DC current, ro+RO=1.2V÷0.0065A≈184.6Ω, ro=184.6-6=178.6Ω.

With the second method, the measured current is 6.3mA, ro+RO+RF=1.2V÷0.0063A=190.5Ω, ro=190.5-6-3=181.5Ω. Obviously, the results of the two testing methods are basically the same. The slight difference of the final calculation results is caused by many factors, such as reading error, resistance RF error and contact resistance. This slight error will not affect the judgment of battery power. If the capacity of the battery to be tested is small and the voltage is high (for example, 15V, 9V laminated battery), the resistance value of RF should be increased.

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