Method for measuring internal resistance of lithium batteries

According to the physics formula R = U/I, the test equipment make the lithium battery go through a large constant DC current(now generally use a 40 ~ 80 a large current) in a short period of time (generally for 2 ~ 3 seconds) , measuring lithium voltage at that time, and  calculate the lithium battery internal resistance according to the formula.

The measurement accuracy is higher, control properly, the accuracy of measurement error can be controlled within 0.1%.

But this method has obvious shortcomings:

(1) can only measure large capacity lithium battery or lithium battery storage, small capacity lithium battery can't load in 2 ~ 3 seconds a 40 ~ 80 a large current;

(2) when the lithium battery with large current, lithium battery internal electrode polarization phenomenon happens, the polarization resistance.So the measurement must be a very short time, otherwise the measured resistance error inside;

(3) the large current through the lithium battery to lithium battery internal electrode has some damage.

Ac voltage drop resistance measurement

Because of active lithium battery is actually equivalent to a resistance, so we put a lithium battery under fixed frequency and fixed current (now generally use frequency of 1 KHZ, 50 ma small current), and then the voltage sampling, after rectification, filter and a series of processing by op-amp circuit to calculate the lithium battery internal resistance.Communication of the lithium battery internal resistance measurement by the pressure drop of the measuring time very short, generally around 100 milliseconds.

This is good also, the accuracy of the measurement accuracy of measurement error between 1% ~ 2% in general.

The advantages and disadvantages of this method:

Pressure drop (1) using ac internal resistance measurement can measure almost all of the lithium battery, including small capacity lithium battery.Laptop batteries, lithium-ion batteries of internal resistance measurement is generally in this way.

(2) the measurement precision of the method of ac voltage is likely to be under the influence of ripple current, as well as the possibility of harmonic current interference.The measuring instrument in the circuit anti-interference ability is a test

(3) measured with this method, the damage to the lithium battery itself does not have the too big.

(4) the measurement precision of the method of ac voltage is dc discharge impedance measurements.

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