Battery internal resistance measuring device having a differential value calculating unit to treat two adjacent first voltage sampling values with first slope value calculation

A battery internal resistance measuring method, comprising following steps:

• (1) providing a battery internal resistance measuring device comprising a voltage detecting unit electrically connected to a battery, at least one measurement resistor electrically connected to the voltage detecting unit in parallel, at least one switch electrically connected to the measurement resistor in series, and a measurement controller electrically connected to the voltage detecting unit;
• and then, making the voltage detecting unit be electrically connected with a load in parallel and providing a switch controlling signal to the switch by using the measurement controller;
• (2) receiving a discharge voltage signal of the battery sensed by the voltage detecting unit by the measurement controller;
• (3) the measurement controller picking up a plurality of first voltage sampling values from a waveform of the discharge voltage signal based on a first sampling rate during a switching-off period of the switch;
• (4) a differential value calculating unit of the measurement controller applying each two of adjacent first voltage sampling values with a first differential value calculation or a first slope calculation, so as to obtain a plurality of first differential values and a plurality of first slope values;
• (5) the measurement controller finding out a first smallest differential value or a first smallest slope value from the first differential values and the first slope values, such that a discharge starting point from the waveform of the discharge voltage signal is determined, and then an open-circuit voltage is picked up from the discharge voltage signal according to the discharge starting point;
• (6) the measurement controller picking up a plurality of second voltage sampling values from the waveform of the discharge voltage signal based on a second sampling rate during a switching-on period of the switch;
• (7) the differential value calculating unit of the measurement controller applying each two of adjacent second voltage sampling values with a second differential value calculation or a second slope calculation, so as to obtain a plurality of second differential values and a plurality of second slope values;
• (8) the measurement controller finding out a second smallest differential value or a second smallest slope value from the second differential values and the second slope values, such that a discharge ending point from the waveform of the discharge voltage signal is determined, and then a short-circuit voltage is picked up from the discharge voltage signal according to the discharge ending point;
• and
• (9) the measurement controller calculating an internal resistance of the battery based on the open-circuit voltage, the short-circuit voltage and the resistance of the measurement resistor.