Do you know how to test the internal resistance and capacity of a lithium battery? The internal resistance of a battery is equal to the open circuit voltage divided by the short-circuit current. The capacity refers to the amount of power stored in the lithium battery. The battery capacity is the main content that determines the quality of the lithium battery. Currently, lithium batteries are widely used in our lives. How do we test the internal resistance and capacity of lithium batteries?

   The capacity of a lithium battery refers to the amount of electricity it can hold, and the unit is usually "Amp-hour" or "Milliamp-hour". For example, the capacity of the lithium battery is 500mAh, which means that if the current of the battery is 10mA when working, it can work continuously for 50 hours.


The significance of testing the internal resistance of lithium batteries:

  1, one of the items of factory inspection in the factory;

  2. When assembling a lithium battery pack, you need to select battery cells with similar internal resistance to form a group;

  3. Because the larger the capacity Ah of the lithium battery, the smaller the internal resistance, so the battery capacity can be roughly judged according to the internal resistance;

  4. The prominent manifestation of the aging and failure of lithium batteries is the increase in internal resistance, so testing the internal resistance of the battery can quickly determine the degree of aging of the battery;

  5. During the maintenance of the lithium battery pack, it is necessary to frequently test the internal resistance of each battery unit in order to pick out the unit with increased internal resistance and replace it with a better one.

Lithium battery internal resistance test method:

According to the physical formula R=U/I, the test equipment forces the lithium battery to pass a large constant DC current in a short period of time (usually 2 to 3 seconds) (currently a large current of 40A to 80A is generally used). The voltage at both ends of the lithium battery and the current internal resistance of the lithium battery are calculated according to the formula.

   1. Measure the open circuit voltage of the battery: U1

  2, a fixed resistance resistor in parallel at both ends of the battery: R, discharge;

  3, measure the voltage across the battery during the discharge of the lithium battery: U2;

  4. Calculate the internal resistance of the battery: r=(U1-U2)/(U2/R)

For example, if the open circuit voltage of a battery is 12V, and a 10Ω resistor is connected in parallel, the voltage drop is 10V, then the internal resistance of the battery is: r=(U1-U2)/(U2/R)=(12-10)/(10 /10)=2Ω.

   Under normal circumstances, the larger the internal resistance r of a lithium battery, the worse the battery load, and the internal resistance r of high-power batteries (such as batteries) is usually very small. Low-power batteries (such as 9V laminated batteries) usually have relatively large internal resistance.

AC pressure drop internal resistance measurement method:

Because the lithium battery is actually equivalent to an active resistor, we apply a fixed frequency and a fixed current to the lithium battery (currently 1kHz frequency and 50mA small current are generally used), and then the voltage is sampled, rectified, filtered, etc. After series processing, the internal resistance of the lithium battery is calculated through the operational amplifier circuit. The measurement time of the lithium battery of the AC pressure drop internal resistance measurement method is extremely short, generally about 100 milliseconds. The accuracy of this measurement method is also good, and the measurement accuracy error is generally between 1% and 2%.

Lithium battery capacity test method:

The lithium battery capacity test is based on the full-charge voltage and the set termination voltage as the parameters, because the minimum discharge voltage of the lithium battery is 2.75V, so the voltage less than 3V has no meaning for the lithium battery test; how much fixed current discharge is generally used C indicates that lithium batteries are generally tested with 0.5C discharge.

   1. Fully charge the battery, the voltage of a single lithium battery after fully charged is 4.2V;

  2, with a multimeter, the lithium battery has a constant current of 0.5C, and the discharge is relative to the battery capacity, and the termination voltage is set to 3v;

  3. Multiplying the discharge current by the constant current discharge time is the battery capacity; check: if the constant current discharge cannot reach two hours, then the nominal voltage is not enough, and the lithium battery may be counterfeit.

There is a professional lithium battery divider cabinet. If you are an individual, find an adjustable load resistance and an adjustable current DC power supply to calculate the battery capacity through the charging and discharging time, charging current × charging time = battery capacity (Charge from 2.7V or 3.0V to 4.2V) or discharge current × discharge time = battery capacity

   Lithium battery performance test mainly includes voltage, internal resistance, capacity, internal pressure, self-discharge rate, cycle life and so on.

Battery from YDL battery, all test in factory, if short of capacity, we refund you all.