Explain the internal resistance and capacity test methods of lithium batteries

Do you know how to test the internal resistance and capacity of a lithium battery? Do you know how to test the internal resistance and capacity of a lithium battery? The internal resistance of the battery is equal to the open circuit voltage divided by the short-circuit current. The capacity refers to the storage capacity of the lithium battery and the uneven capacity of the battery It is an important content of the quality resolution of lithium batteries. Lithium batteries are now widely used in our lives. How do we test their internal resistance and capacity? Lithium battery capacity refers to its capacity, and the unit is usually ampere hour or milliampere hour. For example, the capacity of a lithium battery is 500mAh, that is to say, if the current is 10mA, the battery can work continuously for 50 hours. The internal resistance of lithium batteries is mainly composed of ohmic resistance and polarization resistance. When the temperature is stable, the ohmic resistance is basically stable, while the polarization resistance will change with the factors that affect the polarization level. The ohmic resistance is mainly composed of the contact resistance of the electrode material, electrolyte, diaphragm resistance, collector liquid, and tab connection, which is related to the size, structure and connection mode of the battery. The terminal voltage of a lithium battery refers to the voltage between the positive and negative electrodes of the battery detected when the lithium battery is connected to the working state in the circuit. Its value is equal to the voltage value remaining after subtracting the voltage occupied by the ohmic resistance from the potential of the lithium battery. Lithium battery internal resistance test method: According to the physical formula Ru003dU/I, the test equipment power of the lithium battery passes a large amount of stable DC current in a short time (generally 2~3 seconds) (now 40~80 large current is usually used ), measure the voltage at both ends of the lithium battery, and calculate the internal resistance of the lithium battery according to the formula. 1. Measure the open circuit voltage of the battery: U12. Both ends of the battery are connected in parallel with a fixed resistance. Resistance: R discharge; 3. Measure the voltage at both ends of the lithium battery when discharged: U2; 4. Calculate the battery resistance: ru003d(u1-u2) /(U2/r) For example, if the open circuit voltage of the battery is 12V, and a 10 ohm resistor is connected in parallel, the voltage drops to 10V, then the internal resistance of the battery is: ru003d(u1-u2)/(U2/r)u003d(12 -10)/(10/10)u003d2 ohms. Generally speaking, the greater the internal resistance r of a lithium battery, the worse the load of the battery, and the lower the internal resistance r of a high-power battery (such as a battery). Low-power batteries (such as 9V laminated batteries) usually have high internal resistance. Communication voltage drop internal resistance measurement method: Since the lithium battery is actually equivalent to an active resistance, 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 Take a sample. After a series of processing such as rectification and filtering, the internal resistance of the lithium battery is calculated through the operational amplifier circuit. The measurement time of the communication voltage drop internal resistance measurement method for lithium batteries is very short, generally about 100 milliseconds. The accuracy of this measurement method is also very good, and the measurement accuracy error is generally between 1% and 2%. Lithium battery capacity test method: Lithium battery capacity test is based on the full voltage, and set the stop voltage as the parameter, because the minimum discharge voltage of the lithium battery is 2.75v, so the voltage less than 3V is meaningless for the lithium battery test; fixed current The discharge is generally represented by C, and the lithium battery is generally tested with a discharge of 0.5C. 1. Fully charge the battery. After a single lithium battery is fully charged, the voltage is 4.2v; 2. Use a multimeter to make the lithium battery a constant current of 0.5c, and the discharge is related to the battery capacity, and set the stop voltage to 3v; 3. Have a constant discharge multiple The discharge current is the capacity of the battery; test: if the constant discharge does not reach two hours, the nominal voltage is not enough, then the lithium battery may be counterfeited. If it is a person, find an adjustable load resistance and an adjustable current DC power supply to calculate the battery capacity after charging and discharging, charging current × charging time u003d battery capacity (from 2.7v and 3.0v to 4.2v) or discharge current ×Discharge timeu003dBattery capacity statement: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete the previous one: Bad habits of car use that can easily damage the life of the car’s battery