How to correctly detect the internal resistance and capacity of lithium-ion batteries?

Source: 2020 - 04 - 20 hits, son: you know how to test the internal resistance and capacity of lithium-ion batteries? Battery internal resistance equal to open circuit voltage divided by the short circuit current. At present, lithium batteries are widely used in our life, how to detect the internal resistance and capacity of lithium-ion batteries? Lithium battery capacity refers to the capacity of it, the unit is usually safe, mah. Lithium battery capacity is 500 mah, for example, this means that if the current is 10 ma, the battery can work 50 hours straight. Lithium battery internal resistance mainly include the ohmic resistance and the polarization resistance. Under the condition of constant temperature, basic stable, ohmic resistance and the polarization resistance will change as the factors influencing the level of polarization. Ohmic resistance is mainly composed of collecting liquid and the connection of pole ear electrode material, electrolyte, the various parts of the diaphragm of resistance and contact resistance, this is associated with cell size, structure and connection mode. Lithium battery terminal voltage is refers to the lithium battery in the circuit connected to the working condition detected by the battery voltage between the positive and negative. Its value is equal to the lithium battery voltage minus the residual voltage value after ohmic resistance. The meaning of lithium battery internal resistance test 1. One of the factory factory inspection project; 2. Lithium battery assembly, choose battery internal resistance close group; 3. The greater the capacity of lithium battery, its internal resistance. Therefore, the capacity of the battery can be roughly judgment according to the size of the internal resistance. 4. The outstanding performance of the lithium battery aging failure is the increase of internal resistance, through the test battery internal resistance can quickly judge the aging degree of the battery; 5. In the process of lithium battery maintenance, often need to test the internal resistance of each battery cells, so as to pick out the resistance increase unit, replace the better unit. Lithium battery internal resistance testing method according to physical formula R = U/I and lithium battery test equipment of power through a constant dc current in a short period of time ( Typically 2 to 3 seconds) ( 40 ~ 80 large current is now in general use) , the measures to lithium battery voltage on both ends, and calculate the current lithium battery resistance according to the formula. 1. The measured open circuit voltage of battery: U12. Parallel connection on both ends of the battery, has a fixed resistance: resistance R discharge, 3. When discharge measurement on both ends of the lithium battery voltage: U2. 4. Calculate the battery resistance: r = ( u1, u2) / ( U2 / r) For example, if the battery open circuit voltage of 12 v, after a 10 ohm resistor in parallel voltage drop to 10 v, the battery internal resistance is: r = ( u1, u2) / ( U2 / r) =( 12 - 10) / ( 10/10) = 2 ohm. In general, the bigger the lithium battery internal resistance r, the load of the battery, power battery ( Such as battery) The internal resistance r is usually small. Low power battery ( Such as laminated 9 v battery) Usually has a high resistance. Ac voltage resistance measurement due to the lithium battery is actually an active resistance, we impose a fixed frequency on lithium batteries and a fixed current ( Now generally use 1 KHZ frequency and 50 ma small current) And then the voltage sampling. After rectification, filter and a series of processing, lithium battery internal resistance by op-amp circuit calculation. Ac voltage resistance method of lithium battery measuring time is very short, generally around 100 milliseconds. The precision of this measurement method is very good also, generally between 1% ~ 2% accuracy of measurement error.