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Disadvantages of mixing new and old battery cells

by:Power Kingdom     2021-04-27
The mixed use of different types of batteries, or the mixed use of new and old batteries of the same type, is very harmful. Different batteries have different internal resistances and potentials because of their different internal electrolytes. When using them in combination, if they are connected in series, it may cause excessive discharge of batteries with low internal resistance and low potential, which will deplete the stock at once, and generate internal current exceeding the allowable value, rapidly aging and scrapping. At this time, the new batteries in the battery pack will also be dragged down, causing a chain reaction. If it is connected in parallel, the internal circulation of the battery pack will occur, on the one hand, the external output will be weakened, on the other hand, it may cause the battery itself to heat up or even explode. Even in emergency use, do not mix batteries with different internal electrolytes. For example, mixed use of rechargeable batteries and alkaline batteries is very dangerous. Disadvantages of mixing new and old batteries     Batteries are worn out. Due to a series of chemical reasons, the electromotive force will decrease slightly and the internal resistance will increase significantly. If such batteries are mixed with new batteries, there are many disadvantages. Now take a new battery (E1u003d1.5V, ru003d1Ω) mixed with an old battery (E2u003d1.4V, r2u003d5Ω), and power a 3V/3W lamp as an example for an analysis:   If two cells When the batteries are connected in series. R1u003d3Ω (lamp load resistance)   When a new battery is used for power supply, the current is I1,   I1u003d0.375A  When the new and old batteries are connected in series, the current is I2,   I2u003d0.322A, indicating that the mixed battery is small and falls on the old battery. The voltage drop on the internal resistance is Vr2, Vr2u003dr2•I2u003d5×0.322u003d1.61V>E2, which shows that the contribution of the old battery to the circuit is less than its consumption. This is the lamp for the new and old battery strings, and the brightness of the lamp is often darker. s reason. Use two batteries in parallel to supply power as shown in Figure 2. According to Kirchhoff’s law:   I1u003d(r1+RL)+I2RLu003dE1  I2u003d(r2+RL)+I1RLu003dE2 Then:   4I1+3I2u003d1.53I1+8I2 u003d1.4 available:   I1u003d0.339A I2u003d0.048A  ILu003dI1+I2u003d0.387A   The above data shows that when the new and old are connected in parallel, the current provided by the old battery is very small, and the current through the lamp is different than that of the new battery. It is very small (0.387A-0.375Au003d0.012A), and what is more serious is that once the external power supply is stopped, the key K is disconnected, and the second battery forms its own circuit. The new battery will supply power to the old battery, and its current is I.  Iu003d0.017A, there will be an equivalent self-discharge current of 20mA, calculated when the battery capacity is 3A, the discharge time is T, Tu003d176hu003d7 days, that is, the new battery will be discharged after one week. In short, the mixed use of new and old batteries, whether in series or in parallel, has many disadvantages, so new and old batteries should not be mixed.
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