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Charging characteristics of Ni-MH battery

by:dcfpower     2021-03-25
u003cpu003e The nominal voltage of a single nickel-hydrogen battery is 1.2v, and the charge termination voltage is 1.5v; the discharge termination voltage is generally 1.1v. The charging characteristics of Ni-MH batteries are affected by charging current, temperature and charging time. 'The battery terminal voltage increases with the increase of charging current, and the closer it is to the maximum value, the faster the battery temperature rises. The battery is more susceptible to damage. When the charging current is greater than 0.5C (C represents the battery charging rate), the terminal voltage of the battery will reach the maximum voltage sooner, and the charge and discharge capacity will become smaller, resulting in a decrease in battery performance.u003c/pu003e u003cpu003eu003c/pu003eu003cpu003e The charging characteristics of the 24V/10Ah Ni-MH battery at different charging rates are shown in Figure 1.u003c/pu003eu003cpu003eFigure 1 The charging characteristics at different charging ratesu003c/pu003e u003cpu003eu003c/pu003eu003cpu003e The initial power SOC is 5%, charging at a constant current of 0.5C, it takes about 2 hours to fully charge (SOCu003d100%), the highest voltage is 29.4V, and the voltage has changed by 7.1V ; It takes about 1 hour to charge with a constant current of 1C. The voltage changes by 8.2V, and the highest voltage reaches 30.5V, which exceeds the allowable charge termination voltage. It can be seen that the greater the charging rate, the greater the charging current, and the higher the terminal voltage rises, which will damage the battery. u003c/pu003eu003cpu003eu003c/pu003eu003cpu003e The initial charge SOC of 24V/10Ah Ni-MH battery is 10%, and the terminal voltage change rate curve under 0.5C constant current charging is shown in Figure 2. u003c/pu003eu003cpu003eu003c/pu003eu003cpu003eFigure 2 Battery voltage change rate under constant current chargingu003c/pu003eu003cpu003eu003c/pu003eu003cpu003e From the figure, we can see that the Ni-MH battery is charged at the end The voltage change is divided into three stages. 'The voltage change rate is the largest in the early stage of charging; as the charging time increases, the number of hydrogen atoms adsorbed on the electrode surface increases, making it more difficult to re-adsorb hydrogen atoms, resulting in an increase in impedance in the later stage of charging, and the terminal voltage The ascent rate increases.u003c/pu003eu003cpu003eu003c/pu003eu003c/pu003e
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