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COMPARISON ON STUDY OF LITHIUM ION SERIES & LEAD ACID SERIES CHARGING & DISCHARGING CHARACTERISTICS

¹MEHER KUMAR

¹ Engineering College , Dayalbagh Educational Institute, Dayalbagh , Agra282005

E-MAIL: meherkumarusic@gmail.com

ABSTRACT:-

Lead acid batteries are strings of 2 volt cells connected in series, commonly 2, 3, 4 or 6 cells per battery. Strings of lead acid batteries, up to 48 volts and higher, may be charged in series safely and efficiently. However, as the number of batteries in series increases, so does the possibility of slight differences in capacity. These differences can result from age, storage history, temperature variations or abuse .Fully charged batteries should never be mixed with discharged batteries when charging batteries in series. The discharged batteries should be charged before connection .When a single constant voltage charger is connected across an entire high voltage string, the same current flows through all cells in the string. Depending on the characteristics of the individual batteries , some may overcharge while other remain  in a slightly undercharged condition .To minimize the effect of individual battery differences , use batteries of the same age , manufacturer , amp hour , and history and , if possible ,charge in strings of no greater than 24 or 48 volts .

On the other hand it is highly recommended to charge lithium batteries in series with a multi-bank charger. This means each battery is charged at the same time but completely independent of the other. Charging properly a lithium-ion battery requires 2 steps: Constant Current (CC) followed by Constant Voltage (CV) charging. A CC charge is first applied to bring the voltage up to the end-of-charge voltage level. One might even decide to reduce the target voltage to preserve the electrode.

Li-ion does not need to be fully charged as is the case with lead acid, nor is it desirable to do so. In fact, it is better not to fully charge because a high voltage stresses the battery. In a lithium-ion battery, overcharging can create unstable conditions inside the battery, increase pressure, and cause thermal runaway. Lithium-ion battery packs are required to have a protection circuit to prevent excessive pressure build-up and cut off the flow of ions when the temperature is too high. A partial charge and discharge will reduce stress and prolong battery life. It is recommended to avoid full cycles and stay between 100% and 50% DOD (0-50% SoC).