Structure of lead-acid batteries
A typical lead-acid battery is composed of positive and negative plates, separators, shells, electrolytes, and terminal pins. The chemical reaction of discharge relies on the active materials of the positive plate (lead dioxide and lead) and the negative plate (sponge like pure lead) under the action of the electrolyte (dilute sulfuric acid solution). The grid of the plates is made of lead antimony alloy in traditional batteries, while maintenance free batteries are made of lead calcium alloy. The former uses antimony, while the latter uses calcium. This is the fundamental difference between the two. Different materials will produce different phenomena: traditional batteries will experience liquid depletion during use, because the antimony on the grid frame will contaminate the sponge like pure lead on the negative electrode plate, weaken the back electromotive force inside the battery after full charging, cause excessive decomposition of water, and a large amount of oxygen and hydrogen will escape from the positive and negative plates, reducing the electrolyte. By replacing antimony with calcium, the back electromotive force of a fully charged battery can be changed, reducing overcharging current and decreasing the rate of liquid vaporization, thereby reducing the loss of electrolyte.
Due to the use of lead calcium alloy grid frame in maintenance free lead-acid batteries, the amount of water decomposition and evaporation during charging is low. In addition, the sealed structure of the shell releases very little sulfuric acid gas. Therefore, compared with traditional batteries, it has the advantages of no need to add any liquid, less corrosion to the terminal posts and wires, strong overcharge resistance, high starting current, and long battery storage time.
Maintenance free lead-acid batteries have the characteristics of low internal resistance, good low-temperature starting performance, and longer service life than conventional batteries due to the fact that under normal charging voltage, the electrolyte only produces a small amount of gas, and the plates have strong resistance to overcharging. Therefore, distilled water does not need to be added during the entire use period, and under normal charging conditions, there is no need to remove them for supplementary charging. But during maintenance, the specific gravity of the electrolyte should be checked.
Most maintenance free lead-acid batteries have a hole shaped liquid (temperature compensated type) densitometer on the cover, which changes color according to changes in electrolyte density. It can indicate the storage status of the battery and the height of the electrolyte level. When the indicator eye of the densitometer is green, it indicates that the charging is sufficient and the battery is normal; When there are few or black green dots on the indicator eye, it indicates that the battery needs to be charged; When the indicator eye displays a light yellow color, it indicates that there is a fault inside the battery that needs to be repaired or replaced.
Maintenance free lead-acid batteries can also be recharged using the same charging method as regular batteries. During charging, the voltage per cell should be limited to 2.3-2.4V. Note that using conventional charging methods will consume more water, so the charging current should be slightly lower (below 5A) during charging. Cannot perform fast charging, otherwise the battery may explode, causing injury. When the specific gravity meter of a maintenance free battery displays light yellow or red, it indicates that the battery is close to being scrapped, and even if recharged, its service life is not long. At this time, charging can only be used as an emergency measure.
When conditions permit, maintenance free lead-acid batteries can be charged using charging equipment with current voltage characteristics. This device can ensure sufficient power while avoiding excessive water consumption due to overcharging.
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