Basic requirements for charging of lead-acid batteries
The charging current should be less than or equal to the charging current of the battery. Otherwise, the excess current will cause the electrolyte to consume too quickly, resulting in the following hazards: the loss rate of the battery, the increase of the maintenance workload, the early failure of the battery for maintenance of the battery, the acid fog, the pollution of the environment, the health of the workers, the reduction of the charging efficiency and the energy consumption. Serious waste. The charging process is the reverse reaction process of the discharge electrochemical reaction. If the charge electrochemical reaction process is carried out in an ideal state, the process should be reciprocal reaction, that is, the battery charger charge should be basically equal to the output of the discharge. However, under the condition of serious gas release, the energy consumption of the effective electrochemical reaction process is less than 40% of the total electricity consumption, which means more than 60% of the electricity consumption is wasted. The production of gas is gathered inside the porous electrode of the battery, which reduces the contact area between the electrolyte and the porous electrode, that is, the interface of the charging electrochemical reaction is greatly reduced, the charge chemical reaction speed is reduced, the charging is very difficult and the charging time is prolonged.
Serious gas pollution will damage the battery: (1) the production of a large amount of gas has scouring effect on the active substances of the plate, making the active substances easy to soften and fall off. Under the high polarization voltage, the grid of the positive plate will produce serious corrosion and produce Pb02, which is completely different from the electrified Pb02. It is an irreversible oxide with poor conductivity, and the grid deformation, brittle fracture, loss of skeleton and conduction. Therefore, the overcharge should be prevented as much as possible when charging. Long term charging is insufficient, and the unreacted active substance will produce irreversible and highly positive large particle PbS04 grain (irreversible sulfation), which makes the storage battery capacity decrease, the internal resistance is increased, the charging difficulty is increased, and the early damage of the battery is caused.
Storage battery should ensure sufficient electricity as far as possible to prevent irreversible sulfation. Battery charging depth has great influence on cycle life and basically changes exponentially. This is because the positive active substance is Pb02, its binding fastness is not high, and when the discharge is converted to PbS04 charging, it is converted to PbO2, and the volume of PbSO4 is much larger than that of PbO2 (the volume ratio is about 2:1). Therefore, for the positive plate, the active substance will expand and shrink repeatedly, and make the connection between the particles fall off gradually, so that the battery's active material loses the discharge characteristic as "anode mud", which makes the battery performance decline until the life end. The deeper the discharge depth, the larger the expansion shrinkage, the greater the damage to the binding force of the active material and the shorter the life. Otherwise, the longer the cycle life is. Theoretically speaking, the deep discharge should be avoided as far as possible when the battery is used. It should be done in a shallow way. The premise is that there is a special matching charger. But in practical use, due to the battery charging performance and the battery itself discrete and charging habits and charging speed influence, the charger's voltage is high, more or less have been overcharged.
In particular, most of the charging in the night, the time is generally 6-10 hours, the average of about 8 hours, if shallow discharge, its charging will soon reach the end, at this time the charging efficiency will be lower, will produce overcharge. Longer battery charging time and frequent charging will cause battery life to be greatly affected by charging. The most ideal charging requirements are based on the actual conditions. It is necessary to draw up the charging frequency by reference to the normal operating frequency, mileage, the instructions provided by the battery factory, and the supporting performance of the charger. According to the situation of the vast majority of users, the battery is charged at the discharge depth of 50%-70% for the first time, so that the battery life can reach the best effect. When used, it can be converted into a riding mileage and charged once. The effect of temperature on charging is mainly due to overcharging. When the temperature of the battery increases, the activity of the active substances increases, the positive electrode oxygen potential decreases and the negative oxygen evolution potential decreases (the negative value decreases). Therefore, the charging reaction speed is fast, the charging current is large and the charging voltage required when charging is low.
When the battery is discharged to the terminating voltage, the internal resistance is larger, the electrolyte concentration is very thin, especially in the plate hole and the surface is almost neutral. When the discharge is over discharge, the internal resistance is heated, the volume expands, and the discharge current is large, the heat is obvious (even the heat deformation). At this time, the concentration of lead sulfate is especially large and there is dendrite. The possibility of body short circuit increases, and in addition, the lead sulfate will crystallize into larger particles, that is, the formation of irreversible sulfation, will further increase the internal resistance, the charging recovery ability is very poor, even can not be repaired. The battery should be protected from overdischarge when it is used. It is a very effective measure to adopt "under voltage protection". In addition, because the "undervoltage protection" of the electric vehicle is controlled by the controller, other equipment other than the controller, such as the voltmeter and the indicator light, are directly supplied by the battery. The supply of the power supply is generally not controlled by the controller, and the electric vehicle lock (switch) begins to use electricity. Although the current is small, if there is a long time discharge (1-2 weeks), there will be over discharge. Therefore, it is not allowed to lock for a long time. Over charging has been described in the front. Overcharging will increase the water loss of the battery, accelerate the grid corrosion, and soften the active material, which will increase the probability of the storage battery's deformation.