In a colder environment, the electrolyte of a lead-acid battery may freeze, and the freezing temperature is the number of minutes of the battery’s state of charge. When the battery is fully discharged, the electrolyte freezes at a few degrees below zero, and when the battery is fully charged, the electrolyte can withstand a low temperature of minus 50°C. In cold weather, the battery is usually placed in a battery box and buried in the ground to maintain a constant temperature. Nickel-cadmium batteries will not be damaged in cold weather. Any battery needs regular maintenance. Even a sealed “maintenance-free” battery should be checked regularly for firmness, cleanliness and no damage. For the electrolyte battery, the electrolyte should always be completely immersed in the electrode plate, and the voltage and the calibrated weight also need to meet the requirements.
(1) Failure of the battery
The faults of the battery can be divided into external faults and internal faults. External faults include: shell cracks, pole corrosion, pole looseness, and dry cracking of sealant. Internal faults include: electrode plate vulcanization, active material shedding, electrode plate grid frame corrosion, electrode plate short circuit, self-discharge, electrode plate arching, etc.
Fault 1: The plate is vulcanized. It is the phenomenon that a layer of white coarse-grained PbSO4 is formed on the electrode plate, which cannot be converted into PbO2 and Pb during normal charging. When the vulcanized battery is discharged, the voltage drops sharply, drops to the termination voltage prematurely, and the battery capacity decreases. The reasons may be: ① The battery is under-charged for a long time or is not charged in time after discharge, causing a part of the PbSO4 on the electrode plate to dissolve in the electrolyte. The higher the ambient temperature, the greater the solubility. When the ambient temperature decreases, the solubility decreases, and the dissolved PbSO4 will re-precipitate and crystallize again on the plate to form sulfide. ②Long-term excessive discharge or low-current deep discharge will generate PbSO4 in the pores of the active material deep in the plate. ③The initial charging of the new battery is not complete, and the active material has not been fully reduced. ④ The electrolyte density is too high, the composition is impure, and the outside temperature changes drastically.
Fault two: self-discharge. It refers to the phenomenon that the battery automatically disappears when there is no load. As the battery life increases and the battery temperature increases, the self-discharge rate will increase. For new batteries, the self-discharge rate is usually less than 5% of the capacity, but for old, poor-quality batteries, the self-discharge rate can be increased to 10%~15% per month. If the capacity of a fully charged battery decreases by more than 2% per day and night within 30 days, it is called faulty self-discharge. The reasons may be: ① The electrolyte is impure, and a potential difference is formed between the impurity and the electrode plate and between the different impurities deposited on the electrode plate, and partial discharge is generated through the electrolyte. ②Sulfuric acid sinks when the battery is stored for a long time, causing a potential difference between the plate and the lower part to cause self-discharge. ③The electrolyte overflow from the battery accumulates on the surface of the battery cover, so that the positive and negative poles form a passage. ④The active material of the electrode plate falls off, and the lower part of the deposit is too much to short-circuit the electrode plate.
(2) How to use and maintain batteries
The correct use and maintenance of the battery mainly include the following points: ① Check whether the battery is installed securely and whether the shell will be damaged due to external factors; observe whether there is any electrolyte leakage on the surface of the battery shell. In addition, do not put metal objects on the battery to prevent short circuit. ②Always check whether the pole and the terminal are connected reliably. ③The capacity must be well designed. When two batteries are used in series, the capacity of the batteries should be equal and not over-discharged, otherwise the service life of the batteries will be affected. ④Pay attention to the operating temperature. The capacity of the battery refers to the value of 25°C, and it is generally ideal to use it at 20~30°C.
The service life of a lead-acid battery has a lot to do with whether it is overcharged or overdischarged. As long as the battery is not charged or discharged during the working process of the solar photovoltaic power system, the service life can be extended. The independent solar battery system generally charges the battery to the battery during the day and discharges the battery at night, which requires a controller. When sunlight is irradiated, the DC current generated by the solar cell assembly charges the battery. When it reaches a certain level, the overcharge voltage detection and comparison control circuit and the overdischarge voltage detection and comparison control circuit simultaneously detect and compare the battery terminal voltage. The battery is gradually being fully charged, and when its terminal voltage is greater than the pre-set overcharge voltage value, it is instructed to stop charging. When the battery discharges to the load, the terminal voltage will gradually decrease. When the terminal voltage drops to less than the preset over-discharge voltage value, the load circuit will be automatically cut off to prevent the battery from continuing to discharge and the battery will start charging again.
Most batteries have acidic or corrosive substances, which can be dangerous or even life-threatening if handled improperly. The electrical components of the system cannot be installed near the battery. The acid gas of the lead-acid battery will corrode and damage the electronic components. Any battery is dangerous to humans, especially children, as well as animals, so it should be operated by experienced people, and at the same time, keep the output terminal covered. Because a typical photovoltaic system can produce a large current when the output terminal is short-circuited, although this current only lasts a few milliseconds, the higher the voltage, the greater the damage. Under 12V voltage, if the battery is accidentally short-circuited, the large current can cause a fire.