Supplementary power, normal discharge technology of lead-acid battery and the harm of overcharge and discharge to the battery
2022 Jun 14 By admin 0 comment
  1. Lead-acid battery supplementary technology

1.1 Requirements for chargers for lead-acid battery supplementary power
The charged new battery should be replenished in time after being stored for half a year or before the initial use, and after the battery in use is discharged.
A special charger should be used for supplementary power, which should meet the following requirements.
(1) The charger should have constant voltage control function. The charger output constant voltage distributed to each single battery should be 2.5V or comply with the manufacturer’s regulations.
(2) The charger should have high current output capability. Because the current of the battery in the initial stage of charging can reach more than 6 times the conventional charging current.
(3) The special charger should also have the control function of managing the battery load. When the voltage of each cell of the battery drops to 1.8V, the charger should be able to automatically cut off the electrical load of the battery.
(4) The battery replenishment should be carried out in the range of ambient temperature of 5℃-35℃. The charging time should be prolonged when the temperature is below s°C, and overcharging is likely to occur when the temperature exceeds 35°C. Therefore, the charger should also have a temperature detection control function.

1.2 Two ways to supplement the lead battery
(1) When the battery is used as a backup power supply, float charging (trickle charging) should be used for supplementary power. Because of this type of battery, most of them are idle for backup in normal times, but they are only used as emergency power supply to supply power to the circuit when the mains is out of power. However, when the mains power returns to normal, it should immediately automatically switch to the state of supplementing power with a small current. The charging voltage should ensure that the single battery is 2.1V-22V, or supplementary power according to the current specified by the manufacturer. The initial charging current is generally below 3C10.

(2) When the battery is used for charging and discharging cycles, it should stop discharging when it discharges at most half of the rated capacity, and replenish it in time. The charging voltage is generally 2.4V-2.5V (or as specified by the manufacturer), and the initial charging current is generally below 3C10. In order to prevent overcharging, it is best to install an automatic controller, so that it can automatically switch to the floating charging mode for replenishment at the end of the charging period. When the battery is charged to the voltage and the electrolyte density is stable for 3 hours, it can be considered to be fully charged. (Go to the website to learn more about battery charging)

  1. Lead-acid battery normal discharge technology

2.1 Characteristics of normal discharge of lead-acid batteries
During the continuous discharge of the battery to the electrical load, the sulfuric acid in the electrolyte will “run” to the electrode plate and chemically react with lead dioxide or linear lead to form lead sulfate, which will reduce the sulfuric acid in the electrolyte and increase the water content. As a result, the internal resistance of the battery increases and the voltage decreases.

Detect lead-acid battery capacity by discharge tester
Detect lead-acid battery capacity by discharge tester

As the discharge progresses, sulfuric acid molecules continuously penetrate into the micropores of the electrode plate to form lead sulfate, and the density of the electrolyte decreases due to the consumption of sulfuric acid. In the middle stage of discharge, the micropores of the electrode plate are gradually blocked by the generated lead sulfate, and the sulfuric acid supplied to the electrode plate and the sulfuric acid consumed in the liquid tend to balance. At this time, the density of the electrolyte decreases slowly, and the battery voltage also decreases slowly. At the end of the discharge period, most of the active substances on the electrode plate have become lead sulfate, which blocks the pores of the electrode plate, so that sulfuric acid cannot continue to penetrate into the electrode plate, resulting in an increase in the internal resistance of the battery and a rapid drop in voltage. These are not only the obvious characteristics of battery discharge, but also the normal discharge process of the battery.

When the battery is in use, it can not only discharge power to the electrical appliance, but also periodically discharge artificially when needed. In this way, the active substances inside the battery can be fully activated and the service life of the battery can be prolonged.

2.2 Lead-acid battery normal discharge technology
Regular discharge of lead-acid batteries generally uses C10 current for full-capacity discharge. When the battery is regularly discharged, the termination voltage of its single cell should be maintained at 1.8v, and cannot be lower. When the single cell is discharged to 1.8V, the electrolyte density correspondingly drops to about 1.16g/cm³. This is the standard for the normal discharge termination of the battery.

  1. Harm of overcharge and overdischarge to battery

3.1 Harm of overcharge to battery
If the battery continues to be charged with current after the battery is fully charged, it is called overcharge.
The charging current passed in during overcharging is only consumed in the electrolytic water. That is, the water is decomposed, and a large amount of hydrogen and oxygen gas will be produced at this time, which will make strong bubbles in the electrolyte, and the bubbles will invade the inner layer of the active material of the plate, promote the oxidation of the lead plate, and even wash the active material off. cause the plate to warp. It can be seen that if the battery is overcharged, it will damage the battery and shorten its service life. Therefore, overcharging should be prevented when the battery is normally charged.

3.2 Harm of overdischarge to battery
When the battery is discharged, the active material on the positive and negative plates gradually becomes lead sulfate. When the normal discharge reaches the termination voltage, the discharge is stopped immediately. At this time, the lead sulfate generated on the electrode plate is active, and it is easy to be reduced to lead dioxide of the positive plate and velvety lead of the negative plate during charging. However, when the battery discharges to the discharge termination voltage and continues to discharge, the plate will undergo destructive deterioration.

On the one hand, sulfuric acid will penetrate into the depths of the micro-pores of the electrode plate, so that the electrode plate will generate lead sulfate in an all-round way, weakening the activity of the active material, which directly leads to an increase in the internal resistance of the battery and a decrease in the capacity. activity is more difficult.

On the other hand, excess discharge will not only weaken the activity of lead sulfate on the electrode plate, but more seriously, the lead sulfate generated on the electrode plate will undergo a qualitative change and become a solid crystalline sulfate. Ordinary lead sulfate is easy to dissolve and electrolytic reduction, while solid sulfate crystals are difficult to dissolve in water under normal conditions, and difficult to be electrolyzed. After the sulfate is attached to the plate, the battery can neither be charged nor discharged under normal conditions, and can only be scrapped.
It can be seen that the over-discharge of the battery is extremely harmful.