Lead-acid batteries are charged by:
- Constant current method, and
- Constant voltage method.
In the constant current method, a fixed value of current in amperes is passed through the battery till it is fully charged.
In the constant voltage charging method, charging voltage is kept constant throughout the charging process. The charging current is high in the beginning when a battery is in a discharged condition, and it gradually drops off as the battery picks up charge. While charging a lead-acid battery, the following points may be kept in mind:
- The source, by which battery is to be charged must be a DC source.
- The positive terminal of the battery charger is connected to the positive terminal of battery and negative to negative.
- The charging current should be set at proper value preferably at the value recommended by the manufacturer. If it is not known then the charging rate should be such that full charge can be obtained in 8 hours. Thus an 80 AH battery should be charged at the rate of 80/8= 10 A. This will ensure the maximum life of the battery. If the charging current is too high, it may be harmful to the battery.
- The temperature of batteries should be watched carefully during charging and not allowed to exceed 43oC – 45o The charging current should be reduced if the temperature exceeds this limit. A high temperature is harmful to separaters and active material of plates.
Charge Indications While Lead Acid Battery Charging
While lead acid battery charging, it is essential that the battery is taken out from charging circuit, as soon as it is fully charged. The following are the indications which show whether the given lead-acid battery is fully charged or not.
- Voltage : During charging, the terminal voltage of a lead-acid cell When the terminal voltage of lead-acid battery rises to 2.5 V per cell, the battery is considered to be fully charged.
- Specific gravity of Electrolyte: When the cell is fully charged, specific gravity of electrolyte rises to 1.28 which can be measured with the help of a hydrometer.
- Gassing: When the cell is fully charged, the charging current starts electrolysis of water. The result is that hydrogen and oxygen gases are liberated at the cathode and anode respectively. This liberation of gasses at both the plates is known as gassing. The bubbles thus formed indicate that the cell is fully charged.
Lead Acid Battery Safety Precautions
- If the level of electrolyte decreases, add distilled water. Addition of electrolyte will be necessary only if some of the electrolyte leaks or spils out. The level of the electrolyte should always be above the plates by at least one-half inch.
- Do not over charge a battery.
- Do not deep discharge a battery.
- The gases, hydrogen and oxygen, issuing from a battery under charge can explode if a spark or flame is brought too near.
- The batteries should be charged in a well-ventilated place so that gases and acid fumes are blown away.
- The lead-acid battery should never be left idle for a long time in discharged condition because the lead sulfate coating on both the positive and negative plates will form into hard crystals that will be difficult to break up on recharging. Although it can be left idle for some time in charged condition.
- If acid falls on a piece of cloth, it should be washed with water first and then with liquid ammonia.
Thanks for reading about lead acid battery charging.