| This information was obtained from the Panasonic Sealed Lead Acid Batteries Technical Handbook, 1998-1999
It applies to most sealed lead acid batteries. |
For charging the sealed lead-acid battery, a well-matched charger should be used because the capacity or life of the battery is influenced by ambient temperature, charge voltage and other parameters.
Charging methods are dependent on battery applications, and the applications are roughly classified into main power application and stand-by/back-up power applications.
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(1) Main Power (cycle use)
Cycle use is to use the battery by repeated charging and discharging in turn.
(a) Standard charging (Normal charging)
For common applications of the battery, the constant voltage charge method is advantageous as it allows the battery to exert full performance.
Constant voltage charging method
This method is to charge the battery by applying a constant voltage between the terminals. When the battery is charged by applying a voltage of 2.45 V per cell (unit battery) at a room temperature of 68°F to 77°F (20°C to 25°C), charging is complete when the charge current continues to be stable for three hours. Sealed lead-acid batteries can be over-charged without constant voltage control. When the battery is overcharged, the water in the electrolyte is decomposed by electrolysis to generate more oxygen gas than what can be absorbed by the negative electrode. The electrolyte is changed to oxygen gas and hydrogen gas, and lost from the battery system. As the quantity of electrolyte is reduced, the chemical reactions of charge and discharge become inefficient and hence the battery performance is severely deteriorated. Therefore, exact voltage control and proper charging time in constant voltage charging are essential for securing the expected life of the battery.
Constant-voltage and constant-current charging method
This method is to charge the battery by controlling the current at 0.4 CA and controlling the voltage at 2.45 V / per cell (unit battery) at a room temperature of 68°F to 77°F (20°C to 25°C). Proper charging time is 6 to 12 hours depending on discharge rate.
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(b) Rapid Charging
When rapidly charging the battery, a large charge current is required in a short time for replenishing the energy which has been discharged. Therefore, some
adequate measures such as the Control of charge current is required to prevent overcharging when the rapid charging is complete. Basic requirements for rapid charging are as follows:
Sufficient charging should be made in a short time for fully replenishing the amount discharged.
Charge current should be automatically controlled to avoid overcharge even on prolonged charging.
The battery should be charged adequately in the ambient temperature range of 32°F(0°C) to 104°F (40°C).
Reasonable cycle life of charge/discharge should be secured.
Typical methods to control charging so as to satisfy the above requirements follow.
Two-step constant voltage charge control method
Two-step constant voltage charge control uses two constant-voltage devices. At the initial stage, the battery is charged by the first constant-voltage device SW(1) of high setup voltage (set-up for cycle charge voltage). When the charge current, the value of which is detected by the
current-detection circuit, has reduced to the preset value, the device is switched over to the second SW(2) of low set-up voltage (setup for trickle charge voltage). This method has the advantage that the battery in trickle use can be charged in a comparatively short time for the next discharge.
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Precautions on charging
Charging Index
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