Design a Secret Charger to Maximize the Life of Sealed Lead Acid Battery
Each of the following chargers has its advantages and disadvantages, but using a simple charger design may not be cost effective in the long term. Checking battery condition and replacing batteries with lost capacity is very costly and environmentally unfriendly. So designing a charger to maximize the life of the Sealed Lead Acid battery is very important.
Constant Voltage Charging
This method is the most commonly used for SLA batteries as the individual cells tend to share the voltage and equalize the charge between them. It is important to limit the initial charging current to prevent damage to the battery. However, with a single fixed voltage, it is impossible to properly balance the requirements of a fast charge cycle against the danger of overcharge.
Constant Current Charging
This method can be used for a single 2V cell but is not recommended for charging a number of series connected cells, a battery, at the same time. This is because some cells will reach full charge before others and it is very difficult to determine when the battery has reached a fully charged state. If the charge is continued at the same rate, for any extended period of time, severe overcharge may occur to some cells, resulting in damage to the battery.
Taper Current Charging
This method is not really recommended for charging SLA batteries as it can often shorten battery service life due to poor control of the final fully charged voltage. However, because of the simplicity of the circuit and subsequent low cost, taper current charging is often used to charge a number of series connected batteries that are subject to cyclic use. When using this method it is recommended that the charging time is either limited or that a charging cut-off circuit is incorporated to prevent overcharge.
Two Stage Constant Voltages Charging
This method is a recommended for charging SLA batteries in a short period of time and then maintaining them in a fully charged float (or standby) condition.
Another important factor that has to be considered when charging a sealed lead acid battery is temperature. As the temperature rises, electrochemical activity in a battery increases, so the charging voltage should be reduced to prevent overcharge. Conversely as temperature falls, the change voltage should be increased to avoid undercharge.
Using a combination of the constant current charging and two stage constant voltage charging techniques and also by monitoring the battery terminal voltage and temperature a multi-stage charge profile can be implemented to reduce stress on the battery while giving the shortest possible charge time.
Source: www.leoch.com
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