MAINTENANCEDOE-HDBK-1084-95Lead-Acid Storage BatteriesBatteriesPage 30Rev. 0 same. The most important aspect of charging is matching the charger to the batteryapplication. When choosing a charger, it is necessary to consider the type of battery, theway in which the battery will be discharged, the time available for charge, the temperatureextremes the battery will experience, and the number of cells in the battery (outputvoltage). It is important to consult the battery manufacturer at the time of purchase todetermine the appropriate charging method.In general, lead-acid batteries may be recharged at any rate that does not produceexcessive gassing, overcharge, or high temperatures. Discharged batteries may berecharged at a high current initially. However, once the battery approaches its fullcharge the current must be decreased to reduce gassing and excessive overcharging.A wide variety of schemes exist for charging lead-acid batteries. Although a completediscussion of various charging techniques is beyond the scope of this Primer, a generaldescription of the more common methods follows.Constant-VoltageChargingConstant-voltage (often called constant-potential) chargers maintain nearly thesame voltage input to the battery throughout the charging process, regardless of thebattery's state of charge. Constant-voltage chargers provide a high initial current tothe battery because of the greater potential difference between the battery andcharger. A constant-voltage charger may return as much as 70% of the previousdischarge in the first 30 minutes. This proves useful in many battery applicationsinvolving multiple discharge scenarios. As the battery charges its voltage increasesquickly. This reduces the potential that has been driving the current, with acorresponding rapid decrease in charge current as depicted in Figure 16. As aresult, even though the battery reaches partial charge quickly, obtaining a fullcharge requires prolonged charging. Given this behavior, constant-voltage chargers are frequently found in applicationsthat normally allow extended charging periods to attain full charge. Constant-voltage chargers should not be used where there is frequent cycling of thebattery. Repeated discharges without returning the cell to its full charge willeventually decrease the battery capacity and may damage individual cells.Constant-voltage chargers are most often used in two very different modes: as afast charger to restore a high percentage of charge in a short time or as a float
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