|Sealed Lead Acid Battery Charger / Power Supply Concepts|
When power for the battery is used in parallel with power for the system various problems can develop as the system power is cycled on and off under normal usage patterns. For instance when the system power is off, the battery may overcharge due to excess charge current. Other problems can occur when the system power is cycled on, a dual mode charger may switch into the high charge mode, this could cause the battery to overcharge due to excessive voltage levels continually appearing on it's terminals.
In general, the float charger tends to work better in this scenario, due to the fact that the overcharge replenishment state is not used. In order to counteract the problems associated with excess current when the system power is off, it is possible to use one of two solutions have been used by Jerome Industries in the past.
Solution 1 uses a feedback line from the system power circuitry in order to inform the charger that the system is consuming power. This information is then used to adjust the current limit on the power supply / battery charger between two levels.
Solution 2 requires separate outputs, one for the battery and one for the system power. At the battery system end, then it becomes necessary to automatically hook the two power points together should battery power become necessary. This is normally done with an OR-ing diode. Generally a 1N5822 series schottky diode is used, for it's low forward voltage drop and high efficiency. Although it is conceptually simpler for the system design engineer to contemplate the power supply output as a regulated voltage source, in many instances a smaller and less costly power supply / charger can be designed and manufactured where the power supply output more or less tracks the charger output (in voltage). An example of a 24V system with a 75W power source is available by clicking this link. Jerome Industries power supply engineers can help explain the various intricacies involved when pursuing this option.
Diagrams showing the charger, battery, system power load, and the interactions between them, can be supplied by Engineering, to help clarify the system implementation for these various scenarios.