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Original Publication Date: 2000-Jun-01
Included in the Prior Art Database: 2003-Jun-20

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A method is provided to recharge a primary set of batteries within a battery backup system with a second set of batteries. This method provides a rapid charge of depleted batteries and offers an immediate battery backup once the primary set of batteries has run out. For some battery backup systems, it is desirable to charge the batteries fast, but the system power limitations will not allow fast charging. As an example, a 12V system with 5 minute battery backup capacity is running steady state with good AC. The batteries are fully charged. An AC outage occurs, causing the system to run on batteries for 4.9 minutes. 0.1 minute of backup is all that is left within the backup source. When the AC returns, the system starts charging the batteries, but because of power constraints (AC line current limitation or DC bus power limitations), a 10 hour charge rate is the maximum allowed. For this system, the discharge rate is 48 times larger than the charge rate. Thus, if a second outage occurs relatively quickly after the first outage, the backup battery has a very small charge which will be quickly dissipated, causing a system crash. The present method provides that after an AC outage, once good AC is once again present, fully charged batteries that are smaller than those used for system backup (i.e., quick charge batteries) are used to quick charge the system backup batteries. These quick charge batteries are connected in parallel to the system batteries with isolation switches. The quick charge batteries are charged with the same battery charger as the system batteries, since the voltages are the same. Using quick charge batteries in parallel with system batteries, 2 minutes of system backup time can be achieved in 2 minutes using the quick charge batteries instead of 96 minutes using the standard 10 hour charging rate. 1