Battery Protection in Telecom -48V Rectifier Systems
In telecom power systems using battery backup, the battery size in Ampere-Hours(AH ) is determined by the maximum system load in amperes and the backup time in hours to maintain the system output voltage within acceptable limits during an AC power failure.
Generally, for battery backup requirements exceeding 1.0 hours, multiple battery strings are required. These strings are connected in parallel across the 48V bus and each string should carry it’s equal share of the total system charge and discharge current. During the discharge time the battery supplies the total system load. Each battery string must be rated to supply a current equal to the maximum total system load divided by the number of battery strings. It is good practice to use circuit breaker protection in each string to provide overload protection, and this is also useful in providing a method for manual disconnect for each individual string for maintenance and service. It is recommended to rate the circuit breaker current at a minimum of 25% above the maximum string current as defined above.
During the charge time, after AC power is restored, the battery will be recharged at a current equal to the total rated rectifier current capacity minus the total system load. It is important here to ensure that there is sufficient rectifier capacity beyond the system load to meet the recharge time requirements. In most systems the recharge time requirements are typically substantially longer than the discharge time requirements at maximum system load, and as a result, the battery current during recharge will be lower than the battery current during discharge. Therefore, circuit breaker protection defined for the discharge protection should be satisfactory for the recharge protection.
In telecom power systems using battery backup, the battery size in Ampere-Hours(AH ) is determined by the maximum system load in amperes and the backup time in hours to maintain the system output voltage within acceptable limits during an AC power failure.
Generally, for battery backup requirements exceeding 1.0 hours, multiple battery strings are required. These strings are connected in parallel across the 48V bus and each string should carry it’s equal share of the total system charge and discharge current. During the discharge time the battery supplies the total system load. Each battery string must be rated to supply a current equal to the maximum total system load divided by the number of battery strings. It is good practice to use circuit breaker protection in each string to provide overload protection, and this is also useful in providing a method for manual disconnect for each individual string for maintenance and service. It is recommended to rate the circuit breaker current at a minimum of 25% above the maximum string current as defined above.
During the charge time, after AC power is restored, the battery will be recharged at a current equal to the total rated rectifier current capacity minus the total system load. It is important here to ensure that there is sufficient rectifier capacity beyond the system load to meet the recharge time requirements. In most systems the recharge time requirements are typically substantially longer than the discharge time requirements at maximum system load, and as a result, the battery current during recharge will be lower than the battery current during discharge. Therefore, circuit breaker protection defined for the discharge protection should be satisfactory for the recharge protection.
