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Method for Calculating the Discharge Time of a UPS Uninterruptible Power Supply
Release time:
2019-02-20
a. Basic Formula: Active power of the load × Support time = Battery discharge capacity × Battery voltage × UPS inverter efficiency. Where: Active power of the load = Total load power × Load power factor; UPS inverter efficiency ≈ 0.9; Battery discharge capacity = Nominal battery capacity × Battery discharge efficiency. Battery discharge efficiency depends on the discharge current or discharge duration and can be determined by referring to the table below: b. Calculation Formula: Active power of the load × Support time = Battery discharge capacity × Battery voltage × UPS inverter efficiency. c. Example Calculation: Example: Total load power is 3000 VA, load power factor is 0.7, UPS battery voltage is 96 V, and the required support time is 1 hour. Determine the appropriate battery capacity to be selected. Calculation: 3000 (VA) × 0.7 × 1 (h) = Battery discharge capacity × 96 × 0.9 Battery discharge capacity = UPS (VA) × 0.7 × 1 (h) / Battery voltage × 0.9 Nominal battery capacity = Battery discharge capacity / Discharge efficiency. Result: Battery discharge capacity = 24.3 (Ah); Nominal battery capacity = 24.3 / 0.6 = 40.5 (Ah). Conclusion: A 38 Ah battery (8 units of 12 V/38 Ah batteries) can be selected. The battery discharge within the UPS should be a constant-power discharge, meaning the load power remains unchanged regardless of whether the mains power is normal or not. Battery discharge current = (Load apparent power × Load power factor) / (Inverter efficiency × Total battery pack voltage). Any change in the load characteristics will result in a change in the discharge current. It is important to note that the UPS does not have a concept of constant-current discharge. However, when determining the battery configuration, some battery manufacturers provide battery parameters only for constant-current discharge (because the definition of battery capacity is based on constant-current discharge). In such cases, the constant-current discharge parameters may need to be used. Total load power × Load power factor × Support time = Nominal battery capacity × Discharge efficiency × Battery voltage × UPS inverter efficiency. Support time = (Nominal battery capacity × Discharge efficiency × Battery voltage × UPS inverter efficiency) / (Total load power × Load power factor). Nominal battery capacity = (Total load power × Load power factor × Support time) / (Discharge efficiency × Battery voltage × UPS inverter efficiency). Support time = (Ah × Discharge efficiency × Battery voltage × 0.9) / (KVA × 0.7). Nominal battery capacity = (KVA × 0.7 × Support time) / (Discharge efficiency × Battery voltage × 0.9).
a. Basic formula:
Active power of the load × support time = Battery discharge capacity × Battery voltage × UPS inverter efficiency
Among them: Active power of the load = Total load power × Power factor of the load.
UPS inverter efficiency ≈ 0.9
Battery discharge capacity = Nominal battery capacity × Battery discharge efficiency
The battery discharge efficiency is related to the discharge current or discharge time and can be determined by referring to the table below:
b. Calculation formula:
Active power of the load × support time = Battery discharge capacity × Battery voltage × UPS inverter efficiency.
c. Calculation example:
Example: The total load power is 3000 VA, the load power factor is 0.7, and the UPS battery voltage is 96 V. The required backup time is 1 hour. Determine the battery capacity that should be selected.
Calculate:
3000 (VA) × 0.7 × 1 (h) = Battery discharge capacity × 96 × 0.9
Battery discharge capacity = UPS (VA) × 0.7 × 1 (h) / Battery voltage × 0.9
Nominal battery capacity = Discharge capacity / Discharge efficiency
Result: Battery discharge capacity = 24.3 (Ah)
Nominal battery capacity = 24.3 / 0.6 = 40.5 (Ah)
Result: A 38 Ah battery can be selected (8 units of 12V/38 Ah batteries).
The battery discharge within the UPS should be a constant-power discharge, meaning the load power remains unchanged regardless of whether the utility power is normal or not.
The discharge current of the battery is calculated as follows: (Apparent power of the load × Power factor of the load) / (Inverter efficiency × Total voltage of the battery pack). Any change in the characteristics of the load will result in a corresponding change in the discharge current.
UPS certainly doesn't have a concept of constant-current discharge. It's just that when specifying battery configurations, some battery manufacturers provide battery parameters only for constant-current discharge (because the capacity definition of a battery is based on constant-current discharge). In such cases, the parameters for constant-current discharge might be used.
Total load power × Load power factor × Support time = Nominal battery capacity × Discharge efficiency × Battery voltage × UPS inverter efficiency
Support time = (Nominal battery capacity × Discharge efficiency × Battery voltage × UPS inverter efficiency) / (Total load power × Load power factor)
Nominal battery capacity = (Total load power × Load power factor × Support time) / (Discharge efficiency × Battery voltage × UPS inverter efficiency)
Support time = (AH × Discharge efficiency × Battery voltage × 0.9) / (KVA × 0.7)
Nominal battery capacity = (KVA × 0.7 × Support time) / (Discharge efficiency × Battery voltage × 0.9)
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