How to select UPS battery capacity

by:Power Kingdom     2021-07-08

  How to select the battery capacity of UPS power supply

   During the operation of UPS power supply, if the utility power is interrupted; the battery must be provided to the inverter within the time expected by the user Sufficient DC energy, so that the battery voltage will not drop below the lowest allowable critical discharge voltage under the condition of rated output load. The actual available capacity of the battery is closely related to factors such as the size of the discharge current, the working environment temperature, and the length of storage time. Only after fully considering the above factors, can the ratio of the available capacity of the battery to the nominal capacity be correctly selected and determined. In the following, the main methods and steps for the selection of UPS power batteries are introduced.

   Determine the battery capacity according to the maximum discharge current

   When the UPS specification model, the load capacity after the mains power failure, and the battery inverter maintenance After the time is determined, the maximum discharge current of the battery discharge time and the selected capacity of the battery can be calculated. Maximum battery discharge current:


   where P is UPS Output rated power (VA);

  COSφ is the load power factor (computer load is about 0.7);

  η : UPS output inverter efficiency (0.85~0.9);

  K: battery discharge efficiency (0.95 can be taken);

  E is the critical discharge voltage of the battery pack.

   is usually the critical voltage value under the specified large discharge rate condition. The critical voltage of a 12V battery is 10V, and the critical voltage of a 2V battery is 1.67V, if the battery backup time is long and the battery is discharged at a small discharge rate, the critical voltage of the 12V battery is 10.5V, and the critical voltage of the 2V battery is 1.75V.

Then according to the backup power supply time of the battery pack determined by the user, the discharge rate of the battery pack can be found from the discharge curve of the selected battery specification provided by the battery manufacturer. The formula can be used:

  discharge rateu003dthe actual maximum discharge current of the battery pack/the nominal capacity of the battery pack

  The battery capacity (AH) that should be configured is obtained.

   For example: For a UPS with an output power of 100KVA, the battery backup time is required to be 20min. If the working voltage of the UPS inverter is 384Vx2 (half-bridge circuit), the battery consists of two groups. 32 12V battery packs are connected in series. If the critical discharge voltage of a single battery is set to 10V, the critical discharge voltage of the two sets of 32 battery packs is 320X2. It is assumed that the load power factor is 0.8, the inverter efficiency is 0.9, and the battery is discharged. The efficiency is 0.95, so the maximum discharge current is:


When the battery backup time is required to be 20min, the discharge rate is about 1.5C, so the battery capacity should be 100AH, here is the calculated value, the specific battery should be close to 100AH u200bu200bin the battery specification provided by the manufacturer.

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How should UPS power be equipped?

   First of all, you must determine how powerful your device is. Generally speaking, the power of an ordinary PC or industrial computer is about 200W, that of a Mac computer is about 300W, and that of a server is about 300W. Between 600W, the power value of other equipment can refer to the manual of the equipment.

  Secondly, it should be understood that there are two ways to express the rated power of UPS: apparent power (unit VA) and actual output power (unit W). Due to the existence of reactive power, This difference is caused. The conversion relationship between the two is: apparent power*power factoru003dactual output power

  The power factor of the backup type and the online interactive type is between 0.5 and 0.7 In between, the online power factor is generally 0.8.

   The actual output power of the UPS should be used as the basis for matching when the equipment is equipped with UPS. Some dealers intentionally or unintentionally confuse the difference between (VA) and (W). Point to draw the user's attention.

  Contact: 18038382979


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