Determining the Number of Batteries for a 10kVA Inverter

When considering the number of batteries required for a 10kVA inverter, it is essential to understand that the answer depends on the load you intend to power. This article will guide you through the process of calculating the appropriate battery configuration. Whether you are using lithium iron phosphate (LFP) or lead-acid batteries, the detailed steps and calculations will be provided to help you determine the correct battery bank size.

Understanding the Inverter's Requirements

Firstly, it is important to clarify the voltage and current requirements of your 10kVA inverter. A 10kVA inverter is capable of supplying a wide range of voltages and corresponding currents:

10kVA at 10000 volts 1 ampere per hour 10kVA at 12 volts 833 amperes per hour 10kVA at 120 volts 83.3 amperes per hour 10kVA at 240 volts 41.67 amperes per hour

This variability in voltage and current means that you need to specify the voltage you require before calculating the necessary battery size. Once the voltage is specified, the current can be calculated, and the battery bank size can be determined.

Calculating Battery Bank Size for LFP Batteries

For a LFP battery, it is crucial to refer to the Battery Management System (BMS) documentation. For instance, if the BMS reads a maximum of 40 amps at 12 volts, this amounts to 480 watts. At 48 volts, four LFP batteries of the same capacity would provide 1920 watts. Therefore, the minimum size LFP battery bank needed for optimal use is determined by the documentation for the minimum battery size.

Lead Acid Battery Calculation

For a lead-acid battery bank, the calculation differs. At 12 volts, 10kVA corresponds to 833 amperes, and at 48 volts, it corresponds to 208 amperes. Lead-acid batteries should not be discharged faster than 1C, which conveniently matches the ampere-hours (AH) rating of the battery. Therefore, for a 12-volt system, you need a minimum battery bank of 833 AH, and for a 48-volt system, you need a minimum battery bank of 208 AH.

For example, four discrete 200AH lead acid batteries in series would provide the necessary 833 AH for a 12-volt system. The calculations for a 48-volt system would similarly involve four 200AH batteries in series to achieve a 208 AH minimum bank.

Back Up Time Duration

The back-up time duration is vital in determining the battery capacity. You need to calculate the minimum battery size based on how long you require power to last. For instance, if you require the inverter to last for 20 minutes at full load (10kVA), the battery size can be calculated as follows:

In a 12-volt system, the minimum battery bank of 833 AH will provide about 20 minutes of power at full load. Similarly, in a 48-volt system, the minimum battery bank of 208 AH will also provide approximately 20 minutes of operational time.

Matching DC Input Voltage

Lastly, ensure that the battery bank's DC input voltage matches the inverter's DC input voltage. If your inverter requires a 48V DC input, you can either use a 48V LFP battery directly or create a equivalent 48V system using 4 12V lead acid batteries in series.

By following these steps, you can accurately determine the number of batteries needed for your 10kVA inverter, ensuring reliable and efficient power backup.