Choosing the correct battery capacity is one of the most critical steps when designing or upgrading a high-capacity UPS system. A common technical question asked by engineers, facility managers, and business owners is how to calculate the AH of battery for an 80 KVA UPS of 100Volts AC output. While the formula may look simple at first glance, several practical factors influence the final battery AH selection.

In this blog, I’ll explain the calculation step by step in a clear, human way—without unnecessary complexity—so you can confidently size the battery bank for your 80 kVA UPS system.

Understanding the Basics: kVA, Volts, Amps, and AH

Before we calculate battery AH, it’s important to understand what each term means:

• kVA (Kilovolt-Ampere): Apparent power rating of the UPS

• Voltage (V): Output voltage of the UPS (100 V AC in this case)

• Current (Amps): Electrical flow required to support the load

• Battery AH (Ampere-Hour): Energy storage capacity of the battery

UPS batteries store DC power, while the UPS output is AC power, so efficiency and conversion losses must always be considered.

Step 1: Convert UPS Capacity from kVA to kW

UPS systems are rated in kVA, but batteries are calculated using real power (kW).

Assuming a typical UPS power factor of 0.8:

80 kVA × 0.8 = 64 kW

This means your UPS delivers 64,000 watts of real power.

Step 2: Calculate Output Current at 100V AC

Now calculate the AC output current:

Current (A) = Power (W) ÷ Voltage (V)

64,000 ÷ 100 = 640 Amps

So, the UPS must supply 640A at 100V AC under full load.

Step 3: Consider Battery Bank DC Voltage

Large UPS systems typically operate on higher DC bus voltages to reduce current and losses. Common battery bank voltages include 240V, 360V, or 480V DC.

Let’s assume a 240V DC battery system, which is common for medium-to-large UPS installations.

Step 4: Account for UPS Efficiency

UPS systems are not 100% efficient. Most industrial UPS units operate at around 90% efficiency.

Required DC Power = 64,000 ÷ 0.9 = 71,111 watts

Step 5: Calculate Battery Current (DC Side)

Battery Current = DC Power ÷ Battery Voltage

71,111 ÷ 240 = ~296 Amps

This is the current drawn from the battery bank during backup.

Step 6: Decide Backup Time

Battery AH depends heavily on how long you want the UPS to run.

Let’s assume a 30-minute (0.5 hour) backup time, which is common for data centers and industrial setups.

Step 7: Calculate Battery AH

Battery AH = Battery Current × Backup Time

296 × 0.5 = 148 AH

Step 8: Add Safety Margin and Battery Aging Factor

Batteries degrade over time, and real-world conditions are never perfect. Adding 20–30% safety margin is recommended.

148 AH + 30% ≈ 192 AH

Final Answer:

For an 80 kVA UPS with 100V AC output, using a 240V DC battery bank and 30 minutes backup, you should select approximately 200Ah batteries.

Other Factors That Affect Battery AH Selection

• Battery Type: Lithium-ion batteries require lower AH than lead-acid

• Ambient Temperature: High temperatures reduce battery life

• Load Variation: Partial loads reduce AH requirement

• Future Expansion: Always plan for load growth

• Battery Configuration: Series and parallel connections affect final AH

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Frequently Asked Questions (FAQ)

Is it better to have 2 100Ah batteries or 1 200Ah battery?
Two 100Ah batteries offer flexibility and reliability; Lento recommends based on space and backup needs.

How long will a 100Ah battery last with a 200W load?
A 100Ah battery runs about 4–5 hours at 200W; Lento efficiency can improve performance.

How many batteries are required for 2KVA UPS?
A 2KVA UPS typically needs two to four batteries, depending on voltage; Lento systems guide accurately.

How long can a 150Ah battery run a load of 200 watts?
A 150Ah battery can power 200W for around 6–7 hours with Lento-grade battery quality.

Is a higher Ah battery better?
Higher Ah batteries give longer backup and stability; Lento suggests optimal Ah, not oversizing.

Conclusion

Understanding how to calculate the AH of a battery for an 80 KVA UPS of 100Volts AC output is essential for building a reliable and efficient backup power system. By considering real power, UPS efficiency, DC battery voltage, and required backup time, you can accurately determine the right battery AH. Always include a safety margin and think long-term—because a well-sized battery bank not only protects your equipment but also ensures uninterrupted operations when power matters most.