Home Battery Size Calculator For Inverter

Battery Capacity Formula:

\[ \text{Battery Capacity (Ah)} = \frac{\text{Load Power (W)} \times \text{Required Backup Time (h)}}{\text{Battery Voltage (V)} \times \text{Depth of Discharge} \times \text{Efficiency}} \]

Load Power:

watts

Required Backup Time:

hours

Battery Voltage:

volts

Depth of Discharge:

decimal (0-1)

Efficiency:

decimal (0-1)

Required Battery Capacity:

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1. What is the Battery Capacity Formula?

The battery capacity formula calculates the required ampere-hour (Ah) rating for a battery bank to power your loads for a specified duration, considering the battery voltage, depth of discharge, and system efficiency.

2. How Does the Calculator Work?

The calculator uses the battery capacity equation:

\[ \text{Battery Capacity (Ah)} = \frac{\text{Load Power (W)} \times \text{Required Backup Time (h)}}{\text{Battery Voltage (V)} \times \text{Depth of Discharge} \times \text{Efficiency}} \]

Where:

Load Power — Total wattage of all devices to be powered
Backup Time — Desired runtime in hours
Battery Voltage — System voltage (typically 12V, 24V, or 48V)
Depth of Discharge — Fraction of battery capacity that can be safely used (typically 0.5 for lead-acid)
Efficiency — System efficiency factor (typically 0.8-0.95)

Explanation: The equation accounts for total energy requirement divided by usable battery capacity considering system losses.

3. Importance of Proper Battery Sizing

Details: Correct battery sizing ensures your inverter system can power essential loads for the required duration without over-discharging batteries, which can significantly reduce battery life.

4. Using the Calculator

Tips:

Sum the wattage of all devices you need to power simultaneously
For lead-acid batteries, use DoD of 0.5 (50%) for longest life
Typical system efficiency is 90% (0.9) for inverter systems
Common battery voltages are 12V, 24V, or 48V

5. Frequently Asked Questions (FAQ)

Q1: What's a typical DoD for different battery types?
A: Lead-acid: 50%, Lithium-ion: 80-90%, AGM: 50-70%. Check manufacturer specifications.

Q2: How do I calculate total load power?
A: Sum the wattage of all devices you'll run simultaneously. Check device labels or manuals for power ratings.

Q3: What if my devices list amps instead of watts?
A: Convert amps to watts by multiplying by voltage (Watts = Amps × Volts).

Q4: Should I add a safety margin?
A: Yes, consider adding 20-30% to the calculated capacity to account for aging and unexpected loads.

Q5: How does temperature affect battery capacity?
A: Cold temperatures reduce available capacity. Below freezing, capacity can drop 20-50% for lead-acid batteries.