Estimate inverter battery draw, conversion losses, runtime, surge current, cable voltage drop, and practical sizing values for common DC power systems.
Calculated Results
12 V system
AC load
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DC input power
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DC current draw
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Conversion loss
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Surge current
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Estimated runtime
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Cable voltage drop
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Suggested fuse reference
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Selected-mode answer
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Calculator Inputs
Used when load is entered in VA.
Used for efficiency or AC-output modes.
Reference measurement for comparison.
Battery Bank and Runtime
Cable and Protection Estimate
Protection and conductor sizing must follow local electrical codes, equipment manuals, insulation ratings, temperature limits, and installation conditions.
Step-by-Step Working
Enter values, then select Calculate.
Formula Used
AC watts = VA × power factor
DC input power = AC load ÷ inverter efficiency + idle power
DC current = DC input power ÷ DC voltage
Conversion loss = DC input power − AC load
Battery energy = bank voltage × bank Ah × usable DoD × battery efficiency
Runtime = usable battery Wh ÷ DC input power
Cable drop = current × (2 × length × ρ ÷ area), using ρ ≈ 0.0175 Ω·mm²/m for copper
12 V, 24 V, 36 V, and 48 V Comparison
System Voltage
DC Input Power
Estimated Current
Surge Current
Approx. 2 m Drop at 25 mm²
Example Data
AC Load
DC Voltage
Efficiency
Approx. DC Current
300 W
12 V
90%
27.8 A
600 W
24 V
92%
27.2 A
1000 W
48 V
94%
22.2 A
1500 W
12 V
90%
138.9 A
Understanding Inverter Power Draw
An inverter converts direct current from batteries into alternating current for appliances. This conversion always introduces losses, so battery power exceeds delivered AC power. The calculator starts with your appliance load and inverter efficiency. It then estimates required DC input power and battery current. Lower battery voltage produces higher current for the same load. Higher current increases cable losses, heating, and conductor requirements.
Why Efficiency Matters
Inverter efficiency changes with load, temperature, design, and battery voltage. A nominal ninety percent efficiency means roughly ten percent becomes conversion loss. Standby consumption also matters during lighter loads or long operating periods. Entering realistic efficiency and idle power values improves the estimate. Manufacturer test data is preferable when available for your specific model.
Battery Runtime and Surge Loads
Battery runtime depends on bank voltage, amp-hour capacity, usable discharge, and battery efficiency. Series connections increase bank voltage while preserving amp-hour capacity. Parallel strings increase available amp-hours while preserving voltage. Real runtime can differ because battery capacity falls under heavy current. Temperature, battery chemistry, age, and discharge rate also change performance. Motors and compressors may require much higher startup power than steady running power.
Cable Drop and Practical Sizing
DC cables can carry substantial current, especially in twelve-volt systems. Voltage drop reduces inverter input voltage and wastes useful battery energy. The cable estimate uses copper resistance, total circuit length, and conductor area. It provides an engineering reference rather than a wiring prescription. Always confirm cable ampacity, fuse requirements, terminals, and installation rules. Manufacturer instructions and local electrical codes should control final hardware selection. Check terminal ratings before carrying sustained high DC current. Shorter cable runs usually reduce resistance and unwanted heating. Battery monitoring also helps verify assumptions during actual operation. Accurate inputs produce safer, more realistic planning estimates overall.
How to Use This Calculator
Enter the AC appliance load and choose watts, kilowatts, or VA.
Set DC voltage, inverter efficiency, idle draw, and surge multiplier.
Add inverter continuous and surge ratings for overload checks.
Enter battery-bank details to estimate usable energy and runtime.
Add cable length and conductor area for a voltage-drop estimate.
Select a solve mode, calculate, then review warnings and steps.
Export your results using CSV or PDF buttons.
Frequently Asked Questions
For equal power, current rises as voltage falls. That is why high-power 12 V systems can require very large battery currents.
Use the manufacturer efficiency near your expected load. If unavailable, a conservative estimate such as 85% to 92% can be useful for planning.
VA is apparent power. Watts are real power. For many AC loads, watts equal VA multiplied by power factor.
Heavy current, temperature, battery age, chemistry, inverter shutdown voltage, and battery resistance can all reduce usable runtime.
Surge power is the brief higher demand that some loads need when starting. Motors, compressors, transformers, and pumps commonly produce startup surges.
No. It is only a current reference. Use inverter documentation and applicable electrical codes for final fuse, breaker, and conductor sizing.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.