Inverter planning guide

Inverter Sizing for LiFePO4 Batteries

An inverter must support simultaneous running loads and brief startup surges without exceeding the battery bank, BMS, wiring, or protection limits. Bigger is not automatically better.

Continuous wattsStartup surgeBattery current

List loads that can run together

Add the running watts of equipment that may operate simultaneously. Do not add every appliance if the operating plan prevents overlap, but document that control. Include inverter self-consumption in long-runtime estimates.

Use manufacturer startup or locked-rotor data for motors and compressors when available. Generic surge multipliers are only rough screening tools.

Load group	Running watts	Possible surge
Fridge + lights + router	350W	900W
Microwave added	1,550W	2,100W
Water pump added	2,150W	3,500W
Planning result	At least 2,150W continuous	Verify 3,500W duration

Translate AC output to battery current

Approximate DC current equals AC watts divided by battery voltage divided by inverter efficiency. A 2,000W load at 90% efficiency draws about 174A from 12.8V, 87A from 25.6V, or 43A from 51.2V.

Use the inverter’s low-voltage operating range and manufacturer current data for final design. Voltage sag, temperature, and cable loss can raise current or trigger shutdown.

Output at 90% efficiency	12.8V	25.6V	51.2V
1,000W	87A	43A	22A
2,000W	174A	87A	43A
3,000W	260A	130A	65A

Check battery and waveform compatibility

The combined battery bank must support inverter continuous current and surge without BMS disconnect. Confirm inverter low-voltage cutoff, charging settings if it is an inverter-charger, and communication requirements for managed batteries.

Pure sine wave output is commonly required for sensitive electronics and motor loads. Also review neutral-ground behavior, transfer switching, branch protection, and whether the intended installation is mobile, marine, off-grid, or grid-connected.

Continuous AC output at expected temperature
Surge watts and permitted duration
Idle and search-mode consumption
DC voltage range and low-voltage cutoff
Battery BMS current and communication
Transfer and grounding architecture
Required product listings and permits

Avoid oversizing without a reason

A much larger inverter can increase idle loss, cable and protection requirements, purchase cost, and the temptation to connect loads the battery bank cannot sustain. Select enough margin for documented loads and realistic growth.

Home backup and service-connected systems require qualified design and approved transfer equipment. Never backfeed a building through a receptacle.

FAQ

Frequently asked questions

What size inverter works with a 100Ah LiFePO4 battery?

Capacity alone is insufficient. Check battery voltage, BMS continuous and peak current, inverter efficiency, load surge, conductors, and protection.

Should inverter watts equal battery watt-hours?

No. Watts measure power; watt-hours measure stored energy. The bank must satisfy both current and runtime requirements.

How much inverter headroom is needed?

Use documented simultaneous loads and surge rather than a universal percentage. Include operating temperature and future loads only when they are credible.

Can a solar inverter power a home during an outage?

Only if the complete system supports islanded operation with compatible controls and storage. Many grid-tied systems shut down during outages.

Editorial sources

Equipment-specific requirements can change. Check the current manual for the exact battery, motor, inverter, and charger you own.