Path-Q Solar
How should I size a battery system and its inverter to handle startup surges from pumps or compressors?
Answer
Size the inverter for the load's continuous power and verified startup surge, and size the battery for the inverter's required power plus the desired runtime. Use measured or manufacturer-provided starting current where possible; a simple running-watt estimate can substantially undersize the system.
Key points
- Identify voltage, phase, running current, starting current, and starting duration for each motor load.
- Check inverter continuous output, surge output, surge duration, and motor-start capability.
- Account for simultaneous starts and other loads already operating.
- Battery power capability, not only its energy capacity, must support the inverter demand.
What it depends on
- Motor type and starting method
- Starting and running measurements
- Inverter surge rating and response characteristics
- Battery discharge limits and temperature conditions
- Whether loads can be sequenced or soft-started
Risks and trade-offs
- Oversizing for an unverified surge increases cost and may still fail if the surge duration is misunderstood.
- Undersizing can cause nuisance shutdowns, motor damage, or loss of essential service.
- Soft starters or load controls may reduce required inverter capacity but add equipment and complexity.
Information you may need
- Nameplate data or field measurements for every motor load
- Required simultaneous loads
- Desired runtime
- Battery and inverter technical specifications
Your next step
What to do next
Obtain motor-start data and request a design or quote that explicitly states continuous power, surge power, surge duration, and battery discharge limits.
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SQ00367