Path-Q Solar
What battery sizing issue arises when several appliances have high startup currents?
Answer
Several high-startup appliances can create an aggregate surge that exceeds the battery inverter's short-duration output even when their normal running load appears acceptable. The system may need a larger inverter and battery discharge capability, staggered starts, load shedding, or a restricted backup circuit.
Key points
- Startup demand can overlap if compressors, pumps, or motors start at the same time.
- The battery must supply both the inverter's surge requirement and any conversion losses.
- Some equipment has hard-to-predict starting behavior, particularly under unfavorable conditions.
- A load-start sequence can reduce the peak without increasing battery capacity.
What it depends on
- Starting current and duration of each appliance
- Probability of simultaneous starts
- Inverter surge rating and duration
- Battery discharge limit at state of charge and temperature
- Available controls for sequencing or shedding loads
Risks and trade-offs
- A design based only on running watts may fail during startup.
- Oversizing for every theoretical simultaneous start can be expensive.
- Load shedding can preserve backup operation but reduces convenience.
Information you may need
- Appliance motor and compressor specifications
- Measured or manufacturer-provided startup demand
- Inverter surge curve
- Backup priority and acceptable load-shedding rules
Your next step
What to do next
Have the designer model the worst credible overlapping starts and identify whether capacity, sequencing, or load shedding is the most practical solution.
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