Why a 1.5 HP non-inverter aircon trips a 3 kW inverter at start-up
A 24 V LiFePO4 battery, a 3 kW pure-sine inverter and a 1.5 HP non-inverter aircon. Switch the aircon on and watch the inverter fault; swap the aircon or the inverter and it runs. The compressor of a 1.5 HP aircon runs at 1300 W, which a 3 kW inverter carries easily. Starting it is the problem: for half a second the locked rotor draws about 9 kVA, three times the inverter’s rating, and the inverter shuts down on overload before the compressor gets going. A bigger inverter only moves the problem to the battery, whose BMS has to pass 400 A for that half second. The real fixes are an inverter aircon (soft start, no surge) or a soft starter on the compressor.
Build it in the labGuided build, test sheet and fault finding, free in your browser.
Parts list
Test procedure
Each test has an expected value and a pass range, like a factory test sheet:
- Switch on: 1.5 HP non-inverter on a 3 kW inverter
- Reset and fit a 1 HP inverter aircon instead
- Back to the 1.5 HP non-inverter, on a 6 kW inverter and a 200 Ah battery
- 6 kW inverter and a 560 Ah bank (two 280 Ah in parallel)
- Battery current with the 1.5 HP running on 24 V
How it works
What it does: A 24 V LiFePO4 battery, a 3 kW pure-sine inverter and a 1.5 HP non-inverter aircon. Switch the aircon on and watch the inverter fault; swap the aircon or the inverter and it runs.
Build it (guided or ready-made), then run its test procedure below. Every test has an expected value and a pass range, just like a factory test sheet.
Background
Bakit nag-o-overload ang inverter sa aircon? Because the start is not the running wattage. Inverter manuals call it surge or peak power; compressor labels call it LRA, locked-rotor amps.