Home / Guides / Start-Up Surge — Why Your Inverter Trips the Moment a Motor Starts
Motors draw far more current at start-up than while running: a refrigerator or water pump spikes to about 3x its running watts and an air conditioner to about 3.5x, for a second or two. Your inverter must survive the total continuous load plus the single largest start-up surge. A 156W steady load with one 150W fridge on it peaks near 756W, which a 300VA inverter cannot hold even though the average load looks tiny.
A motor at rest has almost no back-EMF, so at the instant it starts it draws several times its running current. That spike lasts a second or two, and it is what makes an inverter beep and cut out on a load that looks perfectly safe on paper.
| Appliance type | Start-up multiplier | Example: running watts to peak |
|---|---|---|
| Air conditioner / compressor | 3.5x | 1000W to 3500W |
| Refrigerator / freezer / water pump | 3.0x | 150W to 450W |
| Washing machine | 3.5x | 500W to 1750W |
| Mixer grinder / power tool / motor | 3.0x | 500W to 1500W |
| Microwave / air cooler | 2.0x | 180W to 360W |
| Ceiling fan / tube light | 1.5x | 70W to 105W |
| TV, computer, LED lighting | 1.1-1.2x | 60W to 72W |
Peak demand = total continuous load + the largest single start-up surge. Only one motor realistically starts at a time, so you add the worst offender's spike to everything already running — not every surge at once.
Worked example: a fridge, two fans and four bulbs draw 326W continuous. The fridge spikes to 450W, so peak demand is 776W — comfortably more than the average-load sizing would suggest.
Stagger start-up: switch heavy appliances on one at a time rather than letting them all restart together when the inverter takes over. Keep total load within 70-80% of the inverter's continuous rating. Where a single appliance is the whole problem, moving it off the inverter circuit is cheaper and better engineering than buying an inverter twice the size for a two-second spike.
Because the compressor draws about three times its running wattage for a second or two at start-up. Peak demand is your total continuous load plus that surge, and an inverter sized only for average load cannot hold it.
Battery Buddy applies a 3.5x multiplier, so a 1000W AC peaks near 3500W at compressor start. That surge, not the running load, decides the inverter you need.
No. Only one motor realistically starts at a time, so peak demand is the total continuous load plus the single largest start-up surge.
Keep steady load within 70-80% of the inverter's continuous rating. That margin absorbs surges, load you add later, and the higher effective draw of an ageing battery.
No. Tripping is an inverter capacity problem, not a battery capacity problem. A bigger battery extends runtime; only a higher VA rating or a smaller peak load stops the overload cut-out.
Battery Buddy is free, needs no sign-up, sells no batteries and shows every formula it uses. It is built by Flocci Technologies, an India-first AI-native software studio behind 30+ apps that share one Flocci identity.