⚡ Surge Watts Calculator

Motor-driven appliances (pumps, compressors, AC units) briefly draw far more power at startup than while running. A power station that covers your running watts but not your surge watts simply won't start the motor.

Reference: Real Surge Ratios From This Dataset

These figures come from this project's own sourced use-case data (mini-fridge.json, well-pump.json, window-ac-hvac-backup.json), not manufacturer nameplate data for a specific unit you own — always check your appliance's own nameplate or spec sheet where available.

Calculate Your Surge Requirement

Which Power Stations Clear This Surge Requirement

How to Calculate Surge Watts

Take the appliance's running wattage and multiply it by its startup multiplier. The result is the figure the power station's surge rating has to clear — its continuous rating is a separate number and will not save you here.

Multipliers in the table above run from 2.4× (rv fridge) to 4× (compact mini-fridge). When you do not know an appliance's multiplier, assuming 3× for anything with a motor or compressor is the safer error — undersizing means the appliance simply will not start.

Why Motors Spike at Startup

A stationary motor has no back-EMF opposing the supply, so for the fraction of a second before it comes up to speed it draws several times its running current. That inrush is brief, but an inverter either rides it out or trips. This is why a unit can run a fridge for hours yet refuse to start the same fridge from cold — the running load was never the problem.

Resistive loads — heaters, kettles, incandescent bulbs — have no inrush worth planning for. Their running watts are their peak watts, which is why a 100 W fridge can be harder to start than a far larger heater.

17 of the 20 units in this dataset have a confirmed surge rating that clears 400 W, the toughest load in the table above.

Surge Watts: Common Questions

How do I convert locked rotor amps (LRA) to surge watts?

Multiply the LRA figure by the supply voltage. An appliance rated at 20 LRA on a 120V supply needs roughly 2,400W at startup. Compressor and pump nameplates usually list LRA rather than surge watts, so this is the conversion to reach for.

My power station has enough watts but still won't start my pump. Why?

Continuous rating and surge rating are different numbers. A unit rated 1,000W continuous may only peak at 1,500-2,000W, while a pump can demand three times its running draw at the instant it starts. The running load was never the obstacle — the startup spike is.

Is a published surge rating always enough?

Not reliably. Many inverters can hold their peak figure for only 100-200 milliseconds, and a hard-starting compressor may need a longer spike than that. Treat a surge rating as a ceiling to stay below with margin, not a target to match exactly.

Do heaters and kettles have a startup surge?

No. Resistive loads draw their rated watts immediately and hold them, so running watts are also peak watts. That is why a 100W fridge can be harder to start than a 1,500W space heater, even though the heater drains the battery far faster.

Only pure sine wave inverters are shown as recommended — modified sine wave and unconfirmed-inverter units can cause motor-driven appliances to overheat or fail even if the surge number looks adequate on paper.