Surge vs continuous watts and motor start loads

One pump, two readings of the starting figure

Honda's wattage guide lists a 1/2 horsepower sump pump at 1,050 running watts and 2,150 starting watts. Generac's generator brochure prints the same 2,150 under a column headed additional starting watts. Its worked example adds the largest starting figure to the total running watts.

On Honda's reading, the pump needs 2,150 W at the moment it starts. On Generac's, it needs 1,050 plus 2,150, or 3,200 W.

That difference decides whether a station fits. The Explorer 1000 v2 prints 3,000 W of surge. That clears 2,150 W and falls short of 3,200 W. Honda also marks both of its sump pump entries as needing 240 V. So a pump's own nameplate is the number to start from.

What stations print

Makers use their own words for the burst figure.

Bluetti's own FAQ calls the same 4,800 W Lifting Power and says it is for resistive loads only. That covers a narrower set of loads than a surge figure for a motor. EcoFlow lists X-Boost as a separate figure from surge on the DELTA 3. So surge, peak, boost and lifting power are four labels for figures that are not interchangeable. Jackery adds a time limit for the 2,000 W step on the 1500 Ultra, 15 minutes at most. It prints no time beside its 3,600 W surge figure.

Why a rating of 2x is common

Many stations print a surge figure at twice the continuous figure. The Explorer 1000 v2 lists 3,000 W against 1,500 W. The DELTA 3 lists 3,600 W against 1,800 W. The Explorer 300 v2 lists 600 W against 300 W.

A pump with a 2,150 W start and a 1,050 W run is itself close to a two-to-one ratio. That is why the starting figure, and not the running figure, usually decides whether a motor load fits.

Why compressors are the hard case

A refrigerator compressor draws far more at start than while running. Whirlpool's tech sheet lists compressors at 97 W and 104 W running. Their locked-rotor currents are 7.91 A and 11.35 A. At 115 V those currents work out to about 910 W and 1,305 W. Honda's guide puts a refrigerator or freezer start at 1,200 W.

A station that prints 300 W continuous and 600 W of surge sits below every one of those start figures. The Explorer 300 v2 is one such station. The running load of 86 to 104 W is about a third of its continuous rating, yet the start is higher than its surge. Locked-rotor current is the worst case, and a running start usually draws less.

Putting the numbers side by side

Compare the appliance's running watts with the station's continuous rating. Compare its starting watts with the surge rating, after deciding which reading of the starting figure the source uses. The runtime calculator does the first comparison and warns about the second. The method notes explain how startup figures and station peaks are lined up. A station can still shut off when a start load lands near its limit.