Surge watts explained: will it start my fridge, pump or power tool?

A motor needs far more power for the first second than it does once it is spinning. To know whether a power station will start it, add the motor's extra starting watts to everything already running and compare that peak with the station's surge rating; the continuous rating only has to cover the running load. A 1/3 HP well pump that runs on 1,000 W but needs about 3,000 W to start fits inside the SOLIX C1000's 1,800 W continuous rating, yet trips its 2,400 W surge. The DELTA 3 Plus's 3,600 W surge starts it.

Three ratings, three different jobs

• Continuous watts cover everything plugged in while it runs. Go over it and the station shuts the outlet off, motor or not.
• Surge (peak) watts are a brief allowance above continuous. They exist for the inrush of motors and compressors, and only count for a moment.
• Boost modes (X-Boost, Power Lifting, SurgePad) are a separate trick for heating elements. They don't add surge, and the engine never applies them to a motor.

BLUETTI's Elite 100 V2 manual puts it plainly: some devices with motors or compressors "may start at 2-4 times their rated power" (BLUETTI Elite 100 V2 manual). When a device has no published starting figure, the calculator uses 3× its running watts, the middle of that range. For pumps and furnace blowers it uses the starting watts in EWEB's generator sizing sheet (EWEB generator sizing sheet).

How the peak is added up

The EWEB sheet sizes a generator the same way the calculator checks a power station: total the running watts of everything on, then add the single largest "additional starting watts" figure. The calculator flags anything within 10% of the surge rating as tight, since inrush varies from one unit to the next.

Worked example 1: a well pump on two 1 kWh class stations

Inputs: a 1/3 HP well pump at 1,000 W running and 3,000 W to start (EWEB), on the Anker SOLIX C1000 and the EcoFlow DELTA 3 Plus.

On the SOLIX C1000 the engine says: Its startup peak of about 3,000 W is above the SOLIX C1000's 2,400 W surge rating. Both stations have plenty of continuous output for the running pump, so the deciding number is surge. Once started on the DELTA 3 Plus, the pump would run for about 48 min of continuous pumping, though a real well pump cycles on and off with demand. See them side by side in SOLIX C1000 vs DELTA 3 Plus.

Worked example 2: a sump pump that fits alone, then doesn't

Inputs: a 1/3 HP sump pump at 800 W running and 2,100 W to start (EWEB) on the SOLIX C1000. On its own its peak is 2,100 W, verdict "Starts". Now leave a fridge (123 W with its compressor on) running at the same time:

Its startup peak of about 2,223 W is within 10% of the SOLIX C1000's 2,400 W surge rating. The fridge's 123 W looks trivial, but it sits under the pump's start and pushes the peak into the margin. In a real outage both can switch on during the same storm, so size for the pump starting while everything else is already running.

Worked example 3: boost mode won't start a motor

The EcoFlow RIVER 2 Pro is rated 800 W continuous, 1,600 W surge and 1,600 W with X-Boost. A 1,500 W space heater is accepted there in X-Boost, but it runs at reduced power: the station delivers at most 800 W. The well pump at 1,000 W running is below that same 1,600 W, but the engine still says: Draws 1,000 W; the RIVER 2 Pro is rated 800 W continuous. It will shut off. Only resistive devices (kettles, heaters) run in X-Boost; motors won't. X-Boost lowers the voltage so a heating element draws no more than the 800 W continuous rating and simply gives less heat. A motor can't be fed that way, which is why the heater is accepted at reduced power while a motor gets "shut off".

Which stations start which motors

Continuous and surge ratings as each maker publishes them, with the engine's start check for one device at a time. Running and starting watts for the pumps and blower come from EWEB; the window fan uses the 3× estimate.

The DJI Power 1000 V2 lists 2,600 W continuous but no surge figure on its spec page (DJI spec page), so the calculator won't call a motor start a pass.

Power tools and other motors without a preset

Saws, drills, compressors and shop vacs aren't in the preset list because starting draw varies too much by model to pick one honest number. Use the tool's nameplate: watts, or amps × your line voltage. If the manual gives a starting or locked-rotor figure, use it; if not, 3× running is the same middle-of-range estimate the calculator applies. Enter both as a custom device and the start check runs exactly as above. A 150 W fan works out to a 450 W estimated start this way.

What changes the answer

• Checking continuous only. A pump under the continuous rating can still trip the outlet in the first second if its start exceeds surge.
• Testing one device at a time. Whatever is already running adds to the peak, as the sump pump plus fridge example shows.
• Expecting boost to help. Boost modes accept heating elements above the continuous rating but still deliver no more than it, and they never help a motor.
• Reading a missing surge figure as "fine". Unpublished means unknown. Ask the maker before relying on it for a motor.
• Ignoring the "tight" band. Inrush varies from one unit to the next, so a start inside 10% of the rating may work one day and trip the next.