What Are Surge Watts on a Power Station? Continuous vs Surge vs Boost

Surge watts are the short burst a power station can deliver for a moment so a motor or compressor can start; continuous watts are what it can supply for hours. Size by continuous watts, then check that your biggest motor's start-up fits under the surge rating, and ignore boost figures, which only help heaters. A fridge that runs at 160 W can need about 1,200 W for the first instant, which is why a station with plenty of battery can still refuse to start it.

What do the three numbers on a spec sheet mean?

• Continuous (rated) output. What the inverter can supply indefinitely within its temperature limits. Add up everything that can run at once and keep it under this number, with some headroom: our quiz wants about 10% spare, and closer to 25% for loads that run for hours.
• Surge or peak. A brief burst for start-up. Makers rarely say how long it lasts; it's typically milliseconds to a few seconds. The EcoFlow DELTA 2 manual, for example, lists 1,800 W total with a 2,700 W surge.
• Boost mode (EcoFlow X-Boost, BLUETTI Power Lifting, Anker SurgePad). Not extra power. It lets a heating appliance rated above the inverter's limit run at reduced power. More on that below.

Watt-hours are a separate question: they tell you how long, not what. A bigger battery behind the same inverter starts nothing new.

Why do motors need a surge to start?

A motor at a standstill has nothing pushing back against the current, so for a moment it draws several times its running current. ABB's motor guide puts direct-on-line starting current at 10 to 12 times full-load current in the first instant, then about 6 to 8 times until the motor is up to speed. Compressors in fridges, freezers and air conditioners, and the motors in pumps and saws, all behave this way. Heaters, kettles, lights and electronics don't; they draw roughly their label wattage from the start.

Fridges with variable-speed (inverter) compressors start much more gently. Older fridges, sump pumps and window air conditioners are the hard starts.

How do you check surge for several devices at once?

Use the rule generator sizing guides use: add the running watts of everything that will be on together, then add the extra start-up watts of the single biggest motor. Only one motor usually starts at a time, so you don't add every surge.

A fridge (160 W running) and a 1/2 hp sump pump (1,050 W running, 2,150 W starting) come to 1,210 W running. The pump's start adds 1,100 W, so the station needs about 2,310 W of surge and at least 1,331 W continuous. A typical current 1 kWh unit lists 1,800 W continuous and 2,850 W surge, so on output it clears both. Runtime is the separate question, and with a pump in the mix our quiz steps up a size; its picks for this pair are below.

What do X-Boost, Power Lifting and SurgePad actually do?

All three lower the output voltage so a resistive heating element draws less current. A kettle or hair dryer rated above the inverter's limit then runs, but at the inverter's rated power, so it heats more slowly. The makers say so in their manuals:

• EcoFlow X-Boost powers high-wattage appliances “at the rated output power”, is “more suitable for heating devices”, doesn't support appliances with voltage protection, and isn't available while the unit charges from AC.
• BLUETTI Power Lifting on the AC180 handles pure resistive loads up to 2,700 W “while its rated output power remains 1800W”, for heaters, irons and other devices made only of heating elements.
• Anker SurgePad switches on when total output exceeds the rated output, “works better with devices that generate heat” and doesn't support precision instruments. Anker also says it isn't suited to motor-driven devices like refrigerators or air conditioners.

Boost does nothing for a motor. At reduced voltage a motor stalls or overheats instead of starting, and electronics with voltage protection shut down. So a boost figure never counts as surge or as continuous power in our quiz. The Anker SOLIX C300 is a good example: 300 W continuous and a 600 W SurgePad figure, with no published surge rating, so we treat 300 W as its start-up limit.

What if the spec sheet shows no surge number?

Then you can't count on more than the continuous rating for start-up. 10 of the 42 current models we track publish no surge figure, including Anker SOLIX C300, Bluetti Elite 30 V2, Jackery Explorer 300, DJI Power 1000 V2, Anker SOLIX C1000 (Gen 1), DJI Power 2000. Some of them very likely handle short peaks above their rating, but without a published number our quiz rates them at their continuous output for motor starts. If one of these is on your list and you need to start a pump or an air conditioner, ask the maker for the surge spec first.

Does pure sine wave matter for motors?

Yes. Modified (stepped) sine wave output can make motors run hotter and buzz, upset some electronics and audio gear, and is a known risk for medical devices; inverter maker Samlex explains the difference. Nearly every current mainstream power station states pure sine wave output. Treat it as a minimum, not a premium feature, and skip any listing that doesn't say it.

What about air conditioners, pumps and microwaves?

An 8,000 BTU window unit needs about 1,599 W to start and 533 W to run, which most 1 kWh units handle on output but drain within hours; see whether a power station can run a window AC. Sump pumps need surge every time they kick on, covered in the sump pump guide. A microwave has no big motor surge but draws about 1,500 W from the wall for its rated cooking power, so continuous output is the limit there; see the microwave guide.