Running Watts vs. Surge Watts for RV Appliances
If a generator or inverter is rated for enough continuous watts to run your appliances but still trips or shuts down the instant your air conditioner kicks on, this is almost always why: running watts and surge watts are different numbers, and most sizing guides only mention one of them.
What's actually happening
Motor-driven appliances — air conditioner compressors, refrigerator compressors, some pumps — need a short burst of extra current to overcome the motor's initial resistance and get spinning. Once running, they settle down to their steady "running watts" draw. But for that first second or two, they can pull 2–3x their running wattage, sometimes more depending on the compressor type.
Non-motor loads — lights, chargers, most electronics, resistive heating elements — don't have this spike. Their running watts and their startup draw are basically the same number.
Why this trips people up
A generator rated for, say, 2,000W continuous sounds like plenty if your appliances only add up to 1,800W running. But if 1,500W of that is your air conditioner, and its surge is 2.5x that (3,750W for that first second), the generator sees a spike it's not rated to survive — even though it's rated fine for the continuous load once everything's running.
This is why RV air conditioners are the single most common cause of "my generator should be big enough but it isn't" — it's not a power problem, it's a surge problem.
How to size for it correctly
- Find your AC's running and surge (or "LRA" — locked rotor amps — converted to watts) spec. Many manufacturers list both; if only running watts is listed, 2–3x is a reasonable planning estimate, but check the spec sheet when you can.
- Only the single largest motor load typically matters for the surge calculation — you're unlikely to have two compressors starting in the exact same instant, so don't just sum every appliance's surge value.
- Soft-start kits exist for many RV AC units and can cut the surge draw significantly (often by half or more), which can be the difference between needing a bigger/more expensive unit and not. Worth researching if your generator is surge-limited rather than continuous-power-limited.