How to size a generator
Generators list two figures: rated (running) watts and peak (starting) watts. Peak is usually 10–30% above rated, available for a few seconds. The recommendation above makes sure both are covered.
Worked example
An RV with a 1,500 W air conditioner (3,000 W to start) plus 1,000 W of other loads runs 2,500 W. With 20% headroom you need 3,000 W running. Starting the air conditioner while everything else runs needs 1,000 + 3,000 = 4,000 W peak. A 3,500–4,000 W generator covers it. A soft-start kit on the air conditioner can drop its surge enough to use a smaller generator.
kVA vs kW
UK and European generators are often rated in kVA. With a typical power factor of 0.8, kW = kVA × 0.8, so a 3 kVA generator supplies about 2.4 kW.
Frequently asked questions
What size generator do I need for a 30 amp RV?
A 30 A, 120 V RV hook-up supplies up to 3,600 W. A 3,000–4,000 W generator covers most 30 A RVs, especially with a soft start on the air conditioner.
What size generator to charge batteries?
Add the battery charger's AC input watts to your other loads. A 40 A 12 V charger uses about 650 W; an inverter generator of 1,000 W or more handles it.