Why your generator stalls when the AC starts
Your generator runs the house fine — then the air conditioner kicks on and everything dies. This is the single most common backup-power complaint, and it's almost always the startup surge.
What's happening
An AC compressor draws a brief, large spike of current the instant it starts — its locked-rotor inrush, often around three times its running watts. A generator may have plenty of running capacity but get overwhelmed by that momentary surge, so it overloads and shuts down.
Three fixes
- Size for the surge, not the run. Your generator must cover running watts plus the single largest startup surge. Use the load sizer to see your real peak.
- Fit a soft-start kit. A soft starter cuts the AC's inrush by roughly 65%, often dropping the requirement by a whole generator class.
- Stagger your starts. Don't let the AC start while the well pump or fridge is also cycling on — bring big motors up one at a time.
Common questions
Why does my generator stall when the AC starts?
The air conditioner's compressor needs a large startup surge — often 3 times its running watts. If the generator's surge capacity is below that spike, it overloads and shuts down even if it can handle the running load.
How do I fix it?
Either size up to cover the surge, fit a soft-start kit on the AC to cut the surge ~65%, or stagger starts so the AC isn't kicking on while other motors run.