What Size Generator Do You Need for an EV Charger?
Quick answer
To run an EV charger (Level 2, 40A) alone, a generator needs at least 9,600 running watts and 9,600 starting watts. A 40-amp Level 2 charger delivers 9,600 W continuously while charging - no motor, no surge, just a large unrelenting resistive-style load. A 32-amp charger draws 7,680 W; a 48-amp charger draws 11,520 W. Unlike most loads, this one runs for hours at full draw.
Running it on a portable
Portable generators in our dataset that clear both numbers on their own:
| Model | Running watts | Starting watts | Approx. price |
|---|---|---|---|
| DuroMax XP13000EH | 10,500 | 13,000 | Around $1,299 |
Running it in a whole-home system
In a whole-home outage load list - the EV charger (Level 2, 40A) plus about 3,225 W of household essentials - the combined math lands in the 18 kW standby class with standard headroom. Standby units in that class from our dataset:
| Model | Output | Approx. unit price | Warranty |
|---|---|---|---|
| Generac Guardian 18kW | 18 kW | Around $5,100 | 5-year |
The honest answer for most owners: don't size for the EV. An EV is itself a battery - pausing charging during an outage costs nothing, and many chargers can be capped at a lower rate (16-20A) from the car or charger settings if a partial charge matters. If charging through outages is a genuine requirement - a long rural commute and frequent multi-day outages is the real case - it adds roughly a full standby size class.
A note on climate
The math above assumes a mixed climate. Two adjustments matter at the extremes, and both are rules of thumb, not measurements. In a cold climate, heating dominates: the furnace blower runs near-continuously, and if the house has a heat pump with electric auxiliary heat strips (typically 5-15 kW), those strips are the single biggest sizing load in the house when they engage - count them at full draw or use load management to shed them. In a hot climate, the air conditioner is the dominant load and runs near-continuously through a heat-wave outage, so installers commonly add roughly 10% extra headroom on top of the standard margin. Our generator size calculator applies both adjustments openly - you can see exactly what changed.
FAQ
What happens if the generator is too small for the surge?
The voltage sags when the motor tries to start. Motors hum, overheat, or fail to start; electronics on the same circuit may reset; the generator's breaker may trip. Repeated failed starts are hard on both the motor and the generator - undersizing is the expensive kind of cheap.
Do I need to count this load if I have load management?
Load management lets a smaller generator carry a bigger list by shedding selected loads in priority order. It works well for deferrable loads (water heater, dryer, EV charger) and poorly for loads you truly need the moment they call (a sump pump during a storm).