WattInverter generators only. This one isn't negotiable.
If you take one thing from this site: the cheap open-frame contractor generator in your garage is the wrong tool for charging a car. Here's the actual reason, stated accurately, because the exaggerated version of this warning is everywhere and it's wrong.
The short version
A conventional generator will most likely refuse to charge your car — faults, throttling, or nothing at all. The less likely but far more expensive outcome is damage to an onboard charger that costs thousands to replace and probably isn't covered under warranty when the cause is an improper power source. You are risking that to save a few hundred dollars on a generator.
What "dirty power" actually means
Let's kill a piece of internet folklore first: a conventional generator does not produce a square wave. It produces a real sine wave, because it's a spinning alternator. The problem is the quality of that sine wave.
| Conventional | Inverter | |
|---|---|---|
| Waveform | Sine, distorted | Sine, synthesized clean |
| Total harmonic distortion | 15–25% | under 3% |
| Voltage regulation | Swings with load | Electronically regulated |
| Frequency | Tied to engine RPM | Independent of engine speed |
| Behaviour under load step | Sags, then overshoots | Holds |
That last row is the one that matters most and gets discussed least. A conventional generator holds voltage by holding engine RPM. Add a sudden load and the engine bogs, voltage drops, the governor overcorrects, and voltage overshoots on the way back. An inverter generator decouples output from engine speed entirely — the engine can wander and the output doesn't.
Square and modified-sine waveforms are real, but they come from cheap DC-to-AC power inverters, not from generators. If someone tells you their generator makes a square wave, they're describing a different product.
What that does to an EV
An EV's onboard charger is a switch-mode power supply. It's designed with input tolerance and protection, which is exactly why the usual outcome is refusal rather than destruction:
- It won't start. Input quality outside spec, charger declines, nothing happens.
- It starts and drops. Charges for a while, a load step causes a sag, the session ends.
- It throttles. Some vehicles quietly reduce current rather than fault, and you get a fraction of the rate you expected without being told why.
- It degrades. The uncommon one. Sustained out-of-spec voltage and repeated transients are not what those input stages were qualified against.
Being straight with you about the evidence
Confirmed, well-documented cases of a conventional generator destroying an EV onboard charger are rare. Most reports are people who couldn't get a charge to start. I'm not going to tell you your car will definitely be ruined, because that isn't what the evidence shows and you'd be right not to trust a site that overstates its case. The argument for inverter-only doesn't need the exaggeration: the likely outcome is a generator that won't charge your car at all, and the unlikely outcome is a four-figure repair. Neither is worth the savings.
Manufacturer position
Automakers generally don't endorse generator charging, and none of them will help you if a non-compliant power source damages something. Assume that a damage claim traced to a generator is your problem, not theirs. That alone should settle the spec question.
What to buy instead
An inverter generator with under 5% THD, a 240V receptacle, at least 6,000 running watts, and a CO sensor. Open-frame inverter models give you the cleanest output per dollar if you can live with the noise — that's the tradeoff I made.
The full spec checklist → · Work out your charge rate →