Prius as generator, worked as advertised

Well, I looked a little more, and grounding an inverter may be more complicated than I thought, if respondent #4 in this thread knows what he's talking about.

the Otherpower.com Discussion Board || Grounding an inverter

At the least, my takeaway is that you need to check the manual before grounding the inverter. If this guy is right its a poor idea to ground the AC side of some inverters and it will destroy them in others.

I'm not sure I follow what the guy says. But I can find several additional warnings about grounding an inverter. Many of them say that the 12v and 120v grounds must remain isolated. I have no idea why. Based on what I see, I understand why you should not ever try to power a house circuit (even after throwing the main breaker) without testing the inverter first. Some inverters put out 60VAC on both legs (hot and neutral), and all house systems bond neutral and ground in at least one spot, so you'd short one of the 60VAC legs to ground. I don't quite yet grasp why merely connecting the inverter AC ground (not the hot and neutral) would necessarily be bad. If I find out anything useful I'll post it. But at the minimum my takeaway is that for at least some inverters some things that would work OK for actual house current will fry the inverter.

 

I admit that I read the instructions only as a last resort.

Briefly, the manual for my inverter says:

The ground terminals on the AC sockets, the neutral terminals on the AC sockets, and the 12V battery negative input are all tied to the grounding lug on the case, which is the chassis 12V ground. The manual stresses that this setup, for the inverter, is analogous to the NEC setup for a house: neutral and ground must be bonded. For installation in a car, they say, connect the grounding lug to the car body, period. So, installing it with a connection to house ground is not indicated, though it is not explicitly contraindicated. For my inverter, at least, I can't see any reason not to ground it to the house system, any more than I can't see any reason not to ground the Prius frame to earth. Except in the case of a lightning strike it should be harmless. (As a former boat owner, I have to add, except for issues related to electrolysis, but that's not relevant here.)

But clearly none of the above would work on an inverter that put out 60VAC on both hot and neutral (180 degrees out of phase). That must be the type of inverter for which the warning about not connecting AC and DC grounds is be relevant. Correlates with the URL cited above, as the guy suggested using a VOM to check for connection between AC ground and case ground before proceeding.

Hope that's helpful. My guess at this point is that: a) you can fry a cheapo inverter by over-zealous grounding (defined as one that puts out two out-of-phase 60 VAC signals on the hot and neutral terminals), b) by contrast, on an inverter like mine, grounding the case ground to the car frame should be adequate, c) on an inverter like mine, it should be harmless (belt-and-suspenders) to ground the AC side to house ground as I originally described. But I have not (yet) gambled my $350 inverter on that one.

Seems like with grounding to the car body only, you remain at risk that the short might exceed the capacity of the battery to absorb the amperage. But in fact, the short can't exceed the capacity of the battery to provide the amperage in the first place (ignoring transients due to large capacitors in the inverter, etc.). So ... yeah, grounding to the vehicle chassis ground has to be adequate, unless you think that somehow your body will provide a better path for the current, to earth, than the ground wire will, back to battery negative. As long as I wear shoes, I can't see that happening.

Ground the inverter chassis to the car frame and ignore what I cited above. That's what I'm going to do.