I've looked into the same generator that you mention. However, I have an existing generator that already runs a good part of the house that is proven to be very even on voltage output. Still, like you I suspect the Harman will hiccup with it. I keep my boat battery in the basement in the winter and have a charger for it. I believe I can run a pure sine Wave inverter off of that combo with the charger hooked to my generator. Problem solved. Anyone else doing this? So the house stays on the Gen and the charger can either plug into a hot outlet or an auxiliary outlet on the Gen.
I do something very similar, and there is a thread or two in which it is discussed on this board. But here's a summary: I took an old UPS for a server that is capable of producing 1800 watts of sustained output with a sine wave form. This is essentially just a sine wave inverter with its own 48v battery and trickle charger, which is all a UPS really is a (self-contained battery, charger, and inverter, whether sine wave or not). This old UPS also accepts "dirty" generator power, which is critically important for you as well because many UPS and some chargers and inverters will simply shut down on generator power if the wave form is too "clipped", or unsmooth. Again, this is a crtical thing to test BEFORE you need this setup in an emergency.
I yanked the old batteries from the UPS when they died, and pulled the cover off. Then I bought four, 12Volt, deep cycle "marine batteries rated at about 110 amp hours, and wired them in series using 6AWG battery cables, to create a battery bank rated at 110 amp hours at 48 volts ( the requirement for THIS old UPS - others may be different, and this is critical). In your case, that would not be necessary and you would just have a 12 volt DC to 120 volt AC inverter running off of a single battery.
Now, my old UPS' trickle charger would probably take days to recharge those batteries, so I purchased four 12 volt chargers rated to do deep cycle batteries at up to a 15 amp recharge rate. I put one on each of the 12 volt batteries and plugged it into an AC outlet so that it can recharge over the course of a day (it still takes several hours). Also, I try not to cycle those batteries lower than 50% discharge when possible, and never below 80%, to preserve their longevity. You will hear people say that you should never go below 50%, but that's for batteries that cycle every day (e.g., on a solar system). For emergency use like this, that's not necessary IMO.
When the power goes out, we have an 8Kw generator that powers most of the house, including those battery chargers (again, a critical point is to make sure they will function on YOUR generator power). Thus, I can power a circuit from this UPS that is always on, producing pure sine wave, surge-protected power. You would be doing the same with your proposed setup, just with a lower power rating (I can do 1800 watts) and a smaller battery reserve.
We ended up running a single dedicated AC circuit that includes the MVAE, security system, home automation controller, FIOS interface, wireless router, and low power media center PC, that I run off of that UPS at all times (it's also plugged into household current, so most of the time it's just a big surge suppressor). My old Whitfield Quest also runs perfectly on the generator, so I haven't put it on the UPS (but may do so today). Even if I add the Quest I would only draw 250 watts at a time without the ignitor of the MVAE. It is also always connected to that converted UPS on that same circuit so I actually have no idea how it would perform on straight gen power, and given the cost of a new board I'm not going to test it. The UPS with that battery bank would easily power the MVAE (and much more) all night even with the ignitor cycling on and off, but I connect it to an identical, single deep cycle battery (MVAE's are designed for that) and just pull the plug at night when we shut down the generator. This allows me to rest the generator and stretch my fuel supply, which can be important in an emergency. I could likely add my refrigerator (maybe two) to this as they are very low power users, but if we keep the doors closed all night the temperature hardly moves, so I haven't done that. I think when the old UPS eventually goes I'll just buy a 48V inverter designed for solar systems, but hopefully that's a ways off.
Hope that helps. What you want to do sounds reasonable to me. Good luck, and keep us posted.
