50ShadesofDirt: Thank you. to your helpful points.
1. The batteries and individual cells certainly read "full" on my AiLi battery monitor and on my multimeter when I test at the individual batteries. Individual cells typically are 3.30-3.35 when the bluetooth app and the AiLi meter read fully charged. Note: the AiLi meter typically reads a collective 14.40v-14.46v when all charging has been stopped by the BMS units.
For a diffferent test, I've now been running on the batteries/inverter for 39 hours with zero solar or other charging. I turned off the solar charging for this little test. My AiLi meter now reads 66.1% capacity remaining (13.04 volts overall). The individual batteries via the bluetooth app range from 13.09v/67% to 13.08v/61%.
Not surprisingly, the battery with the lowest voltage/% charge is the 280Ah battery that has the shortest cables to the inverter. At this moment, that battery is discharging at 7.1amps and the one with the longest cables to the busbar is discharging at 4.7 amps.
The highest power setting I've ever been able to run the inverter microwave on with the inverter is the "Level 7." I tried Level 8 once while also charging with solar (charge controller showed about 23v input at that time). The microwave ran about 45 seconds before the inverter turned off. (I was momentarily ecstatic with hope during the 45 seconds, until my bubble was burst.)
2. There is no possibility of moving the inverter. This is an RV. The "basement"storage area for batteries, inverter, charge controller, etc., is a 40in x 40in x 4 ft cubicle. Very tight space for batteries and equipment.
And, I did not register your other suggestions about a direct microwave connection at first. But, now I have figured out how to connect the micriowave to an AC plug in the back of the inverter. Not easy, but do-able. Per my long post, I am seeking assistance with moving the (built-in) microwave to test the direct connection. I am eager to try the direct connect test. I will let you know.
Al;so, I have a generator. I also have 800 watts of solar, with another 400 watts (4 new panels awaiting my wiring). I ordered more to compensate for the residential refrigerator during the low-solar winter months. Keeping batteries charged, or charging them, is not an issue at all for me.
Thank you, again.
Surprise, SURPRISE! My microwave ran at FULL POWER ! ! !
I got some lifting help and was able to connect the microwave directly to one of the AC outlets on the WindyNation VertaMax 3000 watt inverter.
I started testing at the microwave's "Level 7" power and then one-by-one through the power levels to "Level 10."
The microwave ran without a hiccup. (To be honest, I stopped the full power test just short of one minute because In order to do so I had to connect a heavy-duty 6' extension cord to the inverter and then the microwave to the extension cord. Which, to me, makes it even more surprising that the microwave ran at full power! Because of the extension cord, I didn't want to risk other problems.
My conclusion is that the power loss/inverter shutdown problem is not with the batteries/inverter and wiring.
Rather, the inverter is being limited by the wiring through the (20-year-old RV's) single "kitchen" circuit on my RV's main power panel which has numerous other appliances and AC receptacles. (But not a lot of things running at once.)
The remaining issue, for me, is how to best wire a new connection from one of the inverter's AC receptacles and install a new plug dedicated to (a) the residential refrigerator and (b) the microwave? I had been thinking about that for the refrigerator alone so I could bypass the RV's power panel and other wiring.
Will my idea of a new 8-gauge heavy-duty extension cord run from the inverter and directly wired to a new, dedicated receptacle work?
Is there a better way?
I cannot use the direct connection on the inverter, because it already has a Romex 8-gauge 3/2 wiring running to my 3-way switch and then to the RV's power panel?
Here's the kicker -- although I'm not sure how much it matters. I had been running the system with the solar panels turned off (a test) for over 40 hours. I also was purposely using power heavily with microwave (Levwel 5-6 power, no problem), ice maker, coffee pot and of course refrigerator, lights, computer, TV, charging ports, etc.
The meter on the inverter itself was showing 13.1 volts. My AiLi battery monitor showed 62% of collective battery power remaining and voltage of 13.15, so it was consistent with the meter on the inverter.
And, the microwave still ran at FULL POWER! I could hardly believe it.
I think I will consider a future 24-volt conversion, although I don't really know enough about that. I'll just use my 12-volt system (after the new direct connection for the microwave refrigerator) for a while and see how much I future modifications.
Other thoughts are most welcomed.
To all who helped here, you have my deepest gratitude. The DIY Solar Forum, and those of you who participarte helping low-knowledge beginners like me are simply amazing!
Thank you, thank you, thank you!!!
jesfl