Today's adventure: a couple of rainy days caused low battery levels, but not too low I thought - still 30% or so; these are lithium batteries and can deep cycle. They are "smart" batteries and if one is full in series, none can charge further - so they should all be at the same charge level all the time. But a couple had gotten out of step somehow and when they reached zero everything shut down.
How to bootstrap it? With no battery output (since a zero battery turned itself off and would not let the battery bank show any voltage!) - there is no way to activate the inverter and let street power run the battery charger. With no battery power, there is no way to turn on the MPPT controller and charge the batteries!
I could rearrange the banks to put four batteries with remaining charge in series because I have an 8-battery system, and get things restarted; but if there had been only four like when I first installed the system - I'd be in trouble.
Another thing that happened. Before I figured out the battery problem, I was trying to switch back to street-power. Because power from the street comes to the inverter first and then the inverter powers the distribution panel, when the batteries are down, I cannot get street power to the distribution panel. I could install a manual bypass, but it is not a commonly needed item and it is a large amp switch. So I removed the inputs and outputs at the inverter and bypassed manually. That worked fine. But in the process of disconnecting or reconnecting, I must have loosened the neutral connection to the inverter. So when the inverter was working again and I checked voltage, I only checked across the two hot legs - yay, 240V. I did not check that each leg was 120v from neutral! They were not: one leg was at zero and the other was at 240. I found this discrepancy fairly quickly after only destroying an outlet strip, the oven control electronics from a very old stove we were wanting to replace, and the controls of an old Sharp microwave oven with the 4, 7, 9 and Clear buttons not working. Woohoo we have a new stove out of the deal!
Now this is where a battery alarm (I use a type meant for model planes) and an active balancer (made for this battery chemistry, of course - I use cheap balancers bought on EBay from China) will help.
Since my household has a type of batteries which can burn nastily and they're not in a bunker, I have two autonomous battery alarms and two autonomous balancers. To everyone using batteries from a old electric vehicle, I recommend the same: don't overdischarge and don't overcharge, both do harm in their own way. Have a system that either notifies or takes automatic action to prevent this.
Agreed. I am adding a relay to my system that will alert me and enable grid-power and battery charging when my LiFePO4 battery bank drops below 50V. One would expect that inverter manufacturers would include such a feature in inverters, or at least in the system control panels that one must pay extra to have, but there is nothing like that in my lousy Schneider system except one aux output on the MPPT controller. I sometimes feel I am using their equipment in a way they never dreamed it would be used.