Complex and Complicated are very different. I don't mind some complexity if it makes sense and works.
That's one thing with LFP versus Lead acid. Lead acid is so much simpler. This doesn't matter to us as system designers/builders, but it's a problem if we need someone else to take whatever steps are necessary to turn a system back on. When I had lead acid, I wrote a manual with steps on what to do in various situations such as "no power in the house". I'm putting together the same for my LFP system and it's way more complicated.
Off grid has the one issue where if your battery is diconnected, you typically don't have networking. There is nothing you can do remotely to fix an issue if you have no networking to your bms or other devices. I've heard of some people with secondary lead acid batteries that power critical loads. I've been thinking about looking into a UPS for this, but I think it probably wouldn't power the equipment for very long. If I had this worked out, a contactor might be a more attractive option.
Having said that, critical fault for my system really means low temp or a cell went bad. The battery, inverter, etc is in it's own heated building. Heat is provided by a non-electric propane heater. I have a secondary electric heater setup on a lower temp. If the propane one dies, the electric will come on. I use the following values:
| cell v | 48v | SOC % |
Inverter high cut out | 3.75 | 60.00 | 100 |
BMS high cut out | 3.65 | 58.40 | 100 |
Absorb set point | 3.52 | 56.40 | 99 |
Gen stop on 60% soc | 3.28 | 52.40 | 60 |
Gen start on 15% soc | 3.18 | 50.80 | 15 |
Gen start 2 hr @48v | 3.00 | 48.00 | 9.5 |
Gen start 15 min @47.5 | 2.97 | 47.50 | 9 |
Gen start 30 sec @47v | 2.94 | 47.00 | 8 |
Inverter low cut out | 2.81 | 45.00 | 5 |
BMS low cut out | 2.75 | 44.0 | 4 |
Voltages and SOC are approximate. On the upper side, there is really no way for a high system voltage fault unless there is equipment failure where the equipment is charging at higher than it's configured for. I don't use the inverter high cutout. On the low side, the generator will come on at 15% SOC. If the generator fails to start, then I have 15% of my battery left to figure out a fix.The gernerator voltage start points are in case the SOC drifts. I get alerts on generator activity. The inverter will cut out at about 5%, so I will have some battery left for troubleshooting. So in a nutshell, everything essentially operates within the BMS cutoff points.
One thing that Batrium is poor at is there are no alerts. IMO this would be an easy add on to the software, but for some reason it doesn't exist. You can set the software so it dumps status to a file every minute and I've been thinking or writing an alert engine that parses this file and sends alerts. Pretty crude way to go for something that should be an obvious need. There is guy who put together some tools to parse the UDP (iirc) broadcasts from the Batrium, but i haven't dug into it too deeply.