I'm still trying to figure out the particular top and bottom settings. The 27V - 25V range worked out really well in this last test. Seems like a nice Goldilocks range. But, it required regular attention as I had to set the solar charge controller (SCC) above 28V to maximize the amps (current) to charge the battery in a reasonable amount of time. So I was frequently checking and adjusting the SCC settings to finally get to a resting 27V.
When I'd simply set the SCC to 27V, the bulk charge would end too soon (about 1/3 charged), leaving the absorb phase to charge the remaining 2/3 capacity. I estimated It'd take several days to finish charging before finally settling at 27V. Plus, it would waste a lot of good Sun hours (power potential) at reduced charging. Guess it's one of the problems with using a SCC that wasn't designed for charging LFP batteries. I don't know, even with my Samlex inverter/ charger using the Lithium CC/ CV charging option would take a long time to get that last 5% - 10% capacity to get to 27V.
I'm considering what Will said in this post:
DIY LiFePo4 Solar Battery
Of course, he also has the sticky post:
Recommended Charge Profile for DIY LiFePO4 Batteries *Sticky Post*
Now that I have a good sense-of-confidence the batteries are working as expected. I'll do a little more researching/ experimenting/ fine-tuning and settle on some reasonably care-free settings.
Some things I've recently learned are differences in voltage under various loads vs no-load and settling voltages, both when charging and discharging. Typically need to charge higher with the expectation the voltage will drop some (assuming you're able to let the battery settle/ rest). When discharging, you can go lower than the lower limit you set, knowing the voltage will bounce back some as well (again, if you're able to let the battery rest). So there is some offset estimation. Especially, when setting the inverter low-voltage alarm and cut-off.
I expect the experience will differ when I start continuously using the battery (always under some kind of load). Likely having to estimate some compensation or fine-tuning based on my average usage.
Having some sort of capacity monitor has been very helpful. The Drok meter I've been using shows the total accumulated Ah and Wh used. It also goes in reverse when charging. So, I can see how quickly it's charging back up and when it should be about finished, going back to a zero reading.
For me, with regular daily usage, I think it'll be rare that I'll come close to using 85% potential capacity a day (~12kWh). Probably be around half that. Some days I'll hardly use it at all, other days, I may get a couple days of crumby weather (using solar charging) where the battery will be fully utilized. Heck, it took me about 1.5 days to do my last capacity test and it was powering about 95% of my 120V power usage, even when I'm working from home. Plus, it'll be a nice-to-have if/ when I go 5+ days without grid power again during hurricane seasons.
