Force Charge and FCSOC limit confusion

[alexhill]

I am trying to use mode scheduler to gradually charge my battery to ensure it is at least 85% full when my peak schedule kicks in at 15:00. I don't want to just dump from the grid directly into my battery though, because there is a considerable amount of solar being generated that I can't export, so I want to gradually increase the battery SOC.

So here is my logic:

1. My solar panels can create a max of ~5kw, which will fill 6% of my battery per half-hour if it is operating at full capacity (ignoring household load for now)

2. Knowing I have the potential to put 6% of power into the battery every 30 minute interval, I can set the minimum charge I want at the end of each period:

Screenshot 2025-12-16 144249.png (7.54 KiB) Viewed 140 times

So now I have tried to set up mode scheduler for a couple of those timeslots as a test.

The problem

When the first time period kicked in, the battery was at 73%, above the FCSOC. My understanding is that it would not draw from grid because the current SoC was above FCSOC, and essentially operate in SelfUse mode. What I saw however was that the grid import matched my consumption (i.e. house was running 100% from grid), with the full solar generation going into the battery.

Has anyone found a way to "charge at XX kw, supplementing solar with grid if required, until the battery hits a certain SoC, then stop drawing from grid"?

I'm heading towards a modbus/homeassistant route where I can implement if/then/else logic, but would like to try and get this setup while I wait for the modbus to wifi device etc to arrive.

[Dave Foster]

The only answer is the home assistant route, everything else will be a fudge.

The problems are as you have found if your FCSoC is lower than your battery SoC you effectively put the battery into idle and power will be taken from grid as you found.

The bigger issues are around your 6% every 30 minutes - that 6% is variable and will depend on SoC, temperature and a combination of them both.

As your battery soc increases the BMS will reduce the charge current, it drops in 5A increments (charge power = battery volts * battery charge current)

Similarly temperature modifies the point at which the BMS reduces charge current based on the lowest cell temperature, it starts to adjust at 21C, 16C, 11C and you can't take any of that into account with scheduler so the best you can do with schedules is to set the best possible guess.

With home assistant you can see all of those sensors, max charge / discharge rate, lowest cell temp - but more easily simply watch the battery SoC and adjust as necessary (taking into account solar forecasts etc.. if you want)