For some time now I have noticed erratic behaviour with charging the batteries during cheap hours. Charging will start, but once loads get semi-high (about 6kW total) charging will stop and DESS will discharge battery until loads disconnect. Charging is very low most of the time, only 400-500W and occasionally 2kW. I tried to put the system to “keep batteries charged”, but that ended up discharging the batteries below my minimum SOC. I have limited grid feed-in to 9700W and had both import and export current limits at 25A (per phase) to prevent burning main fuses. I have external grid meter, 1x5kVa Multiplus II and Fronius Symo on acin. No solar during latest tests.
–> I disabled import current limitation, and voila, charging now at ~4kW with over 11kW loads.
I’m currently on v3.70~60.
Is this a bug or have I misunderstood how these settings should work?
DESS itself does not pay attention on the AC-Current limits. It ensures to stay bellow your configured Battery-Limit and the Scheduler will take the Import Limit into account for scheduling - but that’s it.
If limitations are kicking in due to the configured AC-Current limit, that is caused by deeper system-mechanics.
In “Keep Batteries charged” DESS btw. goes inactive as it has nothing todo.
How many phases does your grid have?
How many phases used in the house?
MP on Phase 1?
Majority of Loads on which Phase?
Individual or Sum-of-all-Phases as Multiphase-Mode?
3 phases in total, all in use with MP on L1. Loads are pretty evenly distributed with most of lighting and computers on L1, other electrics (fridge, electric floor heaters etc) on L2 or L3. Biggest single loads are hot tub (6kW) and electric water heater (6kW) which are three phase. As we have net pricing, also MP1 is set to sum of all phases regulation. During these limited charge events current on any phase wasn’t anywhere near the import current limit and as there was no solar, so export couldn’t have possibly been anywhere near 9,7kW even at the MP input, neither at the grid meter.
The import current limiter is broken in the latest stable and beta firmwares. I reported this recently in the Venus OS beta thread. Instead of limiting individual phases, it limits sum of phases when you have 1x MP2 and multiphase regulation enabled. This is obviously wrong, as even the setting explicitly states that the limit is per phase.
Due to this bug, if you consume more than 25A (or whatever your limit is) on all phases combined, it ultimately starts exporting on your MP2 phase to keep total at that 25A max. This is a side effect of the broken logic.
Nice to know I’m not the only one with this problem. Hopefully a patch is coming soon.
Still seems weird though that my system decided to discharge battery when I explicitly set “keep batteries charged” from VRM. Maybe it is somehow related.
Yeah, “Keep batteries charged” is basically the mode to preserve battery for times, when peakshaving makes it required to be able to use the battery, i.e. when grid appears to overload otherwise.
I hope so too. I created my own phase current limiting logic with Home Assistant after waking up one morning with a burned main fuse. I can share it if it’s useful to you. The downside is that it’s a distributed logic, whereas ideally everything would be running on Victron HW.