izak
commented
3 years ago I want to argue for the nice and simple approach: removing the hidden feature.
Since Venus 2.30, hub4control (which controls whether the battery can discharge and how fast) always uses the selected battery service. This was part of making the BMS selection more sane where there are multiple managed batteries.
In short: In an ESS system, selecting the BMV already makes it ignore the BMS, which affects whether the battery can discharge and how fast it can discharge.
Systemcalc however still uses the BMS with the lowest deviceinstance as information source for the Multi and Solar Charger's charge voltages and current limits.
The correct thing would be to make things consistent.
We will however break things for a few people. The reason why we allowed this split is because at the time there were already existing customers using a BMV because the managed battery in that system didn't track SOC very well.
This is due to poor current tracking at low power levels, usually batteries that use a single Hal-effect sensor. The effect becomes worse when there are multiple modules in the battery, each with their own sensor.
Removing the ability to use another battery monitor will affect:
- SOC: There can be substantial SOC drift with an inaccurate current measurement.
- SCS: Writing back the battery current to the solar chargers is affected if the measurement is inaccurate.
A non-exhaustive check on Grafana indicates around 30 sites (with a BYD, BlueNova, or Generic CAN-BMS) that use a BMV as the selected battery monitor even though a managed battery is in the system.
To deal with that, I will create another issue for finding an alternative way to deal with poor SOC tracking and using an "auxiliary" battery monitor.
mpvader
For a system with a BMV and a managed battery, we currently support the user selecting the bmv as the main battery monitor in the settings -> system setup menu.
And then what systemcalc does, is that it still finds the BMS and uses it for BOL control (CCL, CVL, DCL). In case of multiple BMS-es it will use the one with the lowest device instance.
That was made a while back, to allow users using a BMV in combination with their managed battery.
But its not documented anywhere publicly and also the gui doesn’t show it to the user. Ie a hidden feature.
Next step: either finish this (show it in the gui, document it etc) or remove this feature and make it such that if the user selects the BMV, the whole BMS is ignored. Which is nice and simple.