Hi All,
At the moment I have a stable and 3 year running system with:
3x Multiplus2 5K
2x LFP banks in 16S 2P configuration, each string controlled by a 123SmartBMS with a root software integration in the Cerbo.
2x Fronius Symo 4,5 and 6 inverter for PV power generation
1x Cerbo GX MK1 now running stable on V3.71 (3.73 was a kind of nightmare with mny bugs)
I want to upgrade to six strings of each 16 cells to be able to put these in series on a High Voltage Inverter if Victron releases the 15kW 3 phase model that can handle more than 30Amps on Battery side or worse , if another brand 3fase inverter is the only option.
There are two options:
a) the good old and proven REC BMS (1xIQ10M and 6xIQ2 in master-slave setup)
b) a Boostech.de BMS (https://shop4akku.de/bms/) that has a very nice way of daisychaining 96 cells with auto-learning, Victron Sunt adaptation for Coulomb counting instead of guess work with CT clamps only.
I really like the cell level temperature monitoring and high bleeding current (1,6A) of this system but here’s one thing I am not so fond of: Boostech considers all cells as one big system so no shunt measurements of individuel strings and no disconnect when things go wrong in one string. Of course a fuse wil prevent the defective string being smoked out by it’s 5 brothers but that’s the last resource…
Buying 96 new cells wil be no issue but having 3 x banks with 270-ish, 300-ish and 315-ish Amphours capacity, there WILL be a drift over time.
It gets worse when even with new cells, one cell decides to get issues: Boostech only measures cell temperatures and cell voltages to identify issues. No string currents though (their filosofy)…
Here the REC BMS has it’s advantage with reading out and calculating the data of 6 shunts, one for each string.
The high balance capability as well as the daisy chain setup, without the need of external devices (exept for just one little display and a shunt for all strings together) are perfect.
So here’s my thought: adding a second layer of safety bij adding 6 victron shunts and reading this shunts out with a node red script on a separate Cerbo (or the same if this data dosn’t mess up the original cerbo) . This Cerbo can disconnect the main Boostech relais when capacity of one of the batterystrings will drift away too much from the others or when a too low or high current is flowing through one of the 6 shunts, compared to its other siblings in the pack.
Since the second cerbo can be added in the vrm portal, this would be a nice way to daily check your battery if all cells are in good condition PLUS an extra layer of safety if things go south in your battery pack.
What’s your thought about this?