I have a Quattro 48/10000 with solar/wind priority enabled, 16S1P LFP battery bank controlled by an external BMS, plugged into shoreline in the marina. For a week or so it charges up to 54V (set by BMS) from solar during the day (about 99% SoC) and then discharges a couple of percent at night, the Quattro is in Sustain mode.
What should then happen is the BMS is set to allow charging up to 100% SoC (57.3V) once a week for a couple of hours to allow cell balancing and resetting the SoC measurement, then reverts to 54V (all still in Sustain mode) – and this happens OK some weeks, the BMS is in control.
But other times after about a week the Quattro switches to Absorption mode, flags up in VRM that it’s charging to 100% SoC, and sticks there indefinitely – it can’t get to 100% SoC because the charge voltage is being limited to 54V (99% SoC) by the BMS. I can stop the “Charging to 100% SoC” manually in VRM if I spot this has happened, but if not it sits there running everything off shorepower forever.
I can’t see any way to change this behaviour in the Quattro settings either via VRM or VEConfig. Presumably which happens depends on which gets there first, BMS or Quattro – I suspect they’re both set to trigger after 7 days, so it’ll depends on exact sequence of charge/discharge as to which gets there first, BMS (good) or Quattro (bad).
Surely if the Quattro is set to “External control” all this should be dealt with by the BMS, the Quattro should act as a slave?
Since there seems to be no way to change the Quattro behaviour – the documentation for solar/wind priority says it flips from Sustain into Absorption mode if a week goes by without reaching 100% SoC – I guess the fix is to program the BMS to do a charge to 100% SoC and cell balance every 6 days, so it always gets there first.
The BMS controls charging (voltage and current) and calculates SoC, which is what is displayed on the Touch50 by the Cerbo. “99% SoC” is what it calculates at the 54V charge voltage, presumably it uses current integration starting with 100% SoC at 57.3V when it does a cell balancing charge.
So if the Quattro with solar/wind priority enabled sees that SoC hasn’t hit 100% in the last week, it switches from Sustain mode to Absorption and tries to charge to 100%. But since the charge voltage is controlled by the BMS (Quattro appears as “External Control” on the system diagram) and is held down to 54V, it can’t get to 100%, so just sits there using shore power instead of solar.
There doesn’t seem to be any way to either tell the Quattro to stop doing this and let the BMS deal with it or change the one week period, which the solar/wind priority documentation quotes – implying that it can’t be changed by the user. Which is crazy, since different battery manufacturers recommend different periods between cell balancing, up to a month.
Unless Victron update the Quattro firmware to allow this refresh period to be changed (feature request?), the only option I can see is to change the cell balancing interval in the BMS to 6 days so it always happens first.
But this means going to the boat, disconnecting the BMS from the Cerbo and connecting it to a laptop via a programming adaptor, because it’s not remotely editable…
