I have some curly questions on using a Cerbo GX and Distributed Voltage and Current Control (DVCC) to manage the system described below.
The yacht installation I’m preparing will have four Victron 12.8V 300Ah Smart LiFePO4 batteries, arranged in parallel. Their overall voltage will be sensed by a SmartShunt, connected to the Cerbo by VE.Direct. The batteries’ 3 Pole Balance Temperature & Voltage (BTV) cables will be daisy-chained to a Smart BMS CL 12-100. This BMS will control a Smart Battery-Protect 220 via its Load Disconnect terminal. The BMS will also control a Cyrix-Li-Charge 120 via its Charge Disconnect terminal. Three Smart MPPT 100/50 solar charge controllers will send current from 1200W of solar panels to the batteries through the Cyrix. The MPPTs will connect to the Cerbo by VE.Direct-to-USB adapters, into a USB hub and then to one of the Cerbo’s USB ports. Another job the BMS will do is regulate battery charging from a 115A alternator.
The system will include a MultiPlus 12/3000/120-50 inverter/charger, connected to the Cerbo by VE.Bus. Current from the MultiPlus will not be routed through either the Smart Battery Protect 220 or the Cyrix-Li-Charge 120, to avoid damaging those with flow in both directions.
I’ve read Victron’s explanations of DVCC, along with relevant discussions here in the Community. I’m satisfied it will work. What I think will happen (and not happen) is:
- the Cerbo will take the battery voltage sensed by the shunt and assess this in terms of what it was told the batteries are, during setup;
- it will look up its program library of how these batteries like to be treated and will instruct the MPPTs and the MultiPlus how they should serve up amps for charging, or draw on them for inverting;
- when the Cerbo assesses that the battery voltage reported by the shunt is getting low, it will tell the MultiPlus to stop inverting;
- the Cerbo will not be able to stop the DC loads from drawing upon the batteries, as it has no data connection to the BMS or the battery-protect. These two will use their load-disconnect linkage to cut the loads when one of the batteries says ‘Stop!’;
- if something goes wrong and the Cerbo doesn’t succeed in stopping the MPPTs from charging, the BMS will step in when the batteries ask it to and stop the charging via its charge-disconnect link to the Cyrix;
- however, if something goes wrong and the Cerbo doesn’t succeed in stopping the MultiPlus from charging, there’s nothing in the system or the setup to cut it off. I assume that the MultiPlus will not stop itself from charging, given it’s been told to be dumb and work under DVCC rules. Perhaps I could add a Cerbo controlled relay as a back-up, to switch off the MultiPlus if it goes feral?
Please set me straight if any of the above is off-beam.
Some aspects I’m less clear on are:
- will the shunt report the overall charging current from the MPPTs, the MultiPlus and the alternator, such that the Cerbo might instruct the MultiPlus and the MPPTs to ease-off or stop?
- if the batteries are full, does the BMS have the ability to throttle the current from the alternator? Checking … . Yes, it does.
- and last but not least …
… the Cerbo GX has a second pair of CAN-bus ports, called BMS.Can. Little is written about these, other than how they can be used to hook up other-brand CAN-bus BMS equipped batteries or BMSs. So how good would it be to have Victron lithium batteries that can talk directly to a Cerbo over CAN-bus? :-D Has Victron said these are on the way, or ruled them out for some reason?