More Monitoring…

Sunday - I’m still closely monitoring the charging from the Magnum inverter/charger. Ideally, it won’t charge the batteries to 100% every time while we are connected to shore power. I have been adjusting the absorption voltage, absorption time (aka CV duration), and rebulk voltage to get the profile that I think would work for us. I initially started with the BattleBorn recommendations. It made a good starting point. Using their settings, both batteries would reach 100% and their BMS would disconnect from the charging source. So, I would turn off the charger, discharge the battery and turn down the absorption voltage. This is the voltage that the Magnum switches from CC to CV. The charging mode shows on the Magnum remote display. 

Right now, it’s set to 14.3V and 18minutes. The switch to CV occurs at around 96% SOC, and the 18minutes of CV takes it up to 99% before the charger shuts down. Actually, CV duration should be reduced to 6minutes.

The rebulk voltage is now set to 12.9V and bulk mode charging started at 80% SOC. That sounds fine. When I had it set to 13.3V following the BattleBorn recommendations, bulk mode charging started at 99% SOC. The SOK batteries are a different cell design than the BattleBorn cells so that may account for the difference. 

The voltage shown on the HomeAssistant graphs is being measured at the battery terminals by the Victron shunt. The voltages being used by the Magnum inverter/charger are within the unit itself. There is approximately 12 feet of 2/0 cable between the batteries and the inverter with numerous interconnects. So while charging, the Magnum voltages will be higher due to resistance in the cable and high current. Discharge voltage should be close as the current is low. When the RV is not connected to shore power, the Magnum measured voltages would be lower than actual battery voltage due to high current through the cables. 

Monday - I’m still trying to decide if I’m alright with this behavior. Charger off until ~2:30am with SOC of 74% (that’s good), followed by two CC/CV charges in the morning at SOC of 94% (not optimal), followed by the solar charging in the afternoon, then another CC charge in the evening at SOC of 82%. I think that this may be the best I can do with the Magnum inverter/charger. To get a more accurate battery voltage, I would need to add a Magnum BMK or shunt. Not for $180…