Is there a way to set a Victron charger (ex. Phoenix iP43) to automatically maintain an 80% SOC?

Q&A and troubleshooting
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Trying to set my Victron charger Phoenix iP43 to automatically maintain an 80% SOC for lithium batteries. If I understand well, that is a SOC that preserves the life of lithium batteries rather than keeping them at 100% all the time. What I do now is to force a discharge to ~40% once a week, and then I turn back on the charger to 100%. This is for a sailboat mostly connected to a marina shore power. Any other best practices?

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Hi

By setting absorption, float and store charge voltages all to say 13.2 - 13.3V (or the voltage you pick)ā€¦ Setup a pre-set in the app, so easy to swap between store and charge voltage setups.

Can be done using the app, or VE.Direct, etc. I use Home Assistant and an ESP32 and then a single switch to change between ā€˜on the roadā€™ and ā€˜at home so storeā€™ā€¦ using VE.Direct to make the charger settings changes automatically and a relay with a discharge resistor (only 2A load) to discharge the battery to close to store voltage.

Would be great if there was a ā€˜store chargeā€™ button (with user settable values) - for those that believe in keeping lithium batteries at a store charge level between tripsā€¦ Even better if the charger incorporated an appropriate discharge resistor - even if at very low current because of heat dissipation issuesā€¦. It does not really matter if the battery takes a few days to get to store voltageā€¦

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Thanks Andrew. In my case, i have a refrigerator at the boat that is always on, so discharging is not an issue. Will look at your suggested settings. I have Renogy lithium batteries that state that between 13.1 and 13.2v is approximately 80% SOC. Will play with those numbers.

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I feel that the 80% SOC is a hangover from older types of lithium batteries and doesnā€™t apply with LifePo4.

I charge by solar and have charge voltage set to 14.2v, float at 13.5v and critically Absorption set at 30mins*. This means that when itā€™s sunny although the battery hits 100% it drops after half hour to 98% and it never hits the BMS cut off. Fogstar, the battery manufacturer, says this is the correct for their batteries and who am I to argue especially as it gives me roughly 20% more usable capacity.

  • Battery manufacturer Fogstar says 30mins per 100Ah of battery bank.
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LiFePO4 batteries can be loaded to 100% SOC every day without any problems. Since at 3,45V per cell the ā€œrealā€ SOC is at 98%, I would let the BMS set the SOC to 100% after 1 hour of 3,45V x number of cells, i.e. for a 16s battery this is 55.2V. One hour at this voltage should give the battery enough time for aborption and balancing. It is a good idea to use an active balancer.

But donā€™t do this with other types of Lithium batteries like Lithium-Cobalt, which always have the risc of a thermal runaway. LiFePO4 batteries donā€™t have this problem.

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