I have a small off grid system at a remote location. 700W PV, 100/50 smart solar, phoenix 12/1200, smartshunt, ras pi with VenusOS connected to vrm over mobile internet. Battery is 12v 300ah lifepo4. It is a cheap sealed pack so no communication with bms. As the days got shorter, capacity issues got obvious. At 50% capacity, voltage started dipping below 12.1v inverter limit when fridge compressor would kick in.
Anyway, I will not be able to phisicaly reach the location in the next few months so I would like to try to help the battery balance on site only on solar. As it probably has an integrated passive balancer it would probably benefit from a long charge with small current with voltage in the high knee (above 13.8v).
Currently the battery SOC goes down to 98% during the night with the inverter off.
Is it possible to automate (with Venus) the smart solar charge current limit to let the max current during bulk charge in the morning until the voltage rises to the absorption voltage (13.8+) and then limit the current to 2A for example in the absorption and float stages?
If you have a shunt to dc loads connected to the venus os, then they will be compensated for with the MPPT.
I assume that is what you are trying to do.
Set your absorption length to a few hours to help.
The current should automatically be dropped, just the voltage held longer.
No separate smartshunt for DC loads, only one for the battery.
The issue with just keeping the higher voltage for longer is that at some point (when the current gets down to some low value ie. 3A) overcharge protection starts kicking in and the current gets throttled. I am guessing that it is due to one or more cells reaching the 3.65v limit. From what I’ve seen if I limit the current to 2A or 1A I can continue a stable charge.
Another guess is that at that level the current is low enough that the passive balancer can ‘burn off’ the excess energy at the full cells and let the cells with lower level to continue charging.
If I just set the fixed limit to such a low level I would lose half of the daylight just to get the voltage level high enough to balancing to start, making a very slow process even slower
