LFP battery absorption and float - report
Bought this 120AH LiFePO4 a while ago https://www.lynaclithium.com/wp-content/uploads/2022/03/12.8V-100Ah-True-Series-Quick-Sheet-USA.pdf. 120AH marketed as 100AH.
Don't see this now but on the older page (and most other LFP manufacturers) recommendations for LFP are - very short or zero Absorb time, no Float or set ~13V (for 14V battery). Now I see them recommending Tail Current 2A-5A, this is where you should completely stop charging, be it Bulk or Float or whatever but I doubt this would work for me (see below).
Set Victron MPPT to Float 13.2, Absorb time 10 min, controller wouldn't accept values <10 min.
Was drawing ~ 30-40 AH a day. Was harvesting slightly less, because it wasn't fully charged upon reaching Absorb 14.4, and there was zero Float current. When loads kicked in, Victron increased Float current to slightly below the load demand - ex. fridge thermostat 2A, Float 1.5A , pump 10A, Float 8A etc - so no joy here.
Victron MPPT won't start Bulk charging again until it can't sustain 13.2 Float anymore - which is usually the last few minutes before sunset - doesn't make much difference.
As a result the battery was getting lower every day, with plenty of sun.
Interestingly, Victron pre-set mode for some "Victron Smart LFP" is 2 hours Absorption time and 13.5 Float.
Set Absorb to 3 hours to see how long it takes to bring tail current to zero. After a few days when battery was finally fed well and was getting some charge during Float to compensate for Loads draw during the day, it took 1 hour 45 minutes to stay in Absorb to drop the current to roughly what loads demand. Well, at parallel 28 it's still winter, max 20A current from a modest array (8A when it became getting full charge every day).
Same story with Renogy DC-DC converter - when set to Li, it was getting lower every day with 6-7 hours driving and the only load - 4A fridge at 60% cycle. Set Renogy to Led Acid battery. Hopefully it won't try running equalization.
Don't see this now but on the older page (and most other LFP manufacturers) recommendations for LFP are - very short or zero Absorb time, no Float or set ~13V (for 14V battery). Now I see them recommending Tail Current 2A-5A, this is where you should completely stop charging, be it Bulk or Float or whatever but I doubt this would work for me (see below).
Set Victron MPPT to Float 13.2, Absorb time 10 min, controller wouldn't accept values <10 min.
Was drawing ~ 30-40 AH a day. Was harvesting slightly less, because it wasn't fully charged upon reaching Absorb 14.4, and there was zero Float current. When loads kicked in, Victron increased Float current to slightly below the load demand - ex. fridge thermostat 2A, Float 1.5A , pump 10A, Float 8A etc - so no joy here.
Victron MPPT won't start Bulk charging again until it can't sustain 13.2 Float anymore - which is usually the last few minutes before sunset - doesn't make much difference.
As a result the battery was getting lower every day, with plenty of sun.
Interestingly, Victron pre-set mode for some "Victron Smart LFP" is 2 hours Absorption time and 13.5 Float.
Set Absorb to 3 hours to see how long it takes to bring tail current to zero. After a few days when battery was finally fed well and was getting some charge during Float to compensate for Loads draw during the day, it took 1 hour 45 minutes to stay in Absorb to drop the current to roughly what loads demand. Well, at parallel 28 it's still winter, max 20A current from a modest array (8A when it became getting full charge every day).
Same story with Renogy DC-DC converter - when set to Li, it was getting lower every day with 6-7 hours driving and the only load - 4A fridge at 60% cycle. Set Renogy to Led Acid battery. Hopefully it won't try running equalization.
