LiFePo voltage sagging
120 AH, , nominal 12.8V. 12.95V unloaded, 12.8 under 4-5 A load. According to discharge curve 12.8 is 30% (they measured at much higher 0.5C rate discharge): Lynac 12.8V 120 AH . Quite a bit of sa...
Forum Discussion
I don't have access to BMS, sealed unit, don't want to open and wouldn't know what to do if I opened 🙂
The battery is mostly for back-up, there is grid power. I'm trying to find a middle ground btw the popular mantra "Don't keep for long in Absorb, don't float, don't keep it 100% all the time" on the one hand, and the need to keep it near-full in case of blackout on the other hand. Blackouts happen a few times a month.
I would like it to stay at 80% and cycle shallow. What I do now is letting it charge on solar + converter, and then shut converter off for the night to reduce floating time.
Ideally, I would like to store it unloaded at 50% charge for a longer life but this is unrealistic and I doubt that my life will be much longer than 4000 battery cycles (6 months a year = 180 cycles a year = 22 years).
haha ya thats what I meen, I was all worried about getting the most life out of mine, I believe it was an old habbit of the flooded cell days, treat them right and you will only have to buy new ones every 8 years, with the LFP I am finding after two years on my 280AH running at 100% to 10% I havent lost one bit of capacity. well 100% to 10 are my cutoffs, it rarely sees under 50% , because of the extra capacity I built in, but always is charged back to 100%. its kinda funny people are still afrade to go to 100% of capacity for the charge, if you look at all the people running big 48V battery back up systems on their homes they charge to 100% every day with a specified amount of adsorbtion time then they drop off to 13.4 to 13.6V for the float. and these guys are cycling every day, and floating as long as the sun is up. I honestly don't know where half the rhoumors and old wives tails came from in the rv world that we can only use 80% of the capacity, don't float, don't fully charge and so on. most of them are totaly BS and prevent people from using there batteries to the fullest. the one hard one is don't charge below 0C , and don't float at 14.6V if you have a float have it set for 13.4 to 13.6 depending on your school of thought. idealy a 3 stage charger that you can customize bulk, adsorb and float voltage (and time in the case of adsorb) would be ideal.
thats not to say park your rv for the winter and leave it floating for 6 months, thats concidered storage and I take my battery to 90 to 100% and shut it off ( battery disconect that leaves no parasidic loads) and it sits like that till camping season is close. even during camping I don't charge between trips, just charge it to 100% the day before I leave, then the solar handles the charging during the trip which takes it to 100% every day.
As of this morning I have taken my old battery (280AH) out of the camper and it is going to a friend for his camper and I am just working now on the replacment battery for my camper. upgrading to newer larger cells and if they are good I am buying 16 more for the 5th wheel. the biggest advantage, aside from larger capacity, is the ability to run at -35C (discharge only, and only 10 degrees colder than the old cells) and increased cycle life (3500 to 4500. ) at 100% usage
There is some rationale behind charging to 80%, cycle life is longer. Having max available energy is more important for me so I'm going to ignore this. Besides, charging to 100% takes care of cells balancing.
OTH in storage, say unused for more than a week or two, I don't see why not discharge it down to 40-60% as per recommendations. Even if it saves me 5% of capacity in several years. Hot storage is the worst: https://www.uschemicalstorage.com/lithium-ion-battery-storage-requirements/
because the link you provieded doesnt say which chemistry of Li it is referencing, we don't know which kind of Li they are refering to. for example battle born and dragon fly recomed charging to 100% and turning the battery off. eve who makes the cells I use says 3+ months is concidered long term storage saying to charge the to a minimum of 50% and up to 100% remove the battery and store it in a cool dark place 0C to 25C. there are people in vegas who have been playing with cheep 100ah batteries and leaving them in the sun outside cycling every day and havent been able to kill them.. what does kill them is leaving them at 0% for long periods of time.
I would be more concerned about the bottom 20% than the top 20%, unless you are going for huge cycle life. the setting youer bottom at 20% and your top to 90% will get you upwards of 7000 cycles. if you use yours from 100 to 20 you still have 100ah as they built in an extra 20, and by not using that bottom end you get 6000. 100% use will probably drop you to 3500-4000 but unless we know the brand of cells we are only guessing.
so many of the myths and rhumors are exactly becasue of that link you posted which PT is now going to post everywhere inorder to bring about the rise of overpriced special agm batteries again 😁
