HighTechLab
AKA Dexter - CTO of Current Connected, LLC
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- Sep 23, 2019
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- 1,691
Just use the battery...it will do what it needs to do automatically...not really a need to babysit it.
charging/discharging LiFePo efficiently to maximize life
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alright, thanks. just trying to do what's best for it. seems like every piece of info conflicts w/ something else so it's just confusing to me.
Alpine_Junky
New Member
I found the off-grid garage youtube channel of value in helping me with understanding. I also have a system where I am only using roughly10% of its battery capacity. The video titled: "Charging LiFePo4 (LFP) to 3.4V and 3.5V with and without Absorption. What a difference!" is the one I am referring to.
The settings I settled on with help from those who have replied in this thread are:
3.45V Bulk
3.35V Float
5 minute absorb timer (I plan to keep an eye on this and increase if warranted as the seasons change to winter)
The batteries are maintaining a balance of about avg .004 difference. The temps are staying nice and cool. I am using 16 LF280K cells with an Overkill BMS. The system has been online now for about 2 months and I have been keeping a watchful eye; so far, seems good.
The settings I settled on with help from those who have replied in this thread are:
3.45V Bulk
3.35V Float
5 minute absorb timer (I plan to keep an eye on this and increase if warranted as the seasons change to winter)
The batteries are maintaining a balance of about avg .004 difference. The temps are staying nice and cool. I am using 16 LF280K cells with an Overkill BMS. The system has been online now for about 2 months and I have been keeping a watchful eye; so far, seems good.
thanks! i was going to migrate towards those values, but after seeing my bms starts to balance at 3.45v, i boosted mine a little as i wanted to make sure they all/most of them got over that value. i have watched several of OGG's videos and a couple about his settings.
what i find confusing is, if it will only balance while idle or charging, not while discharging, seems like using them all the time would never allow for balancing. right now they are 200mv off after charging. they will settle down to almost perfect balance after time, but probably 200mv below the value i want them to be at. but they are still new, so i imagine it's not going to happen in a cpl days.
i also don't have a good inverter so i can't really use them yet any way. waiting on the verdict from zonna about my outback before i decide if i'm going to have them fix it or get a new one.
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Your concern totally makes sense, especially when you want to maximize the life of your LiFePO4 batteries.
Yes, there are ways to use solar power directly to run loads without charging the batteries, and it's commonly referred to as "load diversion." Essentially, you can set up your system to supply power to your loads directly from the solar panels when the batteries are at a certain state of charge (SOC). Once the batteries drop below a set SOC, the system can switch back to charging them.
Some charge controllers and inverters have these capabilities built-in, allowing you to program how and when to divert power. You might want to look into inverters with these specific capabilities, or you may explore additional accessories like a load diversion controller that can work with your current setup.
This way, you won't be wasting any solar power, and you'll be able to manage the charge cycles of your batteries more effectively, keeping them in the optimal SOC range for longer life.
Yes, there are ways to use solar power directly to run loads without charging the batteries, and it's commonly referred to as "load diversion." Essentially, you can set up your system to supply power to your loads directly from the solar panels when the batteries are at a certain state of charge (SOC). Once the batteries drop below a set SOC, the system can switch back to charging them.
Some charge controllers and inverters have these capabilities built-in, allowing you to program how and when to divert power. You might want to look into inverters with these specific capabilities, or you may explore additional accessories like a load diversion controller that can work with your current setup.
This way, you won't be wasting any solar power, and you'll be able to manage the charge cycles of your batteries more effectively, keeping them in the optimal SOC range for longer life.
It’s just going to take time and low charge current to get them to balance. Your limitations are; low balance current, balancer only active on charge, active above balance start voltage all while not triggering a cell over voltage. http://support.sokbattery.com/bluetooth-bms-cell-balancing/
HighTechLab
AKA Dexter - CTO of Current Connected, LLC
- Joined
- Sep 23, 2019
- Messages
- 1,691
This is entirely irrelevant to the SK48v100 batteries with LCD that the OP has. This only applies to the Bluetooth BMS in the 12v batteries and budget 48v battery.
What is the balance current for the OP’s batteries and does it balance during charge AND discharge when in range?
seems the AIOs have the option to pass the solar directly to the loads. i think i will be ok as i'm set up, it will just pass the solar through the battery, charging or not. i was just thinking that i didn't want to do that in certain cases, but it sounds like it's not a problem to use the batteries as in my scenarios.
sunshine_eggo
Happy Breffast!
The small balancing current on a cell with a battery at rest will pull it down below the balance voltage relatively quickly. The battery needs to have enough incoming current to offset the small voltage drop from the balancing current.
SOME AiOs that can operate without battery can do this, but the MPPT in the AiO is ALWAYS converting high voltage DC to battery DC and then feeding it to the inverter, so it's not really what you think it is.
i've noticed that the batteries (2 sk48v100 in parallel) do not show the same SOC even though they have the same voltage. all cells on both are are the same voltage, let's say 3.31 for example (53v), but one battery says 93% SOC and the other says 83% SOC. the amp hrs seem to correlate to the SOC (the higher SOC has a higher ah remaining). i thought it would correct itself once they got full again, but it seems like it's been doing it for at least a few days.
is this some sort of 'drift' because i'm not discharging them far enough? or does it indicate some sort of problem? they seem to charge/discharge evenly based on voltage, it's just doesn't seem to be recording the ah correctly.
at full charge, they still are not balanced too well (about 150mv spread), but again, i haven't been discharging them very deeply so the actual 'charge cycle' count doesn't go up very fast....though i presumed it would balance the same once it got to 3.5v regardless if it went from 100% to 20% back to 100% or 100%-80%-100%. under operation, the cells are all pretty much equal voltage.
is this some sort of 'drift' because i'm not discharging them far enough? or does it indicate some sort of problem? they seem to charge/discharge evenly based on voltage, it's just doesn't seem to be recording the ah correctly.
at full charge, they still are not balanced too well (about 150mv spread), but again, i haven't been discharging them very deeply so the actual 'charge cycle' count doesn't go up very fast....though i presumed it would balance the same once it got to 3.5v regardless if it went from 100% to 20% back to 100% or 100%-80%-100%. under operation, the cells are all pretty much equal voltage.
