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Nobadays
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# Posted: 4 Nov 2024 05:54pm
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We have a 400ah @ 48v - or- 19.2kwh lifepo4 battery bank. It has operated flawlessly for three years. I do need to check battery voltages; 4 x 24v/200ah - 2s2p (Chins did not offer 48v batteries when we bought these.)
Daily consumption is ~80ah/4kwh per day... yes high for a cabin, but we live here most of the year so it is really a home not a cabin... electric refrigerator, freezer, microwave, dishwasher, etc.
We usually never let the bank go below about 60/65% before we run the generator and bring it back up. Partly because my inverter/ charger puts out about 30amps so the lower we go the more hours the generator has to run.
Would it be better to occasionally let the battery bank deplete down to, say ~20% or is our method appropriate?
BTW, Schneider 4048 inverter/charger, and Schneider 150/60 charger controller along with 2500w of solar.
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Steve_S
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# Posted: 4 Nov 2024 08:40pm
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I would check each pack voltage as a matter of course because if one starts to get wonky, you want to know. Even better if they have a SmartBMS with Phone App so you know what's up inside.
4kWh is nothing, I use pretty much 4.0-4.5kWh a day everyday year round. Maybe more when I use equipment.
60% is subjective, relative to what ?
51.6V is roughly 60% if you stick to the working voltage range of 3.000-3.400vpc / 48.0v-54.4v ÷ 2 for 24V packs.
Your fine keeping it as you have been but it may be worthwhile to test the real capacity by running it down so you know exactly how much power you have available in case something happens. Always good to know where (E) really is. Then you just have the PITA of a long genset run to recharge fully.
You can easily push up to 200A at that bank because it will be spread across (divided) between packs and their BMS won't allow more than they need. MUST be 2-stage CC/CV Charging only !
Interesting coincidence. My system is at 61%, 26.1V or AVG Cell Voltage 3.2625 between all packs in my bank ATM.
BTW: These seem to be quite popular and a fair price for a 48V/100A smart-charger for LFP batteries.
https://www.currentconnected.com/product/eg4-chargeverter-v2-48v-100a-battery-charger /
I myself have 4 ways of charging should a need arise but I live way the hell out in the middle of nowhere so... and sometimes without outside access for periods.
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gcrank1
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# Posted: 4 Nov 2024 09:15pm - Edited by: gcrank1
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I have run my two bats down to the LVD (under watch) to find out where it is at. And at a certain point in state of charge I start watching my loads to see if they are dragging the bats down toward that threshold. That is futzy but I wanted to know and tagged each with a FrogTape note so I can 'pull the plug' before the LVD.
Counting the WH's was something I did initially to find out if the bats were as advertised (and provide a baseline). Now I don't keep track other than to see if Im staying within the 'comfortable working range'.
But Ive been recharging at home, typically to 3.45v/cell (13.8v @ '12v') and they settle to 13.4. If I was cycling daily I think Id be doing the same and checking/noting my usage/day and where they drop to, then how long it takes to bring back up to at least 13.4 (3.35/cell). That daily 'working range' and recharge would dictate how Id schedule my gen time.
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Nobadays
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# Posted: 5 Nov 2024 02:33pm
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Quoting: Steve_S I would check each pack voltage as a matter of course because if one starts to get wonky, you want to know. Even better if they have a SmartBMS with Phone App so you know what's up inside.
Yes this needs done, it's been over a year since I put a meter on them. No smart BMS so no app to read them from.
Quoting: Steve_S 60% is subjective, relative to what ? 51.6V is roughly 60% if you stick to the working voltage range of 3.000-3.400vpc / 48.0v-54.4v ÷ 2 for 24V packs.
The lowest I've ever seen is 52.2v. This morning first thing the SCP showed 52.6v @ the inverter ( something was likely running, fridge, freezer?) And 52.9v @ the SCC and 52.9v on "System Status" screen. Very limited charging yesterday because of snow storms.
The chart I've gone by shows 52.8v as 70% and 52.3v as 60% It shows 51.6v to be just over 30% perhaps I'm looking at the wrong chart? Maybe I'm in way better shape than I think! (Chart attached)
Quoting: Steve_S Your fine keeping it as you have been but it may be worthwhile to test the real capacity by running it down so you know exactly how much power you have available in case something happens. Always good to know where (E) really is. Then you just have the PITA of a long genset run to recharge fully.
I guess I should run the bank down... but part of the reason for the large capacity is so I don't run down/out! Unfortunately my generator will only supply 30amps so I don't really have the option to pour 100/200amps into the bank. My solar array actually charges way faster than my generator. PITA is right if I go too deep and have to rely on the generator! Not only does the generator power the charger but also shares loads so in actuality I get something like 20/25amps of charging.
Our true consumption, having charted it over about a week in the past was:
3,500wh/day or 73ah/day or 3.5kwh/day
400ah storage is ~20kwh @ 80% = 16kwh - usable so ÷ 3.5 = 4.5 days autonomous
Maybe I worry too much about running out of power. I guess the only real test would be to run the bank down to the LVD and see just how much I've got.
Thanks for the help!
BTW, LiTime did refund my money on the rv battery that swelled up. I haven heard what they found but I'm pretty sure it was a bad BMS. It can't show 53% SOC one day and without receiving any charging, the next day read 100% SOC.
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gcrank1
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# Posted: 5 Nov 2024 03:54pm
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The 'charts' are notoriously wrong, even for LA, but more so with LFP because the working voltage band is So narrow and needs to be metered to a min. of 2 decimal places.
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Steve_S
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# Posted: 5 Nov 2024 04:08pm
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That chart is based on "Allowable Voltage Range" which is not the Working Voltage Range for LFP (3.000-3.400 volts per cell).
You are staying well within the working range and causing zero stress by doing so. If all your packs are individually at the same voltage (2 decimal accurate) then all is well.
My inverter/charger is actually capable of charging at 100A but I keep it at 80A for comfort. It pulls 120V/23A from my L5:30 on genset(s) (I have 2). I monitor the amps/watts real time when I run the generators. In case you wondered how much an external charger can pull. Not all are the same so expect some +/- draw due to efficiencies.
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Nobadays
Member
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# Posted: 6 Nov 2024 12:37am
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Thank you! We've got 3 days of snow coming so I should get a chance to put a meter on the battery packs.
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Steve_S
Member
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# Posted: 6 Nov 2024 11:36am
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You have Snow (so does Saudi Arabia & Hawaii right now too) we are having a Heat Wave in the low +20C range and Twisters blew through New Brunswick of all places ! So Messed up !!!
A good smartshunt between the battery bank & the SCC/Inverter can be such a valuable asset to tell you what exactly your battery state is at. There are some well priced decent Chinese ones about 1/2 the price of a Victron Shunt (for now).
Ohhh well... everyone in the US can now expect to see 100% + Duties plopped on everything from China and scaled duties on all other imports. Get what you can NOW while you can.
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Nobadays
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# Posted: 6 Nov 2024 05:15pm
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I did put the meter on my batteries this morning. I have a Klein Meyer with unfortunately only 1 decimal place. Each battery read exactly the same/way.
I didn't turn anything off or rest the batteries but there was no charging coming in, certainly a small draw (SCP showed -3amps) Each battery pack came up at 26.5/6. It would show 25.5 then flip to 26.6, then back to 26.5. Each pack did exactly the same thing.
I'm "guessing" the packs are pretty well balanced. Our system on most days hits float by noon. I split the difference between your (Steve) recommended settings (one of your posts) so bulk @ 55.1, Absorbtion @ 55.2/5 minutes, Float @ 55.1. It will usually stay at the 55.1 for 3-5 hours each sunny day. Admittedly I have limited knowledge on lifepo4 battery packs but my feeling is staying @ 55.1 most days for several hours is kind 9f top balancing all 4 batteries.
All this said I would guess a balancer s around $50 -$75 would be a good investment for the longevity of my battery bank.
Thanks!
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Steve_S
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# Posted: 6 Nov 2024 06:12pm
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55.1 is really the "sweet spot" for LFP
The klein's are great, means it's likely 25.550 to 25.575 because it's flipping, I believe that by default, they'll round-up at .08 to the next decimal, if memory serves.
Honestly, given what you've said, I'd say you have it all dialed it just right. Besides, any "balancing" has to be at cell level within a pack for Lithium Batteries, that external stuff doesn't do much other than cause issues (it's for FLA).
I'd say, leave it all alone, make sure it's clean, dry & kept like you have and "Enjoy" the fruits of your labours !
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Nobadays
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# Posted: 6 Nov 2024 07:47pm
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Sweet! Good to know the external balancers aren't the way to go. My understanding is these Chins batteries have and internal cell balancer integrated into the bms. My set are only lacking cold disconect, which doesn't really bother me since our bank is under the stairwell inside the house.
Thanks for the peace of mind!
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gcrank1
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# Posted: 19 Nov 2024 07:50pm
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Been keeping track of my 2 12v/100ah lfp's of late, bottom line is I don't real get much past 13.0 and very little below 12.8, which after they 'fall off the cliff'.
If it were an emergency Id go past 12.8 for an led light or usb charge but in my real world use swapping out at 12.8 is just fine.
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Fanman
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# Posted: 20 Nov 2024 01:54am
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Quoting: gcrank1 Been keeping track of my 2 12v/100ah lfp's of late, bottom line is I don't real get much past 13.0 and very little below 12.8, which after they 'fall off the cliff'. If it were an emergency Id go past 12.8 for an led light or usb charge but in my real world use swapping out at 12.8 is just fine.
Is that voltage under load or resting?
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gcrank1
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# Posted: 20 Nov 2024 04:10am
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That 12.8 is after a bit of a rest after load, often only 1/2 hr I see the bounce back from a lower load voltage to that. Ive been monitoring the recovery from my regular loads, though not keeping a log.
During load the bats will dip lower and a couple times Ive hit the inverter cut-out. After a bit the bat recovery kicks the unit back on but it will cycle like that in an ever increasing rate.
Now I know when to start watching closer toward 'the end', or just swap the bats out. Remember that Im not recharging on site, it is a total loss system.
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