The voltage charts I've found are not specific to ah, so does it matter if its 200ah vs 100ah in using the voltage chart to determine SOC in 12v LFP batteries. My uneducated mind says it doesn't matter since ah relates to the time it takes to drop a specific amount of voltage, but the measured voltage drop is the relative indicator of discharge from capacity.
Voltage chart LiFePO4 question re SOC
- Thread starter John Wolf
- Start date
sunshine_eggo
Happy Breffast!
SoC is not specific to Ah, so yeah. Same voltage for a 1Ah battery or a 1000Ah battery at the same SoC.
HOWEVER, voltage is a very unreliable way to accurately measure SoC, and it ONLY applies when the batteries are neither charging nor discharging for several minutes, i.e., completely at rest. Even then, you may have imbalanced cells within the battery thus making estimates that much less accurate. Also, it's worth noting that there's only a 0.1V difference covers a full 30% difference in SoC (13.1V/40% vs. 13.2V/70%).
If SoC matters to you, get a good battery monitor:
Stay away from the bottom 3.
HOWEVER, voltage is a very unreliable way to accurately measure SoC, and it ONLY applies when the batteries are neither charging nor discharging for several minutes, i.e., completely at rest. Even then, you may have imbalanced cells within the battery thus making estimates that much less accurate. Also, it's worth noting that there's only a 0.1V difference covers a full 30% difference in SoC (13.1V/40% vs. 13.2V/70%).
If SoC matters to you, get a good battery monitor:
Off-grid Solar Battery Monitors
Building a vehicle mounted solar power system? Let me help.
www.mobile-solarpower.com
Stay away from the bottom 3.
I've got that exact victron smartshunt but it's not really good for checking an idle battery, it never goes below 100% unless I'm actively drawing power. When the battery sits for a few months, the shunt does not go below 100%. A couple weeks ago I charged the battery (victron 15amp smartcharger) to see how much it leaked down and it did charge, for several hours, even though the shunt said 100% soc before I charged it. Maybe I'm doing something wrong.SoC is not specific to Ah, so yeah. Same voltage for a 1Ah battery or a 1000Ah battery at the same SoC.
HOWEVER, voltage is a very unreliable way to accurately measure SoC, and it ONLY applies when the batteries are neither charging nor discharging for several minutes, i.e., completely at rest. Even then, you may have imbalanced cells within the battery thus making estimates that much less accurate. Also, it's worth noting that there's only a 0.1V difference covers a full 30% difference in SoC (13.1V/40% vs. 13.2V/70%).
If SoC matters to you, get a good battery monitor:
Off-grid Solar Battery Monitors
Building a vehicle mounted solar power system? Let me help.www.mobile-solarpower.com
Stay away from the bottom 3.
sunshine_eggo
Happy Breffast!
Sitting idle for a few months with no load on it might only lose 0.5-3%.
Is it the only thing connected to the (-) of the battery bank, i.e., every load or charge passes through it?
Did the 15A charger provide 15A for "several hours?"
Is it properly configured for sync?
Is it the only thing connected to the (-) of the battery bank, i.e., every load or charge passes through it?
Did the 15A charger provide 15A for "several hours?"
Is it properly configured for sync?
"Sitting idle for a few months with no load on it might only lose 0.5-3%."
I thought this too! The only thing connected to the battery is the shunt. Last I charged it, it started at 15A and then dropped down as it completed the charge cycle. Can't remember how long at 15A but it did not take it long to reduce A. I'm going to charge it again since it's been a few weeks, and check my sync settings to make sure they align (I did before but to double check). One thing I didn't do last time is hook the neg up to the shunt i/o battery terminal when charging. Rookie mistake. I'm going thru the shunt this time to see the charging results on the shunt. Will report findings. Thanks eggo!
I thought this too! The only thing connected to the battery is the shunt. Last I charged it, it started at 15A and then dropped down as it completed the charge cycle. Can't remember how long at 15A but it did not take it long to reduce A. I'm going to charge it again since it's been a few weeks, and check my sync settings to make sure they align (I did before but to double check). One thing I didn't do last time is hook the neg up to the shunt i/o battery terminal when charging. Rookie mistake. I'm going thru the shunt this time to see the charging results on the shunt. Will report findings. Thanks eggo!
sunshine_eggo
Happy Breffast!
Thinking about it...
Shunt pulls a current (more when connected to bluetooth).
BMS bulls a current.
It's possible the two together may pull a noteworthy amount of capacity over long storage periods. Many LFP battery manufacturers recommend a full charge every 3 months or so - likely to address BMS drain and uneven cell self-discharge.
Also note what they said about the BMV - must be charged to full a couple times a month. This is to address normal operation; however, it applies to storage - when you put the battery in storage, you're going to lose SoC accuracy.
IMHO, in that case, after storage, use the app to override the SoC % based on a LFP voltage vs. SoC chart prior to charging.
Shunt pulls a current (more when connected to bluetooth).
BMS bulls a current.
It's possible the two together may pull a noteworthy amount of capacity over long storage periods. Many LFP battery manufacturers recommend a full charge every 3 months or so - likely to address BMS drain and uneven cell self-discharge.
Also note what they said about the BMV - must be charged to full a couple times a month. This is to address normal operation; however, it applies to storage - when you put the battery in storage, you're going to lose SoC accuracy.
IMHO, in that case, after storage, use the app to override the SoC % based on a LFP voltage vs. SoC chart prior to charging.
burgerking
New Member
A fully charged LifePo4 cells is 3.65V. The moment charger is disconnected, voltage starts dropping. But this does not imply SOC drops as well.
Any separate chart for SOC when charging and discharging?
I know active monitoring is better... unfortunately JK does not communicate with inverter.
Any separate chart for SOC when charging and discharging?
I know active monitoring is better... unfortunately JK does not communicate with inverter.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
THIS post in another thread will answer your questions.
diysolarforum.com
The Full Allowable LFP Range is (2.500--3.650) Volts per cell
The "WORKING" Range is (3.000-3.400) Nominal being 3.200 Volts per cell
This is where the "Deliverable" AH comes from below or above the Working Range is the Cliff Drop or the Cliff Climb accordingly and serves no real purpose. The ONLY Time to charge cells to 3.600+ is for Top Balancing and allowing the amps taken to fully Saturate the cells by dropping to approximately 5-7 Amp Taken using a Bench Power Supply.
NOTE: IF you charging above 3.450, the Cells WILL begin to deviate, and eventually Runner Cells will hit 3.650 and create Cell Over Volt disconnects. Additionally draining below 2.850 will again create Runner cells who will hit 2.50 (or Low Volt Cutoff Point as set in BMS) and generate errors.
General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V
I've looked at several places for a simple, easy to read at a glance "chart document" for LFP. I could not find anything comprehensive. I discovered an XLS Worksheet in my stored file and took parts of that to create this chart, I did not...
diysolarforum.com
The Full Allowable LFP Range is (2.500--3.650) Volts per cell
The "WORKING" Range is (3.000-3.400) Nominal being 3.200 Volts per cell
This is where the "Deliverable" AH comes from below or above the Working Range is the Cliff Drop or the Cliff Climb accordingly and serves no real purpose. The ONLY Time to charge cells to 3.600+ is for Top Balancing and allowing the amps taken to fully Saturate the cells by dropping to approximately 5-7 Amp Taken using a Bench Power Supply.
NOTE: IF you charging above 3.450, the Cells WILL begin to deviate, and eventually Runner Cells will hit 3.650 and create Cell Over Volt disconnects. Additionally draining below 2.850 will again create Runner cells who will hit 2.50 (or Low Volt Cutoff Point as set in BMS) and generate errors.
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