LiFePO4 Voltage Chart?

[Steve_S]

I Have 4 Packs of Grade A Cells (Fortress Power eFlex 5.4KW Batteries) and I just ran some test on the most recent one with only 10 cycles on it. It will charge to the factory recommended 55V but will drop down to 53.5V after an hour or so. I did some Log checks on the other three batteries and found the same thing with no measurable degradation as they reached the 340th cycle. They started at 53.5V and are still at 53.5V. This equates to 3.43V per cell at the 100% charge point.

I can force them higher but they will eventually still settle down at 3.43V per cell. I also have one EG4LL which brings the bank size up to 27KWh.

1) This is perfectly Normal & Acceptable for LFP to Settle to "Working Voltage from Full Charge. Charging Above the working range can reduce lifecycles over a shorter time period.
2) If settling at 3.43, that IS the top of the Working Range (3.000-3.400) shows A) High-Quality Cells B) Well operating BMS You are getting 100% Working Range.
3) At 55.0V Charge you are at the "edge" of the effective charge range. Generally 3.425 / 55.8 is the Peak Target point. so you are peachy.

Steve

 

[carl2591]

Just read some interesting stuff about my charger. Please let me know if this is the proper charging method for Lifepo4 batteries. Thanks!

PD9245CV 9200 - The full rated load is available for load, battery
charging or both. When functioning as a regulated
battery charger the converter has a nominal voltage
output of 13.6 VDC for 12 volt models and 27.2 VDC
for 24 volt models. The system is designed to sense
voltage on the battery and automatically selects one
of three operating modes (normal, boost and storage)
to provide the correct charge level to the batteries.

BOOST MODE: If the converter senses that the
battery voltage has dropped below a preset level the
output voltage is increased to approximately 14.4
VDC (28.8 VDC for 24 volt models) to rapidly
recharge the battery.

NORMAL MODE: Output voltage set at
approximately 13.6 VDC (27.2 VDC for 24 volt
models).

STORAGE MODE: When the converter senses that
there has been no significant battery usage for 30
hours the output voltage is reduced to 13.2 VDC
(26.4 VDC for 24 volt models) for minimal water
usage. When in storage mode the microprocessor
automatically increases the output voltage to 14.4
VDC (28.8 DC for 24 volt models) for approximately
15 minutes every 21 hours to help prevent sulfation
of the battery plates.

that sounds like a lead acid battery charger.. if you use it,, i use a 3 stage boondocker 45 amp charger on my RV, only use it to charge the lithium when needed.. I keep mine unplugged 95-99% of the time only using when many days of low or no sun or under tree in RV park so the solar get little sun to recharge them.. If you have solar use solar for the most part..

 

[carl2591]

SOC	V		Cell	My Limits	My Limits	My Limits	My Limits
	48V setup			Self imposed	Self imposed	Self imposed	Self imposed
					12V Setup	24V Setup	48V Setup
100.00%	58.40		3.65	3.294	13.2	26.4	52.7
99.50%	55.20		3.45
99.00%	54.00		3.38
90.00%	53.60		3.35	3.277	13.1	26.2	52.4
80.00%	53.20		3.33	3.260	13.0	26.1	52.2
70.00%	52.80		3.30	3.242	13.0	25.9	51.9
60.00%	52.40		3.28	3.225	12.9	25.8	51.6
50.00%	52.20		3.26	3.208	12.8	25.7	51.3
40.00%	52.00		3.25	3.191	12.8	25.5	51.1
30.00%	51.60		3.23	3.173	12.7	25.4	50.8
20.00%	51.20		3.20	3.156	12.6	25.2	50.5
14.00%	50.40		3.15
9.50%	48.00		3.00	3.156	12.6	25.2	50.5
5.00%	44.80		2.80
0.50%	40.60		2.54
0.00%	40.00		2.50	2.950	11.8	23.6	47.2

View attachment 5359
My self imposed limits are based on what the cells return to after a bulk charge. For the first month, I was bulk charging to 3.55V per cell, they always returned to 3.295V on their own, so why try to force them. Let them be happy at 3.295 and "call it 100%".

These are for USED cells.

New cells are just that. Battleborn expressly states to use them 100 to 0, but charging them to 90 will let the cells last far far longer. It takes 3 times more time to go from 80% to 100% as it does from 0% to 80%. But it takes about 30 minutes to go from 100% to 80%, and 24 hours to go from 80% to 0%.

I set my 0% SOC at the top of the slope down to zero at about 15% SOC actual, I simply don't use that very low end so I can avoid further degradation. LiFePO4 cannot be fixed once degraded, it's a one-way process.

LiFePO4 Battery Voltage

Sheet5 How to Find Happiness With LiFePO4 (Lithium-Ion) Batteries <a href="https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/">https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/</a> These are big graphs, SCROOL RIGHT -----> for more info about HIGH V...

docs.google.com

 

[carl2591]

I am in the same boat.. adjusted the CC to 13.5 and float at 13.4.. don't need the high volts to fully charge a lithium.. or charge them to a good point for long life..

 

[100kwh-hunter]

Long life?
46 to 56V
You will not see the end of them nor your children.
Now they will see 70%soh left.
In the meantime, you expand.
In 20 years from now, there will be a other type of battery or chemistry, your kids will not even want your "old/obsolete" lifepo4.
Not even 500kwh 70%soh...