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How much capacity is lost if only charged to 3.58v..?

MCJEFE

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Jan 21, 2021
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I'm building a 16S CATL 202ah pack and have a 57.4v charger left over from a 14S Nissan Leaf build from a few years ago. It was 57.4v vice 58.4v to maximize cell life of the used cells.

My question is how much capacity will I loose if I only charge my lifepo4 CATL cells to 3.58 volts per cell?

I know the golf cart will have around 100 miles per charge at 3.65v per cell so I can afford to loose a little but I don't want to cut too deep.
 
Regular charging to 3.65 will turn your cells to scrap in no time. Even 3.58 is high. At 3.4 volts you're over 99% capacity.
 
They will not turn to scrap. The CATL cell is rated for 3000-4000 cycles (depending on what spec sheet you look at) charged to 3.65v. People just like to charge lower to extend that even further.

I personally charge to 3.57v because I have a runner after that. There is only a few watts above that.
 
LFP Full Acceptable Voltage Range is 2.500-3.650.
Working Voltage Range is 3.000-3.400 with Nominal Voltage being 3.200Vpc. 48.0V-54.4V for a "48V" pack.
Grade A+ working range is typically 2.850-3.500 +/- a bit.

BTW: You can charge LFP to 3.650V per cell and fully saturate the cells to where they are taking less than 1A charge. Stop charging and within One Hour, the cells will have settled to around 3.500 +/- a bit. Within Two Hours they'll drop a bit more. This is Absolutely NORMAL for LFP.
2.500-3.000 and 3.400-3.650 are the "Charge Cliffs" and only represent about 5% of total GROSS Capacity of an LFP cell.

What is Gross ?
When A+ Cells are tested, a typical 280AH cell will test out at 285-290AH from 2.500-3.650 but still have 282AH capacity from that cell from the "Working Voltage Range" The "Gross" is the Whole Capacity from the Full Voltage Range, not the Net Working Voltage Range.

Some Gotchas:
Cells will deviate during discharge at a greater rate once the cells fall below 3.000Vpc. Weaker Cells will run to lower voltages that can result in LVD Low Volt Disconnects by the BMS.
Cells will also deviate more above 3.375V-3.400 at that is the top of the working range.
-!- Matched Cells will generally remain close together within the Working Voltage Range and a bit beyond.
The Higher the Amperage Draw, the quicker deviations will occur during Discharge.
The Higher the Charge Rate (not to exceed 0.5C) again will also cause the cells to deviate quicker & farther above the 3.375-3.400 range.
-!- Again Matched cells will deviate less until a higher voltage is reached.

Bulk Commodity cells can be expected to deviate by as much as 1mv per AH capacity of the cells.
Voltage & IR Matched is NOT properly Matched & Batched cells (which have to run through charge & discharge cycles while being Voltage & IR sampled.

You may want to download THIS resource: The PDF File is High Rez chart.
General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V

Also this will help you with additional details and information with regards to assembling & setting up your packs. (Applicable to all LFP)
Luyuan Tech Basic Lifepo4 Assembly Guide

Hope it Helps, Good Luck
 
LFP Full Acceptable Voltage Range is 2.500-3.650.
Working Voltage Range is 3.000-3.400 with Nominal Voltage being 3.200Vpc. 48.0V-54.4V for a "48V" pack.
Grade A+ working range is typically 2.850-3.500 +/- a bit.

BTW: You can charge LFP to 3.650V per cell and fully saturate the cells to where they are taking less than 1A charge. Stop charging and within One Hour, the cells will have settled to around 3.500 +/- a bit. Within Two Hours they'll drop a bit more. This is Absolutely NORMAL for LFP.
2.500-3.000 and 3.400-3.650 are the "Charge Cliffs" and only represent about 5% of total GROSS Capacity of an LFP cell.

What is Gross ?
When A+ Cells are tested, a typical 280AH cell will test out at 285-290AH from 2.500-3.650 but still have 282AH capacity from that cell from the "Working Voltage Range" The "Gross" is the Whole Capacity from the Full Voltage Range, not the Net Working Voltage Range.

Some Gotchas:
Cells will deviate during discharge at a greater rate once the cells fall below 3.000Vpc. Weaker Cells will run to lower voltages that can result in LVD Low Volt Disconnects by the BMS.
Cells will also deviate more above 3.375V-3.400 at that is the top of the working range.
-!- Matched Cells will generally remain close together within the Working Voltage Range and a bit beyond.
The Higher the Amperage Draw, the quicker deviations will occur during Discharge.
The Higher the Charge Rate (not to exceed 0.5C) again will also cause the cells to deviate quicker & farther above the 3.375-3.400 range.
-!- Again Matched cells will deviate less until a higher voltage is reached.

Bulk Commodity cells can be expected to deviate by as much as 1mv per AH capacity of the cells.
Voltage & IR Matched is NOT properly Matched & Batched cells (which have to run through charge & discharge cycles while being Voltage & IR sampled.

You may want to download THIS resource: The PDF File is High Rez chart.
General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V

Also this will help you with additional details and information with regards to assembling & setting up your packs. (Applicable to all LFP)
Luyuan Tech Basic Lifepo4 Assembly Guide

Hope it Helps, Good Luck
Thanks, I'm actually really familiar with NMC cells and their charge/discharge profiles but recently branched out into Lifep04 packs. I was pretty sure I wouldn't loose much if any real capacity above 3.5. But wasn't sure.. I was actually looking for the charging chart and was striking out and trying to use the graph on the spec sheet and a ruler. Lol
 
The short version is:

- Charge at a slightly lower voltage as you suggest.
- You will lose maybe a few percent capacity at most.
- You will extend the life of your pack.
- You will avoid lots of problems.
- You won't need to adjust your settings constantly.
- Your BMS and charge controller will have a much easier life.

My experience is: It's better to add additional batteries to add capacity, than try to charge to the limit.
 
Thanks, I'm actually really familiar with NMC cells and their charge/discharge profiles but recently branched out into Lifep04 packs. I was pretty sure I wouldn't loose much if any real capacity above 3.5. But wasn't sure.. I was actually looking for the charging chart and was striking out and trying to use the graph on the spec sheet and a ruler. Lol
LFP is also the closest match Lithium Chemistry for FLA Replacement, voltage curve & amperage wise. LFP only requires CC Constant Current to get the cells to 95% and then CV/VC Constant Voltage/Variable Current to top off... NEVER use DeSulphation / Equalize.

Below are my Midnite Classic-200 SCC Settings for LFP.
I have 3x280AH & 2x175AH in one bank. Have done severe Thrash Tests and much more and having a Mixed Bag of cells... 2x280 = Bulk Cells, 1x280=Matched & Batched, both 175's are used EV Grade LFP (different animal) so I got to test various extremes, which for me is critical being very rural & quite remote (I can be snowed in for days)

I do FLOAT the battery packs because that allows the Full Cells to level up and the balancers enough to bring everything nicely up within a short period of time. NB: I use Chargery BMS8T 300A with 300A DCC's (Solid State Contactors) and 1 QNBBM-8S Active Balancer on Every Production Pack in the bank.

All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT) see link in my signature on how to do it.
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
NB: Victron Forum discussion says EndAmps = TailCurrent
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.

** Coulumbic Efficiency for LFP is 99%

Hope that further illuminates. Good Luck
 
Regular charging to 3.65 will turn your cells to scrap in no time. Even 3.58 is high. At 3.4 volts you're over 99% capacity.

OK, scrap was a strong word. It still puts an unnecessary strain on the cells and if you have a runner, it will cause more problems.
 
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