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Charge termination current varies with Voltage.
Charging Marine Lithium Battery Banks | Nordkyn Design
nordkyndesign.com
Manufacturer-specified termination condition 3.65V @ 0.033C 3.65V @ 0.05C Cell voltage (V) Termination current (C) Termination current (C) 3.370 0.000 0.000 3.400 0.004 0.005 3.425 0.006 0.010 3.450 0.009 0.014 3.475 0.012 0.019 3.500 0.015 0.023 3.525 0.018 0.028 3.550 0.021 0.032 3.575 0.024 0.037 3.600 0.027 0.041 3.625 0.030 0.046 3.650 0.033 0.050
You should never put your trust in random internet strangers, me included. Read the cell manufacturer's datasheet instead. There has to be a reason behind every single (decent) server-rack battery sold today coming with a RS485/CAN communication port.What I’m wondering is if the article is valid perhaps OP has misread it. Or if the article is invalid or bad advice, then OP has read it correctly but is misinformed.
There has to be a reason behind every single (decent) server-rack battery sold today coming with a RS485/CAN communication port.
You should never put your trust in random internet strangers, me included. Read the cell manufacturer's datasheet instead. There has to be a reason behind every single (decent) server-rack battery sold today coming with a RS485/CAN communication port.
EVE:
http://www.dcmax.com.tw/LF105(3.2V105Ah).pdf (Section 5.3)
(Section 4.2)
CALB:
https://cdn.shopify.com/s/files/1/1820/0269/files/L160F100B_data_sheet.pdf?v=1622844198 (Section 4.2.1)
All three say the exact same thing about charging. It is only a matter of reading them.
There has to be a reason behind every single (decent) server-rack battery sold today coming with a RS485/CAN communication port.
...
The problem that I faced was the same as everybody else faces here: Cells no longer in balance (showing 0.040 V deviation) even after a 'full charge' to 3.5V the very next day. (you will soon realize the reason behind these quotes later)
Clearly, If I was doing everything 'right' according to what everyone on the internet is doing my cells should retain their balance at least.
Overtime, people have tried to attack this problem by saying passive balancing simply isn't enough and how there is basically a need for active balancing to be the default offering in all BMS's in order to keep the cells in 'daily' balance.
Overtime, this has resulted in the demand for higher Active Balance Current in BMS's.
...
Finally someone who went to the length of reading things and even more importantly actually understood what is meant.Excellent post, thanks for sharing this @shvm. The Nordkyn page you refer to also contains a lot of useful information.
Here are my notes and understanding for what it is worth. I have experience with lead acid, but no practical experience with LFP, so it should be taken with a grain of salt. Using the pack I'm building as an example below.
Any charge (absorption) voltage in the acceptable range (3.37 - 3.65 V) will result in a fully charged battery, it just takes longer with a lower voltage, but on the other hand the risk of hitting OVP for a cell is also lower. Charge voltage is just a matter of preference. Most people seem to be in the 3.45 V - 3.50 V range.
Over charging is an issue that can damage the cells. How damaging it is and how sensitive the cells are is a question mark, but why not try to avoid it if we can. It will occur at any charge voltage above the 100% SOC resting voltage (3.37 V) if you keep the cells there long enough. Overcharge is not something you can "see", it just results in cell degradation over time.
Charge should be terminated by measuring the charge current into the cell and stopped when it drops below 0.03C (or what ever the datasheet for your cell says). The 0.03C value is stated for a standardized 3.65 V absorption voltage, so it must be adjusted down if you use a different voltage. For example if you use 3.50 V the value is 0.023 C. (Look at the linked document in the OP). For a 600 Ah pack that is 13.8 A.
Since we can't use the current termination method, we use absorption time instead. Set the charge controller to 3.50 V absorption, 1 hr absorption time, and then disconnect the inverter, and start the charging. Go through the bulk, and then as soon as absorption starts (voltage reaches 3.50 V), measure how many minutes it takes to drop to 13.8 A. Stop the charge and enter this value as the new absorption time. This will ensure that even in the worst condition (full charge current and inverter turned off), the absorption stage will never over charge the cells. Most of the time the cells will instead be slightly under charged, which is not damaging.
Set the float to 3.37 V (the resting voltage of a 100% SOC cell) to prevent over charging. This will also prevent the cells from being discharged if the inverter takes a load (for as long as the sun shines). In theory it will also very very slowly get the cells to 100% SOC if that was not done in the absorption stage, but practically this will never happen in a reasonable time frame.
Precisely! Even with people not having access to BMS-Inverter comms, they can modify existing settings when it comes to when to turn balancing on or which voltage to float to emulate the correct model of charge termination.This procedure is not possible for most of us, because we don't have a fancy charge controller that can talk to the BMS and get the charge current. The charge controller doesn't know what current flows into the cells, it just knows the sum of what current flows into the cells AND into the inverter.
Finally someone who went to the length of reading things and even more importantly actually understood what is meant.
Except, there's a difference.Or those who better spent their time doing things the way they always have been for years (wrong according to you) with no problems (and have still balanced cells). <shrug>
My cells need balancing on the order of weeks to months.
Nice card you just played right there.Then perhaps it is you that is doing something wrong, and not everyone else as you claim.
There are some super smart people around here, you need to do a lot more reading and understanding before you start throwing your weight around buddy ?Nice card you just played right there.
I'm at absolute loss of words !!
Oh, they can be easily recognized by what they say and how they word it.There are some super smart people around here, you need to do a lot more reading and understanding before you start throwing your weight around buddy ?