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LF280K max DISCHARGE current from 0...25C

Zjohn

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Oct 11, 2021
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SOC(%) Temperature1009080706050403020100
55°C2802802802802802802802802802800
25°C2802802802802802802802802802800
10°C28028028028028028028028056560
0°C2802802802802802801401401401400
-10°C28028028028014014014014014000
-20°C140140140140848484282800

When looking at this table taken from the specs for this battery, you can see an 'anomaly' at 10C and SOC <30% since the max discharge current drops radically, and strangely, recovers to .5C at 0C. The question is if you need to interpolate this 56-280A, from 30%..20%, and also from 10..25C . Or perhaps you can do 280 already at 15C? Big difference. Second, I wonder if any existing BMS allows you to program this kind of parameter?
 
seems like an error to me

other temperature vs SOC allowable discharge rate tables for LiFePO4 chemistry did not have that sort of non monotonic change in values like you pointed out around low temp low soc

the table might contain a publishing error is how i feel


regarding how to observe/obey this limit for charge and discharge, i do not know of a BMS that can enforce this.

detecting amps through the pack with a usual shunt resistor

detecting temperature of pack with a usual thermometer

turn on a red indicator and beep when the two incoming data points exceed the table value

this is my current plan for this

eventually i would love to have each dc and ac load on a relay and have a small microcontroller do tiered priority list blackouts to the system to attempt to enforce the limit

this leads to two system modes in a sense:
  • safe mode
  • get to safety mode
where safe mode will do everything necessary to enforce the charge/discharge vs temperature vs soc limit.

get to safety mode would allow the excess amperage rate and just beep

in the space sci-fi video game “elite dangerous” the ship you fly has a simple numerical prioritization system for modules of the ship. usually placing life support as tier 1 encourages success etc.

1638028216954.jpeg
 
Well guys when looking at this I also believed this could be in error, but this is what it says in the specifications and without input from the manufacturer that it is, in fact, an error - one that they have not bothered to correct- I believe we should take this as-is.
As curiouscarbon points out though, there probably is no existing bms that could handle the situation and so, if we assume for a moment that this table is entirely correct, you could very easily damage your batteries under conditions you would not consider suspect.
BTW curiouscarbon the bms I am working on actually provides a temperature sensor for each and every cell... And yes it also incorporates relays to switch of or disable non-essential loads, and that even though I never heard of 'elite dangerous' ;-)
 
Who did you buy the cells from .... If you ask them if there is a chart error .... maybe they can ask EVE.

Most have not had good luck trying to contact EVE directly.

I agree that it is probably an error in the chart and 156 would fit as what it should logically be.

As far as what to do about the current change ..... You could either control the temperature of the battery to keep it in the range where temperature doesn't matter ..... or you could do some sort of exotic external programming with a Raspberry Pi .... or other programmable controller.
 
No idea why anybody would expect the 'wrong' entry to read 156. It should be obvious from the table that every value is in 10% slices of 280Ah - I think they had a spreadsheet with % and an input in Ah to produce the table. The 28A discharge current corresponds to 10%. So if they made an error they made it in two places and it should be something like 50% = 140Ah or 100%=280Ah. That would be MY guess in case of an error, but that would be quite some typo right there.
I tried to find a similar table for other Ah batteries but failed miserably. So no definite answer to the issue. BTW, this table is not in the K but only in the B spec.
 
What is the source of this table?

Ganfeng lists also max charge/discharge at various temperature/SOC's


1638211675526.png
 
10 deg C, 10% and 20% SOC started this

that gangfeng datasheet says…

1638212408851.jpeg

there’s not a similar non-monotonic pattern in this datasheet, in my interpretation. that is, where it goes down then up then down instead of down down down, with relation to dropping temperature.

the datasheet that started this thread is in error in my opinion, unless the manufacturer is using some special mix of electrolyte additives that perform very poorly at 10 degrees C and they are aware of it and communicating it through the datasheet implicitly.

every battery cell (even from same manufacturer same model same batch) has a slightly unique electrolyte, mixture which affects the temperature related performance, from what i’ve heard.


this video goes into the specifics about electrolyte additives and how they can affect battery cell performance and lifespan in different tempereture conditions
 
If we take the Gangfeng data as a LifePO4 base (thanks for posting this DJSmiley) then the LF280 figure at 10°C/10% might actually be correct. However even more other figures in the LF280 table would appear to be off? If anybody has any level of contact with EVE it might be worthwhile sorting this out.
 
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