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Car Battery problem : 1st/last cell issue ?
#1
Hi guys,
with this post i trying to hunt for informations about a strange problem of car batteries.

Is there any reason thinkable, that the first/last battery in an xs configuration gets an issue, given
- it is properly produced and balanced at factory status
- it gets charged and discharge for some (more)  usage/cycles (supervised by the original BMS electronics)


and
- gets the issue, that repeatable the first and last Cell/pack proves to empty before the other Cells in a test. Not equal earlier, but earlier.

Any thinkable reasons for this ?
I have two assumptions, but i dont want to focus your thoughts.

No, i do not have more informations until now, but i may get answers to specific questions you might ask.
The question comes out of the car battery industry, from a person involved.
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#2
Test the cells...

Also what c rate so you Charge and discharge at? Above its nominal?
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#3
(02-13-2019, 06:03 PM)daromer Wrote: Test the cells...

Also what c rate so you Charge and discharge at? Above its nominal?

No results of cell test lnown.

Ist E-Car Battery, BEV, so quite a rough current profile. They have to work, actually.

To specify my very unspecific Request, i just ask for ideas, not for solutions.

Example:

- Electrostatic influence of the Field onto chemical reactions
- would probably affect only 1st or last

- Thermal iinfluence, outer cells hare hotter/Colder than the others
- ??

- BMS connection points, end point(s) possibly different to the connectors between cells
- Depends from BMS "intelligence"


More ideas ?

( For daromer: More Ideas ?)
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#4
The problem could easily come from differences in internal resistance.

Also, where is the 1st cell? Is it in the middle of the pack or outside?
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#5
The most common issue is that the cells arent the same and therefore act different. For instance if you run them really hard the outer will be affected due to thermal and also often bad design on the busbar/wires causing it to happen.

Im not giving you a solution. Im giving you a way to find out whats going on instead of guess work of stuff not related. Without the facts from start including proper tests I wont be guessing on strange scenarios that might not even be in the ballpark
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
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#6
(02-14-2019, 06:29 AM)daromer Wrote: The most common issue is that the cells arent the same and therefore act different. For instance if you run them really hard the outer will be affected due to thermal and also often bad design on the busbar/wires causing it to happen.

This adds to the mechanical/thermal specialties of the outer cells. Thanks.

Quote:Im not giving you a solution. Im giving you a way to find out whats going on instead of guess work of stuff not related. Without the facts from start including proper tests I wont be guessing on strange scenarios that might not even be in the ballpark

Hey man, i asked for ideas, not for solutions.... read my post....  Big Grin Big Grin

( i think i am close to make a training here on problem solving systematics....)

(02-14-2019, 03:47 AM)BlueSwordM Wrote: The problem could easily come from differences in internal resistance.

Also, where is the 1st cell? Is it in the middle of the pack or outside?
It happens regularly on the packs in questions. Its new custom development.
Thanks, position of "outer" cells will be checked.
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