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Discussion Starter · #1 · (Edited)
Hello EV experts!
We are a group of EV owners and have been happily using these cars for part 5+ years.
Occasionally some people have started experiencing issues where the state of charge goes from 25% to 0% on the dash and the car stalls on the road!

Investigations have revealed that there are certain cell voltages are going to zero suddenly and are not charging. These cells would need to be replaced. Once those faulty cells are replaced the car charges fine and all is well again.

The battery chemistry is Lithium Iron Phosphate which does well in heat and summers - they have better temperature tolerances.

The question if there are faulty cells, can there be a failsafe which lets the car continue for few km atleast instead of stalling like this?

What could be cause of such behaviour? Is it a software issue?
Is the issue in the BMS? Or the controller?

Any insights would be appreciated!

Thanks!
 

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Cell-level voltage monitoring could be programmed to display State of Health warnings earlier in the aging process

Of course starting with quality new cells, ideally big prismatics rather than the cylindricals, and stopping discharge at shallower DoD, would ensure longer lifespans in the first place.
 

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Is the actual voltage going to 0, or just the state of charge value going to zero (which I would expect to happen around 3V)?
 

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does this happen in your e20 or on an e-bike? What is the SOC meter device and how is it controlled?

The main controller/computer usually decides the system response to low cell voltage. In some cars it may go to a reduced power turtle mode to help you limp home as the voltage falls close to the cutoff limit. In some power tool devices the controller just shuts off all power at the limit with no warning. This is the programmed software response that was chosen by the system designer, and may not be possible to change or adjust easily.

The root cause could be weak, old or damaged cells triggering a low voltage limit response, or it could ge a defect in the sensor circuit reading the voltage, or it could be an out-of-balance condition of one or more cells.

To troubleshoot i would start at the cells, then the BMS, then the system controller.
 

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If you have cells at zero volts then you don't want to keep going.

Most designs have a low voltage cutoff circuit that would warn you when getting close to the limit.

Sounds like you have some systemic problems who made the car? Don't you have any documentation?

The designer could have done any number of things or nothing at all.
 
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