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The Robustness of a Battery Electric Car.

Bad NewsFirst, a bit of bad news.

At the 20k miles check up, I noticed that the battery terminal on the very first battery cell was loose. Upon closer inspection, I found that the threads on the negative terminal has been stripped.

 

 

 

 

 

 

After polling my EV friends, I found that one other has had the same issue. The problem seems to be the thicker battery ring terminals used to connect to the ends of the pack (the copper ring terminals that connect adjacent cells together are much thinner). I should have used a longer bolt to account for the increased thickness.

Stripped threads on the LiFePO4 terminal

Stripped thread from the LiFePO4 terminal from using a bolt that is too short.

 

 

 

I tried unsuccessfully to re-tap the thread to an M10 from the original M8. Looks like I will have to replace the battery.

Failed attempt at re-tapping the stripped thread on the LiFePO4 cell

Failed attempt at re-tapping the stripped thread on the LiFePO4 cell

 

As a temporary fix, I skipped over the LiFePO4 cell with the stripped terminal and am now running with a nominal 140.8V pack (instead of the original 144V). After 2 weeks of driving, besides noticing that my range has slightly decreased, it has been working fine so far. This is a pretty robust electric car!

Temporary fix to LiFePO4 battery problem

Just skip over the battery with the bad terminal.

Has anyone else had the same issue with their LiFePO4 pack?

 

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Posted in MR2EV

3 Responses to “The Robustness of a Battery Electric Car.”

  • Joey says:

    That is bad news. Good thing you caught it before the loose connection could melt anything and take out even more cells. Did you notice any change in efficiency or was the inspection on the terminal your first indication?

    • Ken says:

      I caught the loose terminal while checking the connections at the 20k miles check up. It was the first indication. I am going to try to tap a larger thread to fix. I’m now driving with 44 cells instead of 45 for quite sometime and it hasn’t been an issue so far. I did have to remember to dial down the full charge voltage on the Manzanita micro charger to a lower voltage so that the cells don’t over charge.

  • Michael says:

    You can easily install a heli-coil in the terminal and still save it. We have done this to some bad cells. Also, the default bolt length is 16mm and like you said, it’s a little too short. We’ve been using 18mm with good luck, and 20 is just a bit too long. Car looks good!


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