This documentation is still very early and not complete nor well written.
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Charge / discharge at 1C? See
Old scenarii
Questions:
  • 3A is 1C for Samsung 35E, but more for EVE and other cells ⇒ less precise on the latter
  • C-rate to charge the cell back to 3.65V

Capacity measurement

Introduction

Our method - without correction

Our method - with correction

Experiment & results

Pistes d’amélioration:
  • We could use a higher than 100mA cutoff (~200) to reduce CV phase time. Even if full-scale Ah value is not precise in absolute, we will use a ratio for the other cells.
  • D’après (1), il faudrait que l’intervalle de tension que l’on utilise pour l’estimation soit plus petit que l’intervalle entier utilisé pour le cycle/la mesure (”the capacity counting has to be delayed from the starting point of the pulse”)
  • S’assurer que la tension finale est bien homogène sur l’ensemble des cellules

Capacity grading

If we use partial capacity estimation:
1) use the sorting machine to group cells by voltage, and 1 group with too-high resistance values
2) group cells by voltage on the racks of the 512 channels in order to have the tests finish at approximately the same moment on each rack (the CCCV phase depends on the starting voltage)

Témoignages sur des forums: <100 mAh precision

Other criteria: ±2.5% matching

Image without caption

Issues with our custom method

100 mAh bin size seems to be good trade-off between precision and storage difficulty

⚠️The estimator doesn’t work the same on all cell models. For example, it can reach 3% on an ad hoc basis.
Let’s say the max. relative error we accept is 3%:
2 Ah
2,8 Ah
3,5 Ah
± 3% =
60 mAh
84 mAh
105 mAh
Then, the capacity intervals should be wider than 105 mAh
Interesting measurements that can be done:
  • Self discharge: voltage change after storage period (cell IR/V meas before xlife pack assembly)