0
\$\begingroup\$

I have individually tested the capacity of ten 18650 batteries with my iCharger 4010. My question is, how much ampacity difference is ok when packing them in parallel ? The following are the readings from my batteries. I was thinking arraigning as below:

  1. 1970mAh
  2. 1876mAh
  3. 1796mAh
  4. 1783mAh
  5. 1635mAh
  6. 1596mAh
  7. 1497mAh
  8. 1457mAh
  9. 1158mAh
  10. 800mAh

Will test the 800mAh again.

\$\endgroup\$
0
\$\begingroup\$

When wiring cells in parallel it doesn't matter what their individual capacities are, since they will be at the same voltage and so will charge and discharge together.

Matching capacities is more important when wiring cells in series, because the same charge goes through each cell so if one has lower capacity then it will charge and discharge faster. Lithium cells will be damaged (possibly leading to a fire) if the voltage goes too high or low due to over charge/discharge, and the charger may not be able to detect the over/under voltage of a single cell in the pack.

Another reason for measuring capacity before making up a pack is to check that the cells are in good health. 10% below nominal capacity may be normal manufacturing tolerance, but 30% is bad. At least 2 of your cells appear to be faulty, and another 4 are suspicious.

\$\endgroup\$
  • \$\begingroup\$ Thanks Bruce. So the set of batteries in series should be good ones and it doesn't matter when the others are connected in parallel for the increase in amps. I am guessing the last two would be faulty. Anyways i will be testing them all again individually. \$\endgroup\$ – George May 6 '16 at 21:24
  • \$\begingroup\$ "So the set of batteries in series should be good ones" - not sure what you mean by that. If your batteries each have several cells in series than you should check the individual cell voltages in each (battery) pack to make sure they are the same (<0.05V difference when charged). \$\endgroup\$ – Bruce Abbott May 6 '16 at 21:28
  • \$\begingroup\$ Well good ones i meant the batteries that are connected in series should be best in the pack as those determine the total voltage of the pack. I did not get the part "difference when charged". Does that mean the difference between the cells ? \$\endgroup\$ – George May 6 '16 at 21:36
  • \$\begingroup\$ yes, difference between the cells. "the batteries that are connected in series should be best in the pack as those determine the total voltage of the pack" - ??? \$\endgroup\$ – Bruce Abbott May 6 '16 at 22:51
  • \$\begingroup\$ You said the batteries should be in good health and since max voltage comes from those connected in series and those bad cells could affect it. Was i wrong with that assumption. Which cells are bad that you've noticed? \$\endgroup\$ – George May 6 '16 at 23:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.