gothicsurf
10 mW
My first plunge into battery construction prior to taking on a project building an ebike pack. Recently I replaced the 18650 cells in four dewalt 20v li-ion packs. Trouble is I forgot to balance the cells before connecting them in series and realized this when the voltage indicator on one of the packs only showed 2 out of 3 bars.
Unfortunately spot welding was the method and have since sent the machine back as it was underpowered to the extent I had to zap each connection a dozen times to form a strong enough weld. For the reason, it would not be possible to take this pack apart again without the terminals shredding.
Therefore I would like to balance the cells while connected in series and the setup is as shown .. test leads from a simple 18650 capacity tester that finishes the cells charged to 4.2V. However, the tester acts a bit erratically connected in this manner and do not know if there is something electrically fundamental I am missing about why this is happening.
When connected the tester displays a voltage that is at least a few tenths difference in voltage, and is verified with different voltages shown at both ends of the test leads, at the battery vs at the tester. Seems to imply there is a voltage drop across the test leads but don't think they are too thin for the .5A current of the tester .. The results from one cell thus far were also almost 1Ah below that of previous tests, while finished leaving the cell at ~3.6-3.7V instead of the usual 4.2V.
I have tried using one of the other packs that is better balanced and it does not seem to have much better run time in a circular saw. I am sure lack of optimal balancing plays a part but also not entirely sure if samsung 30q is the ideal cell for this application. Stock the packs contained samsung 20R, rated about an Ah less than the 30q and was totally hopeful in hacking these packs to have an upgraded capacity without adding weight.
Unfortunately spot welding was the method and have since sent the machine back as it was underpowered to the extent I had to zap each connection a dozen times to form a strong enough weld. For the reason, it would not be possible to take this pack apart again without the terminals shredding.
Therefore I would like to balance the cells while connected in series and the setup is as shown .. test leads from a simple 18650 capacity tester that finishes the cells charged to 4.2V. However, the tester acts a bit erratically connected in this manner and do not know if there is something electrically fundamental I am missing about why this is happening.
When connected the tester displays a voltage that is at least a few tenths difference in voltage, and is verified with different voltages shown at both ends of the test leads, at the battery vs at the tester. Seems to imply there is a voltage drop across the test leads but don't think they are too thin for the .5A current of the tester .. The results from one cell thus far were also almost 1Ah below that of previous tests, while finished leaving the cell at ~3.6-3.7V instead of the usual 4.2V.
I have tried using one of the other packs that is better balanced and it does not seem to have much better run time in a circular saw. I am sure lack of optimal balancing plays a part but also not entirely sure if samsung 30q is the ideal cell for this application. Stock the packs contained samsung 20R, rated about an Ah less than the 30q and was totally hopeful in hacking these packs to have an upgraded capacity without adding weight.
