jimmyhackers said:
i am NOT asking why one cell failed, I AM ASKING WHY THE ONE OTHER CELL DIDNT REALLY DEPLETE ONE BIT.
That's what I just explained, *assuming* that the problem you are describing is that one of the two cells in a parallel group in just one of the 6s2p packs is very low, and the other is still full, and all the other pairs of cells that are in other groups seriesed with this problematic group are at their expected voltages for this point in the discharge curve.
Some different words that say the same thing:
Because it's connection to the rest of the pack on one of it's terminals failed, it isn't supplying any current to the rest of the pack. So no energy comes out of it, so it stays at the same voltage.
And even though you're not asking this, it's still relevant to this specific scenario: Because that disconnected cell isn't supplying energy, the other cell in parallel with it supplies that energy instead, along with the energy it would have supplied normally, which depletes it twice as much as it would have if it still had the second cell in the group paralleled to it.
Again, this *only* applies if the problem you are describing is that one of the two cells in a parallel group in just one of the 6s2p packs is very low, and the other is still full, and all the other pairs of cells that are in other groups seriesed with this problematic group are at their expected voltages for this point in the discharge curve.
See my attached diagram at the end of the post for an example of how the problem could occur.
If the problem you are describing is anything else, then my explanation is probably not relevant.
If the diagram you posted is of the problem you describe, then you're saying the entire end cell group (both parallel cells) is dead, discharged much farther than normal, while the next-inward cell group (both parallel cells) is still essentially full. This is different than the wording you used in the first post, which says: " (its usually only one of the two cells per cell that fail, which is what happened this time)" and is what my explanation above covers.
There isn't any way one cell group in series could stay full while the rest are drained even partly, if they are connected the way they're shown, during a discharge session. (it *could* happen if they're just sitting there and one of the cells in each group, *except* for the one that's still full, failed in a way that drains the other parallel cell down, *and* the lowest group had both cells fail so they drain even faster).
It could only happen during discharge like this if something disconnects the still-full cell group from the series connection, so no current flows thru it, but doesn't short across the cells in the group, yet does bypass the group by connecting the other two groups normally seriesed with it. See the last example in my attached diagram at the end of the post.
What would then cause the last cell group to be more than fully discharged, I don't know; another wiring fault that shorts (or partially shorts, placing a high load on) that group out could do it, or just a random internal failure, but it would be highly unlikely for a random internal failure to happen *at the same time* as something that disconnects the other cell group from the pack.
Without being there to do a visual inspection and test measurements myself directly, I can't tell which specific problem is occuring, to then figure out which problem could have caused it.
jimmyhackers said:
i get what you are saying but that doesnt explain why one cell was at 4.14v when it should of been at 3.98v like all the other normal cells. im not sure if im not explaining right or your not reading it right.
like i said....i check every single cells individual voltage before and after parrallel charging (when they are not connected in parrallel), that was fine before the charge and fine after the charge.
i.e. if you depleted a (fully charged to 4.15v per cell) 6s and killed one cell and the other 5 are all at, say 3.7v.....that's normal
but if you depleted a (fully charged to 4.15v per cell) 6s and killed one cell and only 4 of them are at 3.7v and another one is at 4.14v.....thats not normal.
i am NOT asking why one cell failed, I AM ASKING WHY THE ONE OTHER CELL DIDNT REALLY DEPLETE ONE BIT.
The diagram below shows just the wiring diagram for one 6s2p pack on the top. It only includes one of the three packs you are using. Below that is the pack before discharging. Third down is the pack as it would be after a normal discharge. Fourth down is what it could look like if there were one parallel cell in a 2p group that got disconnected and didn't discharge while the other one overdischarged. Last one is the problem you appear to be describing in the diagram you've posted. If I've got that wrong. please correct me.