I have been fabricating a trailer for the Insight on a stand and the other demos, so I have not been on line and following this thread. I see that our battery experts have added a lot of information to consider.
The stock system:
The stock BCM only charges to 80%, never charges to 100%, and stops discharging at 20%. This has not been confirmed, but has been accepted as gospel, and is the cause of battery pack imbalance.
Charging:
The proposed charger will not stop charging when one or 10 or all cells are full, and will just keep 350MA going into the pack forever, which will fully charge all of the cells, no matter what SOC they started with.This gives us a reliable 100% SOC.
The "smart chargers" that have been used to recondition subpacks try to determine 100% SOC based on the slight dip in voltage that happens when a cell reaches 100% and starts to turn charge current into heat. On the first cycle, this dip will be difficult to detect accurately, since we are looking at 6 or more cells, and some of the cells may be at quite different SOC than the rest, so the dip may be masked by an adjacent cell in the same subpack that is not quite at the 100% SOC, so it may still be rising, while others may be fully charged and into the dip.
That means that the 100% SOC point for all cells may not be reached with the "Smart chargers"
If the proposed 350MA charge is allowed to continue, until the voltage stabilizes for at least 1/2 hour, we will know with a high degree of confidence that all cells are fully charged.
I suspect that some of the AH discrepancies that the "smart chargers" are seeing are due to this premature 100% SOC determinimg effect.
Discharge:
The danger of reversing a cell during discharge is a real issue that we need to avoid. Based on some simple experiments, I think that we are pretty safe for 90% or more of the packs just using a light bulb and voltmeter and stopping the discharge at 120V(1V/Cell), after topping off the charge on the whole pack. The key is that we are bringing all cells to a reliable 100% SOC.
The "Smart Chargers" look for 1V per cell as the zero SOC point, and would likely not see a dead or reversed cell, and could terminate the discharge prematurely, skewing the AH determination.
There may be a pack that has a subpack with a cell that is far below the average AH, and this will damage the cell. To do this so that cell damage possibility is minimized, we would need to monitor the ten subpack taps and look for a rapid drop off of a cell like the car does in normal operation. The car may be the safest discharge method we have, since it already does the monitoring at the 12 cell level.
We can speculate on the best procedures, but at this point, we can get the charge part nailed down, and then work on the discharge, and prove the system with carefully run experiments.
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