AMPhibian <[email protected]
> And people wonder why some of us are simply running with no BMS at all.
> Seems to me a BMS is a bandaid for cells of different capacity and differ=
> resistance. The correct answer would be better cell grouping. No re=
> cells couldn't be grouped at the factory with the same actual AH capacity
> and same internal resistance. Get them close enough and stay away from=
> ends of the charge/discharge curve and you'll likely be fine. Even wit=
> pack varying in capacity of 4 ahs and different resistance I'm not seeing=
> noticeable change in the last 6 months of driving, even when going pretty
> close to 100% DOD a few times.
> Bill Dube wrote:
>> The better systems report a failed cell module or cell group module,
>> but some do not, just as you have said.
>> You mentioned the two most common modes of failure; load open and
>> load closed. There are _many_ modes of possible failure, one of which
>> could be a module that is reporting that it is heathy, but in fact it
>> is not. Another mode of failure is a module reporting that some
>> problem with it or its cell has occurred, when nothing is really wrong.
>> When you add in redundancy, and with it increased complexity, you
>> increase the modes of failure. This can make the problem worse
>> instead of better. The complicated BMS can generate a seemingly
>> continuous stream of fault signals, preventing the vehicle from being
>> operated in a useful manner. Yes, the cells are protected, but you
>> can hardly drive the car.
>> A consensus type system comes to mind, but the costs go out of control.
>> I don't know if there is any perfect answer. One extreme puts the
>> cells at risk, another gets too costly to be practical, while another
>> is too eager to stop the car.
>> Bill D.
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David D. Nelson
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