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Re: (ET) Pack is unhappy, weird!

Yeah, buddy pair had issues though, the big one was if a battery went bad it would drain its neighbor and you would have two dead batteries. Or one would open and suddenly your battery would reverse once you hit 50% discharge, followed by even more reversal and a fire/fun.
19 cells were set to zero volts. The remaining two strings are fine and in fact are taking the same charge profile and 2/3 the capacity for charge as the 3 string pack. It's as if there was nothing wrong right up till the batteries committed mass suicide.
I'll look into them to see if they were dry when I pull all the cells this weekend and replace. It is the oldest string in the tractor, going back 20 years of continuous usage. But that's hardly middle age.
Time to put in contactors to break up the pack into 3 segments. The front will always be on, and the rear ones will click in on charge and when under power. 

C

On 11/5/2024 11:59 PM, David Roden wrote:

Back in the day, when some road EV hobbyists used series-parallel battery
arrangements with 12 volt modules, often AGM lead, they usually "buddy-
paired" the batteries.

That is, instead of creating 2 nominal-voltage (say 144 volts) series
strings and paralleling the strings for more amp-hour capacity and current,
they connected pairs of 12 volt modules in parallel, then connected all the
pairs in seriees to reach the required voltage.

(View with monospaced font:)

This:

B   B   B   B
|---|---|---|
B   B   B   B

and not this:

B---B---B---B
|           |
B---B---B---B

It's been a while since I've torn into a laptop battery, but I'm pretty
sure that I recall that they also use this method.

IIRC, some EV hobbyists added fuses to the parallel connections.


David Roden - 25 Years with ETs

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