How to combine packs without unbalancing them.
Series and parallel rules
Same voltage and capacity when paralleling; same capacity and age when series-connecting.
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Balancing, fusing and monitoring each string
Every parallel string gets its own fuse, and the BMS should see the whole bank.
Questions
Short answers to the ones that come up most.
Can I add a new battery to an old bank?
Not safely — mixed age unbalances the strings.
Series or parallel first?
Build capacity in parallel, then step voltage in series.
Does each pack need its own BMS?
Each pack should have its own BMS, with the system monitoring the bank as a whole.
