[IamIan]

Originally Posted by creeky

Ian, I am trying to keep it simple. And I see plenty of evidence online that good quality lithium cells stay in balance.

Simple to make .. or .. Simple to use ?
At some point one of those must be chosen as more important than the other.

I assumed simple to make .. That's why I suggested the two most simple options .. Basic EV-Display type whole pack and Batt-Bridge.

Batt-Bridge type half pack comparator .. as simple and inexpensive as it gets for informing you if the cells drift out of balance .. If it happens you can manually go in to service the pack .. if it happens often .. than you can always later add the cell level BMS.

EV-Display type simple basic meter to signal whole battery Top &/or Bottom .. and do Battery Ah/Wh counting.

Originally Posted by creeky

But, but, but. So a part of me wants to do the simple and easy thing. Perhaps I could do a similar board dividing the pack into the 6 parallel units?

Although it add complexity and cost .. if the MTBF rate is high enough for the cell level BMS .. Like those seen in OEM BEVs like Tesla's and such ... than it makes a lithium battery pack pretty much a 'black box' that just works , as that cell level BMS does any maintenance for you .. more complex system .. but less complex yearly maintenance/service .. ie .. less simple to make .. more simple to use.

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For parallel .. you have two main paths:

1. Parallel Cells:
   • Pros:
     1. 1 BMS cell circuit can monitor and service all the cells in parallel.
     2. Strong individual Cells can help carry weaker cells they are paralleled to.
   • Cons:
     1. If 1 of the cells in parallel isn't just weak .. but actually goes dead .. it will take all the other cells in parallel with it.
2. Parallel Subpacks:
   • Pros:
     1. If one cell isn't just weak but goes dead .. the BMS might be able to cut that subpack .. preventing the destruction of the others in the pack... Depending on the setup of the BMS.
   • Cons:
     1. To monitor and service each cell would require 1 BMS cell circuit for each and every individual cell.
     2. Strong individual Cells can not help carry weaker cells.