BMS with batteries in parallel

[jktobin1]

Hello everyone, I am currently in the process of designing a 20s 10p battery for an electric bike. I have purchased all of the cells and the 20s BMS to go along with it. I am going to be making two packs in order to make handling easier. I am able to make each pack a 10s 10p pack and then wire them in series, or make two 20s 5p packs and wire them in parallel. I am leaning toward the 20s5p packs in order to reduce the heat generation within each pack and allow full amperage to run through the copper wire rather than the aluminum bus bars that I am using.

My issue comes into wiring for the BMS. In the two 10s10p pack example it is very simple to wire with one lead going to the 10 series connections in battery one and 10 series connections in battery two. When looking at the 20s5p example, am I able to only monitor one packs series connection's voltages and just assume that the other pack which is wired in parallel will have the same voltage. I have included a picture of the current design using two 10s10p batteries

https://drive.google.com/file/d/12dOkcPSizlTaleI15ljyiheOVkueif4i/view?usp=sharing

 

[john61ct]

20s5p packs, wired so that the balance leads are also paralleled across the packs.

So the two #1 groups from sub-packs A & B become one 10P group

same with group #s 2-20

when the two are joined it literally becomes one 20s10p

 

[docw009]

If the packs are going to be separated. I'd do two separate packs each with their own BMS. Then series pack connections add a extra level of circuit complexity, in that if one pack shuts off, the BMS MOSFETS on the other pack has to withstand 84V rather than 42V. I'm sure they can, but parallel has no such worries, so dual 20Sx5 gets my vote.

If you only have one BMS, then you have to bring across 21 balance wire connections, as well as the negative/positive leads. The balance plug might be a bit fussy if you break the parts apart frequently. You also cannot use each pacjk as a stand alone battery. Well I guess you could, just no BMS on one.