Hello Pascal,
thanks for your info about using 32700 Li-Ion cells (powerful batteries!)
BMS (Battery management system) is a quite useful add on.
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They are necessary if you intend to charge the cells while connected in series with an external source of Voltage, moreover if the supply doesn’t regulate the current during the charge. The BMS will be in charge of modulating the charging current individually for every cell iin the pack.
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When you use the pack in the activation, the BMS will control the discharge current at each cell and will make sure you don’t over discharge the pack below the limit level.
So far I have not added a BMS. I will use a charger that will load every cell individually, so not a risk there.
Concerning using the pack without the BMS, it is not a big problem when you use new cells from the same batch and you look after the output voltage during the activation and makes sure you are not overdischarging (say below 10 V for a 3S).
I know every cell degradates with time, so I must be careful and monitor from time to time if there is any battery that is deviating from the rest. If that was the case I should remove and replace that cell or even to replace all of them by new ones.
Anyway, adding a BMS is a good feature.
That’s it; it all depends on what is your current requirements both for RX and TX.
If you need more amps either you sum 18650 in parallel (3S2P, in example) or move to 21700 that is what I did.
73 de Ignacio