I'm building a 3S 18650 Li-ion battery pack, which will be used for fast charging and discharging. Unfortunately, I can't find a 3S battery charging board that is commercially available. I found out that some people are connecting a BMS and powering 12,7-12.8V directly from a DC/DC converter to the whole pack, but I started wondering is that ok for the battery. Furthermore, I'm wondering is the balancing of the cells working in this direction, and what will happen when the battery pack is full? Is it healthy for the DC/DC to pump and the BMS to cut the supply?

I know that the proper charging IC will manage each cell voltage and either switch from CC to CV at some point to reduce the wear, but couldn't find other solution for now.


1 Answer 1


Proper charging happens with a proper charger circuit.

A BMS is not a charger, and a DC/DC converter is not a charger either.

So it is not OK for the battery. The BMS is the part that does balancing if it has a balancing feature.

But a DC/DC converter will not know when to stop charging, and if the current or voltage never exceeds the BMS limits the BMS will also not be able to cut off due to overvoltage or overcurrent.

More of an issue is the DC/DC converter, it will try to output the programmed voltage, and it can't do that at any current because the battery voltage is determining the output voltage. So likely the DC/DC converter keeps hitting overcurrent or undervoltage protections and fail to output anything.


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