I want to implement a few chips for battery management and due to the ADCs of each cell working at bigger voltages each, and each chip(I have to cascade thre ICs LTC6803-4) with a maximum voltage lower than the battery maximum, I have thought if this implementation would work: I have seen something similar in the application example of the datashet of the IC:
Would that schematic work?
This is basically extrapolating LTC’s 2 stage to 3 , so on the surface , there’s no reason it shouldn’t.
But you have a challenge from me.
Define all the qualitative performance reasons to realize this schematic with improvement options.
Define all the quantitative of your charger system specs that matter with this BMS and tolerances with fault detection and correction mitigation functions needed that need attention.
One of the challenges with cascade BMS is that all batteries must be well matched for capacity and ESR in order the the residual error to be dissipated in heat by the Zener internal diodes.
Also consider including individual thermal sensing, which is critical when 1. occurs unexpectedly and the cells are not thermally coupled. -This is best done with diode Or’ing than thermistors.
- considering the wide tolerances on e-caps & bulk supercaps, LI Ion batteries are no different.
- worse yet, because the weakest cell has the fastest dV/dt they will become the 1st to become under or over charged.
- when undercharged the ESR rises rapidly below 10% SOC resulting in more heat loss with shared current during operation but excess current shunting during CC charging if 1 cell reaches 100% SOC at 4.2V per cell while the string has not reached CV mode.
- since CV mode uses declining currents, the %C deviation determines how long BMS must shunt up,to the power Max. being charged to the other cells.
- this may require you to have more than 1 CC mode so the equalization charge layer can catchup in each cell. I.e. CC to 3.8V x36 cells then Monitor IC temp and reduce CC as required by IC temp. or battery temp to 4.2V x36 then go to into CV mode for a time limited final charge. Or consider 4.1Vx36 or longer life.
Disclaimer: I have not used this excellent solution but has great potential for HV packs.(pun intended)