Two isolated grounds from a single ground terminal

Thread Starter

adhith

Joined May 29, 2017
46
Hello everyone...
I'm using a 4S 18650 battery pack and its BMS board in one of my project. I'm using a constant voltage buck boost converter to boost the voltage from 12v to 18v and then using a CC/CV buck converter to buck the voltage to the required voltage of 16.8 for the battery pack. The reason I'm using two of these modules is to due to the lack of availability of an appropriate CC/CV buck boost converter. Anyhow the thing works fine since i have tested it with led strips and works as expected.
The problem starts when i hook the output of the CC/CV buck module to the P- of the BMS (battery management system) Since the ground terminal is common for the P- and CC/CV buck converter input (output ground of CV buck boost converter) and output. So its clear that the resistance for the constant current function is bypassed and thus the constant current function doesn't work and its also mentioned in the circuit board discription that the input and output ground should not be shorted for the board to work properly.
So what I'm looking for is a solution to separate these two grounds from each other. What might be the possible solution.. apart from replacing the entire modules since the project is almost completed and all wiring has been done.
any help would be appreciated...
 

Thread Starter

adhith

Joined May 29, 2017
46
Can't understand you problem.
What resistance for the constant current function?
Post a schematic of what you have.
Thank you very much for your reply. Apologies for not giving the correct details to my question. The resistance that I meant was that we manually set by adjusting the potentiometer in the CC/CV buck module Under the specifications of the board in the website its also written that this resistance will be bypassed when the input and output ground is tied together and the current limiting function wont work.
this CC/CV board is fed to a BMS to charge a 4S1P battery pack. My project could be powered by either by an Ac to DC adapter or by the battery pack. The ground terminal of the power supply and BMS P- is a common wire and the the +ve output from the adapter and the P+ terminals is connected to a switch to toggle between powering the project by the adapter or the battery pack.
The problem is that the CV buck boost module driving the CC/CV buck module has the -ve terminal tied to the common ground wire and when the output -ve terminal of the CC/CV buck converter is connected to P- terminal for charging, the input and output ground of the CC/CV buck module will be unfortunately connected through the other module (since both the input and output -ve terminal of the CV buck boost module are already shorted within the board itself as default and only the +Ve terminals is different in it) so the current limiting function wont work. I hope my explanation is clear.

I have attached a pic of the CC/CV buck module that I'm using and also a schematics of what I'm trying to do.
 

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