Advice on BMS for a 7s8p battery built with Chevy volt modules

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palmtree

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Aug 23, 2021
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I'm planning a battery that would be considered small for a house but fairly large for an RV, which is what it will be used for. I have a battery from a 2017 Chevy volt. My plan is to use two of the 16s modules and two of the 12s modules and modify them to 7s8p. The load will always be low. I can't imagine a situation where I would draw more than 40 amps. However the charging current could be as high as 80 amps under perfect conditions. I don't want to break the bank on the BMS for a vacation vehicle but I do want it to be safe. Of course 90% of the time everything will be powered down and in storage.
I am thinking about running 4 JBD BMS's (1 BMS for every 2 7s batteries). Would this be feasible? I may be missing something important.
Thanks
 

Cheap 4-life

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Aug 3, 2020
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I use 2017 to 2019 Chevy volt batteries. I only use the 16s batteries from the full pack. The Chevy volt batteries are high voltage (300v+) when they are in the vehicle. They series all of the 12s and 16s batteries. I don’t know if it’s a good idea to make a battery out of those that has such a low voltage. I’d like to know how many amps the Chevy volt uses to operate its electric drive motor. Most likely you will be fine. But we wouldn’t want to exceed the amps that the car uses.
 

palmtree

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I'm not sure. This says 430 amps but I'm not sure at what voltage that is.
 

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Cheap 4-life

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Thats a lot of amps they are capable of supplying. So yes I was worried for no reason. These batteries really do have a cake walk life being used for RVs or residential solar storage
 

Cheap 4-life

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I’m using a chargery bms. It does the job
 

palmtree

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Just one chargery? So when your bms reports the voltage of any given cell it is actually the voltage of 4 cells?
 

Cheap 4-life

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Just one chargery? So when your bms reports the voltage of any given cell it is actually the voltage of 4 cells?
When you put a balance lead from the bms to the positive of each of the 6 (i have 6 batteries in parallel) then those 6 cells are essentially paralleled. This means that each of those 6 cells equal out their voltages simply by being wired together via the balance leads. The bms isn’t seeing an average of the 6 cells. The 6 cells actually balance each other to the same voltage. If one of the 6 cells starts to get to high or low then that group of cells (cell number) will show high or low voltage. I read somewhere that having multiple bms in parallel wasn’t a good idea
 
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