Originally Posted by sparrowhawk1
Thanks for the very clear explanation of the importance of keeping the cells balanced. I've read your posts on several threads and watched your YouTube videos, they are a little too technical for me to understand. I've watched videos with mini BMS between the positive and negative of each cell and the explanation that the LED's are showing that this battery(cell) is at the voltage point where current
is being shunted but they don't show how. And I understand that there is high voltage cutoff for charging circuits and low voltage cutoffs. but I've yet to find any drawings or schematics or videos on how exactly it's done. Thanks again and good luck with your project
Sorry if things I explain are not to clear. I try to simplify things as much as possible but I do not always succeed.
Hi and low voltage cut off is quite simple for charging you stop the charging when any of the series connected cells gets to the set high voltage point let say 3.6V.
You need to monitor
each individual cell in order to be able to do that.
Low voltage cut off at discharging is the same way when any cell gets under that point say 3V you just cut the load.
You never care about the total battery voltage just the individual cells.
Not sure exactly about what mini BMS you are talking about but individual cell monitors is common on large battery banks like those on electric
There you have individual monitor
on each cell and those are linked together using a serial
communication protocol to transmit voltage data to a main unit that reads what each individual monitor is sending and takes the decision to cut the power (usually using external relays) if any of the cell has an Hi or Low voltage condition.
For cars they have large voltages even over 100V so they need a large number of series connected cells so it makes sense to have individual monitors and a two wire serial
linked communication to minimise the number of wires going to the main monitoring unit.
For small number of cells like is my case with Solar BMS max 8 cells is easier and more economical to have monitor wire from the main unit to each individual cell just 9 wire for 8 cells.
I'm sure there are some diagrams out there on how to connect everything I must admit I did not do a diagram for my Solar BMS as of now.
I target a more knowledgeable crowd at first do to the nature of my product. Is more a dev board and extremely flexible with fully programmable parameters (over 30 different parameters) so an understanding of each individual parameter is needed else if you introduce even just one wrong parameter you can damage the battery.
Is flexible so that it can be used with any type of existing and future Lithium cells not just LiFePO4 and can even be used with supercapacitors like I do during development.
I can of course set custom parameter for LiFePO4 or even lock the parameters to work only with LiFePO4 but depending on application most of those parameters need to be different for optimum use.
But I'm starting again to go in to complicated details.
In the end a BMS is quite simple it just need to know voltage of each individual cell and keep those cells between a high and a lo level.