AndyMc1970 said:
Sorry when i said CELL, i am not sure what the correct name is called, but one of the parallel packs. I use 14modular cells the same as Paul Kennett.
As they said - basically the current it handles has nothing to do with the current of the overall pack, but just the balancing current. Additionally, you will still need an overall master controller. Maybe it's because I didn't look long enough, but all I saw were slaves - ie: you have individual slaves which read each "cell" (for us each cell is each string of cells connected in parallel such that we have around ~4v which we call a pack) for voltage. It sends that voltage reading to a master module which then tells a slave whether it should start to balance that pack or not. The current rating of the slave modules is how much balancing current it has - ie: how quickly it can burn off excess power in that "cell"/pack.
You still need a master module which reads the voltages from each slave device to determine if balancing is needed, and to tell each cell when to do that. It'll also need to control something else for over/under voltage or current protection.
Maybe it's because I'mobtuse, but it seems to be missing most of what it needs to really work properly - ie: the master module that controls it all.
Also, it just generally seems like you might need to spend more time reading about BMS systems in general.
They are really complicated just in general, which is why the commercial units cost so much. ANY DIY solution is going to require you to spend hundreds of hours learning in a horrifically painful way to get it up and running - there is no easy way out. I'm currently working on a BMS that should be less expensive than any of the other systems out there, but it will still be a DIY solution with bugs and issues that a battriumor electrodacussystem won't have. Your BMS is just as important as your batteries - so it isn't worth skimping on. There are people on here that seem to be manually monitoring their packs and then balance them manually as well. In the end, it just isn't worth it.
Basically, if your battery pack is not going to be that big - buy a pre-made chineseBMS and hope for the best. You can always monitor your pack via bluetooth or whatever, and if it looks strange manually balance or fix it. If you are doing a large battery pack like for a home or over 2kwh that you plan on using constantly - why bother with a manual solution? the reality is that any half-done measure will either be a safety risk, or it'll take so much time to use it properly that you'll just give up on it because it's such a pain in the butt. Or if it is a decent sized battery (think 2-7kwh), and you will use it very infrequently, you can go with the smaller pack BMS systems and their low balance currents will be OK since you are using it so infrequently the BMS will have time to fix any balance issues.
If you decide to go the DIY route, good luck! If you look around, there are dozens of DIY projects from professional electrical engineers that were started, and then months into the project dropped. i couldn't really find any that were "finished" or particularly well documented. One of the best ones I saw (very well documented) is is the Libresolar one, I'd check that one out as it probably has everything you want and need for your BMS - except it's on-board balance current isn't high enough for the super large packs that most of the people on here are using.
