General > General Technical Chat
LiFePO4 balancing.
shapirus:
--- Quote from: Siwastaja on March 09, 2023, 04:26:58 pm ---OP is considering designing their own BMS, for whatever reason. "Why do that when you can buy an off-the-shelf product" is useless advice, although one can and should look at off-the-shelf products for motivation.
--- End quote ---
It depends on the goal. If it's only to get a working product in the end at a reasonable price, then an off-the-shelf component is often the best solution. If it's also for educational purpose, then yes, DIY may be the way to go, however, it's necessary to understand that in this particular case implementing a DIY device may be too complicated (if it is to be done properly) to prefer it over a ready-made one. It very much depends on personal preference, so I'm giving food for thought rather than an advice.
Siwastaja:
--- Quote from: shapirus on March 09, 2023, 05:04:14 pm ---It depends on the goal. If it's only to get a working product in the end at a reasonable price
--- End quote ---
Looking at paulca's threads, it seems to me he wants to explore all kind of ideas, some totally impractical. So DIY designing a complicated active balancer is not a surprising idea from him. Of course, if one just wants to install a battery pack, they use off-the-shelf components. And if one just wants to develop a reliable and usable BMS in least amount of time, while still learning the relevant concepts, they should use the dissipative balancer design because it achieves the same, but is simplest to develop. On the other hand, if one wants to explore as much design space as possible, prototyping active balancers is great fun. My design over a decade ago, designed for 300-400V packs, used a flyback converter per cell, bidirectionally delivering to/from a common 30-40V "balancing DC bus". I hand-wound the transformers, and got finally to some 70% charge transfer efficiency, with synchronous rectification, before losing interest and just develop a simple distributed BMS with dissipative balancing, which ended up working great and being used in a few projects.
paulca:
The reality in my case... today, battery 80-90% full, taking 20 amps at 14.xV and the min-max balance was 0.009V.
Now the panel has fully absorbed them up to 14.40+V I expect a different story.
rteodor:
I am considering building a battery and while enumerating the available options of BMS-es and balancers I ran out of paper.
My current understanding is that active balancing is not really needed because its more expensive and then is excess energy anyway. Still there might be cases for active balancing:
1. bottom balancing (I did not see anybody doing that). Probably done during a polar night when conserving every bit of energy is important.
2. large and aged capacities might need active top balancing. Even more so if charging is done at lower voltage levels (like 3.45 bulk / 3.35 float for LFP). That is because the charging current is bigger at lower voltages and aged cells will have larger differences in capacity.
--- Quote from: Siwastaja ---Fun to see how the world goes on, and it seems Chinese are now producing cheap redistributive balancers and people are apparently buying them. Didn't know that. And I'm sure they work better than the overly expensive and complicated products I have seen years ago.
--- End quote ---
Andy from Off Grid Garage (yt channel) noticed the following about Heltech capacitive active balancer: it is terrible if its used continuously (unbalancing the cells actually) but it does a wonderful job if its only used at top in float. This balancer seems to work great with a BMS capable of activating an external balancer (some JBD variant in his setup). The balancer is also unable to balance advertised [5 or 10] Amps even in a test setup with fully charged and fully discharged cells in the same pack. The voltages are just not enough to drive such currents.
And there are also inductive balancers (Heltech has one too).... And there is JK BMS with integrated active balancer....
shapirus:
--- Quote from: rteodor on March 11, 2023, 06:12:33 am ---Andy from Off Grid Garage (yt channel) noticed the following about Heltech capacitive active balancer: it is terrible if its used continuously (unbalancing the cells actually)
--- End quote ---
I wonder what the application conditions were. I've never noticed anything like this with mine (which I have three of). Whatever happens, it always tries its best to equalize the voltages. Yes, it may fail to balance fast enough, when the charge/discharge current is too high and the cells are too unequal (and the advertised balancing current is not reached, yes). But it doesn't mean that it makes things worse.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version