How to / DIY > Everything else
Lithium cell balancing
BruceM:
This video is unfortunately lacking in legitimate technical information, nothing about what he's doing for BMS/cell balancing, or how he divided up the high voltage packs. Seems he's set up for a nominal 48V inverter/battery bank, but that's not clearly presented either. He states he has only put this battery bank together a week ago; so has zero meaningful experience.
His diagram showing Volt and other battery packs in parallel is wildly misleading- the stock packs are high voltage and must therefor be reconfigured to a nominal 48V, if that is what his Magnum inverter is designed for. I don't know the voltage of the stock battery sub-assemblies of cells are; he has left out all the useful information.
Tanman:
If you want more technical information I’m sure he would offer it. He has responded to some of my questions.
Looks like he’s been running it that way (my first comment) for a while:
https://youtu.be/f36ElNs5WPA
BruceM:
Thanks for that link, Tanman.
It seems the Leaf modules are 2 series by 2 parallel cells , so he's reconfigured at the module level to a 48V nominal system, so roughly 7 modules in series. Getting to use the intact modules is a big help. Apparently the other batteries he's using have similar low voltage modules. Leaf modules are designed to be connected to a BMS and I have found other efforts to replace that BMS. The lack of cell level BMS and poor thermal management caused LOTS of Leaf battery failures, thus lots of used ones for sale.
It's very surprising to me that he's found the cells exceptionally well matched after 48 months with zero balancing other than the full voltage limiting by the PV charge regulator at the 7 series module level. He is fuse limiting each 48V string to 30 amps or 1440 W; he mentions that for his system, 10 amp fuses would be sufficient, so he's only charge/discharging at below 10A or 480W per pack.
I agree with Will Proust on this. He's a young enthusiast, not an engineer, but his technical information is usually quite good. His website is also a good resource for those interested in learning about and using Lithium batteries.
https://www.youtube.com/watch?v=rbkE4jxk3u8
I think most non-EE, non-electronics savy folks would be better served with the packaged 48 or 24V battery systems being sold for server racks. Proust has some good evaluation videos on them.
For safety I'd sure want cell level high/low voltage monitoring and disconnect protection; and with that usually comes some sort of low current passive balancing. If you don't have cell level voltage monitoring, when one of set of parallel cells dies as a short (which seems the most common reported failure mode), all the other cells in the 7 module (14 cell pairs) series string will be overcharged and this can lead to a thermal runaway and fire with lithium ion cells.
It is encouraging that some of the automotive packs are designed with low voltage modules. Once LFP (greatly reduced fire hazard) automotive modules/blades are more available, at good prices, it might be something I'd be willing to switch to.
Best Wishes,
Bruce
photosolo:
Im new here so apologies for being late to the discussion.
I'm living off grid in Mid-Wales (as of Sept 2022)
I built a 16s, 280AH LifeP04 battery with cells that I imported from China via Alibaba.
They were bought before Brexit & was in transit post brexit, so you can imagine the fun I had with that!
I gained most of my knowledge from Will Prowse and his Youtube & Forum.
The BMS I went with is called, 123BMS that was purchased from Holland
We are still in early days obviously but so far so good, touch wood !
With a decent charge on the battery our house can run for about 5/7 days depending. The system is without any Solar input at the moment as I still need to build the PV array. We have 4kw of solar to add when I get the time.
BruceM:
Welcome to the forum and thanks for sharing your LFP battery experience, photosolo. I assume you meant Sept 2021 as your start of off grid operation.
I checked out the 123BMS you selected and it is a very capable unit for those that want bluetooth, smart phone controlled BMS. It supports high voltage strings due to it's daisy chain serial communications and microcontroller per battery approach, and the 1 amp discharge current per cell should be good for larger capacity cells. Getting the current per cell down to only 1.9 ma is very good for this type of design and is sign of a skilled designer.
I hope your PV installation will go smoothly!
Best Wishes,
Bruce
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