wk057's Custom BMS - Visualization, Sunrise to Sunset
So, I've been working on getting my custom BMS project completed. I've been collecting data from it for a while and finally took the time to visualize some of it. It's super cool to see the thing in action. Some of its balancing decisions are immediately obvious, others not so much, but the algorithm is working perfectly and keeping the entire array of 216 cell groups in virtually perfect balance.
This is in spite of the fact that first, the modules are not all matched and are from at least four different Tesla vehicles with varying mileage/use. Also, I had to swap out module 3B with my cold spare (sitting on a shelf since 2015) due to a failed BMS experiment destroying a cell group over the summer. :( You'll see in the video that this module isn't well matched with the one next to it (3A), but the custom BMS does a great job holding them in line with a max ΔmV of around 22mV in worst case situations.
This is all completely custom software running on both custom hardware and modified Tesla hardware (BMBs). The algorithms track usage and monitor how much a cell group is going to need as far as balancing goes and can actively maintain the entire pack through the full voltage range of the modules. So, not just top or bottom balancing. Takes into account module temperature to estimate internal resistance changes as well, for example. It's super complex, but works extremely well even with highly unmatched modules.
I found it fun to watch. :) You can also match up the timestamps with the graph of the day on wk057.solar in this image: https://wk057.solar/netusagegraphs/20... ... I plan on exposing live BMS data on wk057.solar soon.
Same system will be in use in the 3000EV. :) :) :)
Some details:
The system has 216 cell groups (15,984 cells total).
Nominal system voltage is 44V.
The balancing circuits are bleeders at ~39 ohms.
Video is roughly sunrise to sunset packed into 90 seconds
The system uses the original Tesla BMBs (battery module boards) that are on every Tesla Model S/X battery normally. The stock firmware was quite limited in functionality, so I wrote my own overhaul that adds redundancy and a lot of other tweaks.
This has been the main test bed for my upcoming production version.
The representation is the same as if you were looking at the front of my physical battery rack (can easily see things like warmer modules near the ceiling, coolest near the floor). I have no liquid cooling to equalize temps, currently.
Things in the video:
Blue outline around a cell group means a balancer/bleeder was enabled
ΔV = How out of balance the pack or group is
ΔT = Difference between highest and lowest temperature sensor
𝜇 = Average
Σ = Sum
ΣA = Net pack current
ΣW = Net pack power
𝜇A(m) = Average current at the module level
𝜇W(m) = Average power at the module level
𝜇mA(c) = Average current per cell
𝜇mW(c) = Average power per cell
Σ balW = Sum of power being used by balancers
𝜇balW/𝜇W(cg) = Rough effectiveness of balancing against the immediate power situation (even 1% is pretty good)
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057tech.com
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