this post was submitted on 22 Feb 2024
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[Dormant] Electric Vehicles
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Technical magic???
BMS systems are far from it. Lots of technical work going into simplifying measuring techniques, automatic switching between series parallel linking of cells based on system needs (at my company)... but the essentials of measuring current, thermal and voltage? Lmao. I'm making fun of your degree, as a holder and EIT myself.
If you're into BMS systems at all, you know that the ridiculous levels of modeling are chemistry / cell specific, to the point that would make the typical layman's eyes glaze over. A litany of cell types (NMC, LiFePo4, NCA) and more as new chemistries are invented (or go in and out of fashion) requires updates to BMS, the modeling of how the internals of the cells work, and how all of that is related to the voltage/current/temperatures of individual cells.
Measuring voltage/current? Yeah, that's easy.
INTERPRETING voltage/current? That's the hard part. And requires a giant mess of R&D effort on these cells and their individual chemistries.
There's nothing "simple" about that battery pack. The shear number of control systems that go into a modern battery-pack it should be proof enough to you.
https://stock-tesla.com/en/asy-tested-bms-96s-mdls-1021970-00-b
Not only is there difficulty in building and manufacturing this... there's also difficulty in maintaining this item. I mean yeah, we don't maintain it, its just replaced wholesale. But there's also the whole 400V will-instantly-kill-a-technician problem if they're not careful.
Sorry, I have designed complex 4 and 6 layer high speed FPGA boards, this BMS board looks moderately dense but not crazy, nor does it look like it's dealing with high speed signaling.
Try dealing with RF or something, those PCBs are quite a bit crazier.
The models for the cells are implemented in software. You know what's easy to update in place? software. You know what's hard to update in place? Mechanical systems. That's my point.
Then I'll chalk it up to another FPGA programmer dissing Power Engineering and the complexities of handling of high voltage lines.
Lmao go for it, I deal with systems shoving kiloamps at multi-tens of kv around quickly, I'll chalk it up to a small fry "power" electronics engineer not knowing better, as is customary for you so far.
GaN MOSFETs, because igbts are too slow, tech you, @[email protected], haven't even gotten to touch yet. TeChNiCaL MaGiC in your parlance.
So you do touch BMS systems and understand that the hundreds or thousands of MOSFETs that control the electrical currents of a ten-thousand cell battery pack are arranged in systems of series and parallel ... Running advanced modeling software that tries to peer into the internal chemistry of modern cells...
Yet you want to convince me that this is simpler than the like, 15 gears that make up Toyotas Powersplit Device?
In the long run, yes.
How do you account for tribological degradation in tolerances over time? There are techniques to negate the problem entirely, my 40+ year old Japanese motorcycle uses high-ish pressure hydrodynamic bearings to allow oil to be the "wear" surface... But it isn't foolproof.
Newer techniques rely on better metallurgy, oil additives which precipitate on designated surfaces, etc etc etc. It's one of those things you and I have both observed where the more you look at it, the more complex it gets.
Now change gears (haha) and observe the complexity of analog/digital systems. You and I front-load the complexity, so that any configuration changes should (mostly) be possible in software. "Oh no, we didn't use this particular junction of p-n MOSFETs"... They added $3 to the BOM, but our flexibility/redundancy is increased.
Look, you should know as well as any EE that solid state systems, when run within parameters, have a tremendous unchanging mtbf. While there are currently issues with undersizing MOSFETs and igbts, I expect our engineering models (in our heads) of what to expect from these evolving electronic components to adapt to these new operating environs, the already reasonable reliability will only increase.
Failure of these packs and their bms' are low enough that we can point to specific failures, versus how often we see someone with serious ICE engine issues in the local mechanic's shop.