ahh beat me to it. I hadn’t thought of the “higher total potential when stacked” bit, I’ve only seen isolation in boards where you’re trying to keep a battery away from an idiot (user), or mains away from a measurement instrument or something
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I have been doing some poking around in the datasheets and app notes for the TI automotive BMS chips this year so the isolation stuff they have to do for the modules that are stacked up in an EV was fresh in my mind. 
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I can be completely wrong about those modules stacking though. 
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Awesome information, thanks y’all!
I think y’all are definitely onto something here. I just checked, we have 1 white module for every 5 black modules. There were 6 modules per battery pack. So whether the white is the “master” or whether that isolated circuit is simply out of necessity from being the highest voltage point in the pack, it’s definitely special.
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ayyy cool cool, yeah 96S (6x16S in series) is fairly standard in commercial EVs, or it certainly was a couple of years ago when my textbook was written and my supervisor was in industry
Bit of background: the threshold for where you need to worry about isolation depends on a lot of stuff[1] but the very loose rule is <60V - Safety Extra Low Voltage, you’re probably ok, >60V - hazard. A single fully charged 16S module is a little above 60V, and there is a whole whack ton of energy there if you screw up, so I think that every module has “basic” protection built in, but the aim is to keep them in “safe” discrete packages and not have to worry about stacked voltage. If you just keep each module in a very mechanically secure plastic housing that’s a good insulator, you get to pretend they’re all ~60V units that exist on their own and you’re probably fine. That way the board never has to worry about being 200V from anything, because the only stuff that’s anywhere near it is roughly in the 60V range.
The problem is that logic signals are almost always referenced to ground, so the second you try to communicate with an external grounded logic part you don’t get to pretend you’re a separate isolated “60V” unit. You’re now 400V up, talking to something that only speaks 3.3V.
If the ratio was 1 black to 5 white, then definitely the black ones are the cheapo ground level units, and the white are all of the others that have to be extra protected lads. But because it’s the other way around I’m fairly sure that it’s “everyone be careful, and the little portion that speaks for the whole pile gets a secure enclave”
[1]
- How powerful the energy source is if something goes wrong - static electric shocks from rubbing your hair on a balloon are technically thousands of volts, but because there’s no real current flowing the consequences are non existent
- Environmental conditions that could make arcing easier - if it’s humid salty air then sparks go much further and with more energy
- Margin of error in case stuff changes - is this a permanent installation that needs to stay in place for years, are you in a situation where impacts and vibrations can ruin your day like an EV
- Frequency of the voltage changes - idk spooky shit can happen
- Inductive spikes that can temporarily push you over the edge etc
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Hmm…I’m leaning towards white being the master then. The white module would handle and isolate the comms for all six modules from other circuitry. It seems to have an MCU (or some other controller chip) that the black modules don’t have.
The TI battery monitor chip the modules use have their own chip-to-chip (module-to-module) comms so the isolation in the white module would just be for isolating the entire stack of modules from other stacks or from the ECU. This would make the white module the “bottom” one in any stack.
…maybe. 
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Forgive me for haunting this thread a little, but I have a request/bit of feedback for the ebay store
I appreciate the the clear statement of “manufacturer rated” and the bold disclaimer on variance, good stuff. The request is if you’re using a quote for the discharge rating, could you give who it’s from or what level of confidence we should have? Knowing that the capacity claim is from the manufacturer is good for folks who want to dig deeper, so having the same context for discharge rating is helpful. I interpret Samsung/LG discharge ratings very differently from Exway, and (if I was more informed, I assume) from BMW
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This is some really cool hypothesizing! It’s really fun to try an reverse-engineer these designs and figure out what the manufacturer’s intentions were Thank you both for your input!
In that vein, I have been trying to figure out a discharge rating for these cells/modules. Either Samsung is very tight-lipped about specs for their prismatic cells, or I am looking in the wrong places.
After a whole lot of looking, the closest thing I can find that gives me a hint is a performance spec sheet for the car that these modules came out of. According to Car and Driver, the 2018 BMW 530e has an 111 horsepower electric engine (in addition to it’s 180hp gas engine). 111hp is equal to 81.6kW.
Divide 81.6kW by 6 modules in the pack, and you get 13.6kW per module, or roughly 230A per module (and I’m assuming that would be a max value).
I think i’m doing that math right?
The problem is that I dont know if that “81.6kW electric motor” rating is the theoretical max for the motor, or the actual peak power output of the whole system, or what. Seems kinda thin, and so I probably wont put it on the spec sheet when I list these modules.
I’m wondering what yall think about that? I have reached out to Samsung SDI requesting a datasheet for these cells, but I have absolutely no expectation that I will get a response, much less a datasheet haha.
This is a great point, and ties in really well with questions I have been asking myself already (see above haha). I am going to remove that line from the Fiat module product listings. That quote is from the old product listing that someone before me (either my predecessor in this position before I was hired, or my boss before this position existed) wrote, and I carried over to this new product page when I was cleaning up and relisting all our old/expired listings. I have absolutely no idea where that info came from, or whether it’s just complete speculation.
It’s important to me to provide accurate, verifiable info for everything I sell. It’s not just performance that’s on the line after all, it’s the safety of the user who may be blindly trusting what they read in a product description.
So for now, unless Samsung gets back to me or I can find a datasheet or something, I’ll just leave those specs blank if I cant verify them confidently! 
If anyone has suggestions about where I should be looking to find information about cells/modules like these, please let me know!
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80+ kW, while not technically groundbreaking, is perfectly respectable for a basic city EV[1]. For a hybrid big boi that’s (in my noob-adjacent opinion) very much in line with expectations. My money is that that would be driving the motor pretty hard - ie generating more heat per second than it can sustain for extended periods, but definitely not setting the thing on fire - it’s probably what the system is realistically rated for in real world loads. Non-racing-focused EV use is bursty, and also a fairly nice representation of what the system can actually pull. I (again, haven’t worked in industry) would be quite happy rating the battery, power electronics, and motor around what the manufacturer states. Cars don’t generally state silly numbers, because they get sued into oblivion if they’re caught.
True true, but to be honest representative information that gives the buyer a real picture of what they’re getting is great 99% of the time. The ability to cross-reference stuff is important for us nerds, but as long as there’s some internal tracability or confidence in the statements it’s still relatively useful for sales purposes, you probably don’t need to go scorched earth on anything that can’t be peer reviewed
[1] - eh I couldn’t find an amazing source, you can poke at this unwieldy spreadsheet below if you like and sort by column K from lowest to highest for all vehicles sold in the US this year by power http://www.epa.gov/system/files/documents/2021-08/21tstcar-2021-08-25.xlsx
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They are verrrry tight-lipped about those things. IMO they won’t say anything unless they know you are serious about buying millions of them a year.
Here are a few links for ESS and automotive, just to possibly lead you to better info…
https://www.batemo.de/products/batemo-cell-library/cs0495rt001a/
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hm, that chip is ISO26262 compliant… intresting
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TI has some stuff that can get you to ASIL-D.
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This is really what I’m going for, yeah. I just want to make sure that the info I’m listing is as accurate as I have been able to get it, and I definitely want to avoid passing off hearsay as fact in a context where it might later be sourced as credible info. (see: “Information Laundering” and “Trading up the chain”)
Anyone up for a group buy? 
You are a saint, John! Have I ever told you how glad I am to have friends who are this much smarter than me?
https://www.batemo.de/products/batemo-cell-library/bmw-530e/#get-data-popup
Wow, this website is amazing! They have tested the exact cell that is in these 16s BMW modules!
Reading through their data-collection and testing methods, it seems like everything they list is very well researched. I really like how they define their Continuous Current vs Peak Current ratings.
I feel pretty confident using Batemo’s numbers on my product listing, unless there’s something I am missing? My one concern is that the page I linked says these cells are 29Ah, when all my other research into these cells says they are 26Ah. Perhaps that’s a typo? Or maybe Batemo is testing the capacity all the way down to 2.5V, while the modules in the car are not discharged that far? Hmm… 
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Could be.
Or it might be a different cell. 
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Thats what i’m worried about. However, I have been looking and I cant find anyone else on the internet mentioning a 29Ah Samsung SDI cell, especially not one that came out of a 2019 BMW 530e 
Other than that one spec, the Batemo report seems to line up perfectly with the cells that I have here.
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I hear great things about Bumblebee on insightcentral.net. however the previous owner got my 1st gen Honda Insight batt from Greentec
Cool to see!
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From my understanding, the Honda Insight community is a big chunk of our Hybrid battery business, even to this day Our owner (Eli) is/was pretty active in those communities. Seems like the first gen insight has become something of a cult car for some people, and they will do anything to keep them on the road
I have been considering other communities which would potentially be interested in the EV modules we sell. I’ve been building a list of forums which I think are applicable, though a lot of other forums are not nearly as vendor-friendly as this one (some are even pay-to-play for vendor accounts, even if you are not using your account to promote your business at all).
If any of yall have any suggestions of forums/facebook groups/communites that yall are a part of that would be interested in cheap EV modules, let me know! I would love to make a presence in more places to answer questions and get our name out there.
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16s BMW modules w/BMS are live!
I also dropped the price on all other battery modules by around $100 each, and added free shipping. If you have any questions, let me know!
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$220 per KW for used cells? Maybe just me but this seems pricier then battery hookup or battery clearing house. I thought they usually shot for $100 per KW, but maybe that’s just because your listing includes shipping.
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Are there capacity tests done on these batteries to see how much they still have?
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