Love seeing this here. So much tasty esk8 knowledge. Thanks, @janpom .
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Great thread, I actually started collecting knowledge for the no BMS adc option, I’m in contact with a professor at work specialized in electronics, liion and fuel cell tech already. I’m using the graupner Ultramat 18 for balance charging up to 12s btw, it’s missing in the list.
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Absolutely incredible write-up. Thank you so much for taking the time to do this.
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That LLT Power Smart BMS is using this IC:
http://www.ti.com/lit/ds/symlink/bq76920.pdf
Essentially just an analog front end for measuring cell voltages and performing active balancing. That BMS uses the IC alongside an atmel processor like whats on an arduino nano and some proprietary FW. If all you wanted to was actively balance cells and run charging current but bypass discharge the BMS could be made MUCH tinier.
It is also possible I reckon to simply add an I2C connection to this, connect to arduino or vesc and balance without onboard MCU but that seems a bit more sketchy to me.
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Really detailed thanks Jan, basically I need an Android phone or PC. Currently the only way to do it with an iPhone is Metr/DieBieMS which is a problem space-wise on max batt builds…love both of ‘em mind. I wasn’t aware of the option of a LLT Power Smart BMS with a 3rd party app, the DaveGA option is amazing!
Maybe an old dedicated Android, everyone has one in a drawer somewhere.
Can’t imagine how much work went into this. Professionally this report would cost multiple €k’s!
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Hopefully you can add FlexBMS soon. shows a vital part of ESK8 maintenance and monitoring is a lack of suitable convenient options with out a high level of knolage
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This thing is tasty!
I guess I should put this here too. I’ve been playing around with talking to the smart bms via raspberry pi onboard BTLE and python. The idea being to remote scrape pack health periodically, graph, and alert. This is actually really useful if you have multiple boards with this bms.
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For 10S it also exists a 2000W version of the 1010B+.called 4010 Duo. 70 amps in synchronous mode. 40 amps on each channel in asynchronous mode.
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I have been using the LLT Power smart BMS for quite a while now in a few builds and highly recommend it. seems reliable and runs cool. Being able wireless connect and see bms voltages is invaluable.
It also seems like a great starting point for a open source BMS. It uses a standard arduino MCU and has the programming headers already broken out on the PCB. There is already example arduino code for using the bq76920 chip and even another open source BMS firmware designed to run on the LLT power BMS hardware (designed for scooters).
I would love to see a way to connect this to VESC / Unity and see this data within their respective apps. it would also be great if the VESC / Unity was able to use this data and do its battery level throttling based on lowest single cell voltages rather than whole pack voltages. This feature would save a lot of dead battery packs and be far safer. Something like the Unity seems like the ideal companion for a BMS like this as it already has the built in ewsitch.
A micro charge only, Unity compatible Open Source BMS would be a real game changer.
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Thanks for the well organized write up.
I have some questions regarding the LLT bluetooth BMS.
What balancing accuracy settings do you recommend?
The default values seem a bit on the low side, in terms of accuracy, for me.
I use the BMS wired for discharge and have to drain the battery before riding to avoid over voltage cut outs while braking. Since you can set the over voltage limit, up to which value would it be save to accept short over voltage during braking eg. 4.3V, 4.4V?
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This is fantastic @janpom thank you! May I suggest that you include the words ‘smart bms’ in the title?
I would love to see some other people’s experience with different Smart BMS’s. I currently have one from Aliexpress called an ANT BMS but I havent put it to use yet. Will be sure to post here with as much info as i can once I get it up and running.
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I just ordered 5pcs of the bq76940 9-15s version on aliexpress. If anyone in the EU interested is I’ll sell 2 when they are here 
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The balancing range seems okay to me? It’s ±0.03v, right? The software shows you so many digits of precision that it confuses my brain. 
But realistically the system (balance wires, contacts, etc) will not allow for accurate measurements of cell voltage to 3 digits. At least for me every method of measurement seems to give different results. Nice high end multimeter, cheap lipo monitors, high end hobby chargers… Plus the more time you spend balancing minute differences, the more arguably unnecessary wear you’re putting on your batteries.
Unless you desperately need the capacity, wouldn’t it be far better to terminate charge at 4.1v/cell? I believe the bms with default settings will still balance.
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Yes, I want to mainly charge only to 4.1V but even at this voltage the BMS will cut regen brake charging. I did a bit of research but couldn’t find anything useful about the safe margin of overcharging 18650 cells.
Ah I see where you’re coming from.
I wanna say back off charge voltage .05v at a time until you get to a spot where bms doesn’t mess with you. Or take a quick uphill run before commencing with the ride? That usually sheds the extra voltage enough for me, for regen to not be a concern.
It’s a slippery slope, defeating bms protections one by one to get what we want. This is why we remove bms from the discharge path, so there’s no chance of interruption of power/braking. But if you do that, really, you’re giving up most of the protection. You’re left with pack overvoltage and cell overvoltage during charge. And balancing. Arguably the bms remains only to do balancing.
At that point I’d rather have just cell level monitoring/alerting, and do manual balancing offline when needed.
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The chip, or whole bms? Isn’t the chip like $7 on mouser/digikey? EDIT ah I see it’s like $10 for 5pc in ali-e
I also wondered why flexibms, diebiems went with LTC6308 which appears to be a lot more expensive.
If you’re doing something cool with the chip plz make a thread!
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For sure I’m new to pcb layout so I need some feedback. I have help at work as I said but more eyes won’t hurt In the datasheet seems to be most info that I actually need to achieve this btw I want to do a balance charge connector variant first for testing and when I’m sure everything works a thin but long version fitting a single layer battery heightwise since my decks are usually overcrowded
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Good idea, done.
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I added it the list. Honestly though, for the price I would much rather get the Chargery C4012B since it supports up to 12S and doesn’t require external DC power source.
