How many of your prospect customers will be running this with 8s or lower packs? A 10-12s BMS ir probably 80% of the market anyway, with the other 15% being 13s+ 
Well, I run an 8S pack, which I had planned to use this BMS for. 
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I do myself also need a BMS for my smaller non-EV projects, which would likely be in the 2S-6S range, so I’ll likely just partially populate this boards design for those ones and swap the linear regulator for one that works with a lower input voltage range. And this design should scale to 18S(+?) with higher voltage rated components, so it would became a good basic level BMS, just to protect from weird chargers and cell overcharging. For example somebody using a 12S charger for 10S pack.
I’ll make the firmware available same as with the FlexiBMS FW, so if somebody wants to modify it, they can.
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How would you guys like if I scaled this thing to support up to 16S packs? I’ve found an interesting battery stack monitor IC from TI, which would reduce the total component count (faster assembly), cost and space need and give better control over the balancing and allow for individual cell voltage measurements, which also means that it would be possible to use multi-chemistry cells?
Same PCB size, same prize and S-pack support upped from 12S to 16S and multi-chemistry support hardware side (needs firmware re-flash to change). Go big or go home?
- Yes, please
- No, thank you
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EDIT: Balance connector is gonna PITA though, as the JST PH -serie goes only up to 16-pin wide and it needs at least 17 for an ideal connection… after that the connectors start to go double-row
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16s would likely keep the OneWheel crowd a bit happier (especially given it’s so small), although 20s seems to be popular for them these days. OneWheel XRs/Pints are 15s, so this could be a good option to replace the OE BMS although it’s not usually necessary.
Any chance of throwing a CAN transceiver on there along with the MCU? Would be great just to be able to read p-group voltages out of it.
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Yeah, any chance of scaling it up to the 18-20s territory?
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Not in this formfactor, unfortunately. Not enough space to add all needed comms ICs and connectors + CAN also needs a beefier MCU that has the hardware support. Maybe a non- or opto-isolated USART would be possible at most.
Did want the CAN with the idea of it being plug-n-play with VESC and a Metr Pro or a DAVEGA?
Not enough space. AFAIK the only single IC battery stack monitor that supports up to 18S is the LTC6813 and it is way more expensive and also slightly bigger then the TI’s option.
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Was thinking VESC, but just the read parts of the BMS CAN protocol. I’ve got an arduino+mcp2515+oled display showing the basic stats read off a FlexiBMS Lite via CAN. Works well, but it’s a lot of bits to wire up and pack in. CAN straight to VESC where I can just view the data on mobile would be a simpler solution.
That said some kind of serial connection would be great. Would leave the option open to connect something else up to talk to the VESC via CAN. Although I’ve not had much luck finding something like a small arduino with all the CAN stuff on it.
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You could use a 16 pin connector and rely on the B- pad for 16S usage. Aren’t the B0 and B- connected together anyway? Some BMS I’ve seen don’t have B0 at all on the balance connector. Though it’s more common to have it, from what I’ve seen. Would that also mean things need to be connected in a certain order? B- would need to be connected before the balance wires are plugged in?
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says “dumb BMS” right in the thread title
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The reason why you usually see the dedicated wire for the B0 is that it provides a kelvin connection to the bottom-of-stack, as otherwise it’s relying on the actual pack’s negative terminal lead, which will have some extra voltage dropp over it during charging/discharging, which then causes the lowest cell’s voltage to read slightly askew. With the B0 wire, there isn’t any other current except for possible
cell balancing current to cause voltage drop.
Same as with the FlexiBMS. I recommend first connecting the pack’s terminal leads P+ and P- and then plugging in the balance connector. This allows everything to get biased to the battery pack, so there shouldn’t be any big voltage spikes when connecting the balance connector afterwards.
That being said, I’d like to make it pretty simple configuration wise.
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I support 16S as long as 8S compatibility doesn’t get thrown under the bus.
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I’ve had some time again to develope the new board version (0.2) further and I really like how it’s turning out. I think I can make the whole layout one-sided, which would be BIG assembly wise and it also shows how much the total component count has gone down from the initial version.
I’m thinking of putting all the components on the bottom side and then leaving all the connectors and solder pads on the other side. PCB size is still the 18x65mm
WIP pics.
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haha this went from “dumb and simple” to smart pretty fast 
If dirt cheap is important, theres some RISC V based mcus for 0.1 buckaroos.
Hard to beat the ESP32 as well, but guessing that already crossed your mind 
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Watched the EEVblog video, didn’t ya?
If I can make the thing have better feature set, have less components and still be cheaper to manufacture, I think it would be just dumb not to do it 
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all hail Dave, our lord and savior
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“Dumb BMS”
has MCU
Updated first post and topic title.
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Layout wise I believe it’s doable to fit everything in a one-sided 18x65mm formfactor, but at this point it would probably need another dozen hours to optimize the layout for it, so I think at this point I want to start getting further on testing the new ICs and not spend optimizing the layout completely, so I’ll probably stretch this functional test version couple mm extra in the width direction, just so I can fit everything in faster and get started on the electrical testing and firmware writing.
WIP pics, couple components and connectors still missing and the layout is not finished.
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Where are you sourcing those 17 pin JST PH headers? I know they exist because the 16s Daly BMSs come with them, but when i tried to source them for my own purposes, I couldn’t find them anywhere.