2.87 to 2.73 is the voltage spread at discharge. not great but not that bad and typically the spread at the bottom is where they spread. the simple cheap solution for me would be setting the pack low voltage cut off a bit higher and I’d just keep going with the cells and see how it does and feel if it’s warm.
Are you talking about the first graph? The blue line dips off the graph, which cuts off at 2.5v. That cell is toast! If you’re top balancing and have no bms for discharge, you’d never catch this unless you’re checking cells after discharge. Well, at some point the pack will blow up or start sagging horribly or BMS won’t allow you to charge I suppose…
that looks like the power line in blue, but the current going up…hummm maybe it is a cell
The board is always attended while riding, but not while charging.
Ah oops 
But the point still stands. As packs age the voltage spread will get worse and worse.
Ah sorry that’s a behavioral quirk for me. Always attended during charge. I have a timer on the charger too.
think it is a cell and the blue line on top of the graph is power. a toasted cell.
I still feel safe with just the lv cut off and having it set high, checking the cells individually with a discharge balancer, and bulk charging. just saying. you guys are all into the bms. I know of another pack ruined over the weekend by another faulty bms. they seem more trouble than they’re worth to me at this point. and the common cheaper ones all work while charging,…how would that play out if they cell realllly sucks and the balance discharge function only dissipates a fraction of an amp and you were to hook it up to a high power charger? It seems like it could result in having a bms, and feeling safe, yet not knowing your dud cell is so bad that the bms cant burn off its power as fast as it’s being charged and the cell could still be going way beyond 4.2. No? seems with a typical low discharge bms you cant do a fast charge safely unless you know for sure what your cells are at.
@Hummie @deucesdown The line that dips is a cell. The blue line at the very top is power. This was a constant power discharge, which is why the current increases as voltage drops.
I have a protection circuit which limits power when any cell hits 2.5V so as the low cell hits the 2.5V mark, power is decreased in order to keep that cell at 2.5V. That is why the end of the graph shows current and power going down fast, because a higher load would sag that specific cell under my 2.5V limit.
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A BMS monitors all cells and if any cell goes past the LVC/HVC then power is cut off. That is one of the most important features of a BMS. Even the cheapo BMSs should have this feature; that said, the only cheap BMS I use are Bestech BMS
Stop trusting random YouTube videos of people in their garages. Stop giving wreckless advice based on said info.
All advice I give is based on my research and knowledge from work experience as well as data coming directly from manufacturers.
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No; what really needs to stop is “person A did it and was fine, so this is fine to do” – aka folks who don’t understand statistics
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my link is far from some guy in the garage: https://www.youtube.com/channel/UCcMfCkN1juSa49DJFYltOTw and if you watch the video too you can maybe have a specific thing to talk about other than saying it’s wrong
@PXSS what reckless advice? I haven’t said anything which isn’t said widely on endless-sphere.
Actually this is the electric samba guy. He’s well informed and careful! Learned lots from him.
But I agree. @Hummie you tend to leave out all the testing and all the safeguards and practices these people use to stay safe while doing nonconventional stuff. In that regard I think some of the stuff you post is irresponsible.
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I have a job. Cant watch YouTube videos all day.
how about any of you saying I’m posting irresponsible stuff, how about saying what it is specifically so we can have something to talk about
I know who he is. My point still remains. That you should not give any advice on things that are dangerous just because you saw it on YouTube or read it on a forum. I shy away from this topic because of this. Most people give advice based on what they saw someone do without realizing that there is a 13yo somewhere reading their posts and thinking its okay to do.
I reserve my opinions because of this. I don’t want someone hurting themselves because of advice I gave. Always err on the side of caution.
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FlexiBMS will allow load to push current into battery even if discharge FETs are turned off. Current can go from load towards source through the body diodes.
You mean to have a brake resistor and then connect the enable signal from that to the VESC? I am adding the CAN-bus in the next iteration, so we can communicate with the VESC directly.
Clarification?
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If the discharge power has been cut, the ESC’s MCU has shut down and can’t turn the brakes on. Did you think of a way to mitigate that? Because otherwise, that’s awesome
Running in bypass means routing the discharge wires around the BMS from battery to ESC. Exactly the thing @PXSS suggests not to do, and for good reason, but there are problems to be solved before this can stop
The ESC’s MCU should stay powered if it’s not driving/accelerating the motor and the motor is spinning,which will generate enough BEMF voltage for the DC bus to keep the MCU powered. Regen braking will push more current back to the DC bus and raise the voltage, so regen brake should keep the VESC on, until the speed has dropped quite a lot.
I guess it could be possible to share the 3V3 and GND from the CAN connector on the BMS to the VESC’s CAN connector, but that might break something if there is any DC offset between the BMS and VESC.
Sounds better to add a logic out that can be read with the ESC and in esc firmware we can cut power but not braking
Always cool to have an inside of a professional opinion on stuff on here! Thanks for that? Do you have a link to the charger you mentioned you bought a year ago in an groupbuy. I remember something about that…