I have a 4-battery packs with cells in 16S (EVE 280K) and am using the WatchMon-CORE kit with a CellMate-K9 for each pack. I have had issues with a few cells not staying balanced in different packs. What is confusing to me is the voltages batrium is reporting...if my pack voltage is 55.20 that would mean I should either be at 3.45 at each cell OR some cells should be above 3.45 and some cells should be below 3.45. In the screenshot below, you can see none of the cells are above 3.45 but there are 3-4 outliers below with the lowest at 3.38
I don't understand how that can be, and I'm a bit frustrated I can't get my cells in balance. I want to avoid having to open my pack and manually balance them. My charge controller is set to bring the pack up to 55.2V (3.45/cell) for 1-hour, and then go to float at 53.6. My batrium BMS is set to start balancing at 3.45, so any cell above 3.45 it will start using it's resistors to bring the cell(s) down.
I can't get these few cells back into balance for the life of me. What am I missing here? How can the pack be at 55.20 when not one cell is above 3.45 but multiple cells are below?
Any help/input appreciated, thank you.
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It does make you wonder about the mysterious workings of these wizard BMS balancers and it seems to me that the Marketing Depts have found a means to confabulate the whole industry with proprietorial magic with super hype claims and $$$$ cost to go with it. After all, back to basics, what are we really trying to do? Adjust charge rate to suit individual battery needs - given that not all of the 100's of 18650's say in a powerwall are born equal.
Those early recyclers from10 years ago discovered mountains laptop battery packs which were deemed "worn out" when in fact they needed simple re-balancing after a few years of use and were good to go for many more years (as my personal experience found when I forcibly dismembered the battery packaging and performed a crude recharging of individual cells (3s,4s)). I now have a very usable collection of premium grade laptops with my coveted Win XP SP3 OS available for use as required (bought off Ebay for $ when they first cost $$$$).
Thats what Industry Hype and Marketing mischief does to us all
Fortunately we have a site like this where Users can share their own experiences
Well given all that yada yada - my current frustration is (as per OP) monitoring and controlling of all these cells. How can this be done reliably. If I have to spend countless hours puzzling over the deliberately mysteriously working of a Makers system cos its not up to spec as claimed then its surely failed in its job. I have seen several posts of poor performance from the above - didnt live up to its promise - no support from maker - and so on.
Industry would have you believe that you must constantly fret over balancing when reality shows that you maybe only need to address such matters once a month after a full charge. Im sure the venerable Mountain Off-Gridders have years of experience here and dont get cheated so easily.
Notice how these systems (supposed to take the grief out of manual balancing of 100's of cells), instead flood you with a massive amount of figures flashy graphs and loads of parameter knobs to fiddle and adjust. Before all these bells and whistles you never had any of this info overload (as per my laptop example above). Your battery pack capacity just faded (as with lead acid AGM batteries - what a massive con trick there) as cells came out of balance .
Whats the answer?
IMHO - AI
I think within a year there will be AI apps that can digest all this data and present you with the Executive Summary - ie do this.
Im in favour of controlling your own data. Make your own measurements. I recently came across small 5 digit accurate Volt meters on Ali. for ca £3.50 each - what a bargain. These cheap 4 digit display are useless here. You need 3.765V +/- 5mV.
Sadly - industry dirty little secret - there is no cheap ready made equivalent of the Electomech relay SPDT (or better still DPDT), so scanning all your cells with a DVM cant be done cheaply in solid state (yes there are differential DAQ systems $$$$$ - very silly money).
However the old school EM relays are plentiful, cheap and reliable - to wont fail disastrouly to s/c. Scanning speed can be 1cell/sec. Even the humble Arduino can collect the data for you and send it to your PC in csv form which you port to Excel and have fun. You are in control.
So I propose an array of DPDT relays across of power wall, that can be addressed and periodically scanned across an entire bank and the data collected/ charge adjusted by whatever means you choose. Does it sound ridiculously crude and messy - or do you prefer a mysterious balancer you cant understand and dont trust? With this crude array your own system can determine which individual cells to fix and inject/extract using addressable relays as needed.
Thats all from my Colorado Cabin (I wish) - Garden shed. Watch out for vested interests who roam around sites pouncing upon heretics like me who dont support the Party Line. Just cos Im paranoid doesnt make me wrong