Searching for balance

[hobbit]

While we've seen a handful of pictures from opened-up Kona and Niro packs, I don't think anyone's ever
analyzed how their BMSes do cell balancing, if at all. I've been nerding out a bit studying active balancing
vs. passive / bleed-off, and the active inductive-transfer architecture seems beautifully simple. It could
basically run all the time regardless of pack SOC or string length.

In the Kona service info there is a hint that some kind of balancing *is* done...

but there's no further detail about methodology. Do I have to sit at 100% for several hours, or not? How
much power would the balancing circuitry need to dissipate? Where might the tech community be able
to find such answers, not just for Hyundai but any other manufacturer / model too?

I'm surprised that the ETA3000, which is a series of built boards as well as its control chip, is such a
relatively new product and not even commonly available yet. Any BMS worth its salt should have had
this kind of capability integrated 20+ years ago.

_H*

 

[electriceddy]

other manufacturer / model too?

FWIW both my old Leafs (24 kWh and 30 kWh packs) would attempt balance at any voltage or SOC, although it was always a guarantee to occur @100 SOC. The duration of "balancing" at 100% was about 5 minutes, and if you left it plugged in- it would try to cram another few watt hours in for good measure- probably designed that way to maximize what little range they both had. (This was observed running LeafSpy software).
That same software also showed me that it was all in vain, as cell differentials in both packs were ~ 180 mv . (Nissan would not do anything about the issue until that level had reached 250 mv )
I have never charged to 100% in either of my Kona EVs, as I believe the operation is the same- that is a continuous balance at all times when the pack is being de-energized.
Those who run diagnostic software should be able to confirm that.

 

[KiwiME]

I was searching for similar info a few weeks back and stumbled upon this DIY site which has some discussion the re-use of Kona/Niro battery packs. https://openinverter.org/forum/

From there I found a Hungarian DIYer's site: https://varsanyipeter.hu/ which has a colourful description of the Kona pack internals. I translated it into English paragraph by paragraph using Google Translate and no additional editing, PDF attached. I'll let you draw your own conclusions, but from what I can see (as we speak) that points to the MAX17845 to handle balancing, but the closest datasheet I could find quickly is for the MAX17843, which is also mentioned.

Pages 40, 41 of the datasheet points to resistive discharge balancing.

As a note, I rarely hit 100% and usually stay under 70 but I didn't see any change in cell balance over four years on my original 2018 battery with the problematic E63 cells.