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[grmarks]

The most I have seen on cell balance with my 2015 SR is 5 mV. 150 mV seems really high. Maybe this is the biggest factor in differing SOC cut backs?

If you have seen this at less than 5% charge it would be so incredible I think it would be a first in history.  Check it the next time your pack is below 10% or so.  The lower you get the higher the difference will be.  I look forward to your response in a few days to see.  If you truly never get above 5% you have an amazing motorcycle!

Have you heard of the cars built late on a Friday - have lots of issues, and other cars that have much much better fuel economy than normal. The latter is just blind luck where all the components (pistons, conrods, crank shaft) are all within a very fine  tolerance of balance. I.e. it is like a balance engine from an engineering shop.

Well I guess it would be possible to get cells that are all within similar tolerances by blind luck. The Aurora solar car assemble their packs by only putting cells together that are almost identical in tolerances. i.e lets say you have 100 cells, maybe you only use 20 or 30 of them, the ones that are very similar to each other. The rest are used for something else. This gives them the most stored (and usable) power for weight The figures are only an example not actual.   

[mrwilsn]

grmarks,

Cell balancing begins as soon as you plug in your charger. On Saturday when I plugged in my SR I watched the app for several minutes. The cell balance began dropping immediately.  Vinny

I think grmarks is talking about the BMS balancing function, which only occurs at the end of the charge cycle.  When you charge, the cells will naturally start to come back within balance of each other right away (as long as you don't have any bad cells).  At the end of the charge cycle the BMS uses the balance wires to ensure each cell is at the same voltage and will only charge the cells that need to be topped off, not charging the whole pack.  The BMS balancing is only required in order to get the cells to the very small tolerances you see when fully charged (2-5mV).  If you stop charging before the BMS balancing takes place you might still get within 20-30mV or better....others could probably comment better...my bike currently isn't connecting via bluetooth so I can't check on my bike right now.

OK I am confusing "cell balance" with "pack balance".
So cell balance is the cells joined in parallel to form modules (and give the required amp/h) that are then joined in series to make the pack voltage, correct?

The BMS uses the balance wires to ensure that cells wired in series are at the same voltage.  Cells wired in parallel will automatically be at the same voltage.

For example, the 2016 ZF13 Zero SR has 4 bricks that each wired in parallel.  Fully charged each brick will be 116V.  Cell balancing is not required to get each brick at 116V, it happens automatically.  Each brick has 28 cells wired in series (28 cells x 4.15V = 116.2V).  Cells wired in series do not automatically balance.  At the end of the charge cycle the BMS will try to get every cell in the brick at exactly 4.15V.  This happens in all 4 bricks.  When you look at the app it's telling you the difference between the cell with the highest voltage and the cell with the lowest voltage (the max difference....the max difference can be between two cells that are in different bricks).

As Terry described, the cells get balanced when fully charged.  But each cell doesn't discharge at exactly the same rate so by the time you get down to 0% the max difference in cell voltage is much higher (150mV has been mentioned in this thread as somewhat normal).  When you charge the battery from 0% they will also charge a slightly different rates and so the cell balance naturally gets back in alignment, to a point.  The BMS cell balancing feature takes care of the last little bit to try and get every cell to 4.15V.

[ultrarnr]

So I decided to take the long way home from work today and see what the numbers were like.

At 22% SOC the cell balance was 12mv
At 12% SOC the cell balance was 64 mv. I could also accelerate to 60 MPH (possibly higher) at 12%. This is compared to being cut at 14% SOC to only 25 MPH on Saturday.

At 11% SOC the cell balance was 80 mv.(and I was home)

When I started to charge:
At 12% SOC the cell balance had dropped to 66mv
At 14%  SOC the cell balance had dropped to 21 mv
At 16% SOC the cell balance had dropped to 8 mv

I can only assume that the cell balance at 22% SOC was a lot higher on Saturday. It is something I will watch closer on longer trips. At least until I get a 2016 SR.