Herm
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Re: SOC vs RAhC

Wed Jul 20, 2011 7:55 am

garygid wrote: Open Questions:
5. If they never follow an 80% charge, must a car be charged
to 100% occasionally to maintain cell-equalization?
There is not need to equalize the cells if you never charge to 100%, but its guaranteed that when you do charge it to 100% after a couple of months of 80% it will go into an equalization cycle at that time.. it all depends on how well matched the cells are and how even the heat is distributed across the pack.. hotter cells will have a higher voltage.

lincomatic
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Re: SOC vs RAhC

Wed Jul 20, 2011 9:07 am

Herm wrote:
garygid wrote: Open Questions:
5. If they never follow an 80% charge, must a car be charged
to 100% occasionally to maintain cell-equalization?
There is not need to equalize the cells if you never charge to 100%, but its guaranteed that when you do charge it to 100% after a couple of months of 80% it will go into an equalization cycle at that time.. it all depends on how well matched the cells are and how even the heat is distributed across the pack.. hotter cells will have a higher voltage.
What exactlly happens during an equalization cycle?

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TomT
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Re: SOC vs RAhC

Wed Jul 20, 2011 9:41 am

One of the reasons why I do a 100% charge every month or two regardless of whether or not I need to...
garygid wrote: There is not need to equalize the cells if you never charge to 100%, but its guaranteed that when you do charge it to 100% after a couple of months of 80% it will go into an equalization cycle at that time.. it all depends on how well matched the cells are and how even the heat is distributed across the pack.. hotter cells will have a higher voltage.
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DaveEV
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Re: SOC vs RAhC

Wed Jul 20, 2011 11:46 am

Herm wrote:There is not need to equalize the cells if you never charge to 100%
Sure there is - unless the charging algorithm stops when the lowest cell is 80% full, you still want the cells balanced to maximize your 80% range.

Herm
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Re: SOC vs RAhC

Wed Jul 20, 2011 1:00 pm

drees wrote:
Herm wrote:There is not need to equalize the cells if you never charge to 100%
Sure there is - unless the charging algorithm stops when the lowest cell is 80% full, you still want the cells balanced to maximize your 80% range.
There is no need, as long as the BMS never lets you discharge a cell below its safe point, it would take a really severe imbalance before your 80% range was affected.. probably enough to trigger a warranty event. We dont know but the Leaf may do an occasional balancing at 80% also

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garygid
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Re: SOC vs RAhC

Wed Jul 20, 2011 8:24 pm

No, it only takes a small imbalance to lose range, even if charging to 80% instead of 100%.

And even a "comparatively severe" loss of range is not likely to trigger a warranty event, if it APPEARS to be "capacity" related.
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Re: SOC vs RAhC

Thu Jul 21, 2011 4:30 pm

I don't know for sure, but I'd guess balancing only happens at 100%
In the mid range (5-95%) it's very hard to detect cell imbalance. Because of the charge curve of the chemistry it's much easier near zero or full.. The pack would have to be pretty unbalanced to see anything at 80%. I wonder if the car would ever go to 100% even if told to do 80% for a long time...

5 minutes low current on and 45min off sounds about right.. I would assume when any cell hits 4.15 or 4.2V during charge, then charge stops and resistive balancing drains the high cells down to 4.10v.. At probably 1/10th the charge speed.. Otherwise the resistive elements would generate too much heat. If after this cycle some cells are still 4.10v then the cycle repeats.. More charge till some guys get too full then discharge them down to 4.1v

Someday we'll be able to see the individual cell voltages then we'll know for sure.

So 2 cycles (45+5min) is the most anyone has seen?
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