Battery life - Charge to 80% or 100%

[DaveinOlyWA]

This is not true. Leaf Spy or LeafDD or any other CAN device will confirm this.

The pack will get balanced at any time it deems necessary, even if you never charge over 80%.

What exactly occurs in sub-100% balancing?

that is a VERY GOOD question and by rights balancing is balancing so why does top end seem to be more effective?

well, I don't know but that never stopped me from inputting my thoughts so here goes (and I could be completely wrong so beware!)

in a balance situation we always have a plus/minus variance that triggers the balancing effect right? IOW, the cells have to have a voltage difference before balancing can happen, right?

but is that still true at the top end? I think not which means the delta is smaller by half since there is no over? IOW; the top is it. so at the top you either have "full" or as full as the BMS allows or you have and "not full" cells.

in the middle you have either "below target SOC" (balancing upwards cells) "at target SOC" (no balancing) or "above target SOC" (balancing downward cells) with the only real question being how is the balancing downward done? is it high cells feed low cells or is it more of a "cascading effect" acting like water seeking its own level?


pretty sure its the latter so both mechanisms are in place in the middle but only one mechanism is in place at the top (downward balancing) right?

make sense? it does to me... or at least it did for a second or two

 

[LeftieBiker]

Until I'm told otherwise I'll assume that sub-100% balancing consists of the cells 'passively' equalizing by bleeding charge to each other while charging, while near an indicated 100% the BMS is directing charge to only the low cells and not to all of them. Whatever balancing occurs at 80% it doesn't seem nearly as effective as the full charge balance...

 

[DaveinOlyWA]

Until I'm told otherwise I'll assume that sub-100% balancing consists of the cells 'passively' equalizing by bleeding charge to each other while charging, while near an indicated 100% the BMS is directing charge to only the low cells and not to all of them. Whatever balancing occurs at 80% it doesn't seem nearly as effective as the full charge balance...

hmmm?? would the BMS be required to drop the voltage as cells no longer need balance which would lead me to believe your scenario is not correct

 

[LeftieBiker]

If I understand you correctly, my response is that the BMS provides each cell with the correct voltage for one cell, regardless of the number of cells being charged. That's why BMS wiring tends to be so spaghetti-like.

 

[BrockWI]

Adding to what Dave said, I think it is a "time" thing as well. While I see that while charging to 80% or at any time charging, the BMS is regularly doing it's job, but just as things pop up or a get a bit out of line. When it's up near the full level it starts actively looking at cells and that is more of what it is doing. Sort of like during main charging session the primary point is to charge the cells and balance them if necessary, while at the top end the situation flips, spending more time balancing the cells and charging as needed which does a better job of balancing them overall.

 

[DaveinOlyWA]

Right. Which I think is the reason people have reported a few hours of inactivity then a short charging session starting up again

 

[Bob]

Just a clarification. I think that balancing involves bleeding energy from individual cells. It would cost a lot more to build electronics to recover that energy, so my guess is that Nissan doesn't recover that energy and just wastes it. In other words, I believe that they just load the high cells with a resistor.

Either way, balancing involves discharging a cell partially. So although it seems like a great idea to have a really well balanced pack, constant balancing could actually reduce cell life. After all, it's more charge/discharge cycling.

Lots of disclaimers: I don't have first hand knowledge of the guts of the Nissan BMS. I am not a battery expert. Please don't sue me.

Bob

 

[DaveinOlyWA]

If I understand you correctly, my response is that the BMS provides each cell with the correct voltage for one cell, regardless of the number of cells being charged. That's why BMS wiring tends to be so spaghetti-like.

umm, no i think at least if my understanding of your statement is correct.

previously several have reported a short charging stint during their charging profile. iow, a charge would finish at say 3 am but then would kick back on at 6 am but just for like 10 minutes. I think the balancing was happening and lowered the voltage of the higher cells sufficiently enough to warrant another boost. now this was widely reported in the 2011's and not sure this is still happening with the newer MYs but that action implies that the only input voltage is what is supplied to the entire pack.

so turning off some cells because they are complete can't happen so what does happen (i think) is as soon as the higher cells reach the set point, the charging stops so they do not overcharge. this should happen BEFORE the pack is full. then the balancing (which is ongoing all the time) brings up the lower cells into balance which means the higher cells have been drained to provide this boost since there is no other source of power (no charging from the wall) and this lower voltage in the high cells starts the charging process again.

 

[LeftieBiker]

That would be a bargain-basement way to balance (my bicycle pack does it the right way, for crying out loud), so I'll wait for a definitive answer. I do recognize, however, that Nissan likes cheap approaches.

 

[TimLee]

Everyone would be better informed and make less inaccurate guesses if they read through the Cell Balancing 101 thread from back in December 2011.
See http://www.mynissanleaf.com/viewtopic.php?f=9&t=7360&hilit=sophisticated&start=0#p161396" onclick="window.open(this.href);return false;.

The LEAF uses a sophisticated top-balance system with an array of MOSFETs that can bypass current around cells that are at a higher SOC than their neighbors, thus allowing those with lower SOC to "catch up" so that all cells have parity. This is all carefully controlled and monitored by the battery ECU located in the battery box.

LEAFSCAN now has a screen that shows which Balancing MOSFETs are enabled at any given time. I have seen them activate at any time, even after charging completes. While they will work anytime automatically, you will not get the full benefit of a top balance without an occasional full charge, but then again, if you only ever charge to 80%, then you probably don't mind losing 15% anyway.

Here's the summation: You don't need to do anything special for the pack to maintain itself within certain bounds, but if you want to insure that all capacity will be usable if you perform a full charge (~95% SoC), then I recommend you allow a full charge occasionally to allow the balancing to peak your pack properly. I recommend leaving the charger connected overnight after your full charge to allow for additional peaking. I've seen it restart charging up to 5 times so far.

Leaving your pack at full charge for 24 hours once in a while is not going to degrade anything, and in fact, will give you more usable range as it will stay in balance better.

-Phil

The MOSFETS have a current limitation. IIRC 1 amp, although I didn't find the reference.
Although some balancing can happen any time, the most effective balancing is when charging current is very low, because of the current limitations of the MOSFETS.
The 2011 and 2012 do not taper the current down to very low levels near the end of charging to 100% like the 2013 forward does.
If you want the LEAF to have maximum capacity and driving range, on a 2011 or 2012 charging to 100% say once a week is best.
On a 2013 forward, once a month may suffice.

 

[LeftieBiker]

The LEAF uses a sophisticated top-balance system with an array of MOSFETs that can bypass current around cells that are at a higher SOC than their neighbors, thus allowing those with lower SOC to "catch up" so that all cells have parity. This is all carefully controlled and monitored by the battery ECU located in the battery box.

Thanks for that, and to several others here: apology accepted. ;-)

 

[smnewport]

My 2015 Leaf is about 2 weeks ago. I went on the Nissan website about a week into driving the car to inquire about this, especially given the new lizard chemistry. The official response from the chat rep was that with the new chemistry, they encourage charging to 100% now as there is no long-term harm to doing a full charge.

 

[cgaydos]

My 2015 Leaf is about 2 weeks ago. I went on the Nissan website about a week into driving the car to inquire about this, especially given the new lizard chemistry. The official response from the chat rep was that with the new chemistry, they encourage charging to 100% now as there is no long-term harm to doing a full charge.

Yet another clue that the lizard battery was present in the 2014 LEAF, since that is when they dropped the 80% charging option, and probably in at least some 2013s as well so that they could test that theory before dropping the option.

 

[DaveinOlyWA]

My 2015 Leaf is about 2 weeks ago. I went on the Nissan website about a week into driving the car to inquire about this, especially given the new lizard chemistry. The official response from the chat rep was that with the new chemistry, they encourage charging to 100% now as there is no long-term harm to doing a full charge.

just to emphasize; in my blog the key thing to take away from it is that either charging profile is probably just as "ok." but not doing top end balancing may cause you to not have as much range as you can have. Now what are we talking about? maybe a mile or two I am guessing, iow, not much but in my turtle event, it probably saved my butt.

what I would concern myself MUCH more is not letting the car sit for extended periods at full charge or a very low charge.

on the full charge thing; try to keep the sitting period in the 24 hour range or less. the low charge, I personally think the time should be even smaller. I always plug in immediately in those situations as soon as I get home even if just for an hour.

 

[TimLee]

^^^ I agree with you Dave.
Someone like myself that is retired and may not drive it at all for three or four days straight just should not leave it in the garage at 100% unused for multiple days unless their potential limited plan ahead time trip demands 100% range.

I leave my at 80% too much.
If it had a 60% setting I would use that.
It is just inconvenient to use timers to accomplish that.
Nissan did the LEAF customer a disservice by eliminating the 80% charge option on 2014 forward.

And if they are telling people to don't worry about it just charge to 100% that is likely bad advice.

 

[DaveEV]

My 2015 Leaf is about 2 weeks ago. I went on the Nissan website about a week into driving the car to inquire about this, especially given the new lizard chemistry. The official response from the chat rep was that with the new chemistry, they encourage charging to 100% now as there is no long-term harm to doing a full charge.

There is always long-term harm to doing a full charge. It's just that now with the lizard chemistry Nissan feels that the durability of the battery is sufficient that one should not have to worry about it - like nearly all the other < 100mi EVs (Focus, Spark, Fit, etc).

If you charge to 80% instead of 100%, your battery will last longer. The only exception might be if an 80% causes you to discharge below 20% or so (low battery warning), at which point it's hard to say without actually testing it.

 

[DaveinOlyWA]

My 2015 Leaf is about 2 weeks ago. I went on the Nissan website about a week into driving the car to inquire about this, especially given the new lizard chemistry. The official response from the chat rep was that with the new chemistry, they encourage charging to 100% now as there is no long-term harm to doing a full charge.

There is always long-term harm to doing a full charge. It's just that now with the lizard chemistry Nissan feels that the durability of the battery is sufficient that one should not have to worry about it - like nearly all the other < 100mi EVs (Focus, Spark, Fit, etc).

If you charge to 80% instead of 100%, your battery will last longer. The only exception might be if an 80% causes you to discharge below 20% or so (low battery warning), at which point it's hard to say without actually testing it.

I think Nissan's unofficial thoughts on the subject were that the LEAF was simply much more fun to drive than customers had anticipated. Too many reported getting the car as the 2nd vehicle for commuting only to realize that they did not want to park it when they got home or on weekends. Their previously beloved gasser had simply lost its appeal for too many.

I can identify with that. I went from Prius lover to... well, Prius tolerater... :?

 

[TomT]

First, without some other more substantial information - the official Leaf Customer Support people are legend for being misinformed - I'd take the 100% recommendation with a very large grain of salt.
Anecdotal evidence, however, has showed that the difference between 80% and 100% did not seem to play much of a part in battery degradation one way or the other as far back as 2011, so its effectd may have always been overstated...

Second, the remove of the 80% option was purely to game the EPA range test and the Lizard Battery played no role in it. Thus, it is not proof one way or the other.

Yet another clue that the lizard battery was present in the 2014 LEAF, since that is when they dropped the 80% charging option, and probably in at least some 2013s as well so that they could test that theory before dropping the option.