Cold Weather Observations

[arnis]

jjeff, you recommend running down to turtle one or two times when you first get a leaf to balance out the cells, right?

The Leaf's cells, like most if not all lithium packs, are top balanced, so balancing occurs as charging finishes, not as it starts. There is no reason, ever, to run a Leaf down to Turtle mode to balance it! It can be a good idea to run it down to the first or second Low Battery Warning, but that is to establish the car's range, and has nothing to do with balancing the pack.

Actually BMS gets fresh information about weaker cells when pack is discharged heavily.
At low SOC weaker cells have noticeable lower voltage.

I usually see BMS starting balancing process either after 100% charge or after getting to very low state of charge.
Usually after 100% charge all but few cells are being discharged. In very low state of charge 5-20 cellpairs are discharged.

There is nothing bad in getting down to turtle if a) not tortured with heavy accelerations b) kept for hours c) done in not hot weather
I've done that almost a hundred times now and my battery is in extremely good state.

 

[LeftieBiker]

Actually BMS gets fresh information about weaker cells when pack is discharged heavily.
At low SOC weaker cells have noticeable lower voltage.

This is interesting information, but that isn't the same as the BMS needing it to balance the pack. I have run my 2013 leaf for almost 4 years, never down anywhere near Turtle mode, and it is well balanced, with 87% capacity remaining. Running it that low may have diagnostic value, but I see no evidence that it is needed to keep the pack balanced.

 

[gregn]

In reference to the optimum operating range of a lithium ion battery. Do we know if Nissan has already accounted for that range in setting up the 100% vs turtle operating rage? They seem to er on the safety side of things so I am wondering if it is fine to use our cars withing the displayed range they gave us. I know mine seems to like being used. I run from 100% to LBW quite often. I will QC to about 60% then either L1 or L2 back to 80-100% again. I sent you EVSE in for an upgrade and had to rely on public charging for w week. I couldn't charge at work so had to make the 64 miles on one charge with heat. and in freezing to below 0ºF weather for most of that time. Speeds varied. If I went on the interstate@ 65 mph I would hit LBW for sure. If I went the back road @ 45mph I arrived with 20% battery in the same conditions. During that my battery health went up according to LeafSpy. Reached 99% actually. It was at 94 when I first got Leafspy and that was a month after I got the car.

I think in the 18k miles I've put on the battery has improved. Broken in if you will. I have QCed 6 times in a day on a long trip and raised the battery temp to the highest mark before red. Health went up.

As you can see in my signature this is a 2016 with the 30kWh battery. May be some of this behavior is due to some new chemistry there.

Now that I can charge at work with 240v I can pretty much drive the way I want on my commute.

I do notice QC charge rates when the battery is at 3 temp bars or below are not much better than L2. Don't expect a fast charge with a cold battery.

 

[LeftieBiker]

There seems to be no harm in running the car to the first LBW, or a little lower, as long as it's recharged on arrival, at least to above 20%. The question here is running it down below the second warning (VLBW) to Turtle. Nissan was trying to get the range as close as possible to 100 miles - and failed - so I don't think they left a lot of reserve in the pack below Turtle.

 

[bongo2]

Do we know if Nissan has already accounted for that range in setting up the 100% vs turtle operating rage?

This site ( http://blog.evandmore.com/lets-talk-about-the-panasonic-ncr18650b/ ) says that "Nissan limits maximum charge level of the LEAF to 90%" and I think I've read that Nissan won't let you go to the very bottom of the charge either. I don't know where they got that information.

Once it warmed up a bit I did run it down to 5% charge once (not quite turtle) and leafspy showed a small increase in the max Ah (about 0.5) the next day. I don't know if that's a real capacity increase or if it just changed the way the computer estimates it.

 

[arnis]

There seems to be no harm in running the car to the first LBW, or a little lower, as long as it's recharged on arrival, at least to above 20%. The question here is running it down below the second warning (VLBW) to Turtle. Nissan was trying to get the range as close as possible to 100 miles - and failed - so I don't think they left a lot of reserve in the pack below Turtle.

There is absolutely nothing left right before the turtle. When the last capacity bar disappears and leaf is driven at normal highway speed pack voltage drops at 1V per second. Voltage drops from 300V down to 270V pretty much within a minute, depending on driving speed.
Pack dies when first cell reaches exactly 2.6V. Pack is around 260V at the moment of death. LeafSpy says that there is 0.3-0,4kWh of energy left. I estimate that it indeed is 0.3kWh of energy. If I would continue driving at the pace right before turtle pack voltage would drop about 50V per every 0.1kWh energy used.

No harm in running into LBW. Going below it will just heat the pack more than usually. Going down to VLBW appears to be fine. I do it every week and have no degradation. But voltage starts to drop extremely fast right after VLBW warning. Due to lowering voltage current goes up. That tortures the cells more and more. Generates heat extremely fast.

There is definitely more capacity at the upper end. Leaf is 100% charged when cells are between 4.1-4.14V. My phone is 100% charged when cell is at 4.4V. It goes from 4.2V to 4.4V extremely fast (I think it only counts for 2-5% of the whole capacity). 4,4V is extremely high and it did degrade phone battery a lot within 10-12 months. Limiting Leaf to 80% charge will lower the top voltage down to slightly above 4V per cell. This is far from full. AFAIK people who charge their Leaf (my climate) to 100% on daily basis have very very small additional degradation speed. Less than 10% faster degradation.

Leaf is absolutely fine between 100% and 10% charge state. This represents voltage +/- 0.5V above-below nominal cell voltage 3.6V (3.1V-4.1V).

 

[gregn]

There seems to be no harm in running the car to the first LBW, or a little lower, as long as it's recharged on arrival, at least to above 20%. The question here is running it down below the second warning (VLBW) to Turtle. Nissan was trying to get the range as close as possible to 100 miles - and failed - so I don't think they left a lot of reserve in the pack below Turtle.

There is absolutely nothing left right before the turtle. When the last capacity bar disappears and leaf is driven at normal highway speed pack voltage drops at 1V per second. Voltage drops from 300V down to 270V pretty much within a minute, depending on driving speed.
Pack dies when first cell reaches exactly 2.6V. Pack is around 260V at the moment of death. LeafSpy says that there is 0.3-0,4kWh of energy left. I estimate that it indeed is 0.3kWh of energy. If I would continue driving at the pace right before turtle pack voltage would drop about 50V per every 0.1kWh energy used.

No harm in running into LBW. Going below it will just heat the pack more than usually. Going down to VLBW appears to be fine. I do it every week and have no degradation. But voltage starts to drop extremely fast right after VLBW warning. Due to lowering voltage current goes up. That tortures the cells more and more. Generates heat extremely fast.

There is definitely more capacity at the upper end. Leaf is 100% charged when cells are between 4.1-4.14V. My phone is 100% charged when cell is at 4.4V. It goes from 4.2V to 4.4V extremely fast (I think it only counts for 2-5% of the whole capacity). 4,4V is extremely high and it did degrade phone battery a lot within 10-12 months. Limiting Leaf to 80% charge will lower the top voltage down to slightly above 4V per cell. This is far from full. AFAIK people who charge their Leaf (my climate) to 100% on daily basis have very very small additional degradation speed. Less than 10% faster degradation.

Leaf is absolutely fine between 100% and 10% charge state. This represents voltage +/- 0.5V above-below nominal cell voltage 3.6V (3.1V-4.1V).

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