Wednesday, October 29, 2014

80% Charging; Why I Don't Miss It And Why You Shouldn't Either

Guess what? Unless you want to do the math EVERY NIGHT and mess with the timer on your LEAF, you can't do 80% charging any more.  So why did Nissan decide to remove "long life charging" mode?  Well, maybe they figured out what I did.

Some background for the two people not familiar with my story. I work for an Marketing/Audit/Inventory company.  We do our work at our client's location and my district's territory covers Western WA from Seatac, WA South to Centrailia and West including the entirety of the Olympic Peninsula and South to Long Beach WA on the coast.  That is a LOT of territory!

We generally only have a choice of company vehicles when the one way commute is greater than 100 miles. After that its our POV so my driving need is beyond the norm.  FYI; my 15,000 mile annual lease limit is now been exceeded by 890 miles and I still have almost 2 months to prepare for my LEAF's Birthday...

So needless to say, even if I had 80% charging, I would never use it. Had it on my 2011 and never used it there either but there are other benefits to fully charging your LEAF such as conditioning your LEAF to better address your driving needs.  Sounds confusing? let me explain.

Based on my lease mileage issues and the start of the rainy season, I have to drive the Corolla more.  It sits outside under a tree and if I don't drive it regularly (unlike the once every 4-6 weeks this past Summer) it will become a haven for mold, mildew and other things I am guessing I won't appreciate. So the LEAF has spent the last 6 days mostly sitting the nice dry garage unplugged.

I actually went 3 days not plugging it in at all with the rest of the time just plugging it in for an hour or so here and there never getting past 11 charge bars. So what happened?

Well, as expected, my battery stats plummeted. I have blogged previously about how battery stats can be manipulated which was really more of a curiosity than anything else but the results did suggest that top end balancing was a good thing that should be done on a regular basis.

ahr went from 66.37 to 63.56
kwh available from 22.0 to 21.4
GIDs from 284 to 276
Hx from 102.58 to 97.58

So what does all this mean? probably not a whole lot.  There is NO evidence whatsoever that top end balancing or lack thereof causes any permanent damage.  So whether you do it every day like I do or once a month, you are probably ok.

But this does bring up some interesting observations.  I have contended from day one that my 2013 LEAF has more range than my 2011 and it was not a popular idea at first. Now that a lot of people have claimed the same thing, its now "somewhat" accepted to be true. And to be fair; its only a few miles more like about 4 or 5 so easy to miss, ESPECIALLY if you have not properly "trained" your battery to do a range test.

Tony Williams does a great job of testing ranges of various EVs by going thru great lengths to insure the testing conditions are as similar as possible but the one thing he has not done is conditioned the LEAF by charging it to full for several days in advance of the test and this is likely why his tests show only 21ish kwh (FYI; My LEAF when new showed 22.7 kwh available... wondering just how big my LEAF's pack is nowadays?) available and that is EXACTLY what mine shows as available when I don't do any top end charging.  In Tony's defense, he is testing cars that are not his so he has no control over the charging habits of the tester car and realistically, its a few miles; not really that important in the overall picture.

But the question remains; Should you charge to 80% (or any level below full) or 100% and what is the best thing to do?

Well, a few things to think about.  Pack balance is important. Only a well balanced pack can give you the chance to get the full range from your LEAF and sometimes every little bit can help. I am pretty certain this fact kept me from walking one day!  Now batteries are pretty flexible so they can take a lot but there is a breaking point and that happens when you charge too much or discharge too deeply. Now, Nissan has taken care of the "charge too much" thing limiting us to no more than a 97% SOC on the top end but the bottom end is a bit of a different story and the reason is an unbalanced pack means its possible a single cell could be overly stressed leading to a premature end.

Now a well designed BMS is supposed to protect against that and I have no doubt Nissan has addressed this issue but the delta in an unbalanced pack is greatest at lower SOC.  Normally my voltage delta is 20 mV or less.  10 or 11 mV is normal but when the SOC gets low...

 
So the potential for damage is MUCH greater.  So its 328 mV variance or  this.  You decide.



The other thing to think about is... well getting there! We all know the LEAF's range is limited but then again is it? Despite my "slightly" greater than normal need, I have only been forced to gas it 6 times in 10 months.  I have actually driven the gasser more times just to keep it active.  But is it better to run the SOC from 80% to 15% or  100% (or whatever) to 35%?

I think its the latter and not because of the screen shots above.  "Experts" say we drive 38 miles a day but do we really?  We may commute that much but some of us have lives! My "unexpertise" analysis says Life adds another 20 miles to the equation making "want" needs to be more like 60 miles.

So charging to 100% really just allows you more options, less stress, more ready to EV it! So how can that be bad?

10 comments:

  1. I've been setting my end timer to about 5 hours after I leave in the morning, which results in a 85-97% charge in the morning. This is charging on L1. Once I get my L2 next year this game becomes much more challenging to time it right and I will just switch to 100% charging. Or maybe I'll just do it early now that winter is around the corner. Thanks for the post.

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  2. In my case, I don't need extra range on most days, so why not give the batteries a little break and just charge to 80%? I know that other factors like heat are far more important to the battery health, but when you own the car and plan on keeping it for 10+ years, these little things add up over the years.

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  3. Hello, I am a new owner of a 2011 Leaf. I have found that the battery will only charge to around 92% and don't know why. Any info would be greatly appreciated. I am learning a lot about the car and it is very interesting and intriguing to find about what is going on under the hood.

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    1. Rich, if you want to see what is happening with the batteries. I suggest that you get Leaf Spy. The images above are from Leaf Spy. https://play.google.com/store/apps/details?id=com.Turbo3.Leaf_Spy_Lite

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    2. I am using it and it is very informative. The app is how I found I am only charging to around 92%?

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  4. Rich; your batteries have probably degraded a bit from their original capacity which is why they are not charging to full which is just over 97%. What is your ahr, Hx and kwh available on a full charge? All these numbers need to be considered to get the best overall picture of your pack's status

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  5. My 2015 SL charges to 100% each time I plug it in for the night with my L2 EVSE. The manual suggests that you run it down to under 80% before recharging, but I don't always do that. When you use a DC charger, it charges quickly to 80% capacity, then slows down till fully charged. The "guessometer" suggests a range based upon how you have been driving it. If I was on the highway today, it'll show less range tomorrow, than if I was driving at city speeds today.

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    1. Sometimes it can be tough to predict how far you will drive the next day especially if its not a structured day like a work day commute or some such. But if you know your needs will be so low that you will not even use 20% of your SOC, its ok to skip the charging and yes, there have been times when I charged to 100% and then ended up not going anywhere. Today is a good example. I went out for lunch but that was all of a 4 mile round trip and thinking the rest of the day will be vegetating on Netflix...

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  6. There are several things you can do to keep your battery in better condition. If you don't, you will likely still maintain good enough health that you don't have warranty issues, but I bought mine and plan to keep it for 10+ years, so I want to keep the battery running as good as possible, and a few simple things that will give me a few more percent or even 10% more life at that time are well worth it to me. After all, I have to save face with all the nay sayers that tell me I'm crazy to drive an electric and the car won't last for more than a few years, so this is war!

    One is just charging efficiency considerations, when you charge to 100%, you are loosing a lot of energy. On my 2014 leaf with L2 6.6kw juicebox charger, it takes about an hour to trickle the last few kw in to the battery, when the charge rate drops under 6.6kw. I can log it with juicebox and also leaf-spy. So I try to stop charging once the 6.6kw charge rate drops off.

    https://avt.inl.gov/sites/default/files/pdf/fsev/SteadyStateLoadCharacterization2015Leaf.pdf

    Another is heat, we all know that it is a problem, so do what you can to minimize it, park in the shade and in your garage, charge when it is cool at night:

    http://www.electricvehiclewiki.com/Battery_Capacity_Loss#Battery_Aging_Model

    The last few are 1) Don't leave the battery at a high charge for long periods of time, use a timer to reach the charge level you need just before you use it, ie, don't charge to 100% and leave it all night or all weekend. 2) Don't charge until it's under 80%, unless you really need the extra miles of course.

    http://livingleaf.info/2012/07/care-and-feeding-of-the-nissan-leaf-battery/

    More info on increasing battery life:
    https://teslamotorsclub.com/tmc/threads/why-do-li-ion-batteries-die-and-how-to-improve-the-situation.27109/

    Battery loss aging model based on location:
    http://www.electricvehiclewiki.com/Battery_Capacity_Loss#Battery_Aging_Model

    Using partial capacity of the battery, say 30% to 70%, you can cycle the battery almost indefinitely.

    http://www.mpoweruk.com/life.htm

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    Replies
    1. Great advice! and something I have repeated several times here. A few things to consider (there is trade offs on EVERYTHING in life) Heavy reliance on timers can play havoc on your 12 volt battery. The charging profile for the 12 volt battery is not ideal for lead acid and everything runs on the 12 volt system when the car is not actively charging.

      Another thing to add to your list is only fast charging the bottom 3/4ths of the pack. Better to stop twice for a few quick sips than to stop once for a big glup!

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