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Marktm
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Re: Curious about "refurbishing" the Leaf HV battery

Sat May 26, 2018 1:49 pm

The reality check for me is the seemingly strong effect of temperature on Li tech batteries (likely any battery technology is affected to varying "degrees" - pun intended) and how temperature affects degradation at varying "throughput" ratios. My Leaf has been in south Texas exclusively and I'll bet in 2-3 more years it will be back to a 8 bar car - even with a "Lizard" pack.

http://forum.solar-electric.com/discussion/352333/lifepo4-balancing-voltage-limiting#latest

Referring specifically to chart post #18 (although many useful charts), my conclusion would be that unless a "refurbished" battery is constructed of essentially all new cells, who knows what "throughput" ratio (total ahrs/ahr) the battery has been subjected to - and at what temperatures.

Careful matching of every module/cell may might help to some extent, however, using only new cells would seem to be a requirement - and a strong warranty.
2012 Leaf SL; 36,000 miles. Battery replaced November 1st, 2016.
Rural cabin with 6750 watts Grid tied PV. Off-grid solar Leaf charging capable (level II).

LeftieBiker
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Re: Curious about "refurbishing" the Leaf HV battery

Sat May 26, 2018 1:56 pm

Pack builders for smaller vehicles like e-bicycles have had good luck using manually matched used cells, but I agree it's more of a risk with larger packs - especially when the target capacity is only 'better than 80% of new'.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

mux
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Re: Curious about "refurbishing" the Leaf HV battery

Sun May 27, 2018 12:23 am

The biggest issue DIYers struggle with is the fact that they don't actually get new cells. The majority of people get cells from some form of commercial reseller, often ultimately from the grey market. This means your cells are going to be mixed batches, mixed age and often mixed environment and imbalance is almost guaranteed in such a situation.

Well-manufactured lithium ion cells don't see much beginning-of-life (BOL) variation at all, and if used in a similar application, will see very similar degradation over time. Typically, new cells from the same batch are well within 1% of each other, often within 0.1% (based on charge). End of life, you're typically looking at <3% imbalance, and that's typically defined at 80% of initial capacity left.

Now, that leads into another problem: The Nissan Leaf doesn't visually treat 80% as end of life. In fact, for all intents and purposes an 80% pack looks almost new, it's an 11 (or only just 10) bar pack! That means Leaf users who are savvy in Leafspy see these giant differences in bottom voltages in the pack and assume this is normal. My pack has over 100mV difference between the strongest and weakest cell at VLBW, which is absolutely ridiculous. But that's because the pack is at 75% SoH, i.e. completely broken and dead and ripe for landfill. 9 bars by the way.

There's another big factor in fast Leaf battery degradation, and that's consistent high-drain use even though the chemistry is not very well-adapted to that. LMO chemistries like the '11-17 Leaf, CAN do very good peak current, but they don't have good cycle life at constant >1C use. These are essentially laptop cells on steroids. Nissan should have used NCA. LMO isn't completely unusable in electric cars, but if they would have used that, it would have been a much better fit for e.g. a Zoe 41kWh - where the peak power is much lower and the battery capacity much higher, reducing the effective load on the batteries.

WetEV
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Re: Curious about "refurbishing" the Leaf HV battery

Sun May 27, 2018 9:39 am

mux wrote:End of life, ... and that's typically defined at 80% of initial capacity left.


End of life is usually defined in economic terms, and 80% isn't the typical EOL threshold. 70% EOL or less is more common, see the numbers below to understand why.

Suppose you need 1Wh of capacity. You could define EOL as any percentage, for example if you define EOL as 80% you would need to start with 1.25Wh. If you define EOL as 70% you would need to start with 1.4286Wh. With EOL at 60% start with 1.6667Wh.

If loss is linear with time/usage, then the 80% battery would need to be replaced every 2T, and the 70% battery would need to be replaced every 3T. The 60% battery every 4T.

The cost of replacements over time is:

80%= CostPerWh*1.25Wh/2T = 0.65 CostPerWh/T

70%= CostPerWh*1.4286Wh/3T= 0.4762 CostPerWh/T

60% = CostPerWh*1.6667Wh/4T = 0.416666667 CostPerWh/T
WetEV
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2012 Leaf SL Red (Totaled)
2014 Leaf SL Red

mux
Posts: 128
Joined: Sat Jan 13, 2018 3:52 am
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Re: Curious about "refurbishing" the Leaf HV battery

Sun May 27, 2018 10:20 am

Sure, 60% and 70% is more common these days as a definition of end of life. It's a squishy definition, I totally agree.

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Marktm
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Re: Curious about "refurbishing" the Leaf HV battery

Mon May 28, 2018 9:32 am

mux wrote:
There's another big factor in fast Leaf battery degradation, and that's consistent high-drain use even though the chemistry is not very well-adapted to that. LMO chemistries like the '11-17 Leaf, CAN do very good peak current, but they don't have good cycle life at constant >1C use. These are essentially laptop cells on steroids. Nissan should have used NCA. LMO isn't completely unusable in electric cars, but if they would have used that, it would have been a much better fit for e.g. a Zoe 41kWh - where the peak power is much lower and the battery capacity much higher, reducing the effective load on the batteries.


mux;
Can this be the basis of a "refurbishing" business using duplicate style/dimensions of modules, with better chemistry so that the many Leaf's headed for "junk" can be revived economically? Potentially re-flash of BMS/charge control software/firmware to handle the new cells? What I am experiencing is a very well designed and built auto with really one glaring weakness of it's battery - going on the second one! Being in Texas has likely been somewhat of an issue, but that is just a matter of degree (literally and figuratively). If I could buy the modules at a reasonable price and with some guarantee of performance, I'd do that myself when it becomes time.
2012 Leaf SL; 36,000 miles. Battery replaced November 1st, 2016.
Rural cabin with 6750 watts Grid tied PV. Off-grid solar Leaf charging capable (level II).

mux
Posts: 128
Joined: Sat Jan 13, 2018 3:52 am
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Leaf Number: 6177

Re: Curious about "refurbishing" the Leaf HV battery

Mon May 28, 2018 10:06 am

Man, I couldn't agree more with your sentiment. Yes, it is a crying shame that the Leaf is let down by its battery tech.

In case you've been following this thread, I am already very much planning to commercialize battery extender packs for the Leaf to combat this problem. A package of batteries, mounting hardware and a bunch of electronics to make everything play nice together and not get you stranded with lots of error messages, all for a price that handily beats the upgrade to a 'better' EV. Certainly less than a replacement pack.

I'm technically capable of and very much willing to try and see how hard it is to retrofit the main battery pack with something better. I'm certainly going to do that with my own car, but obviously that is at my own peril. The big problem here is that it is really hard to properly design something like this. Once it's installed, it is out of sight, it has to be weathersealed properly, there are a ton of things that can go wrong in that shell. If anyone on this forum is willing to go at this problem with me or knows people who can, I'm all ears. Nissan clearly isn't willing to fix their old cars (so far for a sustainable image...), but at the same time I'm not going to expose myself to massive lawsuits and liability.

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Marktm
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Re: Curious about "refurbishing" the Leaf HV battery

Mon May 28, 2018 4:14 pm

I agree - I installed a simple cable and anderson connection into my Daughter's Prius (PriUPS generator) as part of my off-grid system and I know that I'll have to break back into the pack area to remove it when they sell it - I cannot have someone unknown messing with a 200 VDC cable/connector in the trunk!

It will be a couple of years before I'd even consider the rebuild, but would also like to try IF high quality modules are available that are simple to retrofit - likely some big ifs. COR has done substantial work with the battery replacements - maybe he has something to add?

My near term goal is to be able to drive my Leaf into my solar shed, hook up the CHAdeMO connection to my hybrid solar system and use it as the storage battery for emergency use, plus experiment with energy arbitrage. I think it is getting close.
2012 Leaf SL; 36,000 miles. Battery replaced November 1st, 2016.
Rural cabin with 6750 watts Grid tied PV. Off-grid solar Leaf charging capable (level II).

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