Update on Nissan LEAF Battery Replacement

[DaveEV]

My data shows that pack temps jump 10-15F immediately during QC and continues to rise for quite some time after that. The temp sensors are measuring air temps in the pack, not cell temp, so there is some delay there.

L2 does very little.

As QueenBee states, it's physics which determines heat rise. Charging at 35 kW instead of 3.5 kW generates exponentially more heat. P = I^2*R. A newish pack has a resistance of about 0.1 ohms. 3.5kW L2 is around 10 amps, QC is around 100 amps, or 10 watts compared to 1000 watts. That's 100 times more heat when charging 10 times faster.

Not only that, but because the pack is relatively well insulated, that heat has nowhere to go. L2 charging heat is negligible when compared to QC.

All that said, once daily QC will only have a moderate effect on rate of capacity loss, accelerating loss of capacity perhaps 20% as shown in in INL ATVA testing.

 

[Stanton]

As QueenBee states, it's physics which determines heat rise. Charging at 35 kW instead of 3.5 kW generates exponentially more heat. P = I^2*R. A newish pack has a resistance of about 0.1 ohms. 3.5kW L2 is around 10 amps, QC is around 100 amps, or 10 watts compared to 1000 watts. That's 100 times more heat when charging 10 times faster.

This is true for any type of charging system, and why I didn't even buy the QC option on my Leaf (and that's before any of us knew there was a heat problem). Here is some data on "C" rates I present when giving EV presentations:

(0.06C) 1.44 kW Nissan Leaf on 120v / 12a
(0.16C) 3.84 kW Nissan Leaf on 240v using EVSE Upgrade 16a (2011 and 2012 with 3.3 kW charger)
(0.2C) 4.8 KW Nissan Leaf on 240v using EVSE Upgrade 20a (2013 and 2014 with 6.6 kW charger)
(1.83C max) 44 kW Nissan Leaf quick charge port (CHADEMO L3)

You can see there is a huge difference between L2 and L3 charging, which must result in additional heat generation and a degrading affect on the battery pack.

 

[dhanson865]

As QueenBee states, it's physics which determines heat rise. Charging at 35 kW instead of 3.5 kW generates exponentially more heat. P = I^2*R. A newish pack has a resistance of about 0.1 ohms. 3.5kW L2 is around 10 amps, QC is around 100 amps, or 10 watts compared to 1000 watts. That's 100 times more heat when charging 10 times faster.

This is true for any type of charging system, and why I didn't even buy the QC option on my Leaf (and that's before any of us knew there was a heat problem). Here is some data on "C" rates I present when giving EV presentations:

(0.06C) 1.44 kW Nissan Leaf on 120v / 12a
(0.16C) 3.84 kW Nissan Leaf on 240v using EVSE Upgrade 16a (2011 and 2012 with 3.3 kW charger)
(0.2C) 4.8 KW Nissan Leaf on 240v using EVSE Upgrade 20a (2013 and 2014 with 6.6 kW charger)
(1.83C max) 44 kW Nissan Leaf quick charge port (CHADEMO L3)

You can see there is a huge difference between L2 and L3 charging, which must result in additional heat generation and a degrading affect on the battery pack.

reminds me of this post of mine from 2014

Look at it in KW divided by the KWh of the battery. Charge rates below 1 are slow enough to be a complete non issue. Charge rates above 1 require more cooling and or degrade the battery depending on how high you go.

(0.06C) 1.44 KW Nissan Leaf on 120v / 12a
(0.16C) 3.84 KW Nissan Leaf on 240v using EVSE Upgrade 16a (2011 and 2012)
(0.2C) 4.8 KW Nissan Leaf on 240v using EVSE Upgrade 20a (2013 and 2014 assuming they have the "6.6 KW charger")
(0.25C) 6 KW Nissan Leaf with "6.6 KW charger" on a 27a or higher J1772 charger.
(1.83C max) 44 KW Nissan Leaf quick charge port (Chademo) but it varies because not all chargers offer the max charge rate.


9.6 KW Tesla Model S on UMC 240v 40a (0.16C for a 60kwh, 0.11C for a 85kwh)
~20 KW Tesla Model S with dual chargers on a HPWC (0.32C for a 60kwh, 0.23C for a 85kwh)

Supercharger charge rates in terms of C vary but they run big loud fans during the supercharging process so they don't overheat the battery pack while charging that fast

90KW / 85 KW (90 KW supercharger on model S with 85 KW battery) is only 1.05C
120KW / 85 KW (120 KW supercharger on model S with 85 KW battery) is 1.41C
90KW / 60 KW (90 KW on model S with 60 KW battery) is 1.5C
105KW / 60 KW (120 KW supercharger limited to 105KW on model S with 60 KW battery) is 1.75C

and if anyone doesn't believe the part about loud fans and supercharging see

My Pack Cooler, including the Air Conditioning Compressor DID KICK IN! AND HOLY CRAP! FULL BLAST AS WELL!!! Sounded like a Circular Saw going. Both cooling fans and both radiators + the AC compressor...... WOW

http://www.youtube.com/watch?v=ZYPeequUD4s

the video is over 1 hour long, recording the entire supercharging session so I'm not going to bother to watch it again to tell you a time stamp but I remember him moving the camera around inside and outside the car and discussing the sound the fans made during different stages of his charging session.

I can tell you from more recent Tesla updates even with the fans, radiators, pumps they avoid going over 1.85C

Some can charge at 90 KW (85 KWh A battery pack, near 1.06C charge rate)
some can charge at 105 KW (60 KWh with older battery pack, 1.75C charge rate)
some can charge at 111 KW (60 KWh with newer battery pack, 1.85C charge rate)
some can charge at 120 KW (85 KWh B or D battery pack, near 1.41C charge rate)


Don't know if the S70D is sharing the 111 KW or the 120 KW limit or if it has it's own.

provisional S70D limit possibilities

111 KW (70 KWh, 1.59C charge rate)
120 KW (70 KWh, 1.71C charge rate)

With a 75D out now that adds lower C rates assuming the same 120KW supercharger rate.

We also need to update for the 30 kWh leaf. Can we assume the same 6.6 KW charger and a lower C rate?

 

[nerys]

Was the cooling for the battery or for the charging system?

What is the efficiency of the charging system?

If you pump 100amps at 80% efficiency say that means you have 20 amps of heat generation to deal with.

Where is that 20 amps being lost? Well in the charger and in the battery. How much for each?

 

[QueenBee]

As QueenBee states, it's physics which determines heat rise. Charging at 35 kW instead of 3.5 kW generates exponentially more heat. P = I^2*R. A newish pack has a resistance of about 0.1 ohms. 3.5kW L2 is around 10 amps, QC is around 100 amps, or 10 watts compared to 1000 watts. That's 100 times more heat when charging 10 times faster.

This is true for any type of charging system, and why I didn't even buy the QC option on my Leaf (and that's before any of us knew there was a heat problem). Here is some data on "C" rates I present when giving EV presentations:

And is also one of the reasons why I cringe every time I grab a power tool battery or AA/AAA battery off the charger and it's warm because I wasn't given the option of a nice slow leisurely charge or a 30 minute charge.

 

[nerys]

I would not worry about NIMH batteries. heat does not seem to murder them so much.

I lived by 15min NIMH AA's (they don't get warm. they get hot)

10 years they were still going strong and I abuse the crap out of them.

 

[DaveinOlyWA]

My data shows that pack temps jump 10-15F immediately during QC and continues to rise for quite some time after that. The temp sensors are measuring air temps in the pack, not cell temp, so there is some delay there.

L2 does very little.

As QueenBee states, it's physics which determines heat rise. Charging at 35 kW instead of 3.5 kW generates exponentially more heat. P = I^2*R. A newish pack has a resistance of about 0.1 ohms. 3.5kW L2 is around 10 amps, QC is around 100 amps, or 10 watts compared to 1000 watts. That's 100 times more heat when charging 10 times faster.

Not only that, but because the pack is relatively well insulated, that heat has nowhere to go. L2 charging heat is negligible when compared to QC.

All that said, once daily QC will only have a moderate effect on rate of capacity loss, accelerating loss of capacity perhaps 20% as shown in in INL ATVA testing.

your views are limited by climate options in your area. I have seen as little as a 4-5º rise for "about" 20 mins of charging (rarely charge below 10KW) but my pack started in the upper 50's.

I will say that temp rise varies a ton. I have also seen 15º rises but generally from the mid 40s.

Late temp rises I have only seen when OAT was 80º or higher.

In your case, I suspect part of you temp rise has to do with the weather

**edit**

One thing that I just thought of is the later temp rises I have pretty much only noticed on my 2011. I can't say that I have seen it as much on my 2013 but it also could reflect a change in how I use LEAF Spy since I only run it when I am manipulating range, recording daily numbers or getting ready to quick charge.

This is something I will have to look at more closely

 

[DaveinOlyWA]

As QueenBee states, it's physics which determines heat rise. Charging at 35 kW instead of 3.5 kW generates exponentially more heat. P = I^2*R. A newish pack has a resistance of about 0.1 ohms. 3.5kW L2 is around 10 amps, QC is around 100 amps, or 10 watts compared to 1000 watts. That's 100 times more heat when charging 10 times faster.

This is true for any type of charging system, and why I didn't even buy the QC option on my Leaf (and that's before any of us knew there was a heat problem). Here is some data on "C" rates I present when giving EV presentations:

And is also one of the reasons why I cringe every time I grab a power tool battery or AA/AAA battery off the charger and it's warm because I wasn't given the option of a nice slow leisurely charge or a 30 minute charge.

I spent a year with two cellphones (which are notorious for overcharging to extend talk time) one which was charged overnight, the other only boosted during the day.

The boosted phone was charged to 100% 20sih times because I simply forgot to unplug it

Now after 18 months, I can discern very little difference between the two other than there is a huge difference in time for one phone to go from 100% to 80% verses the other to go from 80% to 60%. The 100%er is way better. I attribute this to likely overcharging though...

 

[nerys]

Actually that is more to do with the phones simply not accurately reading battery capacity.

You need to recalibrate the battery. Then it will read correctly.

 

[DaveinOlyWA]

Actually that is more to do with the phones simply not accurately reading battery capacity.

You need to recalibrate the battery. Then it will read correctly.

how do you do that?

 

[nerys]

https://www.androidpit.com/how-to-calibrate-the-battery-on-your-android-device

 

[DaveinOlyWA]

https://www.androidpit.com/how-to-calibrate-the-battery-on-your-android-device

oh yeah, already familiar with the "no pain, no gain" method. I choose to live a sheltered painless existence...

 

[Cor]

interesting is that I did not lose my 1st bar till 17.2kwh. I thought it was 15% ? I did not lose my first bar until the battery hit 80% which is a 20% loss. 20% "exactly" on the dot.

I was wondering the same. Nissan spec is that losing the first (top) bar (bar nr 12) means that 15% is lost, every next bar should be 6.25%
So I was expecting to lose a bar seeing that my capacity has dropped below 54.4 Ah (which is 85% of 64Ah, so 15% loss).
However, I am in the low 52 Ah now and my display still shows 12 bars.
So, apparently Nissan is not truthful in stating that the top bar is worth 15%, they have moved the scale to show less bar loss,
meaning that the battery needs to degrade much further before it will be an 8 bar loser to qualify for warranty...
Anybody else seeing this effect?

 

[TimLee]

...
Anybody else seeing this effect?

Yes.
Been discussed a lot in other threads.
See mwalsh posts giving ranges for bar loss.
In general the eighth bar loss which Nissan referred to as 70%, and which their specific numbers said was 66.25%, is actually more like 64% on SOH and roughly same on percent capacity.
And once SOH first shows 64%, it can take anywhere from two weeks to possibly more than two months for the ninth bar to disappear.

 

[Yanquetino]

So, apparently Nissan is not truthful in stating that the top bar is worth 15%, they have moved the scale to show less bar loss,
meaning that the battery needs to degrade much further before it will be an 8 bar loser to qualify for warranty...
Anybody else seeing this effect?

YES. Absolutely! See my post on the issue, especially my later reply with more specifics.

 

[nerys]

Ahh what car do you.have that has a 64ah battery?

 

[Cor]

Ahh what car do you.have that has a 64ah battery?

2011 Leaf is supposed to have a nominal 64Ah battery pack, according to the spec of the cells used in that pack. I believe that each cell is spec'ed at just over 32 Ah (at a certain discharge rate and voltage range) so the cell pairs that we have in our battery modules (two cells in parallel; 96 pairs in series) mean that the nominal battery pack spec is 64 Ah. The LeafSpy will give you the *actual* capacity that the BMS computer inside your pack has learned from measuring current and time and calculating Ah in/out while measuring cell voltage while charging/discharging that pack.
I have witnessed that capacity measurement correct itself when you take a BMS that has learned one set of modules and place it on a different set of modules: my BMS was tied to an almost new pack of 2015 "Lizard" modules, indicating 66 Ah and I moved it to a pack of used 2011 modules that was down to 52 Ah. It took almost 1000 miles of driving and more than a month of daily charging (to 80%) to re-learn and drop below the 53 Ah as LeafSpy is reading from the BMS. Seeing the 12 bars still intact surprised me greatly. I need to check with my neighbors as their BMS had to re-learn from their degraded 2011 pack which was down to 48Ah (75%) and is now seeing the "Lizard" cells so it is adjusting up and I expect that it will eventually show the 66 Ah capacity again, I will check with them at which point they regained the 12th bar or that the bar indication is somehow lagging more than the Ah history is adjusting.

 

[Valdemar]

This is a very interesting experiment as we may get an idea of how long the delay is after the Ahr drops below a certain threshold until bars disappear.

 

[nerys]

Ok. I am confused. Leafspy tells me i have 18.5 ah. So what gives?

Or am i confusing units again? Maybe i have 18.5 kwh ?

 

[TimLee]

Ok. I am confused. Leafspy tells me i have 18.5 ah. So what gives?

Or am i confusing units again? Maybe i have 18.5 kwh ?

Screen four Remaining stored energy is in kWh.
But screen three does give a calculated remaining stored energy that is in Ah units.
I personally do not like screen three and the use of Ah units because it allows for confusion with the overall pack capacity when fully charged given on page one which is in Ah.
Turbo3 doesn't like the calculated remaining energy on page 3 either and has considered eliminating it.
The real number from the BMS on remaining energy is the kWh value on page 4.
I think he should at least change the units on the page 3 calculated remaining energy to kWh. But as he has suggested it would be better to eliminate it entirely.

Valdemar is talking about the maximum stored energy capability when fully charged. The page 1 value.