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 Post subject: Re: Battery Degradation
PostPosted: Mon Apr 21, 2014 5:31 am 
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Joined: Fri Apr 12, 2013 7:30 am
Posts: 134
Location: Gardena, CA
JasonA wrote:
10-4 on that. Because now of this, I won't be letting the vehicle sit at 4-6 bars like I have been for the last 3 months which is 40-50% on a Leaf (3.82-3.85v).. But a 18650 should be sitting nicely at 3.7v range for 50% storage for avg 2-3% loss per year.

What a wacky gauge... :roll:


Toyota should have implemented the SOC gauge similar to the health/shield indicator in Halo. 16/16 bars as 80% charge with each each bar representing 5% SOC increments, then 16/16 overlaid on top in a different color for extended charge, with each bar representing 1.25% charge.

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 Post subject: Re: Battery Degradation
PostPosted: Tue Apr 22, 2014 7:00 am 
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Joined: Wed Nov 14, 2012 9:50 pm
Posts: 4068
Location: San Diego
n3ckf wrote:
I assume you're getting your mi/kwh number from the little screen that displays every time you turn the car off and you're driving at fairly low speeds to get 3.7mi/kwh?


No, I get it from the navigation screen devoted to economy. Just reset it with the trip odometer at the beginning of each trip.

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Tony Williams
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San Marcos, California 92078 USA
tony@QCcharge.com
www.QCcharge.com
Twitter: QCPower
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 Post subject: Re: Battery Degradation
PostPosted: Tue Jun 10, 2014 11:45 pm 
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Joined: Wed Nov 14, 2012 9:50 pm
Posts: 4068
Location: San Diego
I drove 120 miles today from San Diego up north to Orange County, with about 15 miles range remaining.

That's 135 total miles / 3.7 miles per kWh is 36.49 kWh available.

36.49 / 41.8kWh when new is 87.28% capacity

19 months, 39,000 miles

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Tony Williams
QC Charge
1780-104 La Costa Meadows Drive
San Marcos, California 92078 USA
tony@QCcharge.com
www.QCcharge.com
Twitter: QCPower
1-844-EV-PARTS
1-844-387-2787
1-760-798-0342 Office
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 Post subject: Re: Battery Degradation
PostPosted: Wed Jun 11, 2014 5:01 am 
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Joined: Fri Aug 30, 2013 6:23 am
Posts: 106
I've been doing a full extend charge every day since mid-Jan. 100+ times. M-F I drive it about 100 miles a day. I've had the car since Sep 2013. I have about 16K miles on it. Probably lost about 5-6% battery since I got it. Pretty good considering I extend charge every day.


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 Post subject: Re: Battery Degradation
PostPosted: Thu Jun 12, 2014 4:05 am 
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Joined: Sun Mar 03, 2013 2:26 am
Posts: 305
Location: Austin, TX
As I've previously mentioned, I purchased some cells which I believe are the most similar to the cells in our RAV4EV to get an idea of capacity fade. It has been rumored that the cells are NCR18650 by Panasonic. This model number comes in many flavors, such as PD, A, B, D, and most recently PF. I chose the NCR18650PD series as it is designed for higher current rates than the others, was available about the time our vehicles were built, and perform better than the higher energy versions that are designed for much lower discharge rates. It's resistance is lower and voltage doesn't sag as much during acceleration-like currents. Searching online shows a spec sheet from SANYO (now Panasonic) as well as presentations from Panasonic, talking about the NCR18650PD and their NCA technology.

Image

This cell is rated at 2.9Ah. The ones in our car may be 2.9Ah, 3.0Ah, or even 3.1Ah, I have no idea.
I also assume our packs are made up of 4508 cells arranged in 92 in series and 49 in parallel producing approximately a 47kWh pack.
I believe the upper 5% and lower 5% are inaccessible, giving us 41.8kWh usable.

Image

Maximum capacity is reached when a cell of this chemistry is charged to 4.2V. However, to reduce stress on the electrolyte to improve cycle life, I think they only charge the cell to 4.15V/cell with a current taper, which provides 95% of rated capacity. This is the charging algorithm used when using Extended Charge. Here is a screen capture of my car finishing charge when extended charge is selected.

Image

Standard Charge charges each cell to 4V without any taper, allowing 80% of rated capacity to be achieved.
This screen capture is of my car when standard charge was selected.

Image

To cycle the cells, I chose a Dynamic Stress Test (DST) which is a standard test used by Society of Automotive Engineers (SAE) for batteries. It is a series of charge and discharge amounts, which for lack of a specific driving cycle, I felt stressed the cell in a similar way to the way one would normally drive.

Image

Most of the loads are between 10-20kW with some bursts of 50-75kW which is reasonable for normal driving (not in sport mode). It also subjects the cells to regeneration power from 10-40kW levels.
I chose to put the cell through this "drive cycle" over and over until a certain amount of energy had been removed.
I tested 4 conditions:
Extended charge then driving 115 miles until the Low Battery Warning light came on
Standard charge then driving 95 miles until the Low Battery Warning light came on
Extended charge then driving 60 miles
Standard charge then driving 60 miles (this is my normal usage pattern)
I charged the cell at C/5 (5 hour rate), similar to what our vehicles charge using the 10kW charger.
Full details of the testing protocol are here.

Image

In an ideal world I would have had many cells to test under each condition and in a climate controlled environment. However, I was only able to test each scenario with two cells each and in an open lab where temperature fluctuated from 20C-30C (68F-86F).
Here are the results cycling the cells through 90k miles of the DST-360 regimen.

Image

The testing took many months and the variation in capacity tests (at every 5k miles) is due to different temperatures in the lab the day that test was performed. After 90k miles these cells lost ~10% capacity under 3 of the 4 situations. Only when they were fully charged (Ext Charge) and completely discharged (down to 15% SOC) did they deviate from the others losing ~13%.
Notice that the cells lost 5% within the first 20k miles, then it took another 70k miles to lose the next 5%. I'm not saying our packs will behave exactly the same as these cells as it will take us 3-4 years to reach this mileage, so calendar life degradation will be additive. Additionally, these cells were not subject to extreme ambient temperatures, nor did they ever sit fully charged (Ext Charge) for long periods of time. All of these factors will cause the cell to degrade faster than what is shown. However, even if the cells decay twice as fast as these in real life. we will still have a ~100 mile range EV after 100k miles!

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 Post subject: Re: Battery Degradation
PostPosted: Thu Jun 12, 2014 6:49 am 
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Joined: Wed Nov 14, 2012 9:50 pm
Posts: 4068
Location: San Diego
EVlearner wrote:
Your case would seem like a really best case scenario -- you take care of battery and still see this % of loss. And do you think the loss would be linear, so at 40,000 miles, one may expect 14% degradation?


Yes, it appears to be somewhat linear, which is quite different than the LEAF battery model.

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Tony Williams
QC Charge
1780-104 La Costa Meadows Drive
San Marcos, California 92078 USA
tony@QCcharge.com
www.QCcharge.com
Twitter: QCPower
1-844-EV-PARTS
1-844-387-2787
1-760-798-0342 Office
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 Post subject: Re: Battery Degradation
PostPosted: Thu Jun 12, 2014 7:01 am 
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Joined: Wed Nov 14, 2012 9:50 pm
Posts: 4068
Location: San Diego
Kohler Controller wrote:
As I've previously mentioned, I purchased some cells which I believe are the most similar to the cells in our RAV4EV to get an idea of capacity fade...
This cell is rated at 2.9Ah. The ones in our car may be 2.9Ah, 3.0Ah, or even 3.1Ah, I have no idea.
I also assume our packs are made up of 4508 cells arranged in 92 in series and 49 in parallel producing approximately a 47kWh pack.
I believe the upper 5% and lower 5% are inaccessible, giving us 41.8kWh usable.
Image[/url]


Truly awesome work. I'm well below your worst cell performance graph.

I'm quite confident we have the 2900ma cell.

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Tony Williams
QC Charge
1780-104 La Costa Meadows Drive
San Marcos, California 92078 USA
tony@QCcharge.com
www.QCcharge.com
Twitter: QCPower
1-844-EV-PARTS
1-844-387-2787
1-760-798-0342 Office
Hours M-F, 9-5 Pacific Time


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 Post subject: Re: Battery Degradation
PostPosted: Thu Jun 12, 2014 3:04 pm 
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Joined: Sun Mar 03, 2013 2:26 am
Posts: 305
Location: Austin, TX
I'm coming up on 30k miles after 15 months, with no observable difference in range. Since 99% of my driving is within the city, I have no way to know about my battery's degradation over the past year. Every September I drive to College Station for a football game (118 miles away). Usually when I arrive my GOM says I have 12-15 miles left after driving 60-65 mph. It will be interesting to see what my range is when I make the trip in September.

I should have put my car on a dyno the first month I got it to perform a range test, then repeat every year. Ugh.
I guess I could start now.

Tony, I hope yours will start to level off instead of a linear decline.

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Kohler Controller
Shoreline Blue
EVSE, AeroVironment 30A, 7.4kW
Reciever Hitch, CURT Class III Round Tube
Cargo Liner
Modified 120VAC EVSE to also accept 240VAC
Hood struts- Sokie Tech
JdeMO Level 3 Charging port
12.6kW PV system
VIN 1396
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 Post subject: Re: Battery Degradation
PostPosted: Thu Jun 12, 2014 5:08 pm 
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Joined: Tue Apr 09, 2013 2:23 am
Posts: 59
Location: Rodeo, CA
Thanks for the great info!

Here is some interesting cell test data, not strictly related to the RAV but shows the PD cell performance:
http://www.dampfakkus.de/akkuvergleich. ... &akku6=507

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 Post subject: Re: Battery Degradation
PostPosted: Thu Jun 12, 2014 7:51 pm 
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Joined: Fri Apr 26, 2013 12:56 pm
Posts: 132
Location: Webster, NY
Kohler Controller wrote:

Image

The testing took many months and the variation in capacity tests (at every 5k miles) is due to different temperatures in the lab the day that test was performed. After 90k miles these cells lost ~10% capacity under 3 of the 4 situations. Only when they were fully charged (Ext Charge) and completely discharged (down to 15% SOC) did they deviate from the others losing ~13%.
Notice that the cells lost 5% within the first 20k miles, then it took another 70k miles to lose the next 5%. I'm not saying our packs will behave exactly the same as these cells as it will take us 3-4 years to reach this mileage, so calendar life degradation will be additive. Additionally, these cells were not subject to extreme ambient temperatures, nor did they ever sit fully charged (Ext Charge) for long periods of time. All of these factors will cause the cell to degrade faster than what is shown. However, even if the cells decay twice as fast as these in real life. we will still have a ~100 mile range EV after 100k miles!



Great work Kohler!

I'm surprised how little difference there is between test conditions. I wonder how much of the real world degradation is due to charging/discharging and how much is due to environment (heat). My range plummeted in the winter but looks to be back close to new now.

Thanks,
Mike

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