JoeS
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Joined: Thu Dec 15, 2011 5:47 am
Location: Los Altos Hills, California

Re: Battery Capacity Testing

Tue Dec 04, 2018 10:17 am

CZeroOwner wrote:...There are other reasons to believe that a natural log model best describes battery aging so with a bit of luck I will have a useable battery for some years to come.
CZeroOwner, thank you for your graphs and analysis. Agree that the log line is perhaps a better approximation, which bodes well for our future.

For myself, I've given up closely monitoring the car and am content with taking occasional samples such as last weekend's 50-mile highway excursion to the San Francisco Auto Show where I plugged in and had RR=84 before the drive home. Good enough, although this replacement battery only has about 30,000 miles on it with CaniOn reading 38.3Ah.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

datom
Posts: 8
Joined: Wed Apr 11, 2018 8:01 am

Re: Battery Capacity Testing

Tue Dec 04, 2018 11:04 am

Guys,
have a look here: https://docs.google.com/spreadsheets/d/1tHPZWJDgSr8zTlYx8h3Vzkc9iAvu376P0HnR_9_IHlc/edit?usp=sharing
I collected capacity and km values from the german C-Zero/In/I-Miev forum and put them into a spread sheet.

The top left figure shows Ah versus age in days, the top right shows Ah vs. km.
The bottom left shows Ah vs (km/age), the bottom right shows a histogram of daily driven km.

Best,
Tom

CZeroOwner
Gold Member
Posts: 17
Joined: Mon Jan 15, 2018 1:47 am
Location: Denmark

Re: Battery Capacity Testing

Tue Dec 04, 2018 1:04 pm

datom's German data shows a much more drastic decline in capacity than I'm predicting. I seem to remember reading that a Li-ion battery can have a long period with constant capacity followed by a sudden decline. The German data supports this.

CZeroOwner
Gold Member
Posts: 17
Joined: Mon Jan 15, 2018 1:47 am
Location: Denmark

Re: Battery Capacity Testing

Sun Dec 09, 2018 12:47 pm

Image

The black dots in the graph above are battery capacities for 44 German owned iMiev/CZero/iOns collected by datom. There is a link in his post above. The green curve is my model (Ah = 50.4 -1.14*ln(km)) for battery aging discussed in an earlier post. It looks like my car’s capacity deteriorated more rapidly during the first kms than was normal for the German cars. On the other hand, my present mileage is 80,000 km and my battery capacity is now average or above average.

I suggested based on my own data that the natural log model was probably the best description of battery aging, but the German data doesn’t support this conclusion. In fact it looks linear more than anything else.

Of the 44 cars 16 owners reported more than one capacity measurement. These are shown as lines in the graph below.

Image

Some show a sharp decline in capacity early in the car’s life and others a slower decline in capacity later in the car’s life. However there is no statistical difference in the rate of decline between low mileage and high mileage cars. What is interesting is the wide range of the rates of decline. This may be due to variations in the manufacture of the battery cells but it could also indicate that there are things that we can do or avoid doing that will extend battery life.

In my case I bought my 2012 CZero in 2014 from a dealer. The car had no previous owner and less than 2000 km. Other than that, I don’t know how it was treated. When I first saw the car, it was in the dealer’s showroom with the charger connected. From 2000 km to 40,000 km we quick (Chademo) charged the car. Since 40,000km we have slow charged 70% of the time. I usually slow charge between the hours of 10 in the evening and 7 in the morning and the car isn’t charged up every day but on the average every second day.

Thanks to datom for the use of his data.

coulomb
Posts: 114
Joined: Sun Jun 10, 2018 8:32 pm
Location: Brisbane, Australia

Re: Battery Capacity Testing

Sun Dec 09, 2018 3:28 pm

CZeroOwner wrote: The black dots in the graph above are battery capacities for 44 German owned iMiev/CZero/iOns collected by datom.

Let's remember that this is the capacity as reported by the on-board BMS. The fact that range can miraculously be restored (real-world, achieved range) after the "battery smoothing" process suggests to me that perhaps the BMS is overly pessimistic about degradation. Perhaps Mitsubishi are happy with this; mostly this should be invisible to the user, and it causes less real depth of discharge, saving the battery (at the expense of potentially a lot of customer inconvenience).

This is one of the reasons that I'm attempting to reverse engineer the firmware. Progress is slow, unfortunately, mainly due to time availability.

What is interesting is the wide range of the rates of decline. This may be due to variations in the manufacture of the battery cells but it could also indicate that there are things that we can do or avoid doing that will extend battery life.

Indeed. Or it could be the BMS being overly cautious / pessimistic. It would be really good to know which it is.

[ Edit: removed graph from quote. ]

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