Malm
Posts: 449
Joined: Mon Jul 22, 2013 12:16 pm
Location: Tábua - Portugal

Re: Battery Capacity Testing

Sat Dec 12, 2015 3:56 am

Riding an i-Miev since 4/2011 in Portugal, 100.000 kms.

bobakka
Posts: 36
Joined: Mon Nov 03, 2014 8:03 am
Location: Oslo, Norway

Re: Battery Capacity Testing

Sat Dec 12, 2015 5:21 am

I have som interesting results that I want to share on the forum.

I have measured battery capacity at the dealer every year since I bought the iMiev i 2011:
Date: Km: CPU: Battery current capacity:
27. 3.2012 19929 1917 42,3 Ah
19. 4.2013 41183 4026 40,8 Ah
17. 1.2014 58661 5596 39,4 Ah
14.11.2014 No battery report, only that "Battery is OK"
5.10.2015 94818 9386 44,1 Ah
1.12.2015 98199 9763 39,3 Ah
1.12.2015 98227 9764 39,2 Ah
1.12.2015 98246 9768 45,8 Ah

It was just after the test in October this year when the battery suddenly was empty (turtle displayed and car stopped) with still one bar left.
It seems like the CPU was fooled into believing there were more capacity in the battery than there actually were.
I also measured battery voltage to be just over 3V (I think 3,050) one day with SoC around 10% if I remember right.

I complained and the dealer performed a new set of tests December 1st.
He found that the battery capacity increased by 15%! during the service and was quite happy!
This is clearly wrong, but what can I do when the dealer says "Battery is OK".

I also performed a battery test yesterday from SoC 56% to 22% with the lowest voltage dropping from 3,885 to 3,540 V.
I can send you the 10 datapoints if you are interested to plot my numbers in your diagram, BlueLightning?
iMiev; New Feb 2011; 119000 km January 2017

Malm
Posts: 449
Joined: Mon Jul 22, 2013 12:16 pm
Location: Tábua - Portugal

Re: Battery Capacity Testing

Sat Dec 12, 2015 6:49 am

Is that last value from 1/12/2005 right?
Riding an i-Miev since 4/2011 in Portugal, 100.000 kms.

bobakka
Posts: 36
Joined: Mon Nov 03, 2014 8:03 am
Location: Oslo, Norway

Re: Battery Capacity Testing

Sat Dec 12, 2015 7:59 am

45.8 Ah is what the report says, yes.
But it cannot be correct
iMiev; New Feb 2011; 119000 km January 2017

kiev
Posts: 811
Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

Re: Battery Capacity Testing

Sat Dec 12, 2015 8:48 am

bobakka wrote:...I have measured battery capacity at the dealer every year since I bought the iMiev i 2011:
Date: Km: CPU: Battery current capacity:
27. 3.2012 19929 1917 42,3 Ah
19. 4.2013 41183 4026 40,8 Ah
17. 1.2014 58661 5596 39,4 Ah
14.11.2014 No battery report, only that "Battery is OK"
5.10.2015 94818 9386 44,1 Ah
1.12.2015 98199 9763 39,3 Ah
1.12.2015 98227 9764 39,2 Ah
1.12.2015 98246 9768 45,8 Ah
...
I complained and the dealer performed a new set of tests December 1st.
He found that the battery capacity increased by 15%! during the service and was quite happy!
This is clearly wrong, but what can I do when the dealer says "Battery is OK".


That is interesting data.

In the service manual for Main Battery On Vehicle there are 2 procedures related to capacity: measurement, and check

Did the dealer perform the automatic capacity measurement at each of these visits (which takes about 6 to 10 hours , or did he just read the BMU data item #23 to check the capacity?

What is the meaning of CPU--it seems to track odometer mileage somewhat.
kiev = kenny's innovative electric vehicle

offgridQLD
Posts: 101
Joined: Wed Jul 17, 2013 4:13 am

Re: Battery Capacity Testing

Mon Dec 14, 2015 7:46 pm

Yes the reported AH capacity is still something we don't understand. How where and why it reports the numbers.

To know the true capacity of your car I feel the only 100% way is to test the weakest cell out of the car.

I could understand the capacity growing and shrinking a little from winter to summer (if test were performed at different times of the year) Though not to much.

Last time I checked my car the ECU's stored capacity reported 38.6AH. Though I have notice no range drop from when the car was brand new. Some say a new Imiev should report 48ah new though I don't believe this as most Imiev's tested with less than 5000km , first few months of ownership report low 40's.....like 20% less than the reported 48ah new car in just a few thousand km driving I don't think so.

So I give up I cant make any sense of this number.

The trouble is if the car thinks it has less capacity than the cells realy do then you get a false low usable range. (Turtle with cells still very strong and to much reserve capacity) If tit gets it wrong in the other direction then you get the turtle popping up with one bar on the dash or more catching you out.

kurt

PV1
Site Moderator
Posts: 2947
Joined: Fri Apr 27, 2012 4:22 pm
Location: Pittsburgh, PA
Contact: Website

Re: Battery Capacity Testing

Tue Dec 15, 2015 5:21 am

Having never been able to get the Ah rating of either battery pack, I tried to do a Wh capacity calculation with SoC.

From 98 to 97% with a 9 kW driving load, consumption showed 130 Wh (making for 13,000 Wh total capacity), but the second calculation from 94% to 93% showed 162 Wh (making for 16,200 Wh, from 100% to 0%). I'm not sure if these are correct as I plugged the car in at work and the SoC jumped 6% higher in a couple of minutes, and this was on level 1.

My friend has a Focus Electric that he has modified, and has a nifty feature showing energy to empty. Unfortunately, I don't think the i-MiEV broadcasts that info on the CANBus unless it is requested by the MUT-3.
:idea: :idea: :idea: :!: :!:

Dropbox maintenance in progress. If any of my links aren't working after November 17, please PM me and let me know which one isn't working.

Thanks.

kiev
Posts: 811
Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

Re: Battery Capacity Testing

Fri Nov 24, 2017 6:24 am

BlueLightning's chart is a very useful tool. My bad cell #47 is only reading 3.95 when all the rest are at 4.1, and the gauge only goes to 10-11 bars. The mut clone device and canion both report SOC at 60 to 66%. So there are several ways to view the issue.

i hope to get the dealer service to run the cell smoothing function using MUT on december 11, but they didn't seem too open to my suggestion. They want to drain the pack, then recharge, then drain again, then figure out what to do...
kiev = kenny's innovative electric vehicle

rnlcarlov
Posts: 81
Joined: Wed Apr 13, 2016 8:30 am

Re: Battery Capacity Testing

Fri Nov 24, 2017 8:46 am

From my trips I understood that I have 14kwh available from 100% to 0% SOC in Canion. I made a trip from 100% to 9% and extrapolated the Wh out (minus Wh reg) to obtain this value. Furthermore, when the average consuption is 140 Wh/km, I see that I consume 1% SOC per each km, leading also to the 14kwh value. I believe this corresponds to the usable value in a new car with the 16kWh baterry (not sure about the 14.5kWh triplets).

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

Re: Battery Capacity Testing

Tue Dec 04, 2018 12:01 am

Image

In an earlier post BlueLightning suggested measuring the fully charged battery capacity by comparing the change in kWh with the change in SoC while charging. I have done something similar using measurements of amps to the battery and the SoC collected from my CZero now and then over the last 4 years. This covers mileage from 6000 km to almost 80000 km. Up to 50,000km the data was collected with Canion at about 1 second intervals. After 50,000km the data was collected with OBDZero at about 4 second intervals. I first divided the data into measurement sets without gaps. This resulted in about 400 measurement sets most of which were quite short. I then used this formula to compute Ah for each timestep:
Ah = (A0 +A1)*dH/2
Where A0 is the amps measured in the previous timestep and A1 is the amps measurement in the present timestep. dH is the timestep (either 1 sec. or 4 sec.) in hours.
For each continuous measurement set I added up the Ah values and the changes in SoC. I then computed the battery capacity using this formula:
CapAh = 100*Sum(Ah)/Sum(dSoC)
Where Sum(Ah) is the accumulated amp-hours to the battery, dSoC is a 0.5% change in SoC and Sum(dSoC) is the total change in SoC in each continuous measurement set.
Most of the original measurement sets were too short to give meaningful results. By setting a minimum of 20% change in SoC for a useful set, 100 sets remained. The capacities computed from these sets are shown as points in the graph above.
The loss of capacity over time is easy to see but there are ups and down along the way. The most obvious of these are the capacity measurements between 40 and 41 Ah at a bit more than 40,000 km. As noted in the graph these measurements were record shortly after the car was serviced at 40,000 km. I believe that as part of the service the car’s battery capacity estimate was reset to 41 Ah or higher. This agrees with bobakka’s observation that the battery capacity seemed to be too large when their car was serviced. This also shows that in reality I’m computing the car’s estimate of the capacity not the true battery capacity. The less marked ups and downs in the capacity may be due to temperature changes and of course errors in the measurements.
The red and green lines in the graph are two models fitted to the data. The green line is:
CapAh = 50.4 - 1.14*ln(km)
And the red line is:
CapAh =40.11 - 0.000036*km
The green natural log line fits the data a bit better than the red linear model. However neither fit is good and I need more data in other to be certain of which model gives the best description of aging. 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.

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