JejuSoul
Posts: 1299
Joined: Wed Jul 08, 2015 6:47 am
Location: Jeju
Contact: Website

Battery Ageing Model

Sun Nov 08, 2015 7:45 pm

I have been looking at the Battery Ageing Model for the Nissan 1eaf - http://www.electricvehiclewiki.com/?tit ... acity_Loss
And wondering what data we need to collect from our cars to create such a model.

For the Nissan this list is sufficient
City: Choose a nearby city from an existing list in the spreadsheet.
Miles/kWh: Estimate your 1EAF driving efficiency. If you do not know, 4.0 is a good starting estimate.
Days/week in the Sun: How many days per week will the 1EAF be parked in the sun, on average?
Estimated Annual Mileage: How many miles do you expect to drive the 1EAF each year?

The most important for the Nissan is the location. The Nissan cannot cope with hot climates.

We have very little data so far for the Soul EV, but so far it does not look at all like the 1eaf
I am interested in knowing what data we need to collect, and how we graph that data.
The current dataset is too small to allow us to know when or whether the battery warranty date would be reached.
The following graph uses data from 3 different cars. (One in South Korea, one in Sweden, one in Canada)
It plots the number of discharge cycles against battery deterioration.
This data is read from the OBD - On Board Diagnostic device.
Image
If these lines are valid, then what explains the huge difference in slope. It doesn't seem to be any of the four factors effecting the 1eaf. We would need more data to make a better guess.
The codes for using Torque Pro can be found by clicking the link in the website icon under my user name on the left.

JejuSoul
Posts: 1299
Joined: Wed Jul 08, 2015 6:47 am
Location: Jeju
Contact: Website

Re: Battery Ageing Model

Thu Nov 12, 2015 11:45 pm

Looking for data for the T esla - I found this site: https://steinbuch.wordpress.com/2015/01 ... tion-data/

One of the images showing battery degradation is
Image
Ignore the trendline, the author states that is just an automatic artefact of his graphing software. What is interesting is the complexity of the equation to get the number of cycles.

In my graph at top I have used a really simple technique to get the number of cycles, just divide the Cumulative Discharge by the Pack Size. This is only easy when the Pack Size is fixed. It is at the moment - all cars in our sample have a usable Pack Size of 27kWh. But when we start to get actual deterioration of range then we need to find a different way. This means collecting different data, possibly range testing - anyone got any good ideas?
Last edited by JejuSoul on Tue Aug 28, 2018 10:33 pm, edited 1 time in total.
The codes for using Torque Pro can be found by clicking the link in the website icon under my user name on the left.

Elmil
Posts: 141
Joined: Mon Oct 26, 2015 9:46 am
Location: Sweden

Re: Battery Ageing Model

Fri Nov 13, 2015 12:42 pm

I think it could be more direct to focus on the actual energy passed to/from the battery, relative to used SOC. By computing a "virtual SOH" value every week or workday I hope any hidden pattern will show up. We have enough knowledge about the BMS info by now. My suggestion is:

Use an OBD2 reader to get the following info:
- SOC(t) (Total SOC for battery)
- SOC(d) (Displayed SOC)
- CCE (Cumulative Charge Energy)
- CDE (Cumulative Discharge Energy)

Use two samples and compute:
Used energy E = (CDE2-CDE1) - (CCE2-CCE1)
SOH(t) = E / (SOC(t) diff) / Total Capacity (30kWh)
SOH(d) = E / (SOC(d) diff) / Official Capacity (27kWh)

The main benefit is that no range- or energy consumption parameters will matter.

I already have 5 days statistics ;) based on my 100km commute:

Mon: SOC=54/58 E=15.6kWh => SOH=96.3/99.6
Tue: SOC=54/58 E=15.3kWh => SOH=94.4/97.7
Wed: SOC=54.5/58.5 E=15.4kWh => SOH=94.2/97.5
Thu: SOC=56/60 E=16.4kWh => SOH=97.6/101.2
Fri: SOC=55/59 E=16.4kWh => SOH=99.4/103.0

Over time we should see battery deterioration reflected in these values, and also if the BMS has any compensation built in for the displayed SOC.
This may already be seen in this limited data; If I use 29 kWh for total capacity instead of 30 kWh, the SOH values are very close to each other, so maybe my battery has lost 1 kWh, but I can still use 27.
Kia Soul EV 2015 / 115,543 km Sold
Kia Soul EV 2019

JejuSoul
Posts: 1299
Joined: Wed Jul 08, 2015 6:47 am
Location: Jeju
Contact: Website

Re: Battery Ageing Model

Mon Nov 16, 2015 9:02 pm

Elmil: Your method seems to have the same the same problem as mine. We do not know what the current Total Capacity and current Usable Capacity actually are. The original Total Capacity is actually 30.4kWh according to data here http://avt.inel.gov/fsev.shtml. The current Usable Capacity will only match the Official Capacity or what I would call the original Usable Capacity for the first year or so. Initially only the Total Capacity will fall, but later both will do so.
There is an image from the Battery University site that helps explain this - http://www.batteryuniversity.com/_img/c ... ge-web.jpg
Image
Although the image is misleading in labelling the last row End-of-life. That row actually represents the point at which Usable Capacity will begin to decrease.

Anyway for now I will continue collecting and displaying data that compares total battery deterioration against number of discharge cycles. This only works when Usable Capacity is fixed. So I am only using it to give an estimate of when we reach the point Usable Capacity begins to decrease. For now none of the cars here (the 9 I have data for) have reached that point. This graph shows one point for each car using the latest data available for that car.

Image
The codes for using Torque Pro can be found by clicking the link in the website icon under my user name on the left.

Elmil
Posts: 141
Joined: Mon Oct 26, 2015 9:46 am
Location: Sweden

Re: Battery Ageing Model

Sat Nov 21, 2015 12:53 pm

JejuSoul:I have more data for you..
This week I had another change (upwards) in the deterioration values during nightly charging. It happened 14 days and almost 1000km after previous change. They are now at 10.3/9.2%.
Last two weeks have been chilly (-4 to +4C) so I have started with 100% displayed SOC every morning, and after 100km commute there has been 38-42% left, i.e around 60% consumed. One deviation, though: On wednesday I decided to start with 80%, just to see the behaviour during cold weather when SOC gets down towards 20%. And expected it did. But when I compared the logged data from that trip with the other days, I noticed that the Accumulated energy counters indicate 14.1 kWh consumed during 80-20% SOC while days where I used 100-40% the energy count was around 16 kWh. And, of course, no charging at work..

It seems like this is an indication of hitting the 'knee' at the lower end of the discharge graph, where voltage is falling more steep and the BMS gets out of linear calculation. It's also well known that battery cells 'shrink' in low temperature, so the knee will happen earlier. On the other hand I need to repeat the 80% trip to see if it's consistent.

Interesting is that my deterioration counters were updated during charging after that trip. Maybe the BMS noticed the deviation and made the adjustion because of it?
Kia Soul EV 2015 / 115,543 km Sold
Kia Soul EV 2019

JejuSoul
Posts: 1299
Joined: Wed Jul 08, 2015 6:47 am
Location: Jeju
Contact: Website

Re: Battery Ageing Model

Sun Nov 22, 2015 7:49 am

Elmil: thanks for the update.
Could you post the CAN data. I can update the graph.

I do not fully understand the Cumulative Energy counters.
They do not seem to match what I put in or use. Here's an example.
On Nov 11th I did a lengthy test drive charging the car before and after.
I took readings at home, a 30 min drive from where I started and finished the 215km round-the-island-on-one-charge-trip.
Total driving for the day was 273km, which took 7.5 hours.
Charging time for two L3 charges and one L2 was 2 hours.
According to the data the Operating Time was 9.7 hours.
Clearly the Cumulative Operating Time data includes the time spent charging.
The readings on the charging machines from the 3 charging sessions suggest I added 35kWh.
Using the reading on the car's display 8 km/kWh suggests I used 34kWh for the trip.
SOC at start = 56%, SOC at end = 62% which is why I charged more than I used.
The Cumulative Energy Charged data increased by 50kWh
The Cumulative Energy Discharged data increased by 48kWh
What is the reason for this disparity 35 / 34 contrasted with 50 / 48
The codes for using Torque Pro can be found by clicking the link in the website icon under my user name on the left.

Elmil
Posts: 141
Joined: Mon Oct 26, 2015 9:46 am
Location: Sweden

Re: Battery Ageing Model

Sun Nov 22, 2015 9:56 am

Here's the data from the moment the deterioration values were updated.
Odometer reading was 19751 km

2015-11-19 04:44:00
2101
7EC 10 3D 61 01 FF FF FF FF
7EC 21 AE 17 DD 23 28 A3 FF
7EC 22 DE 0F 55 0E 0C 0E 0C
7EC 23 0C 0B 0B 00 0F CC 2A
7EC 24 CC 53 00 00 82 00 01
7EC 25 65 92 00 01 60 D6 00
7EC 26 00 83 B6 00 00 7E A0
7EC 27 00 5A 15 99 41 01 84
7EC 28 00 00 00 00 03 E8 00
2105
7EC 10 2C 61 05 FF FF FF FF
7EC 21 00 00 00 00 00 0C 0C
7EC 22 0E 00 00 00 00 17 DD
7EC 23 23 28 00 01 64 0E 0E
7EC 24 00 62 02 00 54 08 B7
7EC 25 00 00 00 00 00 00 00
7EC 26 00 00 00 00 00 00 00

2015-11-19 04:44:10
2101
7EC 10 3D 61 01 FF FF FF FF
7EC 21 AE 17 DD 23 28 A3 FF
7EC 22 DA 0F 55 0E 0C 0E 0C
7EC 23 0C 0B 0C 00 0F CC 2A
7EC 24 CC 0C 00 00 82 00 01
7EC 25 65 92 00 01 60 D6 00
7EC 26 00 83 B6 00 00 7E A0
7EC 27 00 5A 15 A2 41 01 85
7EC 28 00 00 00 00 03 E8 00
2105
7EC 10 2C 61 05 FF FF FF FF
7EC 21 00 00 00 00 00 0C 0C
7EC 22 0E 00 00 00 00 17 DD
7EC 23 23 28 00 01 64 0E 0E
7EC 24 00 67 18 00 5C 01 B7
7EC 25 00 00 00 00 00 00 00
7EC 26 00 00 00 00 00 00 00
Kia Soul EV 2015 / 115,543 km Sold
Kia Soul EV 2019

Elmil
Posts: 141
Joined: Mon Oct 26, 2015 9:46 am
Location: Sweden

Re: Battery Ageing Model

Sun Nov 22, 2015 10:40 am

JejuSoul wrote:The Cumulative Energy Charged data increased by 50kWh
The Cumulative Energy Discharged data increased by 48kWh
What is the reason for this disparity 35 / 34 contrasted with 50 / 48

I am also confused about the Cumulative counters. I have assumed they were originating from the BMS (inside the battery pack), but after analyzing the logged data from an L3 QC charging session, I'm not so sure. After 20 min or so I turned on the heater while charging was in progress. The log shows that the Cumulative Discharge counter started to count up, while still 20kW power was going in to the battery. During the last 10 minutes of charging (to 83%) 1.2kWh was consumed. This points in the direction that some external device is involved in measuring the energy. The battery itself should only see the net current going in or out. But wait a minute - 1.2 kWh during 10m means 7kW of power, and no way the heater system was consuming that much...
So what do we really *know* about these numbers?
Kia Soul EV 2015 / 115,543 km Sold
Kia Soul EV 2019

JejuSoul
Posts: 1299
Joined: Wed Jul 08, 2015 6:47 am
Location: Jeju
Contact: Website

Re: Battery Ageing Model

Mon Nov 23, 2015 9:52 pm

Elmil: thanks for the updated data. Here's the latest graph. We only have 3 cars with at least 3 data points.
The pink dots are my car, the yellow yours, and the blue is from Canada.
As you can see yours and mine form straight lines, but the Canadian car does not.
It is a rental car and will probably be returned soon.
Leaving that odd data in the plot though does help show that we don't really know what is going on yet.
Image

The comparison below is between my car and yours. Both are about 7 months old.
By the end of October you had driven 18000km and I had driven 7000km.
The OBD data starts then. It is the last 4 weeks of driving that I compare.
We have both driven about 1700km in the last 4 weeks. (You are driving less than before?)
We both have a Cumulative Energy Discharged figure of about 400kWh for that 4 week period.
This gives an average efficiency for both of us 23.5 kWh / 100km. In reality I got about 13 kWh / 100km this month. (You?)
But my Cumulative Operating Time is about 100 hours whereas yours is 200 hours for the 4 weeks.
My time is 50% driving and 50% charging. I usually use L2 6.6kWh and occasionally QC. Never L1.
You must either have a 3.3kWh L2 or using L1 frequently (true?)
Your deterioration values at 10.3/9.2% increased by 1.0/0.9% over the period.
My deterioration values at 3.5/0.1% increased by 1.0/0.0% over the period.
It is the big difference in minimum deterioration value that explains the different slopes in the graph above.
Why this should be I don't know.
The codes for using Torque Pro can be found by clicking the link in the website icon under my user name on the left.

Elmil
Posts: 141
Joined: Mon Oct 26, 2015 9:46 am
Location: Sweden

Re: Battery Ageing Model

Wed Nov 25, 2015 10:23 am

JejuSoul wrote:The comparison below is between my car and yours. Both are about 7 months old.
By the end of October you had driven 18000km and I had driven 7000km.
The OBD data starts then. It is the last 4 weeks of driving that I compare.
We have both driven about 1700km in the last 4 weeks. (You are driving less than before?)
Not as much as during summer, but still at least 500km/week

We both have a Cumulative Energy Discharged figure of about 400kWh for that 4 week period.
This gives an average efficiency for both of us 23.5 kWh / 100km. In reality I got about 13 kWh / 100km this month. (You?)
I don't keep records of the displayed consumption, but these weeks probably are around 16-17kWh/100km. It's been below 0C many days lately.

But my Cumulative Operating Time is about 100 hours whereas yours is 200 hours for the 4 weeks.
My time is 50% driving and 50% charging. I usually use L2 6.6kWh and occasionally QC. Never L1.
You must either have a 3.3kWh L2 or using L1 frequently (true?)
I always charge over night using the Kia provided EVSE cable, which delivers up to 1.6kW to the battery. Sometimes QC but sparely.
Your deterioration values at 10.3/9.2% increased by 1.0/0.9% over the period.
My deterioration values at 3.5/0.1% increased by 1.0/0.0% over the period.
It is the big difference in minimum deterioration value that explains the different slopes in the graph above.
Why this should be I don't know.
Kia Soul EV 2015 / 115,543 km Sold
Kia Soul EV 2019

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