Which cell loses capacity fastest? Which retains it best?

RegGuheert
Posts: 6419
Joined: Mon Mar 19, 2012 4:12 am
Delivery Date: 16 Mar 2012
Leaf Number: 5926
Location: Northern VA

Which cell loses capacity fastest? Which retains it best?

Now that we have the capacity to read all cell-pair voltages, I think it would be good to start looking at the performance of our packs to try to determine if there are consistent trends between cars as to which cell(s) lose capacity fastest and which cell(s) lose capacity slowest. This information will be useful in determining if module rotation is warranted and, if so, it should also aid in determining which rotation patterns might be best.

For reference, page EVB-20 of the November 2010 Edition, April 2011 Revision of the Nissan LEAF Model ZE0 Series service manual contains a pictorial view of the layout of the 48 battery modules in the 2011/2012 LEAF. Each module contains two pairs of cells, so there are a total of 96 cell voltages which are measured and reported by the LEAF. The service manual numbers the modules from MD1 to MD48 and the cell voltages from Cell-1 to Cell-96. Cell-1 is at the highest-voltage end of the stack with its positive terminal connected to the positive terminal of the battery. Cell-96 is at the lowest-voltage end of the stack with its negative terminal connected to the negative terminal of the battery. To determine which cells are contained in a given module, simply multiply the module number by two for the higher cell number and subtract one from that product for the lower cell number. For example, module MD23 contains the following two cell voltages: Cell-45 and Cell-46.

Modules MD1 through MD24 are contained in a stack under the rear seat with MD1 on the far passenger's side and MD24 on the far driver's side. Modules MD25 through MD28 are located under the rear driver's side footwell. Modules MD29 through MD36 are located under the front driver's seat. Modules MD37 through MD44 are located under the front passenger's seat. Modules MD45 through MD48 are located under the rear passenger's side footwell.

The exact location of each module can be seen in the MODULE LAYOUT diagram from page EVB-20 of the service manual, shown below:
EVB-20_Module_Layout.png
In order to determine the relative capacity of the cells in your LEAF, please follow these steps:

1) You must first achieve a high degree of cell balancing, which is occurs at the top of the charge range. So you will need to perform at least one 100% charge to balance your pack. Sometimes, you will need to charge to 100% several days in a row to achieve a good balance. I find that charging to 100% using 120V gives the best amount of cell balancing. You can also let your LEAF sit, plugged in, following a 100% charge for a few hours to let it attempt to rebalance once the pack fully cools.
2) Once your pack is fully balanced, measure and record your cell voltages using the one of the methods shown in the second post of the this thread, which I will reserve and update as new techniques for reading cell voltages are developed. This is your record of how well balanced you pack is.
3) Now, discharge the battery pack to a point where the lowest cell voltage is 3712 mV or lower. This voltage is from Nissan's CELL VOLTAGE LOSS INSPECTION procedure found on page EVB-65 of the service manual. In order to do this, Nissan recommends putting the vehicle in READY and setting the following:
- A/C set temperature: Full hot
- A/C fan speed: Maximum speed
- A/C air outlet: Defroster
- Door glass: Full open
Monitor the available charge gauge and watch for it to go down to two bars or less. This should take about four hours if the battery was fully charged. It may take less time if your pack is degraded.
4) Once your pack is at or below 2 charge bars, measure and record your cell voltages. Ensure that the lowest voltage recorded is 3712 mV or lower. If it is above this voltage, repeat step 3) above. This is your record of how much voltage difference there is between all of the cells in your LEAF at a low SOC. If you pack was very well balanced in step 2) above, then the cells with the highest voltages here should have the LEAST capacity degradation and the cells with the lowest voltages should have the MOST capacity degradation. (Note: this test does NOT tell how MUCH capacity degradation your battery pack has, only how much difference there is between different cells in the pack.)

Once you have performed the test, please post images of your results from both step 2) and step 4) here (preferred) or simply type in the top six and bottom six voltages from both steps along with their cell-pair numbers. I will collect the data, perhaps in a Google spreadsheet, and will try to find capacity loss trends by plotting histograms of results which we achieve.

Please post if you find any errors in the test procedure or would like to point out new ways we can measure cell-pair voltages. I can then update either this post or the second one. Thanks in advance!
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RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

RegGuheert
Posts: 6419
Joined: Mon Mar 19, 2012 4:12 am
Delivery Date: 16 Mar 2012
Leaf Number: 5926
Location: Northern VA

Re: Which cell loses capacity fastest? Which retains it bes

- Using ELM327 Bluetooth OBDII Adapter and Turbo3's LEAF Battery App - Thanks, Turbo3!
- Using ELM327 Bluetooth OBDII Adapter and Hyperterminal - Thanks again, Turbo3!
Last edited by RegGuheert on Tue Apr 30, 2013 3:54 am, edited 1 time in total.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

JeremyW
Posts: 1561
Joined: Sun Nov 13, 2011 12:53 am
Delivery Date: 23 Jun 2012
Leaf Number: 19136
Location: San Gabriel, CA

Re: Which cell loses capacity fastest? Which retains it bes

I posted a thread last night in the CAN section of the forum to post screenshots from the Android app. Guess great minds think alike!
Former 2012 SL leasee (6/23/12 - 9/23/15)
Former Honda Fit EV leasee
Former Chevy Spark EV owner
Now driving Tesla Model 3

RegGuheert
Posts: 6419
Joined: Mon Mar 19, 2012 4:12 am
Delivery Date: 16 Mar 2012
Leaf Number: 5926
Location: Northern VA

Re: Which cell loses capacity fastest? Which retains it bes

JeremyW wrote:I posted a thread last night in the CAN section of the forum to post screenshots from the Android app. Guess great minds think alike!
Ha! Very funny!

I thought about posting there, but that area is not widely read. I wanted to gather together the procedures and layouts in one place to try to get a consistent view of data.

Do you know if anyone has done the full test including good balancing followed by testing at low SOC? I don't have the equipment to do it just yet, but I will.
RegGuheert
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

thimel
Posts: 134
Joined: Fri Apr 23, 2010 6:10 pm
Delivery Date: 11 Jun 2011
Location: SF bay area

Re: Which cell loses capacity fastest? Which retains it bes

First of all, let me add my thanks to Turbo and the others who reversed engineered the CAN bus messages and have made this app that uses the ELM327.
I bought my ELM327 on Ebay from romorus for \$10.70 with free shipping. It works with my LG Nexus 4 running Android 4.2.2 without problems.

I did the test of running the battery down from full to nearly empty. As I normally only charge to 80%, two nights in a row I charged to 100% and after it was done, told it to start charging again. This presumably balanced the battery cells. I was surprised to find the SOC starts at only 92.08%. I then drove. I got LBW at 21.6% and VLBW at 10.72%. I then drove slowly home.

The screen shots for fully charged and nearly empty are below.

DanCar
Posts: 1043
Joined: Sat Apr 24, 2010 12:00 am
Delivery Date: 10 Mar 2013
Location: SF Bay area, 94043

Re: Which cell loses capacity fastest? Which retains it bes

RegGuheert wrote:... try to determine if there are consistent trends between cars as to which cell(s) lose capacity fastest and which cell(s) lose capacity slowest. ...
You'll likely find that cells in the middle of the pack which are hottest tend to lose capacity the soonest.
2013 Leaf SL leased 3/10/2013

surfingslovak
Vendor
Posts: 3809
Joined: Mon Jun 13, 2011 1:35 pm

Re: Which cell loses capacity fastest? Which retains it bes

thimel wrote:I was surprised to find the SOC starts at only 92.08%. I then drove. I got LBW at 21.6% and VLBW at 10.72%. I then drove slowly home.
Great data, thanks for sharing! Based on the CAP value, I would hazard a guess that you lived in South Bay. Is that correct? Could you perhaps help narrow it down a little? I have some thoughts on the low maximum SOC, but it's likely premature to talk about it. How often do you charge to 100%? Is the LEAF parked outside or inside at night? Do you do much freeway driving, and if so, how fast would you typically go? Any chance that your car was represented in the PIA battery survey? Hope you don't mind all the questions

EVDRIVER
Moderator
Posts: 6753
Joined: Sat Apr 24, 2010 7:51 am

Re: Which cell loses capacity fastest? Which retains it bes

In my spare time at the end of the month I rotate my cells for longer life. No sense in not dropping the pack once in while and spending a full day rotating modules. I worked on an spreadsheet to track the rotations and a graph on the time spend VS percent capacity gained. I divided that by the number of days in the year multiplied by how I would rather do something else and came up with time spent doing other things would be a better choice. Next up I'm going to plot the wear of my wiper blades from end to end and measure the wear deviations. I may put this on Google Docs.

thimel
Posts: 134
Joined: Fri Apr 23, 2010 6:10 pm
Delivery Date: 11 Jun 2011
Location: SF bay area

Re: Which cell loses capacity fastest? Which retains it bes

South Bay is correct. Sunnyvale to be exact. I got the car in June 2011 and it has 19k miles on it. It is parked in a garage at night and out in the sun on weekdays. I charge to 100% about once every two months. I have quick charged once just to see if it worked. I drive about 25 freeway miles every weekday. Speed is around 65 except when there is traffic.

surfingslovak
Vendor
Posts: 3809
Joined: Mon Jun 13, 2011 1:35 pm

Re: Which cell loses capacity fastest? Which retains it bes

thimel wrote:South Bay is correct. Sunnyvale to be exact. I got the car in June 2011 and it has 19k miles on it. It is parked in a garage at night and out in the sun on weekdays. I charge to 100% about once every two months. I have quick charged once just to see if it worked. I drive about 25 freeway miles every weekday. Speed is around 65 except when there is traffic.
Great, thanks! Now that you have more hard data about the health of your pack, please consider contributing it to Tom Saxton's battery survey. This appears to be the only way we can get some information about longevity and real-world performance of these batteries.
EVDRIVER wrote:In my spare time at the end of the month I rotate my cells for longer life.
Why not purchase a fan and blow smoke at the pack every night? A reliable source told me that this will add one Gid per month, regardless of ambient temperature. Plus smoked Gids are better than raw ones. Or so I've heard. With little luck, the doors will rust through long before the battery gives up its ghost. Look forward to studying the Google spreadsheet!