Pier
Posts: 51
Joined: Tue Nov 15, 2011 9:01 am
Location: St-Aubert, Qc,

A bad cell and a reduce range

Tue Dec 02, 2014 8:38 am

A bad cell and a reduce range

My 2012 I-MIEV, 2 years old, only 16,000 km, seemed to have no reduce range until few weeks ago. Perfect battery voltage on any cell at full charge of 4.105 volt.

Then, after full recharge, only 15 bars and 92% SOC, and cell #85 lower than all others. Every recharge, the soc went down untill it reach 75%, and 3 bars lost. Moreover, the recharge took 3 hours more to finalize. Before, the recharge ended at around 460 Watt at the wall and now it last for ever, between 200 and 400 W. ( something around or below 100W in the car).

I e-mailed Mitsu Canada those details and also to the nearest dealer. After a week, now my car is at the garage (dealership) for test and I hope repair. It was clear for me that cell #85 was at fault, but of course they do not need my advice !! They tried to find if I had any wrong doing. Then Mitsu asked the garage to extract all the data from the computer, like the way I was driving, flat or hilly, fast acceleration, etc... they told me I was driving conservatively which is true. I took care of my battery as if it was a newborn baby, never allowing it to go over 30°C at any time and driving mostly between 20% and 80% basttery capacity.

So what went wrong ?

Anywone experienced a faulty cell ?

Can you tell if a voltage of 4.105 is a sign of no deterioration of battery cell ?

PV1
Site Moderator
Posts: 3055
Joined: Fri Apr 27, 2012 4:22 pm
Location: Pittsburgh, PA

Re: A bad cell and a reduce range

Tue Dec 02, 2014 9:01 am

Although they have to unequivocally prove it to be at fault, I'd be cautious of mentioning CaniOn to the dealer, as they may try to deny a warranty claim, and the battery warranty isn't one to gamble with.

Where are you located? What is the lowest temperature your car has experienced? How often have you allowed a full charge?

Based on earlier failures (there have been 3 or 4 on this forum, same symptoms as yours), I'm wondering if that cell got too cold during a charge and has some plating issues which developed a short. It seems that your car extended balancing time to try correcting the mis-balance, but the cell continues to self-discharge.

Not that it matters to us as far as replacing stuff, but I wonder if a balancer develops a permanent short and discharges one cell continuously. This issue seems to happen suddenly. A failure in a cell (I would think) would gradually show or instantly become a dead short and totally kill the cell. Given that the car can't correct, the cell is discharging at about the same rate as the other cells balancing. Since Mitsubishi replaces the entire pack as a single unit, we don't know what the actual cause is. Either way, cell failure rates are well below 1%.

Was the cell temperature way higher than the rest (either 63 or 64 in CaniOn)?
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
"Koorz" - 2012 Cool Silver Metallic ES with QC - 1/5/2015
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Pier
Posts: 51
Joined: Tue Nov 15, 2011 9:01 am
Location: St-Aubert, Qc,

Re: A bad cell and a reduce range

Tue Dec 02, 2014 2:42 pm

Hi PV1,

Giving all the details from CanIon reading written or verbally didn't cause any problem. They were just suspicious as why I know so much about electricity and ask what was my education ( job). The guy even told me that Mitsu is severe with misuse of the car concerning the warranty. I told him I was just reading from the OBD port, which is good for everyone in knowing what is happening to our battery, and everything was fine. He didn't even wanted to see my canion graph because they have their own test to perform anyway.

I am located in Quebec. It is cold but less than the guy in Sudbury and colder than Niagara falls. I take great care of my battery in very cold weather, I mean not driving or if necessary driving slowly. Being retired I don't need to go out every day. Last winter ( very cold) I experiment twice with recharging below -25°C. Noting happened, refusing to recharge until the afternoon when warmer. The second time I went driving and on return I could recharge, the battery being warmed up a little. But I don't usually recharge on very cold or warm days.

When the cell #85 went crazy it was in temperate weather. Full charge no more than once a week. Never keep battery full charge for hours, but recharge just before leaving. I usually keep battery around 20% - 50% charge.

It seems that the faulty cell is discharging at a faster rate than others. The difference in voltage at full charge ( I mean 80% with bad cell) is 70 mV while it is 180 mV at 12% SOC.

Cell t° was normal min 12°C and max 16°C that morning. I didn't know 63 or 64 was for cell #85.

So I am the 4th or 5th one with this problem on this forum. But how many members are we on this forum to calculate the % of cell failure ? In the future, out of the warranty period, it would be fine to replace ourself the faulty cell , because putting away an otherwise good battery pack just because one cell out of 88 is faulty would be expansive. Autonomy is dependant of only one bad cell.

I am waiting for more info. Mitsu ca decided to replace the pack. They are supposed to have ordered a new battery pack this morning, not knowing yet if it will be shipped from Toronto or Japan.

Pier

nsps
Posts: 97
Joined: Mon Feb 25, 2013 11:29 pm
Location: Salt Lake City, UT

Re: A bad cell and a reduce range

Wed Dec 03, 2014 11:12 pm

When my battery failed, there was a survey in which they asked me about my driving habits, but I got the impression it was more for the sake of tracking the cause than trying to refuse my warranty. However, maybe more batteries have been failing and they're trying to cut their losses.

siai47
Posts: 363
Joined: Fri Jun 14, 2013 5:54 pm

Re: A bad cell and a reduce range

Thu Dec 04, 2014 6:35 am

Most likely the much longer recharge time you experienced when the cell was failing was the BMU trying to balance the voltage on the bad cell. As to replacing a cell in the pack after the warranty runs out, it remains to be seen if Mitsubishi will allow that. I think that an exchange refurbished pack, installed by the dealer, will be the only option. It seems a stupid way to go but manufacturers are so concerned about liability when you get into the high voltage system that I believe they will dictate this solution under the cover of "safety". On the Tesla Model S, there have been a number of failures of one of the main DC contactors which is located within the pack. Even though it would be something that could easily changed, it requires a complete pack swap. Not a problem for customers under warranty, but after it's over, a real hit. There are many other components in the I-MiEV pack that could fail other then a cell. Components like contactors, ground fault detector, current sensors, cooling fans and the like that would be cheap to replace but will be unavailable to consumers to purchase. If you look at the parts book for the I-MiEV, nothing in the pack (or related to it) is available. Unfortunately, in the case of the I-MiEV, an internal pack problem might render the car a total loss as the repair cost would exceed it's value. This is problem that owners of all EV's will face in the future until manufacturers come up with a low cost method of dealing with high voltage system related issues. Someone in the private sector will resolve this problem by retrieving parts from wrecked vehicles and repairing failed packs. High value (Tesla) and high volume (LEAF) will be the first ones the private sector will start working with. However, for a vehicle that is so limited in production numbers like the I-MiEV, there might not be enough incentive for the private sector to get involved.

DonDakin
Posts: 387
Joined: Wed Aug 15, 2012 7:10 pm
Location: Montreal Quebec.....

Re: A bad cell and a reduce range

Thu Dec 04, 2014 6:14 pm

Hi pier,

Thanks for posting this information. I think you are the first person to experience a cell failure and was able to look at the cells with canion.

I would love to understand how the car was dealing with the failing cell. I mean how was the car computing SOC and what was the cell voltage doing during charge and discharge.

Would it be possible for you to post your canion database. Its a file in the bt_can directory of your phone or tablet. I would like to look at it to see if i could understand better how the the car deals with a failing cell. I think others on the forum may be interested in the also.

We have discussed cell failure in the past but we don't really have any data only ideas about what happens when a cell fails.

Thanks again for sharing this information.

Don......

priusfan
Posts: 194
Joined: Mon Oct 08, 2012 7:39 am
Location: France

Re: A bad cell and a reduce range

Fri Dec 05, 2014 7:51 am

Hi
just a detail: the name of this file is btcan.db ....

Xavier

Pier
Posts: 51
Joined: Tue Nov 15, 2011 9:01 am
Location: St-Aubert, Qc,

Re: A bad cell and a reduce range

Fri Dec 05, 2014 9:18 am

Sorry Don, I don't know how to access bt_can directory, transfer it to my computer and post it on here. I am an old scientist but losing interest in fast changing ways of processing data. So much more to learn abut life. But we're not here to philosophize. With my day to day analysis of the data collected and a few notes, I will recall what happenned.

1- Since 2 years (one with Canion), the data were about the same. At full charge, all cells were at 4,105 volt, with sometimes one or few cells with a variation of 5 mV. Nothing special with temperature of cells, as it was also when the #85 cell went wrong. SOC was always 100% at full charge.

2- Come end of october, on a full charge, to my surprise, one bar less and soc 92%. I found cell #85 had lower voltage. Subsequent charges, soc went down to 87.5%, 84%, 79.5%, 82.5%, with bars accordingly of course. Then my trip to dealership, on a cold morning, 100km impossible on a single charge, had to stop at 40km for intermediate charge and arrived almost emty at dealership, and all that at 60 kmh. It seemed to me SOC was even less that morning , other than colder temperature. It was confirmed by dealership with 75% max soc after they say 24 hours charging. Technician told me they could force charge a single faulty cell.

3- Cells T° all that time, as I said, were as usual. Nothing special.

4- Difference of tension between all cells that were equal, an the faulty #85 cell increased with time. At full charge, when around 80% soc , difference was 70 mV. This is 4,105 vs 4,035. When discharged, the difference increased too, from 130 mV to 180 mV, and probably more arriving at the dealership.( Canion crashed 10km before arrival).

5- Time of charge. Regular full charge lasted 4 hours as usual. But the end charging increased considerably, going from 1 hr to 3 hrs. and even more they said at dealer.

6- Long end charging : I once checked the process of end charging on Canion. I didn't see anything particular as I never noticed before the process of equalizing cells on Canion. What I saw was a much lower energy flowing thru the charger. Around or below 100 Watt and 250W at the wall while it used to be no less than 460W (wall) before, at charge ending. That measure of energy flowing was of course varying a bit maybe mainly because of the circulatory pump.

7- Also at end charging, the SOC increased somewhat by a few % very slowly, along volt at the faulty #85 cell. But upon driving, this extra energy went away faster than usual in the first km. It is a kind of "fragile" or "false" energy. I don't know if there is a word for this "phantom" energy.

8- Only one faulty cell makes for max % SOC and range. The faulty cell again makes for turtle at the end, while other 87 cells could could drive range much further, thus range is minimized both end ...kind of...

If you have any other question, I will be pleased to answer if I can. Hoping this helps you.
Excuse my difficulty of writing or faults, I write with the right hand while holding a french-english dictionary in the left hand.......

Pier
Last edited by Pier on Fri Dec 05, 2014 12:25 pm, edited 1 time in total.

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

Re: A bad cell and a reduce range

Fri Dec 05, 2014 9:48 am

I've semi-confirmed that battery temperature has a direct impact on how far each percentage will go. On a cold morning between 30-40°F, with about the same pack temperature, I lost my first bar about 1.5-2 miles before my normal point. Same environmental conditions on a different morning, but with a pack at 60°F, I made it to just about the spot where I normally lose my first bar in the summer. Always a full charge, and pre-heated both mornings. No heat use while driving. So, our reduced winter range is mainly due to a cold pack, not so much higher rolling and aero resistance, though these are still factors. This is the main cause of your even shorter range on the cold morning.

To access this file, you may already have an app along the lines of File Explorer or My files. If not, you can download an app called "File Expert". When you open it, you should see a tab on top for Folders. Tap that, then select SD Card, scroll to the folder called BT_CAN, and there will be the btcan.db file. Long hold on the file name, tap Send Files, tap Share, and from there you can email it as an attachment, or add it to Google Drive or Dropbox if you have one. I'd recommend using Google Drive (unless you already have Dropbox) since you most likely already have a Google account. From Google Drive, you can share a link to the file, which you'll post here for us to access the file. Unfortunately, you have to use a file hosting site like Dropbox or Google Drive, since this forum doesn't support attachments.
"Bear" - 2012 Diamond White Pearl ES with QC - 2/21/2013
"Koorz" - 2012 Cool Silver Metallic ES with QC - 1/5/2015
"Photon" - 2017 Bolt EV LT in Orange with QC - 7/31/2017

Solar-powered since 10/10/2013

Pier
Posts: 51
Joined: Tue Nov 15, 2011 9:01 am
Location: St-Aubert, Qc,

Re: A bad cell and a reduce range

Fri Dec 05, 2014 12:26 pm

nsps-- I agree with you. Using Canion should not in any way nullify the guaranty. I talked openly about reading data with Canion. I even wrote it down in e-mail. Concerning searching for causes ...they told me my driving habits were extracted from my car's computer. Also after the first tests, the technician told me the head office ask for 20 (?) more tests. Some 25 pages of data he told me, send to Japan... surely tracking the causes...

Siai47 --- This is bad news for many owners, meaning the life expectancy of the car might be 8 years. Hopefully for most, the car will last longer, even at the cost of somewhat reduced range. We will see in a few years, things could change then. Did you open a pack and is it easy to replace a cell ? To me it seems that the most difficult part would be to disconnect the pack and put it down.

I liked my own battery because I took great care of it. I am afraid they will replace it with a not so good refurbished pack, practice allowed by the warranty ( let's say with a loss of 10% range). New pack in dealership language doesn't mean a brand new pack.

Pier

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