A bad cell and a reduce range

[Pier]

Having a strong scientific background ( not in electricity) I know how difficult it is to prove without any doubt. Nothing is ever 100% sure. It is more about probabilities. So here I would say there are good probabilities that cold could cause defects in battery cells. Also good probabilities cold is good for longevity of cells, since when I was first interested in Li-ion bat tech , I have red scientific data quite convincing about good effect of cold. We are mostly guessing but also trying hard to observe our own facts surrounding cell defect. It would be great to get data from battery manufacturer. They keep it secret for competition purpose. We are left with students studies partly published on internet without knowing their scientific protocol. It makes us -- EV owners -- struggling to have the best practice for battery longevity.

It is out of topic here but if I had to experiment on the effect of cold, I would do the following. Put cells in different temperature environment from -25°C to +25°C, not one but at least 3 cells in each T° step. An automatic charge/discharge for each. A test every week or so to see capacity. It could last up to a year or more than 1000 ch/disch. Upon the result then, new series of tests with different charge rate, from maybe 0.1C to 5C or more. Then test different discharge rates along with different T°. Upon results, open cells and examine under microscope.... and more... ( also different chemistry). Very expensive isnt't ?

Well back to this topic. We will probably never know for sure the reason of a failure. You gave many possible good reasons. From what we can see, this #85 bad cell cannot accept more energy, logically cause by some mild short. What's the reason ? plating, kind of sulfatation (no sulphuric acid here), impurity in cell making, cold T°. ??

You all very well ask good question about cell failure. Interesting to read . Difficult to prove with our data. We are still asking ourself as DonDakin said : "I just wonder if exposing the car to very low temps can induce a cell failure like you experienced. " I just know that this failure didn't happen while being submit to low temp. last winter, but during mild weather this fall, some 8 month after sub-zero temp. If plating occurs may it take time to develop a kind of short ? ( Yes I think so). Does plating affect all cells in reducing capacity faster or one cell more than others ? (maybe). In other battery failure, was it one or two cells in fault or general degradation ? ( a mix of both I think). Is Mitsu and Nissan allowing us to charge below freezing 5 month a year making a big mistake ? ( could cost a lot to them).

« data on the car but not driving » PV1 . I have a couple of screens but I don't see any relevant info. One at almost full charge, all cells within 5 mV and defective one well below. Nothing moving for just 5 sec thought. Another one, 1min40 nothing moving., about the same but more variation in mV for good cells at mid discharge. May be not looking at the right thing. I am not sure if I saw voltage moving some 5mV on good cells while observing the screen , but nothing registered. Can you see balancer action on data from Canion ?

« It would be interesting to open up the bad cell to see what caused the failure » RobertC. Unfortunately something we cannot do under warranty. I did it on Ni-cad before to replace a defective cell.

Meanwhile, I am waiting for more from dealership. I asked to see their tests. It's always difficult to make them lose time they are not paid for. Lot of smiles but little time !!

Pier

 

[sandange]

Sandange, 4/10/14, St. Sauveur, Quebec, -18°C (-1°F)

Did Sandange's battery actually fail, or was it just the issue of going through chargers?

I did not have any monitoring/testing equipment
From what little I was told -
It was the OBC that failed and two replacements after that - and they tried to pin it on my EVSE upgrade.

Sorry to hear about your battery failure Pier
Sounds like you hardly used the car and when you did you babied the batteries.

Just wondering if like an ICE , an EV (Battery pack) could develop problems from not enough use?

 

[PV1]

« data on the car but not driving » PV1 . I have a couple of screens but I don't see any relevant info. One at almost full charge, all cells within 5 mV and defective one well below. Nothing moving for just 5 sec thought. Another one, 1min40 nothing moving., about the same but more variation in mV for good cells at mid discharge. May be not looking at the right thing. I am not sure if I saw voltage moving some 5mV on good cells while observing the screen , but nothing registered. Can you see balancer action on data from Canion ?

In a short amount of time, you probably wouldn't see an active drop, but if left for a few hours, you might be able to see the cell drop. All cells will drop as the car is consuming energy from the pack, but you should be able to see if that cell is discharging faster than the others just while sitting.

 

[Lithim]

The bad cell discussions makes me think back about a problem with the old VW bugs.
(I earned to drive on a black '61 bug and rebuilt a couple of engines on bugs and vans).
They were air cooled back then and number three cylinder would many times run too hot. The problem as I recall was an oil cooler tower that was in the air flow from the fan and partially blocked the air flow to cylinder head number 3.
I wonder if something similar exists in our battery packs with air flow or lack thereof across certain of the 88 battery cells?
Thoughts??

 

[Pier]

What about this drive ?

Temperature : -2°C (28°F),
Head wind 20 kmh,
15 km hyway at 90-100,
85 km secondary roads, 65 kmh, then down to 50. AVG with few light: 55.4 kmh.

Start at 99% Soc, on arrival : 5%, 8 km on turtle.
RR at start: 90km with 100 to drive.
Tract. battery : start at 360 volt, arrive at 331V
Volt cell: H: 3.750, Low: 3.730V
Avg Wh/km : 128, was 174 hyway.
Wh out : close to 12,000 at turtle and total 12,866 at 5% Soc.
Wh Reg only 117. Heater 23W

So there is only 12,000W available to turtle and max 13,000W to road side assistance.
My old bat. pack after 1½year used 13,000W at 17.5% Soc, at 12°C, light headwind, slow road.
And 13,700W at 8.5% Soc, 21°C, faster tail wind, high hyway speed.

Is this a good battery pack ?

 

[Pier]

A brand new battery pack.

18 days to get my car repair. Cost of new pack is $14,143 all cnd $ value at 0.86 usd. Cost with 2 plug floor, 2 clips eng. room cover, 2 nuts RR susp coil spring, 4 flat washer, labor, $17300. But they gave me a credit of $17300.(!)

The EV technicians doesn't know about reasons of faulty battery of course. He just know how to do tests an turn bolts in and out (!!!)

Here is what is written on the dealer's slip:
Charge battery 24h, give 75%. Give same result 3 out of 4.
Try reset battery : no change.
Try to do smoothing cell : no result.
Try battery capacity : no result.

Told battery pack brand new. Who knows ? I would say probably true since it comes from Toronto headquarters. If it was from Japan I would have some 30% doubts. Battery is in a big metal container as you have seen before and it has to be fixed to the carrier floor. He showed me the angle iron.

They said it is the second battery failure. The other one was from a delivery St-Hubert restaurant. They usually keep it on charge all time.

I would like too perform some tests on this new pack. Do you have any suggestions for future reference ?

Pier

 

[bobakka]

I would like too perform some tests on this new pack. Do you have any suggestions for future reference ?

Pier

I have the following suggestion and you need Canion and an external kWh-meter.

1. Charge to 100% SoC
2. Drive and use energy to get down to at least 20%SoC (maybe down to 10%) - write down Wh-out (minus Wh-reg)
3. Charge up to 100% SoC - write down external kWh-meter value and Wh-reg (minus Wh-out)
4. Calculate Total kWh ((Wh/1000) / (SoC start - SoC end)) for Wh-out, Wh-reg and external kWh-meter (and get their ratio)
5. Repeat 1-4 until you have a consistent number for Total kWh for each three measurement methods
6. Repeat 1-5 once for instance every 10 000km

With this tests you will get available kWh on different points in time.

You will not be able to get total kWh as this probably only is available by M.U.T. III

By the way - did you get the amp hours value from your dealer?
According to other discussions the dealer should have done this test and you should be able to get this number
This number should be the best reference for future degradations

 

[bobakka]

So there is only 12,000W available to turtle and max 13,000W to road side assistance.
My old bat. pack after 1½year used 13,000W at 17.5% Soc, at 12°C, light headwind, slow road.
And 13,700W at 8.5% Soc, 21°C, faster tail wind, high hyway speed.

Is this a good battery pack ?

It could be that it is a good battery pack, but that the system limits the available kWh.
We have had several iMiev owners here in Norway reporting that the range actually increase as the battery gets older.
That must be due to increase of the available kWh.

One way to keep track on that (in my view) is to record battery voltage (average, max and min) for a given SoC.
The recordings must be done in similar conditions like having stopped the car and been idle for example 2-5 min.
I notice that the batttery voltage increase a bit after I have stopped the car standing idle.

I have some recordings of battery voltage versus SoC - and it could be interesting to compare with your battery pack that appearently is brand new!

 

[DonDakin]

Hi pier,

Great news. And that was actually pretty fast when considering the extended times people have been reporting for warranty repairs.


I recently did a longer trip at -4 deg c and my range was about 96 km. its hard to look at range and guess if the pack is good. That being said you seem to be able to get a little over 100 km at -2 deg c which is not bad.

I think the car computer uses temp to sort of "model" the battery. The temp compensation factor i believe limits the amount of wh out. The soc is artificially lowered as the temp drops. So as it gets colder regardless of what your battery can deliver the battery capacity is sort of shrunk in software to protect the battery. This might mean that your 13 kwh at -2 deg c is equivalent to something like 15.8 at 25 deg c.

Reading thru some of the forum threads i believe the canion wh out reading is good for higher currents but inaccurate at lower ones. Also i think the wh reg is not accurate.

So you might try this:

First charge to 100 %.

I would suggest taking a highway drive and trying to do no regen at all just shift to neutral to brake. Then record just wh out and soc. This would be the quickest test but it exposes the car to ambient temp with i guess is getting pretty cold in you area. I think you pretty much already did this test.

Maybe it would even be better to put the car in an indoor garage at 20-25 deg c and let the battery warm up to ambient temp. Then just run the heater and record the wh out down as low as you can go. If you have access to a garage.

It sounds like the dealer could not do a capacity test, I would think you would be entitled to this with a pack replacement.

It would be nice to be able to get a baseline capacity using canion in a controlled way that you could repeat in the future. I think temp has a big effect on capacity so controlling the temp of the battery for a capacity test would be important to get a repeatable method of testing the battery. So even thought it would take a long time draining the battery with the heater in an indoor garage at 25 deg c would be the best test i can think of.

Don.....

 

[Pier]

Tanks for your suggestions. I will collect data for future comparisons. Collecting data for Wh Reg on charging will be difficult because Canion often crashes especially on a long period of 5 hres. Also, the cold of winter isn't a good time to experiment, since temp has some effect on capacity.

Bobakka, I ask for amp/h of new pack but have been told that capacity test was not required and not in the list of « things to do to install a new pack ».

My new pack was built May 2014. It is in the middle of the bar code serial number at the rear end of the pack. (1405).

Capacity : For now, I consider my new pack to have 13 kwh before towing. My old pack last summer, I considered it to be 15 kwh. Two possibilities : 1- rebuilt pack having lost 13% capacity or, 2- a new pack that will improve range with time and/or with higher temp. I will find out next summer.

This morning was the first full charge. Voltage of cells were equal at 4.095 except two cells that were at 4.100 volt. Less than my old pack, equal at 4.105 volt. Might improve with time, I hope.

All in all, I am satisfied with the experience.

I told technician I hope not come back before 2 years !!! He replied no problem it is good business for us !!! ( meaning easy money).

Pier.

 

[RobertC]

This morning was the first full charge. Voltage of cells were equal at 3.095 except two cells that were at 4.100 volt. Less than my old pack, equal at 1.105 volt.

Did you mean:

"This morning was the first full charge. Voltage of cells were equal at 4.095 except two cells that were at 4.100 volt. Less than my old pack, equal at 4.105 volt."

It is interesting that all of the cells in your new battery pack would not charge to 4.105 volts.

 

[Pier]

Thanks RobertC, change done.
Pier

 

[bobakka]

I will collect data for future comparisons. Collecting data for Wh Reg on charging will be difficult because Canion often crashes especially on a long period of 5 hres.

Mine crashed also all the time. When I removed almost all the ticks in "Settings" the stability improved. I just kept "Trip Timer", Battery Status, Battery Temp, Volts History (5 min), SoC History (5 min). The stability improved and it has only crashed 1 out of the last 10 chargings,

Also, the cold of winter isn't a good time to experiment, since temp has some effect on capacity.

I am not sure if the winter has that great effect, and anyhow it is interesting to understand what effect. In my car this morning when it has been unused for more that 24 hours, outside temp was -2 C the Batt Temp Avg var 8,4. That must mean the battery compartment is well isolated.
And also what is very interesting to know for a brand new battery pack is the relationship between SoC and Batt Status Volts -maybe with temperature as the third variable.

Bobakka, I ask for amp/h of new pack but have been told that capacity test was not required and not in the list of « things to do to install a new pack ».

Strange ...

 

[newwaysys]

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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.

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