DBMandrake
Posts: 77
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Is my battery dying ?

Tue Oct 16, 2018 8:20 am

Time for an update on the dying cells situation.

Capacity has continued to drop at an alarming rate and it does indeed seem that cells 25 and 70 are slowly but surely dying, with cell 69 also showing signs of being halfway as bad as 25 and 70, with the other 85 cells still looking relatively normal. First the Ah degradation over time:

Image

The blue dots and line are actual Ah readings taken from the car using either Diagbox or Canion. From 28k miles to 38k miles the degradation rate was linear and approximately 0.1Ah per 1000 miles, after which a series of three large drops has occurred, which I believe are a result of cells 25 and 70 losing capacity much more rapidly than all the others, limiting the effective usable capacity of the pack.

The red line is a linear extrapolation of where I think the Ah capacity would have been if cells 25 and 70 weren't prematurely dying, in other words it should still be at about 38.2Ah instead of the 35.6Ah it is now.

As can be seen from the straight red line, the degradation from 28k to 38k was completely linear before the sudden drops occured. The gradual linear decline will be the programmed in "cell degradation model" the BMS uses in between actual measurements, with the "sudden" drops representing occasions where the BMS has measured the capacity and found it to be well below the predicted level, forcing it to update it's Ah estimate.

Now let's look at the degree of cell imbalance after discharging. For a given Ah capacity mismatch between bad and good cells, the voltage will start off balanced between all cells at 100% and start to diverge at some point below about 50%. The closer you get to 0% SoC the more extreme the voltage difference will become so to get consistent results it should ideally be checked at the same SoC or some extrapolation should be applied.

Here is the voltage imbalance at a 10% SoC from one of my images earlier in this thread posted back in April:

Image

Even as low as 10% SoC the peak difference is 50mV, which is certainly higher than it should be, and it's clear that cells 25 and 70 are weak, but at that point they are not really bad yet. Has it got worse since then ? Unfortunately yes! Here is a reading taken yesterday at 16.5% SoC:

Image

If the condition of the cells was the same as April, you would expect the voltage difference to be less than 50mV because this was taken at a higher SoC of 16.5%. But instead it is much worse - 80mV. So without a doubt the imbalance between cells 25 and 70 and the rest of the cells has got considerably worse since April, meaning that those two cells have continued to degrade at an accelerated rate relative to the rest of the pack. :( It's also apparent that cell 69 is becoming weak, although not as bad as the other two.

Now a snapshot taken during a rapid charge by which time the charge rate has dropped to 20kW. Rapid charging is also a good test of weak cells, because cells with either reduced capacity or higher internal resistance will show a higher voltage during the rapid charge than other cells. Again you can clearly see cells 25 and 70 poking out well above the rest, and cell 69 also poking out significantly:

Image

I don't rapid charge very often but something I've noticed now is that rapid charging speeds start tapering very early now. Even when I plugged in at 30% SoC during this test with a battery temperature of 25C (eg not cold) it only charged at 43kW for less than a minute before it started throttling back, with it down to 30kW by about 40% and 20kW by 60%. In other words throttling back a lot earlier and more than it used to.

I believe this is caused by the BMS limiting the charge rate to keep all cells below 4.105 volts, and if you have cells 25 and 70 peaking up to that voltage too soon due to being weak, the charge rate must be throttled back to avoid subjecting them to over voltage. So my rapid charging rates are significantly knobbled over what they were last year. :(

In short I think I'm in serious trouble here with the high mileage I do. I estimate that I've lost about 7 miles of summer range since the start of this year when the Ah capacity first started to drop suddenly.

More investigation into Peugeot's 8 year 60k mile battery warranty is giving conflicting results. I was originally told that older cars were retroactively increased to the new 8 years, but Peugeot have told other speakev members that have enquired that it only applies to cars sold after 2015 not older cars.

More importantly though there is no guarantee of minimum battery capacity like there is with many other EV's. So unless I have an outright cell failure that stops the car driving it would not be covered anyway, so the warranty is basically worthless.

So I've made the decision that I may have to do a cell swap of cells 25, 69 and 70 myself and am currently in the process of sourcing some cells and trying to talk my other half into the idea that I actually need to buy them even though the car is still currently driving! :lol:

I still have just over 2 years on a personal loan to pay the car off so a replacement pack out of warranty is not an option, and a cell failure putting the car off the road permanently would be a disaster. The good news is that I think I have found a good source of low mileage second hand cells so even though I don't plan to do the swap until next spring if I can last until then (it's getting too far into winter to voluntarily do major car repairs) if I do go ahead with buying some cells I'll get them now and store them at the correct voltage until I need them.

I'm planning to get four cells, swap 25, 69 and 70, and keep one "new" one as a spare for the future.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

kiev
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Re: Is my battery dying ?

Tue Oct 16, 2018 8:59 am

Does the car charge to "Full", i.e. 16 bars on the fuel gauge? Failure to reach full is one criteria for pack replacement under warranty.

What does the canion graph look like when the pack is fully charged using your home EVSE? How much is the peak difference in cell voltage?
kiev = kenny's innovative electric vehicle

DBMandrake
Posts: 77
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Is my battery dying ?

Tue Oct 16, 2018 10:32 am

kiev wrote:Does the car charge to "Full", i.e. 16 bars on the fuel gauge? Failure to reach full is one criteria for pack replacement under warranty.

Yes it does charge to 16 bars, however I've noticed on Canion that sometimes it stops at 98% instead of 100% on a Level 2 charge.

What degree of battery malfunction causes it to indicate less than 16 bars after fully charging ? A usable Ah capacity below a certain threshold ?

You say it is one of the criteria - is this for Citroen/Peugeot in the EU/UK, or for Mitsubishi in the US/EU/UK ? I don't suppose you happen to know all the official criteria that warranty battery pack replacements are based on ? I have even contacted Peugeot UK head office but cannot get any useful information out of them.

I suspect it's not "bad" enough yet to meet any criteria they may have, however the car turns 8 years old next June and I do 12k miles a year in it.
What does the canion graph look like when the pack is fully charged using your home EVSE? How much is the peak difference in cell voltage?

I'd have to check but as far as I know the cell voltage is balanced within 10mV after a full Level 2 charge. It's only after the battery has discharged below about 40% that the voltage of the weak cells starts to drop a lot faster than other cells, suggesting the weak cells have less usable capacity than the rest.

One other thing I forgot to mention is that rapid charging last summer always used to stop at exactly 82% reported by Canion or the Rapid charger. This summer, since the cell problems have appeared, rapid charges often stop anywhere between 74% and 80%, even though the car may have been charging for less than 20 minutes. I don't think stopping before 82% is normal rapid charging behaviour except in extreme cold where it takes long enough to hit the 30 minute rapid charge time limit.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

jray3
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Re: Is my battery dying ?

Tue Oct 16, 2018 2:04 pm

Not that it's worth bragging rights, but I think my battery's sicker than yours. I'm no longer confident to do my longest regular cold season trip, at 54.4 mixed driving miles without a DCFC session. Most recent low SOC capture was a month ago, when resting at 6% SOC, Cell#8 was 3.72V while Cell#18 was way down at 2.90V. That's a pretty big spread! Pack voltage was 304.8.

Previous capture a month prior was again Cell #8 as the highest at 3.70V and #19 down at 3.07V, at 4% SOC, pack voltage 306.5. Pack capacity down to 33.2 Ah

Time to fire up the MUT3 again.
Last edited by jray3 on Tue Oct 16, 2018 2:44 pm, edited 1 time in total.
2012 i-SE "MR BEAN" 94,000 miles
2000 Mazda Miata EV, 78 kW, 17 kWh
1983 Grumman Kurbwatt EV,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

DBMandrake
Posts: 77
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Is my battery dying ?

Tue Oct 16, 2018 2:27 pm

jray3 wrote:Not that it's worth bragging rights, but I think my battery's sicker than yours. Most recent low SOC capture was a month ago, when resting but not charging at 6% SOC, Cell#8 was 3.72V while Cell#18 was way down at 2.90V. That's a pretty big spread! Pack voltage was 304.8.

Previous capture a month prior was again Cell #8 as the highest at 3.70V and #19 down at 3.07V, at 4% SOC, pack voltage 306.5. Pack capacity down to 33.2 Ah

Time to fire up the MUT3 again.

Do you have Canion to capture a visual representation of all the cell voltages at a low SoC to see what kind of cell to cell variations you see ? Are the cells still balanced at full charge ?

What usable Ah capacity does the car report ? I'm guessing a lot lower than my 35.6Ah.... and what sort of range are you still getting ? Any odd behaviour from the car such as charging difficulties ?
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

jray3
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Location: Tacoma area, WA
Contact: Website

Re: Is my battery dying ?

Tue Oct 16, 2018 2:50 pm

I don't have a currently functional CanIon setup. That experience with Android devices convinced me to stick with the iPhone.... :geek:
Pack capacity is 33.2 Ah and falling. I'll give CanIon another try for the pretty graphs, but scrolling through with the MUT3 previously showed a well balanced pack just off charge. (Overnight L2)

I saw 62 or better RR all summer, but these frosty mornings are now more like 45 RR after a preheat, but HVAC turned off, IIRC...

No odd charging behavior since my charger replacement this summer, and a DCFC still takes closer to 20 minutes than 30.
2012 i-SE "MR BEAN" 94,000 miles
2000 Mazda Miata EV, 78 kW, 17 kWh
1983 Grumman Kurbwatt EV,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

PV1
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Re: Is my battery dying ?

Wed Oct 17, 2018 8:33 am

DBMandrake wrote:What degree of battery malfunction causes it to indicate less than 16 bars after fully charging ? A usable Ah capacity below a certain threshold ?

To not show 16 bars after a full charge, pack charge level would need to be 92% or less, as this is when the top bar disappears when driving.

Since all the cells are pretty much balanced at full, that's why the car still shows 16 bars after charging. For some other reported cell failures (such as mine a few years ago), something failed with either the cell or the BMS that caused the cell to discharge. Your cells look like they are simply degrading faster than the others and aren't being individually discharged. Unfortunately, I don't believe this would qualify for warranty replacement under US market warranties. We had to sign waivers stating that capacity loss wasn't covered. However, a loophole to this would be that eventually the degradation would cause the car to not charge to 16 bars, at which point it would qualify. The car will terminate charging if the minimum charge rate causes any cells to go over 4.11 volts.

I would definitely find out about warranty work first. If that's a no-go, then cell replacement is the next step.
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DBMandrake
Posts: 77
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Re: Is my battery dying ?

Thu Oct 18, 2018 2:02 am

PV1 wrote:
DBMandrake wrote:What degree of battery malfunction causes it to indicate less than 16 bars after fully charging ? A usable Ah capacity below a certain threshold ?

To not show 16 bars after a full charge, pack charge level would need to be 92% or less, as this is when the top bar disappears when driving.

Yes I understand that, I was just wondering what scenario would cause the car not to charge to 100%.
Since all the cells are pretty much balanced at full, that's why the car still shows 16 bars after charging. For some other reported cell failures (such as mine a few years ago), something failed with either the cell or the BMS that caused the cell to discharge. Your cells look like they are simply degrading faster than the others and aren't being individually discharged.

Yes, my cells are not self discharging and they are balancing correctly at 100% charge. The bad cells simply appear to have lower Ah capacity and possibly higher internal resistance (based on the voltage rising above the others during a rapid charge) than the good cells, and furthermore their Ah capacity is dropping at a much faster rate than the other cells (at least 3x faster per 1000 miles) and that is the real concern - not that they have less capacity than the others, but that the discrepancy between the bad and good cells is widening at an alarming rate. (It has got a lot worse just between April and October as can be seen by the low SoC voltage balance from April and October)
Unfortunately, I don't believe this would qualify for warranty replacement under US market warranties. We had to sign waivers stating that capacity loss wasn't covered. However, a loophole to this would be that eventually the degradation would cause the car to not charge to 16 bars, at which point it would qualify. The car will terminate charging if the minimum charge rate causes any cells to go over 4.11 volts.

Ah.... I presume this applies to rapid charging as well ? That would explain the premature rapid charging throttling and cutting off before 82%. The bad cells rapidly rise to 4.105 volts (high internal resistance ?) and stay there during most of the rapid charge session, this forces the BMS to throttle the charge rate earlier while the other cells are still at a significantly lower voltage.

From what you're saying it sounds like once the charge rate drops below a certain threshold if the voltage still tries to go over 4.11 volts it aborts the charge early. I can certainly see how that could happen in a rapid charge since the charge rate is high enough to push a weak cell high in voltage, and the balancers are not used during a rapid charge. (and wouldn't be effective anyway) It seems like the cells would have to have a pretty serious fault for this to occur with a Level 2 charge though.

It may also be that rapid charges regularly aborting significantly below 82% and before 30 minutes in warm weather is an early warning sign that there are one or more weak cells.. It didn't happen to me at all last summer (always stopped at 82% on the dot) while this summer I was lucky if it ever got past 80% without stopping, it was always randomly stopping anywhere from 72% to 80% and the charge rate was very obviously slower than last year.
I would definitely find out about warranty work first. If that's a no-go, then cell replacement is the next step.

I'm confident the degree of degradation the pack has at the moment won't be covered under warranty (as there is no degradation guarantee) and that it's extremely unlikely there will be an outright failure in the remaining months of the warranty. So I think I'm on my own doing a 3 cell replacement.

On the upside, if I do the replacement and the problem is as I've diagnosed, I should gain back about 7 miles of precious range, arrest the rapid decent in battery Ah capacity I'm seeing now, and restore full rapid charging performance. All worthy objectives, even if the car is still driveable at the moment.

Finding somewhere with a two post lift that I can work at is the major stumbling block.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

kiev
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Re: Is my battery dying ?

Thu Oct 18, 2018 6:10 am

DBMandrake wrote:...
Yes I understand that, I was just wondering what scenario would cause the car not to charge to 100%.


In my case i had a lagging cell. It somehow discharged below the level of the others and would never come back up. So it was the first to hit the bottom and limited the driving range, and it never made it up, so charging stopped when all the other cells were full (~4.1). The fuel gauge is reading the average pack voltage and the laggard cell brought the average down, so it was showing less than 16 bars.

i suspect the cell may have been okay since it didn't act like as weak or failed cells as in your case (the quick rise to the top voltage during charging)--my guess was that something on the CMU board failed and was always discharging that cell. Over time the voltage difference kept getting larger until a "full" charge was showing less than 8 bars.

If it weren't under warranty i would have taken the pack apart to find the culprit and repair it, but i resisted the temptation and let them trash a whole bunch of good cells and i got a new pack under warranty. But on the other hand here is a link to where Martin's car was acting the same way and he replaced a cell and restored his pack, so it's hard to know what is the culprit.

i think you do have some truly bad or weak cells, but they are manifesting as reduced range or capacity degradation, and not the "lack of reaching full" on the fuel gauge. But it seems that those 2 cells would be getting over-charged if they were held high while waiting for the others to catch up?
kiev = kenny's innovative electric vehicle

Luddite
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Re: Is my battery dying ?

Sun Oct 21, 2018 12:30 pm

DBMandrake wrote:Time for an update on the dying cells situation.



So I've made the decision that I may have to do a cell swap of cells 25, 69 and 70 myself and am currently in the process of sourcing some cells and trying to talk my other half into the idea that I actually need to buy them even though the car is still currently driving! :lol:


I'm planning to get four cells, swap 25, 69 and 70, and keep one "new" one as a spare for the future.


Any luck on the sourcing of cells? I have an ion the same age as yours. Mine only has 35k on the clock and I haven't yet read any values from canion but eventually a few cells will need replacing.
I have seen a few crashed ions on copart for cheap but as I'm not an autobreaker, that would leave me with all the extra "car". Might be worth a few of us clubbing together to get an entire pack.

I did see some on ebay a while back but they were located in Canada and the seller wasn't able to send them.
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2011 Peugeot Ion

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