Is my battery dying ?

[PV1]

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.

That's what happened to my car a few years ago. The affected cell was consistently lower in voltage than the others (and dropping by the day), but it wasn't showing signs of being weak, as during heavy acceleration or regen, it would drop or rise the same as the other cells. In my case, pack SoC followed the weak cell down. It didn't show any real signs of internal short, either. None of the temperature sensors were reading high and it drove totally fine despite the reduced range.

As for the charge cutoff on level 1 or 2, I forget what the number was. The car ramps down charging as the highest cell(s) reach(es) 4.105 volts to hold them at that voltage. However, if a cell sits at 4.11 volts and doesn't come back down while the charger ramps down, then the car will stop charging. Whatever the SoC is at that moment is what the car considers "full" as far as charging goes. This is what prevents the car from reaching 100% charge.

In my case, with a lower but otherwise apparently healthy cell, the other cells in the pack all reached 4.105 volts, and the charger ramped down to avoid overcharging them. At some point, the cells wanted to go higher in voltage, which the car stopped by ending the charge. Day 1 of the failure, this was at 76% charge. In my case, SoC of the entire pack followed the low cell. Since it couldn't reach 4.105 volts without over-charging the other cells, it never reached 100%. SoC followed the cell down to a total range of about 15 miles by the time I took the car to the dealer.

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?

If their internal resistance is high, they would be slower at absorbing the charge. With terminal voltage being held constant, the resistance of the weak cells is limiting charge current for the whole pack. The pack will only charge as fast as the slowest cell can absorb a charge. They would only be over-charged if the car didn't limit per-cell terminal voltage (eg. if the car would ignore the weak cells and try to QC at 361 pack volts).

 

[DBMandrake]

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?

Still working on it.

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.

Not necessarily.

Individual cells going bad while statistically possible isn't inevitable. If you only get gradual even degradation of all cells then a few spare cells won't do you any good. It's only in the case where most of your cells are OK and there are one or a few bad cells would replacement cells be beneficial. And the replacement cells need to have an equal or higher Ah capacity than the existing cells in the pack to ensure that you regain the full potential capacity of the good cells.

So I'd check the health of your battery with Canion before committing to buying any cells, especially when the actual replacement process is somewhat challenging. (Mainly physically getting the pack out of the car so you can work on it) You also need a special battery charger/discharger/tester to test second hand cells to see that they are OK and confirm their usable capacity, and then discharge them to the correct voltage (about 3.7 volts) for storage until they're needed. If you were to leave them fully charged in storage you would lose significant lifetime of the cells just while they're sitting on the shelf. They're also extremely dangerous in the case of short circuits so you'd need a cool safe place to store them.

In Canion you want to check the Ah figure of the pack as a whole, and to check the capacity balance of the cells Level 2 charge to 100%, ensure all cells are within 10mV then drive the car down to 10-20% then check the voltage balance as I did earlier in the thread. If there are no obvious outliers like the two I see, you have nothing to worry about.

 

[DBMandrake]

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.

A bit of a setback on the cell front.

I have been dealing with a guy in Holland who buys EV packs from scrapped cars and sells them for second life use. He has had a few i-Miev packs through recently. Including a 2013 model with much lower mileage than my car.

Unfortunately when he tested 4 of the cells for me their remaining capacity was only 28Ah. I can only assume that the cells have been poorly treated from the time the car was put off the road until he bought the pack - possibly left at full charge in warm weather. At least he tested them for me first rather than me testing them after buying them and finding they were no good.

I now have some doubts about the likely-hood of finding second hand LEV50 cells with sufficient remaining capacity (>39Ah) so I have a question for the experts more experienced with these cars and cells than me.

Would it be acceptable to substitute a few LEV50N cells into an earlier car with LEV50 cells such as mine ? Obviously the cycle life should be dramatically better than the older cells so that as the new hybrid pack continues to degrade those replacement cells would lose capacity much slower than the rest, but I don't think this would cause any problems, in the way that a few weak cells will ?

Of course if other properties like the voltage discharge curve, internal resistance etc are significantly different the BMS may not be happy with the substitute cells... but I don't know enough about the charge/discharge properties of the cells to know how compatible they are in operation and whether they would make the BMS happy or unhappy. Would the BMS just see them as "unusually good" cells among a large number of weaker cells ? Or do the new cells have some disadvantages compared to the older ones ?

Does anyone know or has anyone tried this ? LEV50N cells may be the only ones that will be found second hand still with a useful capacity remaining.

 

[kiev]

...
Would it be acceptable to substitute a few LEV50N cells into an earlier car with LEV50 cells such as mine ?
...
Does anyone know or has anyone tried this ? LEV50N cells may be the only ones that will be found second hand still with a useful capacity remaining.

i haven't done this yet, but i wouldn't hesitate to use LEV50N over the old cells, depending upon the measured available capacity (bench testing). Obviously if the 50N is worn out then there is no benefit, but otherwise newer is better when it comes to batteries and cells. Once the electrolyte gets added and the chemical reactions start, then the life-time clock is ticking and the cell starts to degrade, and there is no stopping it...

With regards to the low capacity of the older cell, i would suggest doing several or 5 charge-discharge cycles to measure the capacity. There are many accounts on other forums of folks getting neglected cells to somewhat revive after several cycles. So it may be worth another look if some 50N's are not available.

 

[DBMandrake]

i haven't done this yet, but i wouldn't hesitate to use LEV50N over the old cells, depending upon the measured available capacity (bench testing). Obviously if the 50N is worn out then there is no benefit, but otherwise newer is better when it comes to batteries and cells. Once the electrolyte gets added and the chemical reactions start, then the life-time clock is ticking and the cell starts to degrade, and there is no stopping it...

Second hand LEV50N cells are going to be newer than second hand LEV50 cells, since they stopped using the latter in mid 2012. So any second hand LEV50's you get hold of will be at least 6 years old now, which is a lot of calendar age degradation, especially if they have sat at a high SoC.

So LEV50's not only degrade much slower (in theory) they will also be younger. Obviously any replacement cells would need to be equal or greater capacity than the remaining cells in the pack to get any tangible improvement, which is why cells with only 28Ah remaining are no use to me.

Getting LEV50N with plenty of usable capacity left seems quite likely but LEV50 now seems a bit unlikely unless you got a low mileage car that had been cared for. (Not left on 100% charge for example)

LEV50N's having a lower degradation rate than the rest of the pack wouldn't pose a problem I think - the BMS should be OK with a few cells that seem to be degrading slower than the rest as they won't limit the usable capacity of the pack, and the balancing system in this car is fairly strong. (Compared to a Leaf with very weak bleeders)

The question is, how do the LEV50N's perform dynamically under load and rapid charging. If their performance in every parameter is at least as good as the old cells, there shouldn't be a problem. But you also have to consider factors like how fast can they be charged at cold temperatures etc... as these assumptions are all programmed into the BMS to keep the cells in a safe operating area. There would be a risk if any particular parameter was worse than the old cells, such as ability to charge at high/low temperatures.

With regards to the low capacity of the older cell, i would suggest doing several or 5 charge-discharge cycles to measure the capacity. There are many accounts on other forums of folks getting neglected cells to somewhat revive after several cycles. So it may be worth another look if some 50N's are not available.

The guy supplying the cells knows what he's doing, he breaks a lot of packs including Tesla packs and he used a professional high power charger/discharger/tester which did 3 full charge/discharge cycles on the 4 cells that were earmarked for me, and after 3 complete cycles the average capacity of the 4 cells was still only 28Ah.

I suppose it's possible that one weak cell was dragging the other three down, since they were tested in parallel, (testing them individually one at a time would have taken far too long for these size cells) but even if that's the case I'd still be dubious of the long term reliability of the other 3 since they were coming from the same 4 cell group in the pack.

By testing them and letting me know they didn't have the capacity I was looking for he was doing himself out of the sale, so I have no reason to disbelieve the result of the test. (I also have a suitable charger/discharger/capacity tester which I would have done my own testing of the cells individually after getting them to verify their performance then store them at 3.7 volts) He says he gets i-Miev/C-Zero/Ion packs a few times a year so I'll just have to watch his stock and try again when he gets another pack in.

 

[DBMandrake]

Thought I'd post an update on the weak cell situation. The car is now up to 51k miles and there has been one further "sudden" drop in Ah capacity, followed by a "normal" steady decline. Ah capacity is now 35.1Ah:

Cell voltage difference at 20% SoC has increased from 80mV to about 125mV, although that may be partly due to cold weather.

Range seems noticeably reduced since before the first big drop in Ah at 38k miles - I now get about 55 miles (mixed cycle) in summer weather without the heater and about 38 miles in winter with the heater. (Near/below freezing conditions) When I first had the car at 39.9Ah I was getting around 63 miles in summer and 43 miles in winter respectively, so I've lost about 8 summer miles and 5 winter miles of range altogether. My 35 mile daily commute in winter is now very tight, with me regularly arriving home with 2 or less bars even turning the heater off the last 5 miles or so.

The range reduction I can cope with as there is a rapid charger on the way home, however another symptom of the weak cells is much slower rapid charging and early tapering of rapid charging due to high internal resistance in two cells - 25 and 70, as shown in my previous cell voltage snapshots.

Even with cell temperatures of around 20C, if I plug the car into a rapid at 20% SoC, it will start at 43kW but start throttling down before 30% SoC. Cells 25 and 70 are reaching 4.105 volts under rapid charging while nearly all the other cells are still at 4.085 volts or less. This causes premature throttling of the charge rate to keep the high resistance cells from going over voltage.

By 50% SoC the charge rate is already down to about 16kW and falling rapidly so getting to 80% takes an eternity. When I first had the car I could charge from nothing to 80% in summer in 20 minutes. Now even charging from 30% to 80% takes about 30 minutes, with the last 20% or so up to 80% being painfully slow. Also quite often the rapid charge will stop at around 73% instead of the normal 82%.

Another possibly related symptom of high cell resistance is that in cold weather the car seems to get confused about the SoC before/after a rapid charge. For example I'll arrive at a rapid charger with 30% SoC reported in Canion, but the moment I plug it in and start a rapid charge session the reported SoC will drop to say 15%. (And the bars drop on the dashboard as well) Then the rapid charge will terminate "early" at say 72%, but if I attempt to re-start another charging session it will suddenly jump to 82%.

It may be my imagination but regenerative braking doesn't seem as strong as it used to be, even in the unlocked B mode - which used to have a very strong action before, now B mode doesn't seem that much stronger than D mode. Since regeneration is just rapid charging, I suspect the same issue of high resistance cells is restricting the amount the car can regen.

So not ideal. The car is still perfectly driveable but I think once I've finished paying it off (under 2 years left now) I'll move it on and use the proceeds to buy something a bit better. Demand outstrips supply in the UK so it should be easy to sell, the problem is finding what to replace it with as the EV market in the UK is now a sellers market...

There are other reasons too - for example I've noticed there is a lot of corrosion on the underbody and chassis inside the "engine bay" area, including where the springs attach, on brake lines etc.

I had read that these cars are not rust proofed to UK salt road standards and, well, that seems to be borne out. My 21 year old Citroen Xantia V6 which has done 90k miles has far less underbody rust than this 8 year old 51k Ion. :shock:

 

[DBMandrake]

Argh, spoke too soon. Checked today and I have had another sudden 1Ah drop in capacity. It's now at 34.1Ah at 51724 miles. So I've lost almost 6Ah in two years and under 25k miles. Not very impressed at all as SoH is now at about 74%.

 

[Gary12345]

I wouldn't see any issue using LEV50N as a replacement for LEV50 if that is what you can find. Testing the replacement cells first is a must though as its quite a bit of work taking the pack out. Testing can be done with a fairly high power RC charger, or any decent RC charger and a separate battery discharger.

I'm still waiting for an 8-pack of cells to arrive, most likely will take a couple more weeks. Once they arrive i'll test them to see what the Ah is, if any good i'll keep a few for replacements in my i-miev and sell the rest.

Thanks,

Gary.

 

[DBMandrake]

I wouldn't see any issue using LEV50N as a replacement for LEV50 if that is what you can find.

I'm on the fence about that. If I was in a situation where a cell had failed and it was the only choice to get the car back on the road, then yes I'd try it. If the cell swap is "elective" to try to improve the usable capacity of a car that is still working mostly OK I'd be a bit more hesitant.

Testing the replacement cells first is a must though as its quite a bit of work taking the pack out. Testing can be done with a fairly high power RC charger, or any decent RC charger and a separate battery discharger.

I have a SkyRC B6AC V2 which can do a discharge capacity test up to 50Ah - however with a maximum discharge power of 5 watts you're looking at a day or two to test a single cell... :mrgreen:

I'm still waiting for an 8-pack of cells to arrive, most likely will take a couple more weeks. Once they arrive i'll test them to see what the Ah is, if any good i'll keep a few for replacements in my i-miev and sell the rest.

Good luck on the cells and I'll be interested to hear what capacity you measure. I approached a seller in Holland for 4 cells last year but when he tested them they only measured 28Ah so the purchase was cancelled. What voltage are you planning to discharge them to when testing their capacity ?

The car charges them up to 4.1 volts and only discharges them to about 3.6 volts - most discharge tests will discharge them much lower (about 3.0 volts) which may inflate the usable Ah capacity figure a bit compared to what you'll really get in the car.

I'd be confident working on the pack once it's out of the car to do a cell swap - I have an electronics background as well as having plenty of experience in fairly substantial car repairs, however for me the issue is I don't have access to a 2 post hoist and trolley to get the pack out of the car safely.

So I'd have to hire access to one from a garage and then have to work in a hurry in someone else's commercial workshop. If I was doing a cell swap I'd rather take my time and work on it at my leisure over 2-3 days.

So while it's tempting I can't see myself doing it unless I end up in a situation where the bad cells get so bad that the car isn't usable. At most replacing the weak cells may get me back up to around 38Ah. Fixing the slow rapid charging it has now would be a worthwhile side effect though.

 

[Gary12345]

What voltage are you planning to discharge them to when testing their capacity ?

I will charge to 4.1v and then discharge to 3v. The Yuasa spec sheets show that they test between 2.75-4.1v but there is very little below 3v. That should give me a good idea if the cells are usable in a car.

I don't have access to a 2 post hoist and trolley to get the pack out of the car safely.

I removed, fixed and replaced my battery pack on the drive without a hoist - its fairly involved but its definitely doable - I had the car up on 3 concrete blocks (the 4" thick ones) under the wheels so the whole car was 12" up, removed the big orange fuse then the thick orange cables, then bolted trolley wheels on a wooden pallet, put this under the car, used 2 trolley jacks with 2x4" on top jacked up underneath the front and back of the pack, then undid the pack bolts and electrical connectors and carefully lowered the jacks with the wood and battery pack on top down onto the wooden pallet, then slid the battery pack out.

I have purposely not described in detail where the fuse and orange cables are, because you need to have researched how to do this part safely - the mitsubishi battery pack removal guide is online and has the relevant safety steps which MUST be followed.

Thanks.

 

[Gary12345]

Oh and i've got a dual 10A RC charger and a separate 10A discharge capacity tester, so in ~5 hours I can do 1 full charge, 1 full discharge and a storage charge (50% charge once they have been tested).

 

[DBMandrake]

I will charge to 4.1v and then discharge to 3v. The Yuasa spec sheets show that they test between 2.75-4.1v but there is very little below 3v. That should give me a good idea if the cells are usable in a car.

Curious to know whether you have received your block of 8 cells yet and if so whether you have had time to test their Ah capacity ? I'm still toying with the idea of replacing four of my cells. Two are quite bad - both high internal resistance and significantly lower capacity than most of the others, a 3rd is nearly as bad capacity wise but resistance seems OK, and a 4th is not far behind the three worst ones. There's then a significant gap to the next worst cell with most of the remaining 84 cells being relatively closely grouped so probably not worth replacing any of the others.

I removed, fixed and replaced my battery pack on the drive without a hoist - its fairly involved but its definitely doable - I had the car up on 3 concrete blocks (the 4" thick ones) under the wheels so the whole car was 12" up, removed the big orange fuse then the thick orange cables, then bolted trolley wheels on a wooden pallet, put this under the car, used 2 trolley jacks with 2x4" on top jacked up underneath the front and back of the pack, then undid the pack bolts and electrical connectors and carefully lowered the jacks with the wood and battery pack on top down onto the wooden pallet, then slid the battery pack out.

I've been following along and helping with the diagnosis in this thread where a CMU is being replaced:

https://www.speakev.com/threads/c-zero-battery-pack-repair.137750/

He has tried two different approaches - both which seem doable to me. The first was to raise the car up high on ramps and stands and then use a hand operated hydraulic pallet mover to lower the pack down and withdraw it from the car. So as long as you can hire one for a weekend this seems like one way to do it, although lining everything up when raising it up again could be fiddly.

Later in the thread he came up with a second method where four of the main mounting bolts are replaced with very long threaded rods with a spacer tube and nut such that once fitted you remove all the other bolts and simply unwind the nuts to lower it down onto a small trolley.

Slower than the hyraulic lift, but very minimal resources required, and in theory it should make getting the battery back up into exact alignment easier as it will be getting lifted up on the threaded rods into perfect alignment. I could definitely see myself able to use this approach so I'm now considering again whether I should do a cell swap to prolong the useful life of the car.

My Ah capacity is down to 34.0Ah now and still falling relatively rapidly, DC rapid charging speeds are much slower than two years ago (due to the two high resistance cells reaching peak voltage too soon) and I believe that were it not for the 4 bad cells the capacity would still be up around 38Ah now.

Tempted...

 

[Gary12345]

Sorry my cells are still not here, i'm relying on a favour to get them shipped 400 miles for free, so basically have to wait until the guy is close to me to get them ! Hoping for soon.

Thanks.

 

[DBMandrake]

In the last few days I reset the BMS in my car, as described in the following thread:

http://myimiev.com/forum/viewtopic.php?f=23&t=3943&start=60#p38994

In hindsight not a clever idea because it resets the Ah capacity back to the factory default of 45.8Ah, and the car is very slow/reluctant to re-learn the true capacity when it differs so much from the factory new capacity! (On a positive note, we now know that the factory new capacity of these packs is 45.8Ah! Thus we can confidently use this figure to calculate % SoH)

Due to this, the BMS grossly over estimates the range of the car and will try to drive the battery right down to the 3.0 volt cutoff point at which point you are very suddenly restricted to 7mph. Not good! So to solve this in a timely fashion I had to do the battery calibration procedure as detailed in that thread. For anyone wanting to force the BMS to re-measure the Ah capacity of the battery in a safe way - just do the battery calibration procedure under maintenance, not the full BMS reset! (battery replacement procedure)

I decided to analyse some of the new data I've found from the latest calibration and recent Canion voltage graphs regarding the state of my cells. Earlier in this thread I noted that I have two cells that are particularly weak and a third that is well on the way to being weak, and that my suspicion for a while has been that these two or three cells are responsible for the majority of the seemingly accelerated capacity loss I've had over the last year, and I think I have the data to prove that now.

So first some Canion voltage graphs. This first graph I've posted before and was taken at 10% SoC in April 2018 at about 41k miles, which was when I first started to notice abnormally fast drops in Ah:

You can see there is a 50mV spread at 10% SoC - not terrible, but not good either. Fast forward to October 2018 at about 47k miles and it is now a 125mV spread for the same SoC. Ouch:

About a week ago I recorded this voltage graph at a slightly higher 14% SoC, and at 52k miles. The spread is now 135mV at 14% SoC - as the spread increases at a lower SoC it's worse than it looks at about 10% SoC it's more like 150mV now. I've highlighted in red the cells that I have particular concerns about and propose replacing:

Also of note is that some cells have high internal resistance. This can be tested by discharging the car to a relatively low SoC like 20% then Chademo rapid charging the car. Cells with high internal resistance will try to go over voltage very quickly. Here is a voltage graph taken only a few minutes into a Chademo charging session where the charge rate is already throttled back due to Cell 25 hitting the maximum allowed voltage. I've highlighted three cells that I have concerns about high internal resistance, not surprisingly 3 of the same 4 cells from above:

The difference between 4.075v and 4.105v might not seem like much, but when repaid charging this can mean the difference between pushing the good cells up to 43kW (before reaching 4.105 volts) and having to throttle way back to 21kW to keep the high resistance cells from going over voltage.

In short, the weak cells are seriously limiting rapid charge speeds as well. In fact no matter what SoC I start at my charge rate only remains at 43kW for less than a minute, as shown in the following graph where I started charging from about 30% SoC - note that it doesn't even last 30 seconds at the full 43kW before throttling back, and it is painfully slow by even 55%:

So I've known for a while the difference between best and worst cells is getting progressively worse but I couldn't put a quantitative figure on it as I can't directly relate the relative cell voltage near discharge to the capacity of the cells.

After running the battery calibration routine I've realised that it actually measures the individual cell capacities and reports the minimum and maximum cell capacities of the pack! And I also ran this calibration and kept the results about a year ago so now I have two data points. So a year ago it reported this:

And now today:

So in the last 12 months and 12k miles the best cell has degraded only 0.5Ah (better than I would have expected!) while the worst has degraded 3.3Ah. So the spread has increased from 2.9Ah to 5.7Ah in the last year.

I've added these new data points to my excel spreadsheet and graph and have come up with the following interesting display of the data:

The dotted blue line is actual Ah measurements taken by Canion or Diagbox, with the yellow line being a linear interpolation of the degradation rate. The red line shows the degradation rate of the weakest cells as reported by the battery calibration routine which pretty much exactly follows the yellow line.

The green line shows the degradation rate of the best cells in the pack - which is dramatically slower than the worst cells, and you can clearly see the gap between the green and red lines opening up...

The question is, if I replaced those 4 cells, what would the new minimum capacity be ? Since the weak cells seem to be significant outliers I think I could recover at least half the lost capacity if I replaced them with better cells - I'm estimating that it would go back up to about 38Ah, and more importantly and hopefully arrest the rapid degradation that I'm seeing at the moment. If I could get it back up to about 38Ah and reduce the degradation rate back to what it was before 40k miles it would add an extra several years of useful life to the car for me.

The way the weakest cells are degrading at the moment I will not be able to make my 35 mile daily commute next winter without a rapid charge on the way home every day - and at the reduced rapid charge rates I'm now seeing, painfully slowly...

 

[jray3]

Nice thread! My data to add won't be as pretty, but yesterday the HV warning lamp came on at the end of a drive that went from fully charged to one blinking bar and 12.5% SOC, no turtle, odometer 102,683 miles.
The warning was due to code P1A4B, "Each Cell Voltage Difference". The highest cell, #8 was at 3.83V, with lucky #13 the lowest at 3.59V, a delta of 0.24V, pretty significant.
Pack temperatures ranged between 104 and 86 F, as I had driven 38 miles, mostly on the highway at 65 mph. My pack capacity now reports at 27.9 Ah, and the pack fully recharged to a resting voltage of 359.3 and only 0.01V maximum cell difference, so the code cleared itself and EVen after that hard drive, today's starting RR was 49 miles.

 

[DBMandrake]

Nice thread! My data to add won't be as pretty, but yesterday the HV warning lamp came on at the end of a drive that went from fully charged to one blinking bar and 12.5% SOC, no turtle, odometer 102,683 miles.
The warning was due to code P1A4B, "Each Cell Voltage Difference". The highest cell, #8 was at 3.83V, with lucky #13 the lowest at 3.59V, a delta of 0.24V, pretty significant.
Pack temperatures ranged between 104 and 86 F, as I had driven 38 miles, mostly on the highway at 65 mph.

Ouch, that's quite a difference in voltage. At 10% mine is up to about 140mV now. I looked up the fault code and found the following:

http://mmc-manuals.ru/manuals/i-miev/online/Service_Manual/2013/54/html/M154945110009000ENG.HTM

Apparently a discrepancy of more than 80mV between cells at more than 4 battery bars (about 30% SoC) at a low charge/discharge rate (under 1 amp) will set this fault code.

This is quite worrying when thinking about replacing faulty cells in a heavily degraded pack. Previously I had assumed that if you were replacing weak/faulty cells that as long as the replacement cells were at least as good as the cells remaining in the pack there would be no problem even if they were much better than the remaining cells.

But if the replacement cells are "too good", eg near new capacity and the rest of the pack is heavily degraded then the new cells being so much better could potentially cause a voltage difference between the new good cells and the worst remaining cells to set this fault code.

Did the fault code prevent the car driving or charging or was it only a warning ?

My pack capacity now reports at 27.9 Ah, and the pack fully recharged to a resting voltage of 359.3 and only 0.01V maximum cell difference, so the code cleared itself and EVen after that hard drive, today's starting RR was 49 miles.

At 27.9 Ah your pack is now down to about 61% of original capacity. This is not great, and at 53k miles my car at 32.9Ah is already down to 72%, so apparently degrading faster than yours. In another two years I'll be pushing about 80k miles at the rate I'm driving.

Mind you, it appears that much of my capacity loss may be a result just a hand full of weak cells so I'm getting myself fired up on the idea of replacing the weak cells, now that I've found a way to do it relatively easily on my driveway without needing a two post hoist etc...

The problem is trying to actually find some good second hand cells. I'd need a minimum of 4 cells and potentially up to 8 cells depending on how far I want to go in evening out the capacity of cells in the pack and the cost of buying them. (3 cells are really bad, another 5 are significantly lower than the median cells)

I wonder how much of your capacity loss is due to specific weak cells and how much is overall degradation of all the cells ? At 53k miles I'm already seeing about a 6Ah spread between worst and best cells which is quite considerable especially when the spread 12k miles ago was more like 3Ah.

I have to wonder whether the quality control of the cell manufacturing was not up to snuff to have multiple weak cells in a single pack mixed in with a large number of healthy cells with a much lower degradation rate... they're not even physically adjacent to each other (thus potentially affected by hot spots in the pack etc) they're more or less randomly distributed throughout the pack. That smacks of manufacturing defects and/or tolerances.

 

[DBMandrake]

Quick question for those who have done cell swaps already or have intimate knowledge of the BMS or properties of the cells - do you think it would be safe and acceptable to fit a handful of LEV50N cells into an older car like mine with the LEV50 cells ? Has anyone actually substituted an LEV50N cell into an old LEV50 car and lived to tell the tale ?

I'm still trying to find 4+ cells for my car and the realisation is slowly dawning that finding second hand LEV50 cells (for example from a wreck) with >38Ah usable capacity left is vanishingly small to nill.

The cells are just too old now as they were only used until 2012, so any 2nd hand cells are therefore 7 years old minimum. As a lot of the degradation is calendar age related, (especially in heat and/or at high SoC) even if they're low mileage just being old may be a problem, especially if they sat in a hot wreckers yard through a couple of summers, and doubly so if they sat fully charged due to the crash occurring at a high SoC.

One set of cells I considered purchasing last year were out of a car with a much lower mileage than mine, but only had 28Ah left when tested by the seller - way below even the worst of my cells that I'm looking to replace.

The LEV50N supposedly has very similar (but how similar ?) properties with the major difference being low degradation rates. I believe that the casing and terminals are the same but I don't know for certain. (Anyone measured them side by side ?)

If their properties are only better in every regard the BMS will probably not even notice and everything will be fine. But if they have certain properties that are worse, that could be an issue.

For example the BMS has a charge rate de-rating curve that it follows when the cells are cold to prevent dendrite formation - if hypothetically the LEV50N's couldn't be charged as quickly when cold, they could be damaged by the BMS trying to charge them too fast while cold. Only a detailed look at the spec sheets of the two cells under different operating conditions like temperature would give any indication of whether this might be a problem.

Basically, is contemplating this wise ? Back when the degradation wasn't too bad I'd say it probably wasn't worth the risk, but I've now established that my 3-4 weakest cells are degrading at a relatively rapid rate and if I don't replace them in the next year the car will become semi-useless to me as the winter range won't do my commute anymore. So the reward/risk ratio of replacing them with LEV50N cells is now much greater and is tempting me...

 

[kiev]

Howdy Simon,

Here is a link to a Yuasa technical paper about the LEV50N, i think they are physically identical and could swap in with no problem


https://www.gs-yuasa.com/en/technic/vol9/pdf/009_01_026.pdf


i recently found the website of a used-cell vendor in UK, second life EV batteries.

https://www.secondlife-evbatteries.com


i'm sure you are motivated to swap some cells out, especially after reading of Rupert's experience to drop the pack, etc.

kenny

 

[DBMandrake]

Howdy Simon,

Here is a link to a Yuasa technical paper about the LEV50N, i think they are physically identical and could swap in with no problem


https://www.gs-yuasa.com/en/technic/vol9/pdf/009_01_026.pdf

Yes I think I've seen that paper before - not sure that I can interpret it well enough to answer my question though. My gut feeling is they would be a suitable replacement, I'm just not completely sure.

i recently found the website of a used-cell vendor in UK, second life EV batteries.

https://www.secondlife-evbatteries.com

Wow, great find! Looks promising, although they are a little bit wishy washy about how much usable capacity they guarentee and whether every individual cell they recover is tested - it doesn't seem so, they seem to do random sampling of cells in a pack - and assume the others are OK. If this was always the case I wouldn't be in the situation I'm in now..

They say cells should have over 85% of the usable capacity left - but do they mean 85% * 50Ah = 42.5Ah (seems unlikely in 7 year old cells!) or do they mean 85% * 46Ah = 39.1Ah based on the 46Ah usable capacity. This seems more believable.

All the same, great find, thanks. Beggars can't be choosers. :twisted: I'll drop them an email with some questions to see what sort of response I get.

i'm sure you are motivated to swap some cells out, especially after reading of Rupert's experience to drop the pack, etc.

Yes that's it exactly. I've been wanting to do a cell swap since last year but a combination of the cells initially found not being up to standard and not having access to a 2 post hoist put me off as realistically I couldn't see how I could get access to remove the pack without a lot of hassle and expense by paying for hoist access at a local garage - definitely a last resort situation for me.

But if I can do it at my leisure at home using the threaded rod approach to get it in and out over a weekend (or more if needed) at relatively low cost then it suddenly becomes quite feasible. And after all the pictures Rupert has posted and the confirmation of your cell layout I feel confident in being able to identify the correct cells, which was one of my original concerns...

 

[jray3]

Did the fault code prevent the car driving or charging or was it only a warning ?

The HV lamp was just a warning, no problem driving or restarting the car.


Rupert's technique for lowering the battery via threaded M12 rods replacing four of the large mounting bolts is excellent! It is found in entries #44 and #50 of the following thread. https://www.speakev.com/threads/c-zero-battery-pack-repair.137750/page-3
The only modification to the technique that I plan is a pair of M12 2 nuts locked against each other at the bottom of the 40 cm long rod in order to hold a second wrench and prevent the rod from backing out of it's weldnut in the car body, and also to turn it tightly into position in the first place This makes the stud into a bolt with a removeable head! Probably unnecessary, but I wouldn't want to be merrily lowering the battery only to have it fall.....