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Re: Is my battery dying ?

Posted: Thu Apr 18, 2019 2:45 pm
by 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).

Re: Is my battery dying ?

Posted: Wed May 15, 2019 5:27 am
by DBMandrake
Gary12345 wrote: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- ... ir.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...

Re: Is my battery dying ?

Posted: Fri May 17, 2019 4:17 am
by 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.

Re: Is my battery dying ?

Posted: Tue May 21, 2019 7:34 am
by DBMandrake
In the last few days I reset the BMS in my car, as described in the following thread:

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:

Image

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:

Image

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:

Image

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:

Image

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%:

Image

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:

Image

And now today:

Image

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:

Image
Image

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...

Re: Is my battery dying ?

Posted: Thu May 30, 2019 2:22 pm
by 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.

Re: Is my battery dying ?

Posted: Sat Jun 01, 2019 4:37 am
by DBMandrake
jray3 wrote: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/on ... 000ENG.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.

Re: Is my battery dying ?

Posted: Tue Jun 04, 2019 2:44 am
by 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 ? :D

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...

Re: Is my battery dying ?

Posted: Tue Jun 04, 2019 4:21 am
by 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

Re: Is my battery dying ?

Posted: Tue Jun 04, 2019 5:00 am
by DBMandrake
kiev wrote: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...

Re: Is my battery dying ?

Posted: Tue Jun 04, 2019 9:53 pm
by jray3
[quote="DBMandrake"]
Did the fault code prevent the car driving or charging or was it only a warning ?
[quote]
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.....