kiev
Posts: 815
Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

Re: Is my battery dying ?

Tue Apr 17, 2018 6:25 am

That's interesting test data, thanks for sharing.

From what little data we can find on the cells, 4.2 V is 100% and they consider drained to 0% at 2.75 V when making cell meaurements at Yuasa.

We don't really know how the car measures and reports battery capacity versus the yuasa procedure, and there are many variables such as discharge rate and temperature to consider in that calculation.

For some reason 25 and 70 are your weaker cells and hopefully they come back up with all the rest after charging and balancing.
kiev = kenny's innovative electric vehicle

DBMandrake
Posts: 84
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Is my battery dying ?

Tue Apr 17, 2018 6:41 am

kiev wrote:From what little data we can find on the cells, 4.2 V is 100% and they consider drained to 0% at 2.75 V when making cell meaurements at Yuasa.

That's what I've thought for a long time as well but I happened on this technical article from Yuasa just today that seems to imply that the 50Ah capacity is measurable from 4.1v to 2.75v not from 4.2v to 2.75v as we first thought. That extra 0.1v makes quite a difference at the top, as it represents nearly 10% of the cells capacity:

https://www.gs-yuasa.com/en/technic/vol ... _1_021.pdf

Note in particular figures 2 and 3 which explicitly say discharging from 4.1v to 2.75v and if you look at the graph they're hitting 50Ah at warmer temperatures and lighter loads. (10A)

In fact there is no mention of 4.2v anywhere in the article.
We don't really know how the car measures and reports battery capacity versus the yuasa procedure, and there are many variables such as discharge rate and temperature to consider in that calculation.

Indeed. The discharge to 0% SOC was partly to try to figure these things out.

I now know for example that the turtle came on at almost exactly 10% SoC, (dashed lines for RR was about 12.5% but I forgot to note it exactly) which based on a usable battery capacity of about 12kWh after degradation to 36Ah is a good 6 miles or so of careful driving at 30mph assuming 6 miles/kWh. (which I seem to be getting at 30mph according to Canion)

This ties in with my one on-road encounter with the turtle where I was forced to creep nearly 5 miles in turtle mode at 20mph and made it to the charger without running out after strongly doubting it would go that far.

Also it looks like the pack shuts down at exactly 320 volts total pack voltage even though the lowest cell was still at a very safe 3.56 volts, certainly a long way above the minimum 2.75v specified in the Yuasa document. So whilst repeatedly discharging this deeply is not a good idea of course, the voltage is not low enough to do any real damage to the cells during a single deep discharge.

I presume as well as a 320 volt cutoff it would also cut off if any individual cell got below a certain, lower threshold, although I don't know what that lower threshold might be and I'm not planning to find out!

3.5v is on the "knee" of the discharge curve at a 10A rate on figure 2, it looks like there is only about 5-10% of raw capacity left between 3.5v and 2.75v so I guess they just decided to stay away from that very low voltage range or keep it as a buffer so that the loaded cell voltage when accelerating stays above 2.75v.
For some reason 25 and 70 are your weaker cells and hopefully they come back up with all the rest after charging and balancing.

They are well balanced in the top half of the SoC range, so I think it's a relatively minor imbalance - the voltage drops very quickly in the lowest 20% SoC so any minor variations between the cells will be greatly magnified at such a low SoC. In fact at 71% the two cells in question show a higher voltage than the others.

So while there is an imbalance it's only visible at relatively low SoC and doesn't look like anything serious, certainly nothing like what I have seen in other posts here... Phew!
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

Phximiev
Posts: 1187
Joined: Thu Jan 15, 2015 7:25 pm
Location: Phoenix

Re: Is my battery dying ?

Tue Apr 17, 2018 8:33 am

See this topic and links therein also: viewtopic.php?f=5&t=3782&p=33402&hilit=yuasa#p33402
2012 iMIEV ES
2014 Chevy Volt

phb10186
Posts: 290
Joined: Fri May 13, 2016 12:58 am
Location: North London suburbs, UK

Re: Is my battery dying ?

Tue Apr 17, 2018 2:22 pm

I dont disagree with the data, but seems unlikely that two cells would weaken at the same time... though I do understand your concerns. I would want to do the cell balancing procedure and repeat this test a couple more times and keep an eye on those two cells.

I checked my 2012 car recently at 100% over a fairly cold month, and was at 42.3 at 100% SOC with 17K on the clock... so it sort of tallies.

Only other thing to say is that if the X axis on your initial chart began at 0, then the recent degradation wouldnt look anything like as pronounced, as we are looking at a heavily truncated axis..

How did you get the car down to 0% SOC... was this by using the heater to drain it out... if you did do that, I wonder if that could have put a large drain at a low SOC to begin with and resulted in the data you see. Certainly a a few balancing cycles and steady discharges may help to identify how repeatable this all is.

Other forum users have reported rapid SOC degradation and RR going to a few bars after about 25 miles or so, with a very significant SOC drop on a single cell, which doesnt seem to be the case here.

I assume your charging practices are fairly typical?

Ben
2012 I-MIEV Keiko Silver 16K
2010 Insight ES-T 43K
2001 Accord Type-V (F23 manual)
2009 Hornet CB600F
2008 SH300

DBMandrake
Posts: 84
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Is my battery dying ?

Wed Apr 18, 2018 3:53 am

Phximiev wrote:See this topic and links therein also: http://www.myimiev.com/forum/viewtopic. ... asa#p33402

I read that thread but I'm not sure what part of it you're drawing my attention to or how it relates to my problem ?
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

DBMandrake
Posts: 84
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Is my battery dying ?

Wed Apr 18, 2018 4:19 am

phb10186 wrote:I dont disagree with the data, but seems unlikely that two cells would weaken at the same time... though I do understand your concerns. I would want to do the cell balancing procedure and repeat this test a couple more times and keep an eye on those two cells.

What "cell balancing procedure" are you referring to ? The car gets a 100% Level 2 charge each night, so the cells are always balanced every morning. I've heard of a cell balancing maintenance procedure in the MUT tester (which I assume is used to get initially very out of balance cells back into balance for example after a single cell replacement) however I couldn't find any equivalent action in PSA's Diagbox.
I checked my 2012 car recently at 100% over a fairly cold month, and was at 42.3 at 100% SOC with 17K on the clock... so it sort of tallies.

Only other thing to say is that if the X axis on your initial chart began at 0, then the recent degradation wouldnt look anything like as pronounced, as we are looking at a heavily truncated axis..

The auto scaling axis is on purpose - I would never be able to see any small variations between summer and winter degradation if the Y axis went all the way to 0. In relation to the previous results I don't think it's misleading.
How did you get the car down to 0% SOC... was this by using the heater to drain it out... if you did do that, I wonder if that could have put a large drain at a low SOC to begin with and resulted in the data you see.

You can't use the heater to get down to 0% SoC. Both the heater and AC are disabled as soon as turtle mode activates at 10%. So I left it in gear with the hand brake on so that the motor is producing a small amount of creep torque. Total power consumption during this according to Canion is about 1.2kW, of which 0.3kW is fixed overheads even with the car in neutral. It took a long time (a couple of hours) to discharge the last 10%. So this is a relatively light discharge compared to the 5kW peak of the heater.
Certainly a a few balancing cycles and steady discharges may help to identify how repeatable this all is.

As mentioned, the car charges to 100% every night so starts the day perfectly balance. (Confirmed by Canion)

I took some further measurements yesterday and the trend looks the same - above about 50% there is no apparent imbalance, by the time you get down to 30% or so cells 25 and 70 are slightly lower but I think it might just be normal manufacturing tolerance variations, for all I know these two might have been slightly weaker from new. But it is consistent day to day:

Image

Image

Image

The RR figure is still unusually low on a full charge - 53 miles this morning compared to 67 after a 12v battery disconnect, but I think that's because I drove like I stole in the day before to run the battery down to 10% quickly for the purposes of testing the low end discharge.

The GOM seems to take a long time to "forgive" you after doing that, and remains very pessimistic for days, even though my consumption since then has been conservative.

I did a few sums today based on my morning drive to work, using Canion figures.

No heater use, 17.3 miles over 41:38 minutes driving, average speed 25mph, (mixed 30mph and 50-60mph motorway) my average Miles/kWh was 5.2 (higher than I expected) with 18% Wh regen, and I arrived with SoC at 75%.

By simply multiplying the distance by 4 I get 69.2 miles which at that consumption rate I could theoretically do from 100% to dead. Of course I wouldn't want to go into turtle mode, which starts at 10% so if we take off 10% we get 62.3 miles range from 100% charge to turtle mode at 5.2 miles/kWh.

Average battery voltage over most of the journey is about 340 volts, times 36.1Ah gives 12.3kWh usable, at 5.2 miles/kWh that is 63.8 miles, so I guess it all tallies up, with the 100% charge RR estimation being based on discharging only until the beginning of turtle mode or about 10%. (Or perhaps until the range figure disappears which is about 12.5%)

So I perhaps don't have anything to worry about if it doesn't degrade significantly further in the next few months. I still have 14 months of battery warranty left so you can bet I'll be keeping an eye on this.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

JoeS
Site Moderator
Posts: 3584
Joined: Thu Dec 15, 2011 5:47 am
Location: Los Altos Hills, California

Re: Is my battery dying ?

Wed Apr 18, 2018 8:35 am

DBMandrake, thank you for posting those images and analyses, and thanks for stress-testing your battery in the interest of science. My impression is that your battery is just fine and does not exhibit the dramatic individual cell failure which some of us have experienced (and which was cause for battery replacement by Mitsubishi).

Yes, balancing is merely charging to 100% and letting the system hold its course until it stops charging. Recognizing that the individual cell balancing current is very low, on the Australian forum, IIRC, one owner's repeated such charging brought back a recalcitrant pack.

For myself, I've never seen turtle and keep the pack between four bars and twelve bars, only charging to 100% (and allowing it to 'balance') just before the occasional long trip. My hope is that such behavior will result in a long-lived pack.

Incidentally the "GOM" (Guess-O-Meter) expression common on the Leaf forum does not apply to our i-MiEV: our RR (Range Remaining) is very predictable and is a simple algorithm which is a moving average of the car's consumption in the preceding 15 miles (24km). Even though the RR is offset by, for example, 20% whenever the heater is turned on, as best we can tell this does not factor into the RR past consumption equation. It is predictable because we know the type of terrain, wind, and type of driving we had experienced and can mentally compensate for any changes in these conditions.

The last thing to stress is that whenever we talk about energy consumption we must distinguish between wall-to-wheels (which some of us had laboriously calculated) and battery-to-wheels which many cars show on their dashboard and we have see on CaniOn. My personal figure-of-merit (efficiency target) for the i-MiEV is 100Wh/km as shown on CaniOn, but I use the wall-to-wheels number of 4.2mi/KWh (meticulously measured over 8000miles) for any calculations.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

DBMandrake
Posts: 84
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Is my battery dying ?

Wed Apr 18, 2018 8:58 am

JoeS wrote:DBMandrake, thank you for posting those images and analyses, and thanks for stress-testing your battery in the interest of science. My impression is that your battery is just fine and does not exhibit the dramatic individual cell failure which some of us have experienced (and which was cause for battery replacement by Mitsubishi).

I think you're right - at least at this point there is no obvious individual cell failure. I guess I just have to come to terms with the likelihood that the battery has been 36.1Ah for some time, perhaps even since before I bought the car but the BMS has been providing a "predicted" figure with a predicted linear degradation providing figures which were considerably higher than the "true" state of the battery, which was not revealed until a full calibration was run. Perhaps this diagnostic tool calibration should be run once a year to ensure the true state of the battery is known and that we're not buying into the BMS's delusion...

I won't know for sure until summer but I suspect that my full charge no heater range will be fairly similar to last summer. Fingers crossed.
Incidentally the "GOM" (Guess-O-Meter) expression common on the Leaf forum does not apply to our i-MiEV: our RR (Range Remaining) is very predictable and is a simple algorithm which is a moving average of the car's consumption in the preceding 15 miles (24km). Even though the RR is offset by, for example, 20% whenever the heater is turned on, as best we can tell this does not factor into the RR past consumption equation. It is predictable because we know the type of terrain, wind, and type of driving we had experienced and can mentally compensate for any changes in these conditions.

If only it were that simple... :twisted:

Yes, the consumption caused by the heater and AC is added on "afterwards" and does not factor into the miles/kWh average that it uses to calculate the base figure (at least as far as I can tell) and yes, while driving it does appear to average your miles/kWh consumption over approximately 15 miles. (Although it seems less than that to me, more like 5 miles)

However.... there is something special about the RR reported after completing a 100% charge that is definitely not just the average of the last 15 miles completed before charging.

Because I often get wildly varying RR on full charge from the exact same work commute with about the same actual consumption. (Judged by the number of bars left when getting home being the same)

At the moment I am seeing a full charge RR of only 53 miles, two full days after driving the car fast, and yet over the first 8 miles of driving the figure actually goes up from 54 to 56, indicating the true figure of distance driven plus range remaining is about 62 miles, which would be about right.

And despite maintaining an average consumption to give 62 miles per charge, the next day I will get an underestimated RR at full charge of 52, which will again go up as I drive.

Conversely I often see a RR on full charge of between 75 and 84 (!) miles despite following the exact same driving pattern, in this case the RR drops rapidly over the first 5-10 miles of driving.

So in my experience the RR figure after completing a full charge is highly unstable and untrustworthy, with figures anywhere from about 50 miles to 84 miles with pretty much identical driving. Only after I have done about 10 miles will I start to trust the RR figure and by the time the battery is down to below 50% it is very accurate.

What's going on to cause this ? I'm not sure. But one thing I'm certain about is it's not just using the average of the last 15 miles driving before charging. It's simply not possible for it to give these kind of figures with my regular commute. I'm still trying to find a correlation to explain where it gets its bizarre full charge RR figures from.
The last thing to stress is that whenever we talk about energy consumption we must distinguish between wall-to-wheels (which some of us had laboriously calculated) and battery-to-wheels which many cars show on their dashboard and we have see on CaniOn. My personal figure-of-merit (efficiency target) for the i-MiEV is 100Wh/km as shown on CaniOn, but I use the wall-to-wheels number of 4.2mi/KWh (meticulously measured over 8000miles) for any calculations.

Yep, I'm well aware of the difference between wall to wheel and battery to wheel.

Prior to getting Canion all my readings were wall to wheel, and that is what matters for working out charging costs and times.

However battery to wheel is what counts for working out driveable range from battery capacity, hence using those figures for the recent calculations.

However to get from 5.3 miles/kWh battery to wheel to 4.2 miles/kWh wall to wheel would imply a charging efficiency of only 80%, which seems a bit on the low side to me. I have a DIN kWh meter in my charge point so I could do a direct comparison between I charge at the wall to the reported figure on Canion to estimate the charging efficiency.


However I think Canion's estimation of current and power at very low powers (like when stationary) is significantly out.

For example it tells me that there is 0.3kW being used from the traction battery when the key is turned on but the car is not in READY mode - which is completely impossible as the contactors are open in this state isolating the battery from the rest of the car! So something is not right with the low power measurements provided by Canion. :lol:
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

JoeS
Site Moderator
Posts: 3584
Joined: Thu Dec 15, 2011 5:47 am
Location: Los Altos Hills, California

Re: Is my battery dying ?

Wed Apr 18, 2018 10:30 am

DBMandrake, I think we're on the same page and perhaps with your permission I might move this efficiency discussion to a separate thread if you wish to continue it - finding these conversations within mis-titled threads in the future is difficult.

My RR always goes up after leaving home: I live up a hill! On the flatlands, especially after a full charge, I can make RR go up or down at will.

The first (16th) bar always takes more driven miles than the rest to drop from 16 to 15. Conversely, at the bottom end, the perception (anxiety-induced?, but unproven) is that the last couple of bars drop faster for miles driven.

I challenge anyone (and I'll put money on it) to predict what their RR will be after their car completes charging! The variability in our driving and our environment is such that I believe this number cannot be precisely predicted. Despite my leadfoot-driving full-charge RR normally in the 50's and 60's, I can still easily achieve a number over 80 after hypermiling.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

phb10186
Posts: 290
Joined: Fri May 13, 2016 12:58 am
Location: North London suburbs, UK

Re: Is my battery dying ?

Wed Apr 18, 2018 2:36 pm

DBMandrake wrote:
phb10186 wrote:I dont disagree with the data, but seems unlikely that two cells would weaken at the same time... though I do understand your concerns. I would want to do the cell balancing procedure and repeat this test a couple more times and keep an eye on those two cells.

What "cell balancing procedure" are you referring to ? The car gets a 100% Level 2 charge each night, so the cells are always balanced every morning.


So - based on the last part of my reply about how you may charge, I would charge from 2-3 bars and leave it overnight until it is fully charged and the charge indicator goes off - and I would cycle the pack a half dozen times in this way. I would also perform a 12v battery pull and leave it for an hour disconnected when you can.

Lastly, just to eliminate any possible incling of 12v battery issues, I would test that as well.
2012 I-MIEV Keiko Silver 16K
2010 Insight ES-T 43K
2001 Accord Type-V (F23 manual)
2009 Hornet CB600F
2008 SH300

Return to “Batteries and Battery Management”