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 Post subject: Cell voltages during discharge - Log data wanted
PostPosted: Mon Jul 22, 2019 11:29 pm 
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Joined: Sun Mar 20, 2016 10:16 pm
Posts: 23
Location: Port Macquarie
Hi all, I have been following along with the battery degradation discussions and was curious of the battery voltage during discharge. I was recently in cold weather and the engine didn't start properly, on the short drive to the petrol station I lost significant power but unfortunately wasn't logging. From another thread it looks like an improper recall, when I restarted the car the engine ran fine for the rest of the trip.

I have a discharge curve from an iMiev to compare to, allowing me to estimate the real capacity for my own car. The discharge curve compares well to the iMiev but I would like to get a few different battery logs to compare.

To log I used PHEV Watchdog and ticked both Logging Settings with an interval of 1 second.

It would be great if a few people could send me a log of a full discharge where occasionally they coasted in B0 for 5 seconds or so. I would especially be interested in a PHEV that has recently had a battery replacement to get a baseline of a perfect condition battery. If anyone is considering performing the new Lindqvist method or a dealer reset a log before and after would also be interesting. I haven't done it yet but I may use the fuel pump fuse trick to get a low SoC reading.

Be aware it may log GPS data, if you want more privacy just untick the GPS option before logging and PMing the file.

I have attached the comparison graph from my single log, for reference my car is showing 29.7Ah and has done 61,000km and 3.6L/100km


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 Post subject: Re: Cell voltages during discharge - Log data wanted
PostPosted: Tue Jul 23, 2019 2:42 am 
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Joined: Mon Sep 26, 2016 11:18 pm
Posts: 1135
Location: Poland
Discharge curve is very specific to:
- Temperature
- Load

In winter on a highway you might expect to see even 3.3v at 50% SOC

In summer on moderate usage, and after some regen .. 4.0v can be seen at same SOC

I don't see how you can use this information

Only valid information is Voltage per BMU SOC, after 2H rest .. but then you can see the BMU Voltage to SOC mapping curve per the BMU EEPROM


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 Post subject: Re: Cell voltages during discharge - Log data wanted
PostPosted: Tue Jul 23, 2019 3:02 am 
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Joined: Sun Mar 20, 2016 10:16 pm
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Location: Port Macquarie
Thanks elm70 for the feedback. I agree to both of those points and to minimise it I have done the following.

Load - I am only taking lightly loaded data points (coasting in B0). When you start coasting the voltage bounces back quickly then slowly increases from there. I am using a lightly loaded discharge curve from an iMiev so voltage should be closer to my sample data then a 2 hour rest.

Temperature - while loaded the voltage will sag more at lower temperature, but recovers similarly at light load. I expect the B0 coast voltage would recover to a reasonable value quickly but if it stays too low it can be identified through the battery temperature information in the log. While driving in EV mode the battery should warm up as well, though I haven't seen by how much in really low ambient temperatures.

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 Post subject: Re: Cell voltages during discharge - Log data wanted
PostPosted: Tue Jul 23, 2019 4:22 am 
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ScottyDont wrote:
Thanks elm70 for the feedback. I agree to both of those points and to minimise it I have done the following.

Load - I am only taking lightly loaded data points (coasting in B0). When you start coasting the voltage bounces back quickly then slowly increases from there. I am using a lightly loaded discharge curve from an iMiev so voltage should be closer to my sample data then a 2 hour rest.

Temperature - while loaded the voltage will sag more at lower temperature, but recovers similarly at light load. I expect the B0 coast voltage would recover to a reasonable value quickly but if it stays too low it can be identified through the battery temperature information in the log. While driving in EV mode the battery should warm up as well, though I haven't seen by how much in really low ambient temperatures.


I don't think you can even be accurate in this way

When voltage get depressed, due to high load and eventually low temperature, it can take hours before the voltage bounce back to the proper unload value .. this is why the BMU take care of the 2h rest before update the SOC after usage.

If you want a more consistent result ... we should make a log of the charging process, eventually after over 2h rest ... and ideally with warm temperature

But, this will require hours of logs ... something that only Anko was doing with his extra OBD2 equipment on the PHEV


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 Post subject: Re: Cell voltages during discharge - Log data wanted
PostPosted: Tue Jul 23, 2019 5:48 am 
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Joined: Fri Jul 05, 2019 7:35 pm
Posts: 112
Location: Aussie Land
I agree with elm70 that logging while driving is extremely variable and difficult to make conclusions.

I can not find original discharge curves for this battery to compare the voltages and DoD. SoC is not a useful parameter for these graphs as we need to see the voltage after how much energy we removed and not how much we might expect.

You might have noticed this link I posted in the Lyndqvist thread.
https://www.gs-yuasa.com/en/technic/vol ... 01_026.pdf

In that report there are discharge charts for the LEV50 under different conditions, like load and temperature and it is reasonable to assume that the LEV40 follows very similar patterns.
In one chart you will see a graph for a 0.2C load. I put the selector in drive with handbrake on and switch on the headlights and wait a minute for the voltage to stabilise. This should give you roughly the 0.2C reading to compare with the chart. Probably good to print out the chart larger and draw in some lines to get more accurate readings.

It is interesting that your car's degradation is almost identical to mine. Despite that being rather disappointing I am starting to believe that 29Ah SoH after 60,000 is all we can expect from these batteries that are really quite small for the 2 ton vehicle they have to push around when they get fully recharged almost every day.
Maybe 2-3 Ah can be squeezed out from those magic resets with deeper discharge without harm but that is not very much.

Maybe some people who have reported up to 200,000km are long distance drivers where the petrol engine did all the work and the battery relatively rarely got cycled.

What kills batteries fast is daily fully charged overnight up to 4.1V but then used the next day and
strong regenerative charge B5 downhills over a minute each day.
Battery degradation all comes down to how these vehicles have been used.

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 Post subject: Re: Cell voltages during discharge - Log data wanted
PostPosted: Tue Jul 23, 2019 8:42 am 
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When you drive long distance the battery gets recharged all the time by the onboard generator...

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 Post subject: Re: Cell voltages during discharge - Log data wanted
PostPosted: Tue Jul 23, 2019 4:22 pm 
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Joined: Sun Mar 20, 2016 10:16 pm
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Location: Port Macquarie
Thanks both for your input, good to be getting more ideas.

MadTechNutter, I had seen that pdf a while ago and originally used that for my voltages, but went with the iMiev discharge curve as it didn't contain the dip around 20 percent. I reread the document and it really suffers in low temperatures, I don't usually get <0C here so can't check voltage recovery myself. My logs show 11 degree C rise over the full drive, not as much as I expected. I added the curves from this document and could possibly scale voltage based on measured temperatures.

I agree reported SoC is not all that useful, but it allows me to compare different capacity cells, plus I have a scaling factor allowing me to shift the plot up and down as if the reported capacity was different. I have kept it at 1 for the initial attachment as it lined up ok, but my test down to 20% today is showing higher than expected voltages, more in line with what the SoC would be for a 33Ah pack.

I feel km driven is useless without long term fuel consumption, even then it only gives a slightly better picture of how much the battery has worked.

elm70, I wasn't aware you can log charging, I might have a look at that. The voltage at rest isn't what I am comparing, as the LEV50/LEV50N data is all constant discharge not rested values.


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 Post subject: Re: Cell voltages during discharge - Log data wanted
PostPosted: Wed Jul 24, 2019 5:10 am 
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Location: Aussie Land
jaapv wrote:
When you drive long distance the battery gets recharged all the time by the onboard generator...


...but not cycled.

It get charged to a certain level and basically stays there and not drained to 30% and back to 100% every 45km.

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 Post subject: Re: Cell voltages during discharge - Log data wanted
PostPosted: Wed Jul 24, 2019 5:25 am 
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Joined: Fri Jul 05, 2019 7:35 pm
Posts: 112
Location: Aussie Land
ScottyDont wrote:
I agree reported SoC is not all that useful, but it allows me to compare different capacity cells, plus I have a scaling factor allowing me to shift the plot up and down as if the reported capacity was different. I have kept it at 1 for the initial attachment as it lined up ok, but my test down to 20% today is showing higher than expected voltages, more in line with what the SoC would be for a 33Ah pack.



Scotty, I don't quiet understand what you are doing.
How to you get the discharge values down to 20% ?
Are you driving ? ...or what load are you using?

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Last edited by MadTechNutter on Wed Jul 24, 2019 5:27 am, edited 1 time in total.

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 Post subject: Re: Cell voltages during discharge - Log data wanted
PostPosted: Wed Jul 24, 2019 5:27 am 
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Joined: Mon Sep 26, 2016 11:18 pm
Posts: 1135
Location: Poland
MadTechNutter wrote:
jaapv wrote:
When you drive long distance the battery gets recharged all the time by the onboard generator...


...but not cycled.

It get charged to a certain level and basically stays there and not drained to 30% and back to 100% every 45km.


No it is cycled.

It get charged up to 33/35% SOC and discharged down to 30%

At high speed the ICE will never stop, but still it charge and discharge the battery around the 30% SOC

Even at high speed, still it is needed the main battery for power the eMotor for reduce the drag, plus there is the 12v system that consume power and need to be charged by the main battery ... so the main battery it is all time used, and need to be charged all the time, unless the car run in pure EV mode


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