ZuinigeRijder
Posts: 110
Joined: Thu Dec 31, 2015 3:59 am

Re: Battery Calibration

Mon Mar 07, 2016 11:19 am

I also did an experiment, because my battery deterioration values were rather constant the last month. And I suspected this was the case, because I always charged to 100%.

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Max Det   Min Det   Max Cell   Min Cell
11.6   10.0   3   15
11.1   9.6      
13.4   11.1   43   51
10.2   8.2      
10   8.4      
10.4   8.4      


The last value above was almost a month constant.
Last week I just charged for 3 days to 80%. And guess, what happened? The battery deterioration got worse.

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11.6   10.4   3   8


Today I charged again to 100% after the remaining battery was 17%. After the 100% charge (3.7 kW charger) the values did improve again

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11.1   9.6   3   83


The battery calibration seems only to work when charging till 100%. Most people do not see deterioration in the winter, because probably most people charge to 100% for better range.

In general it is better to have the battery not fully charged, best is to have a 50% SOC. But apparently the calibration only works above 80%, so this has a negative effect. Conclusion seems to be that it is better to full charge, with 100% charged just before you leave.

Elmil
Posts: 142
Joined: Mon Oct 26, 2015 9:46 am
Location: Sweden

Re: Battery Calibration

Mon Mar 07, 2016 1:09 pm

ZuinigeRijder wrote:In general it is better to have the battery not fully charged, best is to have a 50% SOC. But apparently the calibration only works above 80%, so this has a negative effect. Conclusion seems to be that it is better to full charge, with 100% charged just before you leave.
The same feeling as I have had about this. And from my data logs I can tell, with reasonable confidence, that the calibration is done at around 92% SOC. It did every time the deterioration values changed for me.
Actually, with the relatively high frequency the deterioration values seem to be changing, both upwards and downwards, they might be better called 'Calibration Factors' or something like that... But we still don't know exactly what they do.
We need a BMS snapshot from someone who has got a GDS/KDS printout with SOH less than 100%. If noone's there yet, at least I'm having 2:nd service in next month (30000km) and would be rather surprised if it's still at 100%.
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JejuSoul
Posts: 1419
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Location: Jeju
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Re: Battery Calibration

Wed Mar 09, 2016 6:57 am

ZuinigeRijder wrote:In general it is better to have the battery not fully charged, best is to have a 50% SOC. But apparently the calibration only works above 80%, so this has a negative effect. Conclusion seems to be that it is better to full charge, with 100% charged just before you leave.

Splitting these ideas -
1/ "...In general it is better to have the battery not fully charged, best is to have a 50% SOC..." Yes. Somewhere between 80% and 20% is best.
2/ "...the calibration only works above 80%..." Yes.
3/ "... so this has a negative effect." Mostly No. Battery calibration is entirely neutral as regards the battery. All it does is adjust the BMS SOH data so that the GOM has a better estimate of the range. Calibration can be up or down. The battery does not care what the GOM says. The battery goes as far as its electrical capacity allows. If the driver ignores the GOM and drives the car as usual battery calibration is irrelevant. Similarly the deterioration numbers that the BMS provides are less important than the actual distances the car drives.
4/ "...Conclusion seems to be that it is better to full charge, with 100% charged just before you leave..."Mostly Yes. If you want or need to charge to 100% then it is best that the charging finishes just before you leave. But this has little to do with calibration.

From the Battery University Page about Calibration.
For a calibration to occur this needs to happen.
Image
I normally charge my car up to 80% when it gets down to 30%. The lowest I have ever gone is 15%.
Over the last six months I have had two large jumps up in the deterioration numbers.
The first came after a 100% charge the second did not.
Hence there are other reasons for the deterioration numbers to leap about.
I intend to do a calibration check in the next week or so. Will post again then.

Update: 12th April - I did a calibration check last week
Deterioration values did reset. min det reduced from 6.8% to 5.5% at just above 4.08V (some cells were showing 4.10V) It was at 92% SOC, Battery pack =393V
The numbers changed at 100% SOC as well. Perhaps a cell balancing effect. It is the change at 4.08V 92% SOC that I would like to call the calibration effect.
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JejuSoul
Posts: 1419
Joined: Wed Jul 08, 2015 6:47 am
Location: Jeju
Contact: Website

Re: Battery Calibration

Sat Jul 09, 2016 8:00 pm

-
Here's an interesting comment from the MyNissanL eaf forum that I think is relevant to our discussion on battery calibration.

RegGuheert wrote:Here's my take:
- Capacity, as reported by the instrumentation in the L EAF, is DISCHARGE capacity at a particular discharge rate. This is the capacity which matters when trying to drive a particular distance.
- The discharge rate at which the L EAF estimates remaining capacity is likely rather high: probably a C rate (1-hour discharge).
- The PRIMARY degradation that has occurred in our batteries over time is an increase in the RESISTANCE of the battery. I will guess that the resistance of our batteries has approximately doubled from about 60 mOhms to around 120 mOhms, maybe much more.
- The resistance of some cells increases faster than other cells. This makes it harder for the battery management system (BMS) to keep the cells balanced.
- The L EAF's instrumentation ultimately bases ALL of its estimates of SOC on battery voltages.
- The L EAF's instrumentation seldom has the opportunity to measure the battery voltage under no-load (zero current) conditions. Instead, it mostly measures the battery while it is either discharging OR charging.

The practical result of all of the above is this:
- Our batteries are ABSOLUTELY degraded. They are NOT the same as they were when they were new.
- In normal use, our batteries will typically charge to a lower SOC than they did when they were new and the SOC will drop rapidly when we start driving the car.
- LBW and VLBW occur at significantly higher SOCs than when the vehicle was new. It has been reported that LBW occurred at 17.8% SOC when our cars were new, but I now see it at about 26% SOC. This is quite a bit more of an increase than one would expect from losing 22% of the battery's capacity.
- Under "normal" charging and driving conditions (60 MPH) we likely can only go about 78% as far from full to LBW as we could when the car was new. (Tony Williams has done extensive testing that bears this out.)
- BUT, if we can manage to get the battery well-balanced and charged to a very high SOC AND we drive slowly AND we use L eafSpy to know what the actual SOC is, we can still drive almost as far as we could when the car was new under similar circumstances. But this is only true IN WARM WEATHER.
- Unfortunately, in cold weather (below about 30F), the effects of the degradation are felt much more strongly, even if you try to use all the tricks I have mentioned. This is due to a further multiple increase in the resistance of the battery AND the need to run the heater and/or the defroster in those conditions.

Note that none of what I have discussed above will affect what the instruments in the dash display. You won't see capacity bars return or anything like that.

Now for some notes on charging to a high SOC and achieving a good balance:
- You need to charge to full multiple times over the course of a few days if you want to be able to fully charge the battery.
- If you want to charge to a high SOC in a MY2011/2012 L EAF, you need to charge more slowly at the end of the charge (last hour or more). Here are some ways to do this: A) turn on the air conditioner while charging, B) charge at L1 rates (120V) or C) do both. (If you have a 2014(?) or later EV SEUpgrade, you may have the option to control the charging rate using that, as well.)

The bottom line seems to be that increases in resistance of the L EAF's battery are the most significant form of degradation for many of our vehicles, which means that more of the capacity remains than the instruments let on. The trick is in accessing that capacity when you really need it.

From : LeafSpy reporting only 15.6 kWh after charging 100%?

-
Last edited by JejuSoul on Tue May 29, 2018 9:18 am, edited 1 time in total.
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Elmil
Posts: 142
Joined: Mon Oct 26, 2015 9:46 am
Location: Sweden

Re: Battery Calibration

Wed Jul 13, 2016 9:32 am

Yesterday and today I made a range check, to compare with a similar trip a year ago, although last summer I didn't have the nice Soul Spy stuff. :)

Code: Select all

[km]       July -15  July -16
Odometer    7379     38936
Distance    222.2    212.2
SOC Remain    4%       2.0% user/3.5% battery
kWh/100km    11.6     11.8
Avg speed   45km/h    45km/h
Still reach NEDC 8-) but more interesting is that I let the car run flat when parked at home, so now I have real world measurements of the total available energy capacity!

Rated Discharge Amperage: 75 Ah. Now 73.0 Ah (97%)
Rated Discharge Energy : 27 kWh. Now 25.9 kWh (96%)

The car is charging right now, will do 100% and I'll get back with the new deterioration values.

Edit: As expected, the deterioration values improved, they jumped back from 10.6%/9.6% to 8.5%/7.5%.
The DTE at 100% also improved from 164 km to 170 km.
Charging from 0 to 100% added 74.4 Ah / 26.8 kWh to the battery.

When the car turned itself off, the user SOC was 1.0% and went immediately to 0.0%, while the battery SOC just stepped down from 2.5% to 2.0%. The reverse happened when charging started, user SOC went to 1.0% and battery SOC to 2.5%.
Also, at the off state the 12V system was still fully operating (incl the headlights), and a message was displayed on the NAV screen: The vehicle cannot be started. Connect the charging cable.
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JejuSoul
Posts: 1419
Joined: Wed Jul 08, 2015 6:47 am
Location: Jeju
Contact: Website

Re: Battery Calibration

Fri Sep 09, 2016 5:54 am

For 3 hot summer months I have been charging my car from 20% up to only 50%.
The deterioration counters have been static. Max 8.5%, Min 3.6%

Today I just finished a battery calibration.
On 5th September I charged to 100%.
After this charge the deterioration counters dropped to. Max 8.0%, Min 1.5%

On 9th September I charged from 9% to 100%.
After this charge the deterioration counters also dropped to. Max 7.5%, Min 1.5%
( Annoyingly the battery on my android tablet failed when the car got to 94% SOC 4.10V - so I cannot tell when calibration occurred.
It happened after this.)

The data for the charging session:
The DTE at 100% improved from 178 km to 197 km.
Charging from 9% to 100% added 67.3 Ah / 24.6 kWh to the battery.
Equivalent to 74Ah and 27kWh for a 100% charge.
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Elmil
Posts: 142
Joined: Mon Oct 26, 2015 9:46 am
Location: Sweden

Re: Battery Calibration

Sat Sep 17, 2016 5:14 am

JejuSoul wrote:( Annoyingly the battery on my android tablet failed when the car got to 94% SOC 4.10V - so I cannot tell when calibration occurred.
It happened after this.)
Calibration after 94% is different to what I see in my car. I always have the calibration at 392.5 +/-0.1V battery voltage, 4.08V (0xCC) cell voltage and 91.5-92.5% SOC.

I use the 2.0kW EVSE that came with the car, if you charge using more power perhaps that is the difference.
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slobodanc
Posts: 74
Joined: Thu May 19, 2016 10:57 am

Re: Battery Calibration

Wed Sep 21, 2016 5:00 am

Excellent article Jeju. Here is an example of extensive cell testing showing different energy provided at different power levels:

http://www.candlepowerforums.com/vb/showthread.php?423413-Test-review-of-AW-17500-1100mAh-(Black)-2016

This is just an example of LiIon cell chemistry (Soul EV is different chemistry but should behave in a very similar way). In particular discharge energy chart:

0.2A = 4.2 Wh (approximate from reading chart)
3A = 3.7 Wh

So at 2.7C in this test we get 12% less energy
(again these are approximate from chart)

In summer easy driving will pull around 13 kW which is 0.43C so we get almost max energy output. In winter if you start pulling say 20 kW (snow/wind increased resistance, heating, etc.) now it is 0.7C
Keep in mind during acceleration we pull 1C - 2C

This is another reason (besides increased air resistance at higher speed) why range drops at higher speeds.

Back to balancing,

From the LiIon forums indeed there are discussions about individual cells going out of balance in a pack, especially 4+ cell flashlights. Couple of factors to consider:

- high quality cells (example Eneloop) will have a very consistent performance and will be less out of balance
- new cells will be more consistent, less out of balance
- best way to balance is a slow charge

Here is my interpretation of the best rules to follow based on these factors and stuff I read on forums:

1) for a new pack/car (less than 50K) cells should remain fairly balanced most of the time
2) for older packs (over 80K) increased internal resistance differences for different cells will cause more balancing issues more often
3) so new pack needs less frequent balancing, older more frequent balancing

To balance as pointed above:

Repeat 2-4 times:
1) Level 2 to 90%
2) Level 1 from 90% to 100%

Important point is that you don't need to worry about balancing too much until your car is older, especially when not going below 30% SOC. Even if a particular cell is lower than others at 30% SOC it means it may be 25% or 20% or even 15% which is still fine.

Thanks for the reminder when Level 1 is still useful as other posts were talking about Level 1 being useless and wasteful.

JejuSoul
Posts: 1419
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Location: Jeju
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Re: Battery Calibration

Sun Oct 02, 2016 8:51 pm

slobodanc wrote:Thanks for the reminder when Level 1 is still useful as other posts were talking about Level 1 being useless and wasteful.

I now have a Level 1 trickle ch arger. I decided it was worth having after my camping trip in an I oniq EV.
It's a Delphi made for the i 3. I won it in a raffle.
I will test this at a future date to see if works better for calibration / balancing than L2.

It is less efficient ~85% for the L2 and ~70% for the L1.

Image

Image
Last edited by JejuSoul on Tue May 29, 2018 9:22 am, edited 1 time in total.
The codes for using Torque Pro can be found by clicking the link in the website icon under my user name on the left.

SoulEV2016
Posts: 572
Joined: Mon Jul 18, 2016 6:26 am

Re: Battery Calibration

Mon Oct 03, 2016 9:47 am

good test.

i have already increase the power of my EVSE charger to see if deterioration is linked to the power of the BMS balancer capacity (but, in first objectif to confirm or not the raise of the efficiently of onboard charger).

i do this after the first 5000km at 1,1kW (154 charges).
now, i am at 2,2kW.

and deterioration have raising since this change ... :lol:
and consumption at the grid is very erratic, too ... :?

this aspect indicate that the BMS have, really, a strategy to use the balancer power capacity from charge to charge or to monitor a charge (no balancer used) and do somes corrections on the following charge (result : erratic consumption at the grid) but only on specifics cells (temperature saturation over the balancer power capacity).

This aspect is very hard to monitor.

But, over many charges, i can see this (that's why i only change setting after more than 150 charges).
Kia Soul EV 2016 Ultimate 27 kWh - Mountain hard driving (fast). Drain 1/3 of Battery after 32km. - Unlimited highway speed (153km/h at regulator).

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