Drive battery degradation and the out of whack IMO BMU.

[anko]

So, tried again. After she arrived home, unfortunately it took about 10 minutes before I could read the data from the car. At that moment it showed 27.9% / 7.3 Ah. I started preheating until the reading was 20.2% / 5.3 Ah. Then I turned off the heater. About three hours later, I checked again. The reading was the same 20.2% / 5.3 Ah.

Is that meaningful data?

 

[elm70]

So, tried again. After she arrived home, unfortunately it took about 10 minutes before I could read the data from the car. At that moment it showed 27.9% / 7.3 Ah. I started preheating until the reading was 20.2% / 5.3 Ah. Then I turned off the heater. About three hours later, I checked again. The reading was the same 20.2% / 5.3 Ah.

Is that meaningful data?

Interesting

So apparently your BMU has a good "guess" about the real SOH and capacity of your battery.

Yesterday I did check twice my car while resting .. after ~2.5h and ~1.5h later on ... the battery was 14.1Ah after the trip .. and while resting it was stated at 14.2Ah after 2.5h ... and then 14.3Ah later on ... I never seen the battery going up twice while resting.

It would be looking good ... winning 0.2Ah while resting .. except for the fact that while parked uncharged the night before the battery was going down 2.5Ah from 19Ah down to 16.5Ah (from 16.5Ah down to 14.1Ah was due to a short drive)

In my case the car had from fully charge 2 trips the day before, and 3 small drive yesterday ... but I did not monitor the first trip, so I can't say if in total I lost Ah while parked or not (monitored is -2.5 + 0.2 .. but I bet I must win 1Ah while parked between the 1st and 2nd trip .. still, possibly, as total I lost over 1Ah .. that means my BMU is optimistic about my battery SOH)

Maybe on the weekend I will try to make a proper 40km experiment ... from fully charge to 0EV range .. and check what my BMU will report after rest ... I bet ... my 34Ah declared SOH, is 1Ah above reality ... so my car has just 33Ah capacity at the moment .. that for an almost 5y old battery it is not too bad.

PS: Why did you use pre-heat at the end of a trip ? Bring the battery down from 27.9% down to 20.2% does not sounds a healthy practice ... but ... maybe I can guess why ... still it is a risk on your side

 

[anko]

PS: Why did you use pre-heat at the end of a trip ? Bring the battery down from 27.9% down to 20.2% does not sounds a healthy practice ... but ... maybe I can guess why ... still it is a risk on your side

As I allowed the battery to cool down for some time, I decided to give it a little load again, before taking first measurement :mrgreen: Don't know if it is a big risk. Seen much lower SOCs while driving. Discharge rate in this case was very modest (4 kW). And if the car was not happy with it, it should not allow it

 

[elm70]

Some data from my side:

Trip 1: 33.5Ah down to 27.2Ah (0.5Ah lost (??) compared to fully charge which was finish 1h30min before start the trip)
Trip 2: 28.4Ah down to 22.3Ah (1.2Ah win while parked for 8h)
Trip 3: 22.3Ah down to 20.8Ah (0 change, but was 10min after 2nd trip end)

While resting in the evening car lost 2.3Ah .. down to 18.5Ah
After the night car lost other 0.3Ah ... down to 18.2Ah

So ... in total +1.2Ah - 2.6Ah ... so car lost 1.4Ah ... while using 13.9Ah

I bet on my next few short trip I need today I will gain 0.1 or 0.2Ah .. so ... ending with ~1.2Ah "lost" ... so ... my battery that is 34Ah per the BMU .. is possibly just 32.7Ah .. with the handicap that I can't use the top 0.5Ah .. since the charging process end too fast, (or immediately after charge car lose 0.5Ah) .... so .... it is more like a 32.2Ah ... that is just 85% SOH real

Next day ... after Trip 4 and rest ... down to 15.4Ah ... so further 0.4Ah lost

So .. initial win 1.2Ah
Later ... Total lost : 3Ah
Balance : Lost 1.8Ah .. used ... 16.3Ah ... over 10% waste while "parked"

EDIT update:
Trip 1: 33.5Ah down to 27.2Ah (0.5Ah lost (??) compared to fully charge which was finish 1h30min before start the trip)
Trip 2: 28.4Ah down to 22.3Ah (1.2Ah win while parked for 8h)
Trip 3: 22.3Ah down to 20.8Ah (0 change, but was 10min after 2nd trip end)
Next Day:
Trip 4: 18.2Ah down to 15.8Ah (2.6Ah lost overnight)

 

[anko]

I read somewhere (Andy related discussion?) that it could have to do with voltage? IIRC, something in the line of:

After a trip, voltage slowly goes up. As kWh cannot change, Ah must come down.
After a rest, voltage slowly goes up. As kWh cannot change, Ah must go up.

No idea whether this makes sense

 

[elm70]

I read somewhere (Andy related discussion?) that it could have to do with voltage? IIRC, something in the line of:

After a trip, voltage slowly goes up. As kWh cannot change, Ah must come down.
After a rest, voltage slowly goes up. As kWh cannot change, Ah must go up.

No idea whether this makes sense

No ... kwh is not equal to a simple Ah x voltage ... since voltage is function of the discharge level ... I don't think car care of kwh ... I'm quite sure it does care only of Ah ... only current can be monitored ... also battery discharge diagram always show how many Ah can be consumed .. but never show how many kwh could be extracted from a battery

Yes ... while driving ... SOC is based on initial SOC minus monitored consumption (or flow, since it can have regen and ICE charge too)

While resting ... after enough rest ... the SOC is adapted based on Voltage

This is the tricky part, since the PHEV/BMU must have a mapping table which map voltage to SOC in % ... absolute SOC based on voltage is due to SOH too ... so ... 3.95v should be 66% of SOH ... so .. assuming 34Ah SOH .. 3.95 should be 22.4Ah (on a 30Ah SOH ... it would be 19.8Ah) .. but this apply if there is a linear relation between 3.8v 30% to 4.1v 100% ... but I believe there is a map in the car in charge for this ... possibly this map get updated while battery smoothing is executed

Definitely the mapping between SOC and voltage ... it is off in my PHEV .. since at some voltage the SOC is over estimated , and at other levels it is underestimated

Error/corrections of 1Ah and 2.6Ah ... are quite massive in my view ... and this can cause big confusion on the EV range shown on the dash

PS: I'm partially surprise to have lost 0.3Ah over night, after a lost of 2.3Ah after many hours of car at rest ... maybe the battery was a bit colder in the morning ... or ... there must be some leak in the BMU ... as well ... was also strange to see at some point over 0.02v of unbalance between cells in the back ... which later on at lower voltage and after rest ... got below 0.005v ... something that I may justify by active balancing while driving and maybe while parking too ...

 

[anko]

I understand I think. Maybe kWh is not the right approach. But altogether, there is a certain amount of energie stored in the battery. How many Ah that translates to depends on voltage, right? And for sure, voltage will drop during the discharge. But does starting voltage not have an effect? First (part of an) Ah discharged contains a lot of energy ...?

 

[elm70]

Trip 1: 33.5Ah down to 27.2Ah (0.5Ah lost (??) compared to fully charge which was finish 1h30min before start the trip)
Trip 2: 28.4Ah down to 22.3Ah (1.2Ah win while parked for 8h)
Trip 3: 22.3Ah down to 20.8Ah (0 change, but was 10min after 2nd trip end)
Next Day:
Trip 4: 18.2Ah down to 15.8Ah (2.6Ah lost overnight)
Trip 5: 15.6Ah down to 14.3Ah (0.2Ah lost while parked)
Trip 6: 14.3Ah down to 13.0Ah
Trip 7: 12.9Ah down to 11.8Ah (0.1Ah lost while parked, this was even less then 2h rest)
Trip 8: 11.8Ah down to 10.7Ah
After 3h rest ... capacity is neither going up or down .. is still reported to be 10.7Ah .. 10.7Ah equal to 1km EV range left

So, in total I did 21km + 12km .. so only 33km ... quite a poor result, since I have only used AC on trip 2 and trip 3 only
Total capacity consumed was 13.9Ah + 7.2Ah
Total capacity lost while parked was: 1.7Ah (2.2Ah including the 0.5Ah missing after a full charge)

Anyhow ... possibly the best test would be to fully charge the car .. and consume all the battery in 1 trip .. and then check SOC after 2 or 3h rest ...


EDIT ... after further rest ... I made last check for the day .... battery jump up from 10.7Ah to 10.9Ah (still only 1km EV range left) ... so total battery lost while parked is 1.5Ah instead of 1.7Ah

 

[elm70]

I understand I think. Maybe kWh is not the right approach. But altogether, there is a certain amount of energie stored in the battery. How many Ah that translates to depends on voltage, right? And for sure, voltage will drop during the discharge. But does starting voltage not have an effect? First (part of an) Ah discharged contains a lot of energy ...?

Battery capacity is always in Ah ... just look at the following graph, which can be found in many datasheet for lithium battery

Test is done with different load, which cause a different voltage .. higher the load, is lower the voltage but the Ah is constant (more or less) .. so for higher load the energy extract from the battery is less .. so speaking of kwh is "wrong" ... since we should refer to ideal energy in kwh with the lowest load .. while speaking of battery capacity in Ah .. it is quite accurate independetly by the "load"

PS: this graph is relaive atipical ... normally with higher load (so more current) the capacity in Ah is partially reduced (so not only less kwh (actually much less), but even less Ah)

 

[anko]

That is deep. Really need some time to digest ;-)

 

[anko]

Mitsubishi in the Netherlands have communicated this warranty procedure for the battery:

1. Customer must have filed a complaint regarding EV range (I can take care of that ;-))
2. Use item 18 on the BMU data list (this is the Ah number shown by the Dog / EvBatMon)to determine that the capacity is near the specific threshold value (26 Ah for MY14, 15 and 16 and 28 Ah for MY17 and 18).
3. Perform the “Battery Capacity Quick Check (see appendix)”.
4. If from this (don't know if 'this' refers to step 2, step 3 or a combination of step 2 and 3) it turns out the capacity is below specified threshold value, open a case with Mitsubishi Dealer Community system, specifying:
a) Completed Battery Check Form,
b) Snapshot from BMU data list (from after the capacity check)
c) PHEV Diagnosis report (from after the capacity check)
d) Copy of the work order with the customer complaint

Upon reception of the above we (I guess this is Mitsubishi NL) will submit a warranty request to the manufacturer in Japan. They will decide whether the battery can be replaced under warranty.

I wonder what the "Battery Capacity Quick Check“ is. Obviously, I do not have the appendix they refer to, but there are different appendices for MY14, 15 and 16 and for MY17 and 18.

So, IIRC we knew about these procedures:

- Reading item 18 on the BMU data list
- Cell smoothening
- DBCAM
- BMU reset

What would “Battery Capacity Quick Check” be and where would it fit in above list?

 

[elm70]

That is deep. Really need some time to digest ;-)

Yes .. definitely .. these are deep .. deep discharge graphs

BTW ... how low is the SOH of your PHEV ? .. are you close to be qualified for a new main battery in warranty ?

Looking at the history of your battery (I think you posted in FB) ... you battery lost a lot of capacity already in the first few months of life ... so it is looking like it was not even close to intended capacity when it was new .. very strange indeed

 

[anko]

I have seen the 'official' report that was created by my dealer upon delivery. It said 37.8 Ah. This measurement was also confirmed by Mitsubishi NL.

Currently I am at 26.2. Need to loose another 0.2 or 0.3 for a warranty claim. Last DBCAM was 4 months and 7.000 km ago. After that I was at 28.0. So, I lost 1.8 Ah between 143.000 and 150.000. They always said / predicted degradation would taper off. But with me, this appears not to be the case.

 

[elm70]

As reference ..

 

[elm70]

Even assuming it is normal to get the car delivered with 37.8Ah ...

9 months later, the SOH drop from : 37.8Ah down to 34.5Ah .. or 3.3Ah ... or 0.37Ah a month

My theory of SOH calculation from our BMU, is that this is based on collecting "errors" after a battery left unused at rest and adjust consequently the SOH

When error is limited, the SOH correction happen one a month for 0.1Ah difference.
If the error is "massive" .. the SOH get updated by 0.5Ah .. even more often then once a month

Your 0.37Ah lost a month, it is a clear sign that original battery capacity was not the 38Ah as a new battery

So, in my view, you got a defected, or low quality (B grade battery) in your PHEV

PS: I expect that your car in the early months of usage, if left uncharged and parked after reaching low EV range left .. at the restart most probably did start immediately the engine .. as well .. I would expect that the EV range after parking for around 2h would be much less then what was shown at the end of the trip

PPS: In other words .. at first I did assume it was your usage that cause a fast battery degradation on your car .. but now it looks it is more likely you got an "unfortunate" battery since day 1

 

[anko]

Hey, I recognise that ;-) Kinda matches the history list reported by PHEVWatchDog:

Registered values in BMU history list are 0.1 or 0.2 below the Remaining Capacity Ah values reported by BMU right after the procedure (Not sure about the odometer values, they were estimations I put into my Excel later)

 

[anko]

Thanks for the analysis. Need to chew on that for a bit ...

PPS: In other words .. at first I did assume it was your usage that cause a fast battery degradation on your car .. but now it looks it is more likely you got an "unfortunate" battery since day 1

Not sure if this is the case. But to me for sure it felt like this

 

[anko]

My theory of SOH calculation from our BMU, is that this is based on collecting "errors" after a battery left unused at rest and adjust consequently the SOH

When error is limited, the SOH correction happen one a month for 0.1Ah difference.
If the error is "massive" .. the SOH get updated by 0.5Ah .. even more often then once a month

When you say "error", do you mean deviations between "expected kWh per charge based on Ah value" and "actual kWh per charge"?

 

[elm70]

My theory of SOH calculation from our BMU, is that this is based on collecting "errors" after a battery left unused at rest and adjust consequently the SOH

When error is limited, the SOH correction happen one a month for 0.1Ah difference.
If the error is "massive" .. the SOH get updated by 0.5Ah .. even more often then once a month

When you say "error", do you mean deviations between "expected kWh per charge based on Ah value" and "actual kWh per charge"?

As mention before .. I believe only Ah is monitored and used by BMU ... kwh is a number for the people, not for machine computation

I'm not sure what is the role of charging, possibly it has an impact too.

What I can see is this:
- Car start with X Ah, the BMU monitor the flow of the current while car is used .. when the trip end, the BMU assume SOC is equal to X-flow - Y ... then if the car is left unused ... after a rest time, the SOC is adapted to a new value Z based on Voltage ... and Z-Y is the error to be monitored/aggregated
- At each charge ... possibly the BMU monitor the end SOC , and it may count the charge in Ah and define an error too.

I think you also read in FB, that somebody is convinced that using AC while charging, this does trick the BMU, making it believe more current used for charged in the car, so this person state that using this practice he managed to increase his PHEV SOH
... I will try in winter to schedule a car heat in the middle of the charging process ... and see if I can win any SOH after 1 months of this trick (it will cost me around 1kw extra charge per day .. so ... ~2 euro of waste per month

Anyhow ... SOH and SOC can be wrong in the BMU ... the only real way to know what is the battery condition .. is to fully charge the car .. drive down to 0Km EV ... and wait after rest what will be the updated SOC

 

[anko]

My theory of SOH calculation from our BMU, is that this is based on collecting "errors" after a battery left unused at rest and adjust consequently the SOH

When error is limited, the SOH correction happen one a month for 0.1Ah difference.
If the error is "massive" .. the SOH get updated by 0.5Ah .. even more often then once a month

When you say "error", do you mean deviations between "expected kWh per charge based on Ah value" and "actual kWh per charge"?

As mention before .. I believe only Ah is monitored and used by BMU ... kwh is a number for the people, not for machine computation

I'm not sure what is the role of charging, possibly it has an impact too.

What I can see is this:
- Car start with X Ah, the BMU monitor the flow of the current while car is used .. when the trip end, the BMU assume SOC is equal to X-flow - Y ... then if the car is left unused ... after a rest time, the SOC is adapted to a new value Z based on Voltage ... and Z-Y is the error to be monitored/aggregated
- At each charge ... possibly the BMU monitor the end SOC , and it may count the charge in Ah and define an error too.

I think you also read in FB, that somebody is convinced that using AC while charging, this does trick the BMU, making it believe more current used for charged in the car, so this person state that using this practice he managed to increase his PHEV SOH
... I will try in winter to schedule a car heat in the middle of the charging process ... and see if I can win any SOH after 1 months of this trick (it will cost me around 1kw extra charge per day .. so ... ~2 euro of waste per month

Anyhow ... SOH and SOC can be wrong in the BMU ... the only real way to know what is the battery condition .. is to fully charge the car .. drive down to 0Km EV ... and wait after rest what will be the updated SOC

BMU thinks SOC = X and Capacity is Y. Based on X and Y, BMU thinks a certain amount of charge should be added before reaching the target cell voltage. If that cell voltage is reached earlier or later, then apparently either the SOC or the Ah number was incorrect -> Error.

Is that the idea? Maybe I should have said "coulomb count" instead of kWh?