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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Wed Mar 13, 2019 8:27 pm 
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Joined: Thu Feb 26, 2015 5:58 pm
Posts: 840
Location: Near Port Macquarie Australia
Darkflow wrote:
OK, so latest update over at youtube unplugged EV is that the BMU calculates SOH by applying just two fixed degradation factors:



This is old news. I wrote this previously here viewtopic.php?f=10&t=3487&start=20:

Trex wrote:
Now anko asked me in this thread:

Trex wrote:
anko wrote:
It has been discussed (if I am nor mistaken) how the Current Ah is calculated based on actual usage parameters and done theoretical model. Could these be 2 of the parameters?


Not sure still looking into it. :)


Notice that last sentence from anko "Could these be 2 of the parameters?" ie the Secular (calendar or age) and cycle deterioration.

Well I think they are used to "estimate" the current capacity of the drive battery (or SOH) by the BMU. I will bring in a image I found and put in another thread that I started:

Image

Please note the Calculating total amount of battery (including capacity adjustment) using History of battery usage and History of discharge and charge
on the bottom left of the BMU.

History of battery usage I think is Secular (calendar or age) deterioration.

History of discharge and charge I think is cycle (or Cyclic) deterioration.

They are both stored on the PHEV as we use it and are fed into the algorithm that works out the "estimated" current capacity of the drive battery I think.

Regards Trex.


Hope they are not pinching my research. ;)


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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Wed Mar 13, 2019 10:31 pm 
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Posts: 3399
Location: Netherlands, Utrecht area
zzcoopej wrote:
When the battery is regularly charged using A/C chargers, the BMU wil lget a change to recalibrate itself and overrule the pre-programmed degradation params.
Not sure I agree with the last part. The ICE start is triggered by the BMU when the SoC reaches a certain level. But that level is derived by the BMU from its current notion of SoH. ISo, the BMU would be learning from itself ...


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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Wed Mar 13, 2019 10:33 pm 
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Joined: Mon Dec 01, 2014 11:30 am
Posts: 3399
Location: Netherlands, Utrecht area
Trex wrote:
Darkflow wrote:
OK, so latest update over at youtube unplugged EV is that the BMU calculates SOH by applying just two fixed degradation factors:



This is old news.
In all fairness, I don't think we have ever seen actual percentages per month / Ah for these params, have we?


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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Thu Mar 14, 2019 6:40 pm 
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Joined: Tue Apr 14, 2015 1:57 pm
Posts: 216
Location: Gosford, Australia
anko wrote:
Not sure I agree with the last part. The ICE start is triggered by the BMU when the SoC reaches a certain level. But that level is derived by the BMU from its current notion of SoH. ISo, the BMU would be learning from itself ...


Ah true, I see what you mean, hopefully the SOH would not diverge too far from reality if the chemistry is predictable (which is possibly why hot conditions away from Japan are proving to be unpredictable). Should the ICE be triggered by low cell voltages then?

_________________

Cheers, J.
http://www.EvPositive.com
2010 iMiEV, 2015 Outlander PHEV
PHEV App EvBatMon -
Android https://play.google.com/store/apps/details?id=com.EvPositive.EvBatMon
iOS https://itunes.apple.com/us/app/evbatmon-for-mitsubishi-outlander/id1143901805


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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Fri Mar 15, 2019 3:17 am 
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Posts: 3399
Location: Netherlands, Utrecht area
zzcoopej wrote:
Should the ICE be triggered by low cell voltages then?
Would be nice, but impossible from what I understand. Voltage vary with load, which is why it is so difficult to establish real SoC while the car is being used. Instead, the BMU calculates an estimated SoC based on its notion of SoH, starting SoC and coulomb count.

And this is why a well aligned BMU is so important: if the notion of SoH is too low, the ICE will be started too soon and you mis out on range. If the notion of SoH is too high, the ICE will be started too late and you may be putting more strain on the battery than anticipated.


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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Sat Mar 16, 2019 9:09 pm 
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Joined: Thu Feb 26, 2015 5:58 pm
Posts: 840
Location: Near Port Macquarie Australia
Darkflow wrote:
OK, so latest update over at youtube unplugged EV is that the BMU calculates SOH by applying just two fixed degradation factors:

-0.3% for every month
-1.0% for every 6200 Ah in/out of the battery.

That's if the BMU is set to think that the starting battery capacity is 38 Ah.

Mine is, and that calculation closely matches my current BMU reported SOH.

Apparently someone has been looking directly at the BMU code, which is not sophisticated.


Now I have already replied to some of this post above about it being old news from my previous research but I will now discuss the so called % values that is mentioned here.

It appears to me they are trying to get formulas to match the values for the Secular (calendar or age) and cycle deterioration as shown on the MUT-III reports.

Now I have at least 3 of those MUT-III reports (that I can find at the moment) for my oldest PHEV which I still own.

From what I can see from my quick appraisal of those reports those values are not always lining up with what I am seeing. For example:

1st report with BMU data list number 396 of 35 months I should see according to their so called 0.3% for every month formulae 10.5 %. Secular (calendar or age) deterioration on my report is 12.83% (.273%/month)

2nd report is showing 47 months with Secular (calendar or age) deterioration of 14.55% (.309%/month) their formulae 14.1% Ok closer

3rd report is showing 59 months with Secular (calendar or age) deterioration of 16.06% (.272%/month) their formulae 17.7%

Now lets get to the cycle (or Cyclic) deterioration and their 1.0% for every 6200 Ah in/out of the battery formulae.

1st report in the same order as above Charge and Discharge intergrated current 47,652 Ah actual report 9.25% their formulae 7.69%

2nd report Charge and Discharge intergrated current 65012 Ah actual report 10.76% their formulae 10.48%

3rd report Charge and Discharge intergrated current 75332 Ah actual report 11.89% their formulae 12.15%

Not sure I trust their formulas so far. ;) though they got close a couple times I suppose. :roll: :lol:

Now as for adding those values together to get the so called BMU reported degradation of our batteries lets see what we get.

Now none of these reports have a BMU recalibration (or "Auto Capacity Measured Procedure") done to them so it will not screw up the measurement.

1st report Battery current capacity 100-(32.7 Ah/40 Ah) x 100 gives 18.25% add their formulas together 18.19%. Ok this is close.

1st report Battery current capacity 100-(32.7 Ah/38 Ah) x 100 gives 13.95% add their formulas together 18.19%. Not so close as seen by the apps.

2nd report Battery current capacity 100-(29.9 Ah/40 Ah) x 100 gives 25.25% add their formulas together 24.9%. Ok close again.

2nd report Battery current capacity 100-(29.9 Ah/38 Ah) x 100 gives 21.32% add their formulas together 24.9%. Not so close as seen by the apps.

3rd report Battery current capacity 100-(26.8 Ah/40 Ah) x 100 gives 33.00% add their formulas together 29.85%. Not so close.

3rd report Battery current capacity 100-(26.8 Ah/38 Ah) x 100 gives 29.47% add their formulas together 29.85%. Close as seen by the apps.

So all in all IMHO it is ok in some parts but it has very mixed results for "apparently someone has been looking directly at the BMU code".

I think that so called person might be having us on and is just guessing or "winging it" probably using just one report IMHO.

But I will check those calcs later to make sure I have entered them correctly as I was in a hurry.


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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Sun Mar 17, 2019 6:25 pm 
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Thanks for doing thoise calculations.

It does seem there is more to it than that, especially as noted earlier that SOH has been seen to increase at times.

I do wonder though if it is a moving percentage - so a percentage of the previous calculated result, rather than a percentage of the fixed starting capacity. That will give you curves.


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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Sun Mar 17, 2019 10:14 pm 
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Joined: Mon Dec 01, 2014 11:30 am
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Location: Netherlands, Utrecht area
Darkflow wrote:
It does seem there is more to it than that, especially as noted earlier that SOH has been seen to increase at times.

I do wonder though if it is a moving percentage - so a percentage of the previous calculated result, rather than a percentage of the fixed starting capacity. That will give you curves.
Or maybe the BMU DOES have a learning capacity and they have missed it?


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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Sun Mar 17, 2019 11:51 pm 
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Joined: Fri Jul 07, 2017 11:59 pm
Posts: 17
Quote:
Or maybe the BMU DOES have a learning capacity and they have missed it?


If the SOH has been seen to increase sometimes, it must have. I'm wondering if the default degradation calculation is a moving percentage that then gets a step function correction from time to time.


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 Post subject: Re: Drive battery degradation and replacement.
PostPosted: Mon Mar 18, 2019 1:20 am 
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Joined: Mon Dec 01, 2014 11:30 am
Posts: 3399
Location: Netherlands, Utrecht area
Darkflow wrote:
Quote:
Or maybe the BMU DOES have a learning capacity and they have missed it?


If the SOH has been seen to increase sometimes, it must have. I'm wondering if the default degradation calculation is a moving percentage that then gets a step function correction from time to time.

My battery never showed an increase of SoH (apart from as a result of DBCAMs). But at the same time, mine was always / very frequently charged via AC. According to Mitsubishi, my BMU should have been rather well aligned all the time and there should be no reason to expect SoH to go up. So, looking at my battery, there seems to be no standard "correction from time to time".


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