Quickly decreasing CAC

[drewski]

When I got 1038 in April she had 26,818 miles and a CAC of 150.9

After my first long drive over 100mi the CAC dropped over 1 pt to mid 149's i posted about it and @DeedWest posited that it was fine and the car was learning the true battery capacity because of lack of longer drives from the prior owner.

Now, each time i've gone > 100mi between charges I've lost another 1+ pts and this time last week the CAC was 146.3. OK ~4.5 point correction . . .

Last weekend I drove to slcasner's house which is almost a 100 mile round trip. this time the CAC dropped close to 2.5 points from 146.3 to 143.9!

i've put about 1000 miles on her in 3.5 months that this 7 point CAC decrease occurred.

No fault codes have popped up except the occasional #104 TCM: Lost DMC comms

Can it still be learning or is it time to book a transport to Arizona or Seattle because something's amiss in the ESS?

 

[kwellmey]

Why not send a log file to Gruber for analysis? He will review at no charge.

 

[drewski]

Why not send a log file to Gruber for analysis? He will review at no charge.

why get expert advice when i have the peanut gallery here?

kidding! i messaged Pete

 

[im4uttx]

So, have you been monitoring the logs for which sheet is setting the low bar? You could have 1 sheet pulling the battery CAC down...

 

[markwj]

Suggest you post the ahr.log (from the logs) and screenshot of the little diagnostics ESS screen. Those give a pretty good indication of health.

 

[IslandRoadster]

why get expert advice when i have the peanut gallery here?

kidding! i messaged Pete

As one more peanut in the gallery, I think @CM_007 may have discovered that some of the steady reduction is due to software and not actual battery degradation. Not sure of the details but worth discussing with him.

 

[drewski]

So, have you been monitoring the logs for which sheet is setting the low bar? You could have 1 sheet pulling the battery CAC down...

i'm log illiterate. will need to look into this more.

 

[drewski]

Suggest you post the ahr.log (from the logs) and screenshot of the little diagnostics ESS screen. Those give a pretty good indication of health.

In the first pic, does the SOC being much lower than the other ones mean anything?

 

[drewski]

to my untrained eye, the ahr.log data looks consistent across bricks, so may be the car still learning.

interested in what @IslandRoadster mentioned, though sounds similar to what's been said about battery 3.0 (software, not actual degredation)

 

[im4uttx]

to my untrained eye, the ahr.log data looks consistent across bricks, so may be the car still learning.

interested in what @IslandRoadster mentioned, though sounds similar to what's been said about battery 3.0 (software, not actual degredation)

I pulled the ahr.log into a spreadsheet to compare. Looks like bricks 90 and 91 are the low bricks. In comparing the top data to the "prevAh" data, many bricks are lower, possibly because the low brick has fallen a little more, so none of them charge up to the same point, but I'm a rookie at this analysis. If you have your earliest ahr.log file and can compare that to the current data, it might show if 90 or 91 have always been the lowest or have degraded more than others...or if is still just learning.

 

[drewski]

I pulled the ahr.log into a spreadsheet to compare. Looks like bricks 90 and 91 are the low bricks. In comparing the top data to the "prevAh" data, many bricks are lower, possibly because the low brick has fallen a little more, so none of them charge up to the same point, but I'm a rookie at this analysis. If you have your earliest ahr.log file and can compare that to the current data, it might show if 90 or 91 have always been the lowest or have degraded more than others...or if is still just learning.

these are the first logs i've pulled from 1038

 

[im4uttx]

these are the first logs i've pulled from 1038

No worries...experts might be able to pull more info, and explain the numbers, but use this as your starting point and see if bricks 90/91 remain as the lowest in the data and if they get worse over time. Obviously, Gruber guys can help if it is just a sheet or a brick or two, and you've already messaged them, so ... hope it stabilizes for you.

 

[DeedWest]

I saw similar activity when I purchased mine. It was driven a few miles occasionally and always kept plugged in, so the CAC was resting at 158 at 36K miles. Now, after I've extensively driven it, even bringing it down into lower SOC's since ownership last year, my CAC went all the way down to 148, where it has now rested for six months straight with little to no fluctuation. My pack is extremely balanced according to logs. I'd suspect yours is simply balancing itself out to where its true capacity lies.

Separate from that, I'd contact Carl Medlock in regards to some firmware findings he's working on. Might be worth it to see if those methods help with the accuracy.

 

[Marius]

I have the same experience. Probably it has to do with software. My pack is well balanced and has done a lot of miles. I always see during long time the same CAC and then a sudden drop with 5 or 6 points and then a long time steady number again. Apparently degrading goes with steps of 5 CAC points a time. www.pluginamerica.org has 180 roadster degrading registered. Maybe Tom Sax knows more and has analysis this data.

 

[markwj]

MIN 83% MAX 86% is 3%, and pretty much ok. 3% is acceptable, imho. Leaving it plugged in after it has charged to full (and stopped normally) may help balance it some more.

In the first pic, does the SOC being much lower than the other ones mean anything?