Roadster Owner Based Study of Battery Pack Capacity Over Time

[tennis_trs]

...the number on the lower right incremented slowly for a minute or two then the notification went away....

I'm sure someone has mentioned this elsewhere: the number counts up in hexadecimal to 0X64, which is decimal 100 (indicating percentage, I assume). It does seem to take a fair amount of extra time after hitting 0X64 to finish up (i.e., the count doesn't seem to be a good indication of the percentage of time done for the entire process).

Also, if the display goes blank, you can tap on the display a couple times and the message and progress will be displayed again.

 

[tomsax]

I just sent over my logs. The car is 1 1/2 years old and has 11k miles on it. I've only ever charged it with my 110V adapter since I only do about 20 miles per day on average. I don't think I have ever charged it range mode (maybe once a year ago). When I fully charge it in standard mode, I only get around 167 miles which seems very low. I've talked to Tesla about this several times and they have said that the battery is actually fine but the firmware is showing a lower number than expected because it is not properly calibrated and because I rarely charge it completely or from near empty. Hopefully you can confirm what Tesla is saying.

Do you ever have a chance to not drive the Roadster for a couple of days? If so, I would recommend not charging until it gets down below 30% in Standard, then doing a full Range mode charge. That will take a couple of days with 120V charging. In my experience, the Roadster needs to see how the battery behaves from a low state of charge all the way to the top of range mode in order to get a good idea of what the capacity of the battery pack is.

The range mode charge also helps with leveling the pack. If you have one pack that gets out of sync with the rest, it can dramatically impact your range.

You definitely want to get an accurate measure of how healthy your battery pack is while you still have lots of warranty left.

 

[user497]

Do you ever have a chance to not drive the Roadster for a couple of days?

I have the chance to do that every week but I like driving it I actually brought it down to around 26% and fully recharged it last weekend but I didn't realize I have to recharge it in range mode. I am too charged to do it this weekend but I will try to do it next weekend and report on the change. Thanks.

 

[Alan]

If you are nearly charged then just charge in range mode even if you do not have the chance to discharge first. The "car" needs to learn both empty and full so charging in range mode gives one of th two required answers and may well improve (hopefully) the no of ideal miles when you go back to charging in standard mode.

Go on - I think lots of us want to know if it helps!

 

[Kevin Sharpe]

I have submitted my logs....

 

[richkae]

Here is the summary of all the battery temperature data for all the cars submitted. ( temperature in Celsius )

only 4 of 12 cars spent significant time above 30C

 

[user497]

only 4 of 12 cars spent significant time above 30C

I am planning on charging in range mode tonight (although I am probably about 80% full now - I will charge to charge from a lower SOC next weekend). I believe I am one of the 4 cars with a spike after 30 degrees. But I don't think I am usually getting it that hot when I am driving it. Could it be that charging it with 110V means that it charges longer and therefore gets hotter? I wonder if those 4 are mainly charged with 110V and the other 8 are charged with 220V.

 

[richkae]

I believe that most of the time charging actually cools the battery - even at 110V ( the charging process cycles between charging and cooling to keep the temperature low ) so I don't think so.

I'll post other charts here soon. I didn't mean to imply any particular relevance to the temperature data.
I've gotten tired of manually wrangling the data in Excel and am writing some code to pull all the data together and automate the chart making.

 

[Kevin Sharpe]

I have submitted my logs....

did you get them?

 

[jory]

i submitted my logs last week. not sure if they were received either.

 

[richkae]

Yep, I got Kevin's and Jory's logs. Thanks!
Like I said, there is now enough data that manually loading and manipulating it in Excel is annoying, so I am trying to write some code.

 

[Kevin Sharpe]

Yep, I got Kevin's and Jory's logs. Thanks!

Great! Do you want us to submit them on a regular basis?

 

[user497]

OK, so I brought the car down to about 120 miles ideal and then charged it in range mode. It went up to 208 miles. I was expecting closer to 220. However, based on the image it looks like it only charged about 95% (I guess you need to click the "top off" button for it to complete the remaining 5%?). Since 208 miles is 95% of 219 miles, I think I am seeing what I expected.

My next plan is to let the battery go down as much as possible this week (at least below 100 miles) and recharge it 100% in normal mode and see if I get more than the 167 miles I had been seeing. I would expect around 190 miles.

 

[richkae]

View attachment 3573

OK, so I brought the car down to about 120 miles ideal and then charged it in range mode. It went up to 208 miles. I was expecting closer to 220. However, based on the image it looks like it only charged about 95% (I guess you need to click the "top off" button for it to complete the remaining 5%?). Since 208 miles is 95% of 219 miles, I think I am seeing what I expected.

My next plan is to let the battery go down as much as possible this week (at least below 100 miles) and recharge it 100% in normal mode and see if I get more than the 167 miles I had been seeing. I would expect around 190 miles.

My suggestions:
Pull a new log file and run it through the parser.
If you do the "-b" option the 2nd last section has the average brick amp-hours and the minimum brick amp-hours for each day of history.
See if the average value ( "brickahave" ) increased from before you did the range mode charge.
I would suggest doing another range mode charge from a low state of charge and see if it increases again. If it increases, keep doing the range mode charge cycles until it stops increasing.

If the amp-hour value of the weakest brick ( "brickahmin" ) is significantly lower than the average brick ( "brickahave" ), then that is another reason to do the range mode charges - because it should get the charger to attempt to balance the bricks. ( You know which brick is weakest - it is in the "bricknumber" column )

 

[richkae]

Great! Do you want us to submit them on a regular basis?

The most important thing is to pull a log from the car every couple of months so you keep a complete detailed history.
I'll make more improvements to the parser that gather new data and ask for more logs.

The next thing I am thinking about doing to it is to figure out how much confidence to have in the amp-hour values for the bricks.
From user497s logs - it seems possible that if you don't exercise the battery then the amp-hour values are inaccurate.

 

[user497]

From user497s logs - it seems possible that if you don't exercise the battery then the amp-hour values are inaccurate.

The challenge for people like me (daily driver but only putting about 20-30 miles per week day - further on the weekends) is knowing how often to charge up. I know Tesla officially says you should fully charge every day. But in speaking with my Tesla ambassador, he tells me that it doesn't matter as long as you don't keep it too low for awhile. And of course it looks like if you don't ever let it drain too low and recharge in range mode then the indicators become inaccurate. And then there are the theories that it is better long term to leave the battery pack around 50% charged (some people going so far as to think about only charging in storage mode which isn't a good idea because the batteries aren't rebalanced). They really don't make it easy.

 

[Lloyd]

One of the questions that I asked at the Oct event was "What charging and driving modes will be offered on the Model S?" I was told that it was under discussion and that it was possible that a more limited number of charge and driving modes would be available.

 

[vfx]

... knowing how often to charge up. I know Tesla officially says you should fully charge every day.....

Should probably separate the differences between "charging" and "battery preservation".
That is, you might want to plug in just because your car is sitting in an extreme temperature area.

 

[tomsax]

The most important thing is to pull a log from the car every couple of months so you keep a complete detailed history.

If you drive a lot, capturing log files every couple of months won't give you a complete record. It's the one-second drive records that fill up the detailed transient section. That section fills up with about 60 hours of driving, give or take a couple of hours. Distance doesn't matter; it's time driving.

I just analyzed all of my log files. I see log files that cover anywhere from 29 days to 4 months, between 1500 and 2100 miles, but the driving time is in the narrow band between 58 and 62 hours.

I try to grab a log file once a month, or after any significant road trip.

If you want to know how often to capture your log file, just run one of your files through my parser with no command line options. You'll see a summary of your driving and charging sessions. Note how far back that history goes. That should give you an idea of how often you need to download the log file, more often if you're doing an unusual amount of driving, less often if you do less driving.

There are a couple of potential issues with service calls...

Occasionally, the techs will do something that erases the log file. So, it's a good idea to grab a log file just before each service visit.

Tesla has a way to turn on more verbose logging which dumps a record every second, 24x7. That drops the cycle time to about a week. This issue seems to be a rare problem, but it's a good idea to take a look at your log file to make sure things look right especially if you're about to do a drive that you want to capture in the logs.

I'll add this stuff to my page, and the next release of my parser will show a warning if your log looks like it's capturing verbosely.

 

[bolosky]

View attachment 3573

OK, so I brought the car down to about 120 miles ideal and then charged it in range mode. It went up to 208 miles. I was expecting closer to 220. However, based on the image it looks like it only charged about 95% (I guess you need to click the "top off" button for it to complete the remaining 5%?). Since 208 miles is 95% of 219 miles, I think I am seeing what I expected.

I suspect that your battery is badly out of balance. What that means is that some sheets have more charge than others. The car charges and discharges the sheets evenly, so most of the time they're at the same level. However, small differences add up over time and result in varied amounts of charge in the sheets. The car will only charge until the sheet with the highest amount of charge is full, and will only discharge until the sheet with the lowest amount of charge is empty. The fact that there's more left in the other sheets is useless.

For example, imagine that you had a car with only two sheets, and sheet A had 5% more charge than sheet B. When you charge the car, it will charge both sheets in parallel until sheet A is full; sheet B will be at 95%. Then when you drive the car, when sheet B gets to empty, it stops even though sheet A is at 5%.

In order to fix this, you need to balance the batteries. This happens automatically, but it used to only occur after a full range mode charge. Newer versions of the firmware may be trying to balance after standard mode charges, but I'm not positive about that. Balancing is much slower than charging or discharging, and if your battery is badly out of balance it may take DAYS. I had my battery replaced last spring with a battery that was unbalanced in the extreme. It took about a week of charging up in range mode and letting it sit overnight to get it to fully balance, but doing so added something like 15-20 ideal miles to the standard mode charge.

Your description of rarely if ever doing a range mode charge makes me think that this might be your problem. If it is, you can just do what I did. Be patient, though. While batteries that aren't terribly unbalanced can get to balance in an hour or so, you may take MUCH longer.