Roadster Owner Based Study of Battery Pack Capacity Over Time

[markwj]

Using the OVMS to compare two Roadsters over several days, I noticed that for one of the cars, the battery pack temperature is 8-15 °C higher than the ambient temperature.

Are you sure the temperature subsystem in the car is not "asleep" and not updating?

To be sure, I would suggest that the next time you drive, call up the temp display on the VDS. Also, in the iPhone App tap on the boot of the car and then choose Wakeup to get updated readings.

[lmore]

This is something I have seen over several days, under different conditions. Now, for example, the "warm battery" car has an ambient temp of 10 C while the battery temp is 21 C (car is plugged in and probably done charging several hours ago at 12 amp/220 Volts). I will pull the log files files when I get to access the cars, appreciate the help!

[dhrivnak]

Has the program name changed? I downloaded and installed the Tesla log parser called TeslaGLOP.exe. It does not allow me to pipe files to it. I now have over 10,000 miles and was going to submit my logs again. I have been tracking my range in STD mode for nearly a year now and I have not seen any drop in capacity. Thank you

[tomsax]

Has the program name changed? I downloaded and installed the Tesla log parser called TeslaGLOP.exe. It does not allow me to pipe files to it. I now have over 10,000 miles and was going to submit my logs again. I have been tracking my range in STD mode for nearly a year now and I have not seen any drop in capacity. Thank you

That's a different log parser. For this study, you need to use my command line app.

Complete instructions are here: VMS Log Parser for Tesla Roadster. Download the program then follow the instructions in the "Battery Longevity Study" section. The section "Using a Command Line App" may be helpful for those who haven't used one before.

[Ben W]

Chiming in with a random data point: my 3 1/2 year old Roadster with 31k miles on it just completed a full charge in Range mode, and shows 222 ideal miles. This represents a loss of roughly 3% capacity per year. I can live with that, though I'm still hoping for a 400-mile replacement pack upgrade when it comes time in 2016

[richkae]

Here is a summary of all the data I have.
Some of the data is very old ( 6 months ), a couple of the submissions were made by a very old version of the log parser that had some bugs, and I could not get useful data of it.

Here is a chart of battery capacity vs miles driven:

You'll notice one data point that stands out as having a low capacity after only 11000 miles. That car sat for a very long time unused, and the data was submitted after it changed owners after that long period of disuse.
I believe that the battery needs to be cycled a few times to discover its true capacity, as the computer is being conservative.

Here is a chart of battery capacity vs age in years:

I believe that this is evidence that there is not a lot of capacity loss due to age, it is primarily a function of miles driven. The data point that stands out in this chart is actually a car that has driven 51k+ miles in 1.5 years.
There are fewer data points in this chart because some of the data is truncated - the oldest data is lost - and I don't know how old the car actually is.

[dhrivnak]

Can yo translate capacity to ideal miles or kwh? As i never had it new i am not sure where i am on the chart. Thank you.

[richkae]

Ideal miles in range mode should be = percentage from chart * 245
I used the amp hours from the average brick to compute the percentage, that may be wrong - it might be necessary to use the minimum brick.
The minimum brick is usually within 1% or 2% of the average brick. So that would skew all the numbers down a little, unless the car has one very low brick.

[richkae]

This chart includes the average brick and the minimum brick. Clearly understanding how ideal miles relates to the average brick and the minimum brick is important.

[SCW-Greg]

Hey not that I own a Tesla yet, but working on it... I just want to give a shout-out to Richkae (as well I'm sure of the parallel internal efforts of Tesla), for doing this pioneering research. It will aid Tesla, and it will aid us all in future vehicles/battery packs to be totally brainless/transparent charging efforts. The entire community benefits from those who are sharing their logs, and Richkae's ongoing volunteer work.

thx!