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So I thought I should check out the "MAX RANGE" charging mode on our Model S (85kWh battery) before needing to use it in earnest.  Relative to the STANDARD mode, it increases rated range from about 235 Miles to 270 Miles.  I noticed that the charging slows down gradually over the last 40 minutes of charging.  In STANDARD mode, it charges at the full rate until the very end.  Not that it really matters... ;-)
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Vic Gundotra's profile photoJohn A. Tamplin's profile photoStephen Pace's profile photoDavid Mosberger's profile photo
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Cool graph, what did you use to generate it?  Any idea what the drop-off was just before it started scaling down the charge rate?  I'm guessing that is more likely to be a data collection glitch than an actual change int the rate.
 
I can't speak about the glitch but my understanding of L-ion battery chemistry is that they charge faster until 80% full, then they go slower. iPhones and other common lion batteries also act accordingly.
 
Right, I understand that and that is expected - I was just curious about the spike down just before it slows the charging rate.
 
It's not a data-collection glitch.  You can see the full data here:

 http://proto1.egaug.es/

All the other loads and PV production showed no change during that one minute, so the charging really dropped for a bit.  I assume it went to zero for about 20 seconds.
 
So, maybe there is one process that handles full-rate charging, and then when it reaches the trigger it exits and lets a separate process handle the final charging, and there is a gap between them?
 
Could be.  I don't want to do this too often, since it supposedly reduces battery lifetime, but next time I'll charge in MAX RANGE mode, I'll see if I can catch the transition within 10 minutes.  Then I could view second-by-second data of the behavior.
 
Interesting! I wonder how the sensor works ("I'm at 80% now!"), and if a delay is added intentionally to be sure it was an accurate 80% reading.

Obviously I have no idea. 
 
+Robert Brown I'm not sure how Tesla tracks battery charge-level.  I assume it's based on the cell-voltages, but it'd be interesting to have more details.
 
I would be interesting to see the profile using 110v instead of 240v.  I think if you only drive a few miles in a given day (and for daily maintenance charges to counteract daily drain) 110v may be technically more efficient (albeit slower).  Regardless, I'm looking forward to getting the firmware update that lets you set the 'time to start charging' like the Roadster has.  My town has a 'free power at night' plan that I'd like to take advantage of.  :-)
 
+Stephen Pace I wouldn't expect it to be any different, other than a lower charging level for a longer time.  Depending on exactly how the charge slopes down, I would expect it to keep exactly the same shape as above, just clipped to the maximum power supplied by the source.
 
I didn't think it would be any different either until I was reading some things recently on Tesla Motors Club (and looked at my smartmeter data on how much power the Tesla is drawing).  Since David works for eGauge and has a Tesla, it will be easy enough for him to test.  Also, +David Mosberger , if you know of a trusted installer for eGauge in Houston, please drop me a line.
 
+Stephen Pace Sorry, I missed your question about installers: no we don't really have a preferred installer in the Houston area.  Having said that, any capable licensed electrician should be able to perform the installation easily and the support staff would be happy to assist in verifying that everything is installed and configured properly.
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