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Supercharger charging rate anomaly

Discussion in 'North America' started by Vger, Jul 30, 2013.

  1. Vger

    Vger Active Member

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    Location:
    Salt Spring Island, BC, Canada
    On our first Supercharge at Burlington, WA, our next stop was to be a 70A 235V HPC in Ellensburg, WA. So I wanted to charge until full, OR until the charging rate fell below the rate we have seen at that HPC, which the car reports as about 50 mph or about 16 kW.

    But when, during the SC session, I watched the displays, both in the car and on the iOS app, I saw two divergent values that did not fit any of my prior experience. As the power ramped down, at about 97% SOC, I was seeing 95 mph on the one hand, but only 12 kW on the other.

    Any other observations of this? How can this be? Is it just a bug (lag) in the mph calculation? If so, it suckered me into staying maybe ten minutes too long for optimum time split between the two charge stations (SC followed by HPC). SC caveat emptor!

    ImageUploadedByTapatalk HD1375245860.663124.jpg ImageUploadedByTapatalk HD1375245890.241220.jpg
     
  2. wraithnot

    wraithnot Model S VIN #5785

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    SF Bay Area
    I've definitely noticed that the calculated miles per hour of charging can be pretty far off when using a supercharger. I assume it's due to some sort of time averaging that was designed for a much slower charger. The current seems to be much better correlated with the amount of range added over time. I've data logged my last 12 supercharger stops and I'll try and post more of the results soon.
     
  3. Vger

    Vger Active Member

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    Thanks! I will look forward to that!

    Seems likely. Are you listening, Tesla!? Hopefully this is something that they fix in the firmware update that enables the 120kW charging, or we will be even further off!
     
  4. bluetinc

    bluetinc Member

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    I always see the shown MPH to be significantly off whenever I'm Supercharging also. As a note, the power (12kW) is shown correctly on both displays (405V * 29A = 11.745kW) it's just the mi/hr that is lagging. It's why I cringe when people talk about how fast they are charging on a Supercharger, it would be much more accurate if everyone just talked about the instantaneous power they are receiving.

    Peter
     
  5. wraithnot

    wraithnot Model S VIN #5785

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    #5 wraithnot, Jul 31, 2013
    Last edited: Jul 31, 2013
    Since you seem interested in this topic and it may take me a while to post the data from all 12 supercharger stops, here is the most egregious difference I observed between the reported charging rate and the actual charging rate (as judged by the difference in rated range over time). This data was logged on Monday July 22nd between 11:45 and 13:05 PDT (Hans' script reports in 24 hour time). I arrived at the Barstow Superchargers when there were already people charging and I plugged into charging bay 2B. The car that was charging in 2A unplugged around minute 60 and the current increased dramatically while the reported charging rate only increased slowly. The measured charging rate is simply the (rated range - rated range from previous datapoint) / (time interval between data points).

    update: I probably should have put this all on one plot. I was trying to show all the raw data that came from the car in the top plot and then demonstrate that the current and power are much better predictors of actual charging rate than the reported charging rate in the bottom plot. I didn't realize both plots would be almost identical.
    barstow_2b.jpg
    measured_vs_reported_comparison.jpg
    The raw data from this visit can be found in the link at the end of this post: 1,100 mile road trip to Las Vegas and back with a REST datalogger
     
  6. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    #6 Cottonwood, Sep 22, 2013
    Last edited: Sep 22, 2013
    From what I saw on 9/21 at Glenwood Springs, CO, it appears that the charging rate reported when an MS is on a Supercharger, is the overall average rate for the entire session. When you are charging to near full (range) capacity, that session average will always be far lower than the actual charge rate as the battery approaches full state of charge.

    This is a very different behavior from charging from an AC source. There, the reported charge rate seems to be the average over the last couple of minutes. You can see taper happening at high SOC when charging from an AC source.

    If you have your calculator handy, I found that taking V*A/(308 W-Hr/mi) correlated very well with the actual rate of miles put in the battery, and is accurate until the end.

    The graph below shows the data that I recorded yesterday at Glenwood.

    • SOC is the State of Charge of the battery in miles.
    • Rate(Watts) is the calculated charge rate from I*A/(308 W-Hr/mi) in mph.
    • Diff Rate is the charge rate calculated from successive SOC samples and time in between. It is noisy because time is quantized to minutes and that quantization error can be a 10-20% error in the result.
    • Reported is the reported charge rate from the car and the app.
    • Average is the average charge rate for the session calculated from SOC change in session and session time.


    Glenwood-Charging 20130921.png

    As you can see the Reported charge rate appears to be the average charge rate for the session, and the calculating the current charge rate as V*I/(308 W-hr/mi) appears to track the actual charge rate well.

    My car is running v4.5 (1.33.61) software in my MS. It will be interesting to see what the charge rate profile looks like with 5.0. BTW, the last point were at a SOC of 255 miles. I got to 263 miles on a full range charge at home at the start of this adventure and arrived to Glenwood with 70 miles in the battery.

    If you are interested in my raw data, PM me with your e-mail and I will send you the Excel file.
     

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