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72 kW for a bone-dry S 70D?

Discussion in 'Charging Standards and Infrastructure' started by Missile Toad, Jan 12, 2017.

  1. Missile Toad

    Missile Toad Member

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    So a week or so ago, I'm at the North Houston combined SuperCharger and Showroom. I deliberately ran down my SOC to about 3 RM to see what kind of current the chargers would give me. Since it was close to dawn, I had all six SuperChargers to myself.

    Temperatures were hovering around 27ºF, and this had persisted overnight. Car had been driven at highway speeds for the previous 30 minutes and a 35 MPH for 15 minutes prior to that -- so it was as warmed as it was going to get from driving. Reaching the chargers I found this pattern. Plug in; 30 second ramp to about 110 kW; sustain for 60 seconds; drop to 70 kW (or so) in next 60 seconds. I did this through the entire set of charging stalls 1A through 3B. Through all six, not one could manage 75 kW after being plugged in for 2+ minutes. My pattern was to move to the next stall immediately after this precipitous drop.

    Now, I've seen posts where individual stalls are all wonky, and a move gets you to a suitable kW on the charging curve. What would cause the entire site to behave with such lowered output? My theory is that maybe the utility had something to do with it -- but the weather was clear, and as far as I could see, there was no stress on the electrical grid.
     
  2. LearnedFoot

    LearnedFoot Member

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    Is it possible that your car was the culprit?

    The car was the one constant between each stall. It seems more likely that the charging system determined that the battery pack could only safely charge at 70kW ( probably due to the temperature) and therefore scaled back the charging current.
     
  3. apacheguy

    apacheguy S Sig #255

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    Consider yourself lucky. Many folks are reporting that with <10 miles it takes 30-60 minutes before the power will ramp at all.
     
  4. wraithnot

    wraithnot Model S VIN #5785

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    This sounds pretty similar to what many people have observed in California. Apacheguy proved that the temperature of the charge handle is one factor in having the charging power "throttled" down after it initially giving full power: Some California Superchargers not providing maximum charging rates

    I observed the same thing at Harris Ranch a few weeks ago. It happened exactly as you said- I plugged in, got full power for a short period of time, power dropped, I moved to a different charging stall, saw full power, then it dropped again. Both times part of the supercharger plug got really warm. But for the rest of the trip through California, Arizona, and New Mexico I got the expected power for the whole charging sessions and the supercharger plug never got more than slightly warm. So the problem seems to be with at least two of the supercharger plugs at Harris Ranch rather than something to do with my car. I also noticed some of the sections of the supercharger handles I used at Harris Ranch had larger gaps than I've seen at other superchargers so perhaps they weren't assembled or installed correctly (unfortunately I was too worried about the implications of the slow charging for the trip to remember to take a photo of the odd looking supercharger handles).
     
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  5. LearnedFoot

    LearnedFoot Member

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    Interesting...a poor connection would raise the resistance and result in higher temperature at the charge handle. Did you check for dirty contacts?
     
  6. wraithnot

    wraithnot Model S VIN #5785

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    Unfortunately I didn't have time to take a closer look at things because we had a cranky toddler and I wanted to get a move on before the cranky toddler led to a cranky wife ;-) We were eating lunch at subway which is a bit of a walk from the chargers and I'd already spent some time moving to a new charging bay to try and fix things.

    I agree that some sort of poor connection either between the supercharger plug and the charge port on my car or inside the plug itself would explain things. I wonder how thoroughly Tesla tests superchargers after they install them or change out the charge handles. Do they have some test equipment that can simulate a full charge session on a depleted battery? Or is the test more basic than that?
     
  7. apacheguy

    apacheguy S Sig #255

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    Ive had super chargers throttle back at brand new locations (most recently Gustine) which essentially rules out dirty contacts.
     
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  8. apacheguy

    apacheguy S Sig #255

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  9. Missile Toad

    Missile Toad Member

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    IMG_2314.JPG
    For my part, using six of these stalls, rules out dirty contacts -- and I inspect my contacts every 2 weeks.
     
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  10. Missile Toad

    Missile Toad Member

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    #10 Missile Toad, Jan 12, 2017
    Last edited: Jan 12, 2017
    FYI, Top two pins are power contacts 401, 403. Bottom middle pin 403 is ground contact. Left-pin (below and hidden) is control, and right pin/sensor (below hidden) is proximity sensor. Also, from manual, referencing the ring:

    Blinking Amber: Model S is charging at a reduced current (AC charging only).
     

    Attached Files:

  11. David99

    David99 Active Member

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  12. Saghost

    Saghost Active Member

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    Is your 70D a limited 75, or an older true 70?

    I'm guessing that it's a real 70, since you got 72 kW starting out. The newer chemistry of the 75s and 90s appears to have a much worse penalty than that for very low states of charge - like 15-20 minutes with no visible charging plugged in before the charge rate suddenly shoots up. I've never experienced it, but there are several threads on it and arriving at <5% is the only common factor.

    If you'd been driving in 27F weather down to that low level, I'm going to guess your pack wasn't as throughly warmed as you thought - somewhere in the 10-15% range the cars cut out battery heating to extend the range I believe.
     
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  13. LearnedFoot

    LearnedFoot Member

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    Good idea to check the contacts regularly, my home built EV had occasional problems with the connector; I am going to keep contact cleaner in my frunk when my MS gets here (late March).

    I still suspect cold batteries, but if you are right Tesla needs to fix this.
     
  14. David99

    David99 Active Member

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    I have a bottle of spray contact cleaner in my car all the time. I used it on some Superchargers if they looked dirty.
     
  15. Moonwick

    Moonwick Member

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    Since I suspect the contacts need cleaning fairly regularly, I wonder if Tesla would approve of owners periodically cleaning the Supercharger contacts before plugging in. Assuming we're careful about it I can't see it doing much harm, but there's probably still a possibility of a safety hazard...
     
  16. Missile Toad

    Missile Toad Member

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    #16 Missile Toad, Jan 12, 2017
    Last edited: Jan 12, 2017
    @Saghost I drive the regular/original S70D without software limitations. A cold battery is a good theory, but where did you hear, "somewhere in the 10-15% range the cars cut out battery heating to extend the range"? In many cases, that represents between 35-60 minutes of driving, and I would suppose also results in deteriorating regen. I suppose, if the pack could retain heat enough to push out energy throughout the range that would be OK -- and as you say, extend the range.

    Further, if true, then attempting to "charge from the bottom" is no longer a good strategy at temperatures where temp < XºF. Any guesses at when to go to the "extra buffer" strategy based on temperature?
    • 55ºF
    • 45ºF
    • 35ºF
    I tell ya. Just when you think you understand how to drive fast and charge fast, another wrinkle develops.
     
  17. David99

    David99 Active Member

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    I have monitored the battery temperature reported at the CAN bus while driving for many months now and I can say with certainty that the battery will not cool down when the battery level drops below 10%. Even in very cold temperatures I found the car to be keeping the battery temperature warm pretty well all the way down to 0%. It uses the thermal losses from motor, inverter and DC-DC converter to heat the battery and it is working really well.

    Of course if the car was parked in the cold and then you drive to a Supercharger withing a short time, the battery will still be cold. But if you drive for an hour or longer, the battery will definitely be warm enough.
     
  18. TonyWilliams

    TonyWilliams Active Member

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    It doesn't make sense that the car would order the higher amperage from the Supercharger with a cold battery.

    If the battery is below XX temperature (that we don't know), it just won't ramp up to full power. Charging the battery at full power for two minutes only makes it warmer, so it would be even less likely to need to ramp down.

    I've certainly experienced what you are referring to, but not at every stall.
     
  19. Missile Toad

    Missile Toad Member

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    @David99 said:
    If you drive for an hour or longer, the battery will definitely be warm enough.

    that is all I need to know. Starting from a garage at 40º and driving continuously for 45 minutes is probably close enough to make the ambient 27º to be not a factor.
     
  20. Saghost

    Saghost Active Member

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    Interesting. I read the post about not heating the battery at low SoC here on TMC somewhere, I'll have to try and find it. I don't remember how they reached that conclusion.
     

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