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New Behavior for Main Pack Low Power

Discussion in 'Model S: Battery & Charging' started by Naonak, Aug 13, 2017.

  1. Naonak

    Naonak Member

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    I just discovered some new behavior for low power states in my vehicle.

    Previously, when the main pack ran out of power (or more accurately, reached it's cutoff voltage for shutting down) the entire car shut down, including the main screen, dash, heating/cooling, etc... for all intents and purposes, the car was "dead" until it was recharged.

    I just finished draining my pack (for calibration reasons, I believe it was significantly off), and it was taking much longer than it has in the past -- it "drained" for almost 4 hours with main screens, lights, heater, cold weather package all set to full. At first, I thought the car calibration was REALLY off... but eventually, a new pop-up came up and said the 12v battery was getting low and the car may shut off unexpectedly.

    I believe this is new, or it is at least new for me, where the 12v battery will now continue to power the interior, including minimal heat, until it, too, is exhausted. This makes discharging the main pack even harder now, because there was no immediately identifiable way to know when the main pack was cutoff.

    I just wanted to throw this out there for an FYI for those that like to live dangerously and recalibrate their packs, or are otherwise in need of a full pack discharge.
     
    • Informative x 3
  2. cynix

    cynix Member

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    Maybe try putting the car in Drive and see if it'll let you drive?
     
  3. Naonak

    Naonak Member

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    Yeah, that would definitely tell you if the main pack is depleted. But previously, you don't have to sit and monitor the car... just wait until it shuts off. Now you have to sit and monitor it periodically, checking to see if it's switched over to the 12v source.
     
  4. cynix

    cynix Member

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    Ah good point.

    Is there any real benefit in draining the main pack though?
     
  5. Naonak

    Naonak Member

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    Probably not for the majority of people, no.
     
  6. miimura

    miimura Active Member

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    I think what you are now observing is the expected behavior. The car should continue to operate for a short time on 12V power after the pack is exhausted or the traction battery contactor cuts out for some other reason.
     
  7. MasterT

    MasterT Member

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    12V battery gets topped off by the main pack as needed, maybe the discharge of the main pack inadvertently coincided with 12V battery cycle needed to recharge
     
  8. MP3Mike

    MP3Mike Active Member

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    The 12v battery shouldn't get cycled while the car is on, the DC-DC converter powers the whole car including the 12v side of things.
     
  9. scottm

    scottm Active Member

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    I didn't think the 12v could supply heater coil for HVAC... heat would be coming from the main pack.
     
  10. Naonak

    Naonak Member

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    Yeah, I didn't either, but apparently, it can at very low power. The heat was only luke warming come out, but it was definitely warmer than ambient for almost 2 hours.
     
  11. AmpedRealtor

    AmpedRealtor Well-Known Member

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    Did the recalibration result in any changes to your displayed range?
     
  12. Naonak

    Naonak Member

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    No, it doesn't appear so. The car took 78kWH of power, so it was right where it was before, give or take a kW.

    My wife's P85 has better range than my P90DL. Pretty disappointed in that. Showing 252mi rated range at 100%.
     
  13. MasterT

    MasterT Member

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    I don't think mere timing of the prompt warrants this conclusion.
     
  14. GlmnAlyAirCar

    GlmnAlyAirCar Member

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    That's actually incorrect. Even when the car is on, the 12v battery still cycles, powering the 12v systems and charging off the DC-DC converter as needed. It seems like an odd setup but this is actually needed to allow the first-responder cutoff loop to actually open the high voltage contactors.
     
    • Disagree x 1
  15. MP3Mike

    MP3Mike Active Member

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    I'm pretty sure that the DC-DC converter is on/active anytime the contactors are closed and would be unrelated to the first responder cut-loop. You cut the loop, the contactors open and the DC-DC convertor shuts off.

    In addition WK057 reports that the newer HV packs have an always on 12v output to support the vampire drain and to prevent the cycling on the 12v battery. (Such that the cars doesn't have to close the contactors to activate the DC-DC converter while it is parked to keep the 12v battery from going dead.)
     
    • Like x 1
  16. mspohr

    mspohr Active Member

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    I thought it was bad for the battery to discharge it completely... just like it's bad to overcharge it.
     
    • Helpful x 1
  17. GlmnAlyAirCar

    GlmnAlyAirCar Member

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    This has been worked out at length in previous posts. Unfortunately, I don't have the time to look them up now but will tonight if I get the chance.

    I think we can agree there must be 12v DC coming from the low-voltage battery to keep the contactors closed. Now, with the DC-DC converter were always active, I grant you that cutting the first responder loop would still open the contactors and make the battery safe. However, the fact that the 12v was constantly cycling, even when driving, is cited as a major factor in the short life of the 12v battery.

    Perhaps this logic has changed, which might explain why fewer 12v batteries are failing these days, along with using better deep-cycle batteries.

    I didn't know that about the newer battery packs - that's a great feature.
     
  18. MP3Mike

    MP3Mike Active Member

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    I have never seen anyone suggest that. Given that most cars are parked for ~94% of their life; that is where all of the 12v battery cycling occurs.
     
    • Like x 1
  19. GlmnAlyAirCar

    GlmnAlyAirCar Member

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    Now that I think about it, I think this info came from the service center. So, perhaps it is dubious information.
     
    • Funny x 1
  20. Electric700

    Electric700 Active Member

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    I think you are right about discharging it. As for overcharging / leaving the car at 100% for more than 30 minutes, yes I don't think that's good either for the battery. Your car should warn you about that situation too.
     

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