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Charging Reduced From 40A to 30A

Discussion in 'Model X: Battery & Charging' started by Tgibson, Sep 16, 2016.

  1. Tgibson

    Tgibson Member

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    Location:
    Denver, co
    i took delivery of a Model X 75D on June 24. I have noticed on about 4-6 occasions, my charging rate has reduced when the car automatically went from 40A to 30A. I noticed it happened again this week when I went to my garage and was surprised that the car was making a ton of noise while parked (sounded like external fan). Upon further inspection, I noticed the inside air conditioning had turned on and the charging rate had been reduced to 30A again. It seemed to me these things may have occurred because the car or battery may have been overheating during the charging process. Is this possible? If so, is this a safety concern?
     
  2. 90DPearl

    90DPearl New Member

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    Location:
    Southborough,MA
    I seem to have the same issue. A humming noise from something running when I charge the car and charging at 30A. I have a S and X (S is brand new). No such noise on S and S charges at 40A. Yesterday, I opened up the charger setting and in the settings somehow max charge was set to 30A!!. I changed that to 37A and after I stopped and restarted charing, it charged at 37A. When I talked to SC, they said, battery management decides what rate to charge at based on starting point of charging.

    Try playing with the charge limit settings and see if that helps.
     
  3. TexasEV

    TexasEV Active Member

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    If the car senses a charging issue and drops to 30A, it will stay there for future sessions unless you put it back up to 40A. Search reduced charging to 30A-- you'll see lots of posts with possible reasons, from your outlet wiring to neighborhood power problems.
     
  4. echin

    echin Member

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    Los Angeles, CA
    i haven't tried this yet, but is it an option to go up to 48A with standard home charging via the NEMA 14-50 (240V)?
     
  5. NeilErdwien

    NeilErdwien Member

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    No. You'd think a 14-50 is intended for 50 amps, and that indeed is its maximum capacity.

    But... Cars are considered a "continuous load", and the National Electric Code limits continuous loads to 80% of the circuit capacity -- thus the 40 amp limit.

    To get over 40 amps, you need to use the HPWC rather than a 14-50 and the mobile connector.
     
  6. goneskiian

    goneskiian Active Member

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    Just to be clear, it's not just the continuous load rule in play here. The MAX the UMC will provide is 40amps no matter what it's plugged into.
     
  7. TexasEV

    TexasEV Active Member

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    I think you're confusing the issue in an attempt to be clear. The UMC was designed to be plugged into a 14-50 which draws 40A from a 50 A circuit. It was designed that way because circuits are 125% of continuous load (or load is 80% of circuit rating). The UMC is 40A max because the highest rated outlet commonly found is a 50 A outlet.
     
  8. msnow

    msnow Active Member

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    If it happens often try dropping it to 38 AMPS.
     
  9. goneskiian

    goneskiian Active Member

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    Wouldn't be the first time!

    Thanks though. I'll refrain from trying to clear things up next time. o_O;)
     
    • Funny x 1
  10. Softwizard

    Softwizard Member

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    Location:
    Keller, TX
    I also have noticed this problem since August 8. My SC said it was the charging cable and they gave me a new one. That was three days ago and the problem still exists. I need to try another location to see if I can ever charge at 40A on a NEMA 14-50 plug like I have in my home.
     
  11. Softwizard

    Softwizard Member

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    I stand corrected from my previous post. I decided to check the Charge screen while my MX was charging (slowly) at 30A. For some reason, it was set for 30A, instead of 40A. I dialed it up and VOILA, it charges again at 40A. I don't know how it got set lower. I hope that this is the solution to OP problem too @Tgibson
     
  12. msnow

    msnow Active Member

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    It's sets itself to whatever the last successful charge was at that specific location.
     
  13. SilverUnicorn

    SilverUnicorn Member

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    My X does the same. I can set it to 40amps, and it'll charge a few times that way and then reduce to 30amps. I have a NEMA 14-50 and all new wiring and a new house. I figured it was the onboard computer reducing this to slow down charging. Not sure.
     
  14. SilverUnicorn

    SilverUnicorn Member

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  15. ishak

    ishak Member

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    My electrician came back and moved the 50A breaker from the end of the panel to the top and I haven't had a reduction to 30A since. Could also be related to the fact my AC is not running with milder temps so overall power consumption in my house is less.
     
  16. Remital55

    Remital55 Member

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    I had the same problem, and have NOT had any further problems since installing an HPWC in place of the 14-50 outlet- on the SAME circuit. Have not seen this problem with the travel cord on a 14-50 outlet recently installed at river cottage.
     
  17. kyalami

    kyalami Member

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    I have had the same experience over the past 18 months. I have a CPO Model S P85. Car will charge at 40 and then every so often back down to 30 amps. Wiring is correct and new and everything is in good shape. Since I charge overnight I am not losing any sleep over it but it is curious.
     
  18. Solarman004

    Solarman004 Member

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    I would recommend caution. My electrical engineering brain would not be comfortable with constantly resetting to 40 A, after the car reduced the rate to 30 A, without knowing the underlying cause. This is like resetting a circuit breaker after it trips, without finding the fault.
    Is the UMC cable or box getting very hot at 40A? Is the breaker hot at 40 A? Is the breaker loose? Are the breaker wires loose or corroded (I've seen this even a few months after the terminal screws are properly torqued)? Is the grid power showing surges or dropouts? Are there other devices or appliances on the same UMC circuit? Is there an issue with the internal MX charger? Is there a loose terminal in the NEMA 14-50 socket?
    Seemingly benign symptoms can often point to dangerous issues, especially when dealing with high amperage circuits.
     
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    • Informative x 1
  19. Frankman60

    Frankman60 Member

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    I'm wondering why all of the people that posted to this thread experienced the car automatically de rating the charge rate from 40 to 30 amps, when the adjustments in the vehicle can be in 1 amp increments. Why does it drop a full 10 amps? I have also experienced this occasionally, where the car adjusts from 40 to 30 amps for one charge. But after I adjust it up to 40 amps it will charge at that rate for a while before automatically de rating down to 30 amps. I think I'm going to try to manually adjust the charge rate to 35 amps to see if it will consistently stay at that rate. If that rate works consistently, I will increase it 1 amp at a time to see where it falls back to 30 amps.
     
  20. Saghost

    Saghost Active Member

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    The car measures the voltage drop from the resting voltage to the full load. If it sees a large drop, it reduces the current, so that the wires or plugs don't melt. If another large load causes the line voltage to drop, it can cause the failsafes to kick in.
     

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