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Car keeps resetting to 30 Amps

Discussion in 'Model S' started by jfoxny, Aug 3, 2016.

  1. jfoxny

    jfoxny Member

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    I am charging on a NEMA 14-50 on a (dedicated) 50 amp breaker and had the car set to charge at 40 Amps but it reset to 30. At first I thought it was the recent software update but it did it again today. I seem to recall someone else posting about this but couldn't find it. Any ideas?
     
  2. msnow

    msnow Active Member

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    It used to happen to me before I went TOU with the electric company and they checked their power from the street. While they were working on it I set it to 36 or 37 AMPS and it never down amped after that.
    Although it still happens rarely I have it back at 40A.
     
  3. Jeff65

    Jeff65 Member

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    It has happened to me since day 1 (2 years ago). I have 200 amp service and even before the Tesla, noticed voltage drops when turning on large appliances. My 50 amp circuit is brand new and very short distance from the main panel. Tesla replaced the charger but it made no difference. I just think that my total load at times causes the drop and then the car goes to 30 amps to protect itself. If I set it at 35 instead of 40, it is usually happy enough and doesn't reset lower.
     
  4. Saghost

    Saghost Active Member

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    The car will do this automatically if the voltage drop is large enough in an attempt to protect the wiring/connectors on the house side.

    You should probably have someone check your power and wiring. What does the screen show as the voltage before and during charging?
     
  5. webbbcam

    webbbcam not-so-junior member

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    Did your Tesla give you any warning about why it decreased the charging rate?
    When I tried charging at my brothers house he had only 110v outlets available. When I tried one circuit outside of his garage my car gave a warning box saying that the voltage drop on the circuit was too much and recommended the wiring be checked and stopped charging entirely. After I plugged into an outlet closer to his circuit breaker box all was well.

    If you car detects a drop in the voltage that is out of its tolerances it will "dial down" the amperage it asks for.... hence your 30amps.
    Could be bad outlet, undersized wiring, overloaded sub-circuit breaker box, undersized service line (electric heat?, air conditioners?)or even undersized transformer from your power company that can't handle an extra 40amps of load.
     
  6. scottreds2k

    scottreds2k Member

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    I have a dedicated 100 amp circuit going to my HPWC, and my S only charges @ 40 amps. I have had it reduce the charge to 30a while charging overnight. I''ve never bothered to figured out exactly why it does it, but by downloading data from my thermostat and pulling data from the Tesla using Visible Tesla (?), I could tell that sometimes when the AC kicked on the charge dropped to 30 amps. It doesn't do it often enough for me to bother having someone try and diagnose it, but my guess is it is some type of feedback from the AC startup that is causing it.
     
  7. Btrflyl8e

    Btrflyl8e Active Member

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    My first Tesla started doing this after some time. A good cleaning of the contacts solved it for me.
     
  8. jfoxny

    jfoxny Member

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    #8 jfoxny, Aug 3, 2016
    Last edited: Aug 3, 2016
    Huh, interesting. I installed the outlet myself, to code, using the proper wiring. Voltage is usually around 230 but I did not specifically see what it was before the drop (or if it was at 30 amps from when I plugged it in). No warnings or messages given by the car.

    I wonder if it could be caused by the compressor in a beer fridge on the same panel kicking on. I also have a Clipper Creek charger on the same panel (dedicated 40 amp breaker) for my i3 and have had both cars charging at the same time with no issues. Both are on a 100 amp sub panel with little else on the panel.

    Seems random but at least this gives me a lead.
     
  9. EdA

    EdA Model S P-2540

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    My car (2012) does it fairly frequently. I never see any indication on the screen.
    My wife rarely charges at home but I've never seen it on her car (2014).
    I suspect it is a function of other load on my 200A service.

    Once it downgrades you have to manually ratchet it back up to 40A on future
    charging sessions.
     
  10. msnow

    msnow Active Member

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    I'm pretty sure mine is 240v or higher.
     
  11. TexasEV

    TexasEV Active Member

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    Your 230 volts is likely the problem. Have an electrician determine why you're not getting 240V.
     
  12. jfoxny

    jfoxny Member

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    My understanding is that +/- 5% is an acceptable variation.
     
  13. msnow

    msnow Active Member

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    Maybe take a look at the FAQ from @FlasherZ
     
  14. supratachophobia

    supratachophobia Active Member

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    I had pretty good luck on the first Tesla by setting to 38amps when it did this. Oddly enough, 2nd Tesla has never done this.
     
  15. msnow

    msnow Active Member

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  16. scaesare

    scaesare Active Member

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    Contact cleaning largely resolved it the first few times for me as well. Now I rarely can keep it happening with my HPWC at home. I think my HPWC charge connector is having a hard time with the connections for the pilot signal..
     
  17. supratachophobia

    supratachophobia Active Member

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    Could it be the constant plugging and unplugging of the cable that is causing it to not have as good of a connection?
     
  18. mikeash

    mikeash Active Member

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    I don't think it would be the pilot signal. I'm far from an expert on these things, but from my (no doubt incomplete and incorrect) understanding of J1772, the pilot signal is simple and tough to misunderstand. For that to cause the car to back off the amperage, the bad connection would have to somehow cause the car to see a shorter duty cycle on the pilot line than the HPWC is sending. Seems much more likely that the car is backing off due to voltage fluctuations on the power lines, due to bad contact at the plug or trouble elsewhere in the wiring.

    If anyone who knows this stuff better disagrees, I'd welcome the knowledge!
     
  19. scaesare

    scaesare Active Member

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    I think the issues is that if the car doesn't see a "good" pilot signal for 40A, it defaults to what is considers a "safe" current for the voltage and adapter combo it sees, and I suspect that's 30A for the NEMA 14-50 on a 240V circuit.

    So I don't think it's a matter of not reading the correct duty cycle on the pilot pin.. I think it's not getting a correct pilot at all...
     
  20. mikeash

    mikeash Active Member

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    The pilot signal is what tells the car which adapter is connected. The UMC reads a resistor from the adapter, figures out the corresponding amperage, and then generates a J1772 pilot signal for that amperage. Without a pilot signal, the car would have no idea what it could safely draw, it could be far below 30A, or the EVSE could be trying to indicate an error over the pilot wire.
     

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