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40amp to 30amp Charging Drop Update

Discussion in 'Model S: Battery & Charging' started by supratachophobia, Nov 9, 2015.

  1. supratachophobia

    supratachophobia Active Member

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    Regarding the car lowering voltage during charging from 40amp to 30 amp in the middle of the night. Per Jerry33 (whom I can't quote because of his sig), I have manually set the amps to 38 for the last three months. I've had zero instances of auto amperage drop in that time. So for anyone experiencing that 25% drop, I think this is a great solution. Sure you don't get that extra 2 amps, but you also don't get the unpleasant surprise that your car isn't done charging in the morning.
     
  2. Tedkidd

    Tedkidd Member

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    Hmmm. Another software improvement suggestion: optional email/text if charging stops before reaching setpoint.
     
  3. aus

    aus Member

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    I'm new here. Why would the car drop the amp while charging?
    And why would setting it at 38amp prevent it from happening?
    Thanks.
     
  4. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    It's perfectly okay to quote inside TMC. The sig is meant for quoting outside TMC. (There were some problems with this early on)

    - - - Updated - - -

    Amps are reduced when the car perceives a charging problem or voltage drop to prevent fires. Reducing the amps from 40 reduces the possibility of the charging being reduced. I suspect it also improves the life of the UMC because the UMC runs cooler. This also works well in RV parks, which often have substandard wiring.

    - - - Updated - - -

    The App alerts for stopped charging.
     
  5. supratachophobia

    supratachophobia Active Member

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    I'm going to quote the crap out of you now.....
     
  6. msnow

    msnow Active Member

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    Very interesting and timely post for me. To save money I just started using our local Southern California Edison Time of Use program which is in effect from 10:00 PM to 8:00 AM every day. I'd always scheduled charging at 40 amps starting at midnight. Last week I changed the schedule of my swimming pool pumps to run during the TOU period to take advantage of the lower rates. The very next day I noticed that the Tesla "down amped" to 30 and left it as the setting which I think is also saved GPS. After a couple of days of this as a test, I changed the start time of the car to begin when the pool wasn't running and it held at 40 amps and stayed that way for the last couple of days. My guess is that the load was causing the voltage to fluctuate outside of Tesla's tolerances. I'll try it at 38 and see what happens.
     
  7. TexasEV

    TexasEV Active Member

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    Maybe the car is telling you to not charge while the swimming pool pumps are running. Maybe you should listen to it.
     
  8. Lloyd

    Lloyd Active Member

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    Already there: Go to "Notifications" under the settings tab of the Tesla App!
     
  9. msnow

    msnow Active Member

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    No, that's not what it's telling me.
     
  10. William13

    William13 Member

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    My charging went down from 40 to 30 amps a few times this summer at my Dad's house. I thought it was from the AC turning on. Later on a hot night the circuit breaker tripped in the middle of the night. I now charge at 27 amps and/or check charging status frequently. The plug is less than one foot from the circuit breaker but on the outside wall. Maybe water, maybe bad circuit. I am not qualified to evaluate.
     
  11. scottreds2k

    scottreds2k Member

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    Back in the summer, I had my charge rate drop from 40 to 30 in the middle of the night several times. I have a thermostat that records data from my Heat Pump/Furnace setup and I could tell that sometimes when the AC came on in the middle of the night, the charge rate dropped to 30 amps, according to data retrieved through Visible Tesla. What doesn't make a lot of sense to me is that I have a 100 amp circuit running the HPWC, I'm only drawing 40 amps, and there is enough of a fluctuation in the draw when the AC comes on, that the Tesla recognizes it as a big enough fluctuation to drop the charge amperage.

    It has now started again when the heat pump comes on.
     
  12. msnow

    msnow Active Member

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    Same here. Adequate capacity and no circuits are tripping but the car is dropping the amps. Could be the voltage is fluctuating too much for the cars specs to sustain 40 amps due to these other things drawing power. I'll try the 38 setting and see if it helps.
     
  13. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Likely a bad connection or perhaps a bad breaker. If it was installed professionally, on a 50 amp breaker, then the materials should be fine but perhaps it's a matter of loose connections at the breaker. If it was installed by someone else, they may have used wrong conductor size or something.

    - - - Updated - - -

    This can be the result of a bad start capacitor in your heat pump's motors - either blower or condenser - or a worn motor, bad bearings, etc. Even in an unloaded motor with good bearings, the current inrush during the first half-cycle can be 20x the running load. As the motor begins to spin, that inrush current reduces to about 8x the motor's normal load, and as the motor comes up to speed the current reduces to running load.

    If you have a bad capacitor, or your motor is "sticky", then it will draw a higher load than normal for a longer period of time. This higher load can drag down the voltage across smaller conductors, near-capacity transformers, etc., for long enough that the Tesla recognizes it.

    (As noted in the other threads, I had a bad fluorescent ballast trip the algorithm.)
     
  14. William13

    William13 Member

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    Thanks Flasher Z, do I need an electrician to look at it or is my dad safe as long as no further tripping of the breaker occurs?
     
  15. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I would get it checked out by someone who knows basic electrical work. Make sure the breaker connections are tight (and you don't see burned/charred/melted insulation on the wires there), and ask them to make sure the wiring is the right size (for 50 amp circuit, #8 minimum for conduit, #6 for NM/Romex cable). It doesn't necessarily have to be an electrician unless you see something out of sorts, but I would have someone look at it.

    If you're willing to take the screws out of the front of the circuit breaker panel and collect a picture of the wiring going into the breaker that tripped, I can let you know if I see any signs of something that needs to be addressed here.
     

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