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The 1-volt, now-it's-there, now-it-isn't dance, right after plugging in UMC

Discussion in 'Model S: Battery & Charging' started by brianstorms, Mar 31, 2014.

  1. brianstorms

    brianstorms Member

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    #1 brianstorms, Mar 31, 2014
    Last edited: Apr 11, 2014
    ...

    I'm sure this is a FAQ but I didn't know where to look so here goes.


    Often, when I plug my UMC into my NEMA 14-50 at home, I notice on the 17" screen that the car seems to be sipping tiny bits of electricity for a few minutes from the plug. Understand, I have my car programmed to charge after midnight to take advantage of the super off-peak electricity rates. This little 0V then 1V then 0V then 1V flickering thing happens for a few minutes, when I park the car in the garage for the night, often 5-6 hours before the car starts charging proper. Sure, it's a negligible amount of power, but I was curious what is the Model S doing? Is it querying the quality of the power? Testing something? Anyways, after a few minutes the 1V settles down to 0V and stays at 0V.


    Another reason I ask about this is because I am starting to notice on my monthly electricity bill, small amounts of the bill are going to off-peak or peak rates, even though I am obsessively careful to NEVER let the car charge during those times. So how is electricity leaking into the car if I've told the car not to charge? Am I seeing the accumulation of lots of millivolts or 1V over a month's time, adding up to say $3-5 of my $50 monthly bill?
     
  2. Kalud

    Kalud Member

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    Do you mean 1A (amps) instead of 1V (volts) ? If you see something like 1V then the relay in the UMC is not active (open circuit) and you are not consuming any electron from your utility. I've seen some 0V - 1V -V from within VisibleTesla app while not plugged in or when plugged in but not charging. Probably some rounding error when it sees 400 to 600 mV (less than 1 V)

    If you meant 0A - 1A - 0A you would have some > 200V reading and then yes you would be consuming some power from the utility, like 200 to 300 Watts.
     
  3. captain_zap

    captain_zap Electron tamer

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    I'm pretty sure this is just stray AC voltage being picked up by the high impedance open circuit, when the UMC relay is open. I've seen it, too. As for it coming and going, that's harder to explain. It could depend on the line voltage, which varies regularly with the time of day.
     
  4. SCW-Greg

    SCW-Greg Active Member

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    Mine does this too on occasion. Sometimes as much as 4+ amps. I attribute it to doing maintenance of sorts (heating, cooling, leveling, etc), using shore power while it can. Most of the time not.

    The maintenance reminder card I got from Tesla service center mentions this kind of activity, as the car takes care of itself.
     
  5. TexasEV

    TexasEV Active Member

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    This appears to be the stuff that makes "a connected Model S is a happy Model S" even when it is not charging.
     
  6. SCW-Greg

    SCW-Greg Active Member

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    Exactly!
     
  7. NigelM

    NigelM Recovering Member

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    The car is checking the connection and power flow; you can reduce this cost by only plugging after midnight although the cost of waking your spouse/partner every night may be higher.
     
  8. VolkerP

    VolkerP EU Model S P-37

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    This is a feature that was broadly demanded to add to the car.
    Video of the car using Shore Power for the AC

    If plugged in, the Model S uses shore power for HVAC/dash board display/touchscreen/music instead of drawing from the battery. The scheduled charging is solely for charging the battery, as in increasing its state of charge. Not for avoiding power draw.
     
  9. brianstorms

    brianstorms Member

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    Ok, I figured as much. Thanks all for the explanation.
     

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