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Charging Amps per outlet

Discussion in 'Charging Standards and Infrastructure' started by acentre, Aug 9, 2012.

  1. acentre

    acentre Member

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    What determines the onboard charger's ability to know the rating of the outlet that it is drawing power from. If I plug a Model S into a 20amp line, how does it know that it is limited by that rating?
     
  2. Lloyd

    Lloyd Active Member

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    It is determined by the configuration in the plug adapter on the UMC (Universal Mobile Connector) supplied by Tesla with each car. You can see the adapters that Tesla sells for the roadster on the Tesla site now. HERE Charging supplies for the Model S are a little more compact and streamlined and should be on this site very soon.
     
  3. cinergi

    cinergi Active Member

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    Well, it won't know for 120v whether it's 12 or 16 (15 vs 20 circuit) and for 208/240 whether it's 24 or 40 (30 or 50) for example. You can set the amperage draw on the car itself. And if it's like the Roadster, it ties this to GPS location and remembers it so you don't have to set it every time (if you have special circumstances where you can't draw the max for the particular outlet configuration you're using).
     
  4. Lloyd

    Lloyd Active Member

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  5. cinergi

    cinergi Active Member

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    You mean if I use the 120, it'll default to the max of 16? Or did you mean it'll default to the "safer" 12? (It's been my experience it defaults to 16 in the Roadster. I usually have to dial it down.) Less of an issue with the 208/240 outlets as the full current is more frequently available than it is with a US 120v outlet. Unless Tesla will require the use of a T-slotted 120v plug to draw 16a on the Model S. That would be nice.
     
  6. bluetinc

    bluetinc Member

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    Each of those plugs has it's own defined current limit:

    NEMA 5-15 (standard socket) is 15A (12A when over 3 hours)
    NEMA 5-20 (The T plug you mentioned) is 20A (16 when over 3 hours)

    This is also true for the various 240V outlets, and I have been told that while the Tesla design will let you lower the charging current, you will not be able to override it upwards (i.e. you won't be able to pull 40A from a NEMA 14-30, rather a max of 24A).

    Peter
     
  7. TEG

    TEG TMC Moderator

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    Another thing to keep in mind - in some cases a breaker could be shared among more than one device.
    For instance, if the EV is plugged into a garage outlet that is on the same breaker with an electric garage door opener, you want to reduce the current draw so that the car charging + garage door motor running don't trip the breaker.

    More likely to happen with 120V, but occasionally you find shared 240V too.
     
  8. cinergi

    cinergi Active Member

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    Except that the Roadster comes with only a NEMA 5-15 for both 15 and 20 amp circuits. You can pull 16A using a 5-15 plug in a 5-15 outlet and trip the breaker. That may be the only case where it's really an issue. I don't know if the Model S with come with both a 5-15 and a 5-20.
     
  9. TEG

    TEG TMC Moderator

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    By the way, here is the visible difference between a 5-15 and 5-20:

    [​IMG][​IMG]


    Tesla could have put a special plug-end on the adapter "keyed" for 5-20 use only like this:
    [​IMG]

    But they picked the much more common vertical blade and leave it up to the user to turn down the current if they aren't plugging in to an actual 5-20 outlet.
     
  10. bluetinc

    bluetinc Member

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    Cinergi and TEG,

    Thanks for the info, I didn't realize that was how Tesla did it for the Roadster.


    Peter
     
  11. neroden

    neroden Happy Model S Owner

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    Ahhhh. This explains a comment I was confused by from the person I was talking to at Tesla.

    From what he was saying, the model S will not do this. A 5-20 adapter for the Model S will cost extra. The model S will come with a 5-15 which will only draw at the limits for a 5-15.

    (If you have a ten-amp circuit, which is actually fairly common with 5-15s, you'll still have to dial it down yourself or trip the breaker. There is no separate 5-10 plug.)
     
  12. Doug_G

    Doug_G Lead Moderator

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    I suspect most Roadster owners don't know about the two kinds of 110V plugs. The thing is, "continuous" really isn't much different from "instantaneous" when the electrical code defines the latter as several hours. So in reality you could probably get away with drawing the higher power from the 15A circuits.
     
  13. ljwobker

    ljwobker Geek.

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    Hmm... DISAGREE. "Continuous" is defined by electrical codes to prevent heat build up. Charging a car absolutely qualifies as a continuous load. And these codes exist for a lot of very good reasons. You don't want to be intentionally flaunting the code by doing something like intentionally over-currenting a circuit and/or cordset. If you have the knowledge and background to interpret circuits, their loading parameters, your particular installation, and are comfortable with the increased risks (i.e. anything from tripping a breaker to burning down your house...) then that's one thing. But encouraging others to do so (even indirectly) is a big no-no.
     
  14. Doug_G

    Doug_G Lead Moderator

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    I wasn't encouraging people to do that, but the Roadster defaults to the higher amperage so a lot of people are probably doing exactly that without realizing it.
     

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