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Why are some stations 208V?

Discussion in 'North America' started by tdiggity, Feb 19, 2013.

  1. tdiggity

    tdiggity Member

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    Is there something extra needed for 240V?
     
  2. mitch672

    mitch672 Active Member

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    Because commercial 3 phase power is delivered as 120/208, that's the only reason.

    Only residential single phase service is 120/240.
     
  3. dhrivnak

    dhrivnak Active Member

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    I think you will find the VAST majority of public charging to be 208V or one leg of three phase power. This combined with the fact that most stations are limited to 30 amps we have an effective charge rate of 6kw. This is SLOW when on a trip.
     
  4. mknox

    mknox Well-Known Member

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    ...it's actually two of the three phases that delivers 208 volts. On a 120/208 volt 3-phase, 4-wire system, each phase to neutral gives 120 volts and phase to phase voltage is 208 volts.
     
  5. strider

    strider Active Member

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    Darn it! I finally knew the answer to an electrical question and you all beat me to it! :crying:
     
  6. tdiggity

    tdiggity Member

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    Cool. I knew it had to be something simple. Not ideal, but at least the answer makes sense.

    Is it easy (cost effective) for commercial sites to convert to 240V?
     
  7. ElSupreme

    ElSupreme Model S 03182

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    Not really no. They would need a transformer and/or separate power distribution. The 208/120 three phase is generally a 'better' way to transmit power than 240/120 split phase.
     
  8. rolosrevenge

    rolosrevenge Dr. EVS

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    Depending on the power factor of the building, a really big capacitor could kick your voltage up to near 240 as well, but it's unlikely.
     
  9. doug

    doug Administrator / Head Moderator

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    And every time you get 208V on an EVSE you can wonder at what might have been if we had adopted the Mennekes (Type 2) connector here in the US which supports 3-phase, instead of the inferior Yazaki J1772 design.
     
  10. Doug_G

    Doug_G Lead Moderator

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    Our office connection to Ottawa Hydro is 600V, 200A, 3-phase. One phase provides 347V, which powers the lighting directly (yowch don't touch those wires!). There are a couple of 3-phase step-down transformers for feeding the 208V / 120V circuits.

    It's a fair distance from the transformer/panel out to the parking lot. Despite beefy wires, when I draw 70A the voltage ends up being only 198V.

    In contrast, when drawing 70A at home, I get 238V or more. There's a 20% power difference between the two locations!
     
  11. mknox

    mknox Well-Known Member

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    347/600 volts 3-phase, 4-wire is kind of a Canadian thing. It is fairly common in commercial settings. As you say, lighting is often 347 volts (one phase and neutral) with dry-type transformers in the building to step down to 120/208 volts for receptacles and such.

    EVSE aside, there are a lot of 240 volt devices that have 208 volt equivalents so that you don't suffer the reduction in power (they just use a few more amps at the slightly lower voltage to give you the same power). My friend with the cottage bought a used stove from an apartment dweller without realizing it was a 208 volt range. When he hooked it up to his 240 volt supply at the cottage, the elements lit up like light bulbs! He ended up having to replace all 4 stove top elements and both oven elements with 240 volt counterparts. Some devices, like electric water heaters, have 2 wattage ratings, depending on the voltage applied and are designed for both 208 and 240 volt circuits. When hooked to 208 volts, they just take a little bit longer to make hot water.
     
  12. TEG

    TEG TMC Moderator

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  13. ElSupreme

    ElSupreme Model S 03182

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    There is also 480V three phase (which is what industry in the US uses) It is the same configuration but with 480V between legs, and 277V from a leg to neutral.
     
  14. wycolo

    wycolo Active Member

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    #14 wycolo, Feb 20, 2013
    Last edited: Feb 20, 2013
    Yeah, yeah, like blind men inspecting different parts of an elephant. Distinct points of view.

    "Uncle Willy, why is there 3 phase??" [the *real* question, here and always]:

    Because electrical motors designed for 3 phase power run more efficiently than single phase motors. Area under the 3 curves > area under single curve. True.

    Because florescent light bulbs run on 3 phase are more efficient than running on single phase. Maybe true or not(?).

    Because resistance heating elements are more efficient using 3 phase. Maybe true or not(?).

    To piss off EVers by offering only 0.87 the power they enjoy using their single phase power at home. True.

    And remember Eyore, that voltage has nothing to do with it; i.e. choose higher voltage to use thinner wires but then pay extra for more insulation. Uncle Willy has 14k volts feeding his pole pig. Are there any electrical distribution systems running at a higher voltage? Don't think so. Now Eyore, go build your campfire but don't build it directly under that 14k volt line or the rising ionized air will draw lightning to earth(!!).

    Oh, also, to run a 5 hp 3 phase motor at full power on a single phase supply: get a 10 hp 3 phase motor and hook just one leg to single phase (at proper voltage). Then connect its three phases directly to the 5 hp motor. The 5 hp motor will now give full power. The 10 hp motor's shaft is not connected to anything- it is a motor-generator only. Efficiency? Don't ask, you got the 5 hp motor to do its thing, right??

    That's all I know about three phase. :cool:
    --
     
  15. Doug_G

    Doug_G Lead Moderator

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    Thermodynamically impossible. Inefficiency results in heat generation. So a resistive heater is always 100% efficient.

    The wiring leading to the heater can lose energy, but that's also generating heat and arguably just warms up the building too.
     
  16. Robert.Boston

    Robert.Boston Model S VIN P01536

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    Question for the electricians: I've got 120v/208v power at my house. What would I need to transform the 208v line feeding my NEMA 14-50 up to 240v? Since I'm limited to 40A continuous, I might be willing to buy the 15% upgrade if the price isn't too steep.
     
  17. mknox

    mknox Well-Known Member

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    277/480 is the US counterpart to the Canadian 347/600 and is found in similar applications.
     
  18. rolosrevenge

    rolosrevenge Dr. EVS

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    http://variac.com/staco_50006000_series_3_9_motor.htm This should do the trick. Just dial it up to maximum and you'll be good to go.

    - - - Updated - - -

    Actually, since you're limited to 40 A this will be cheaper http://variac.com/variacs_motor_driven_50001_2coils.htm
     
  19. mknox

    mknox Well-Known Member

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    In theory, if you could find a 208 to 240 volt transformer with the proper capacity rating, you could step your 208 volts up to 240. HOWEVER, since you are limited to pulling 40 amps from your 208 volt circuit, you would only be able to realize about 35 amps continuous (minus any transformer losses) on the high (240 volt) side, meaning that you're still delivering the same amount of POWER to the car. There's no free lunch. (Power (watts) = Voltage (volts) * Current (amps))
     
  20. FlasherZ

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

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    Right, I think they're likely saying that to maximize the car's draw, because it's based on amps, that installing a 208:250 transformer with a 60A primary rating could give a full 10 kW @ 250V/40A on the secondary, to the car.
     

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