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Charging @ 40AMP - Volt differences

Discussion in 'Model S: Battery & Charging' started by bcampbelllds, Nov 10, 2016.

  1. bcampbelllds

    bcampbelllds Member

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    I'm curious if anyone can explain why on a 40AMP circuit there are different volts at two separate locations I use to charge my 2015 Model S. My home 240 outlet gives me 248V at 40AMP and a public charging location gives me 206V at 40AMP. See attached pictures. What would be the reason for the differences on voltage?
     

    Attached Files:

  2. brkaus

    brkaus Active Member

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    I believe many public/commercial locations are getting their power from three phase sources. Which ends up 208 Line to Line.
     
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  3. bcampbelllds

    bcampbelllds Member

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    Would this make my home outlet a single phase then?
     
  4. John5396

    John5396 Member

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    Yes,

    standard residential is 240 single phase with center tap for return.
     
  5. Rocky_H

    Rocky_H Active Member

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    Not quite. The usual term for it is "split phase". It has to do with the frequency of the alternating current on the different lines and how far they are shifted off from each other. Here is a good easy to see explanation of single phase, split phase, and three phase.
    3 Phase Power vs Single Phase Power • OEM Panels

    Single phase is just a 120V line to neutral.
    Split phase has two different 120V lines, which are 180 degrees shifted from each other, so they are always totally opposite voltage from each other, which equals 240V total difference between them.
    Three phase has three different lines at 120V, but they are all shifted by 120 degrees apart from each other, so the usable voltage difference between any two lines is 120V times the square root of 3, which works out to about 208V.
     
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  6. Rocky_H

    Rocky_H Active Member

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    It does seem fairly common, though, that split phase systems are sometimes referred to by the term single phase, which is unfortunately a little confusing.
     
  7. bcampbelllds

    bcampbelllds Member

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    Thank you for the explanation.
     
  8. NewJerseyMS

    NewJerseyMS Member

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    At home I get 230 to 235 volts. I hit 27 mph charging. Asked electrician and he said the utility is required to deliver from 220 to 240 volts and I'm usually around the middle.
     
  9. Rocky_H

    Rocky_H Active Member

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    In most places, I think I have read that the guideline is supposed to be a target of 240V with variance of about +/- 5% allowed.
     
  10. gavine

    gavine Petrol Head turned EV Enthusiast

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    I learned this the hard way when I was expecting to get 29MPH on a 40A public HPWC, only to find that it was only 24MPH. My 240V/40A at home is 9600 watts but the 208V/40A is only 8000 watts.

    Volts X Amps = Watts and watts are what matters.
     

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