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Charging rate from 40 amp J1772 question

Discussion in 'Model S: Battery & Charging' started by invisik, Aug 11, 2014.

  1. invisik

    invisik Member

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    Hi!

    I have a Leviton J1772 charger at my office (208v). It says on the front of it that it is 40 amp. When I plug my car in, it charges at 30 amps. VisibleTesla shows the pilot current is 40 amps (attached screenshot of when charging).

    Shouldn't the car charge at the full 40 amps in this situation? I understand when charging off a 14-50 or similar plug it uses 80% of the line capacity but I didn't think that applied to fixed-mounted EVSE's like this (or for that matter a Chargepoint or Blink unit out there in the world). I am using the J1772 to Tesla adapter. If not, shouldn't it charge at 32 amps (80% of 40) ?

    Is there something wrong with the installation of this unit or is this normal?

    Thanks.

    -m

    Untitled.jpg
     
  2. swegman

    swegman Member

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    Its 80% of a 40 Am circuit breaker (derated per code). But you only have 207 VAC, not 240 VAC, so it probably cuts back a bit.
     
  3. Cosmacelf

    Cosmacelf Active Member

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    If the pilot current is truly 40 amps, then, yes, you should be able to charge at 40 amps. Can you take a picture of your car's screen when charging? It doesn't have anything to do with the voltage. Perhaps the current got limited by the car due to a perceived charging fault, or you dialed down the charging current in the car for that location and forgot to dial it back up? What model Leviton is it?
     
  4. TexasEV

    TexasEV Active Member

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    #4 TexasEV, Aug 11, 2014
    Last edited: Aug 11, 2014
    This is a common source of confusion. EVSE makers identify their equipment by the amperage of the circuit that's needed, not the output of the unit. For example, one of the high amp level 2 chargers is the Clipper Creek CS-60, which requires a 60A circuit and has 48A output. Perhaps it's a safety measure, so an installer doesn't see "30A" on the label and assume it uses a 30A circuit?

    EDIT- My mistake. Leviton apparently doesn't follow this convention. Here they advertise a "40A charging station, requires 50A circuit":
    Evr-Green 400 Charging Station, Surface Mount, 25-Foot Cord, 40-Amp, Requires 50Amp Circuit, EVB40-PST : Electric Vehicle Charging Station

    So it's probably a resistance in the circuit somewhere that's causing the car to drop the amps by 25% to 30A for safety.
     
  5. invisik

    invisik Member

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    Hi, I ran down there and started it up charging again. No errors. Saw the amp number on the touchscreen said 30..... So I tapped the up arrow for the hell of it and it increased.... my bad, I was able to increase it all the way to 40 and it ramped up all the way to 40. I have no idea why/when I set it to 30. My fault, sorry.

    But this brings up a point, we should see full amp from a Chargepoint or similar, not 10% less, right? The car is smart enough to know when it should limit by 10% and when it shouldn't? Or is that the pilot number that is the amount it can pull?

    Thanks...

    -m
     
  6. tga

    tga Active Member

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    The pilot signal indicates the max amount of current the car can pull.

    It is up to the installer of the EVSE to use wiring and a breaker that is 25% greater than the pilot signal to provide an NEC compliant installation.

    In your case, the 40A Leviton EVSE requires a 50A circuit to be compliant (20% derating for EV charging loads).

    (Before anyone corrects "25%" in line 2, 40A + 25% (10A) = 50A, 50A - 20% (10A) = 40A)
     
  7. TexasEV

    TexasEV Active Member

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    Chargepoint charging stations have max 30A output:
    https://www.chargepoint.com/files/CT4000-Data-Sheet.pdf
     
  8. PhilBa

    PhilBa Active Member

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    Then it should deliver 32A, not 30. The voltage doesn't make a difference unless you are calculating watts.
     
  9. FlasherZ

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

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    Due to voltage fluctuations, it is likely that the car reduced charge current then stayed there. Good to see you could increase it to 40A.
     
  10. Canuck

    Canuck Active Member

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    True in theory but my Clipper Creek CS-60 charges at 50 Amps even though the car says 48 Amps the charge rate is 50:

    20140506_093548_resized.jpg
     
  11. Cosmacelf

    Cosmacelf Active Member

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    Well, of course. In Canada, those are imperial unit amps, not the regular American ones :)

    Looks like a bug to me. I too have a CS-60, but only a single charger, so it just reports 40/48 Amps for me. Maybe tell/email Tesla ownership and see what they say.
     

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