TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Standard Outlet Extension Cord?

Discussion in 'Model S: Battery & Charging' started by Soundchasr, Mar 28, 2016.

  1. Soundchasr

    Soundchasr Member

    Joined:
    Mar 8, 2016
    Messages:
    246
    Location:
    Very close
    Is there an extension cord for a standard outlet that is recommended? When I go to visit my family I'd like to charge a little overnight (the dryer is in the basement so I think that's out..).

    Thanks!
     
  2. liuping

    liuping Active Member

    Joined:
    Jul 23, 2013
    Messages:
    1,858
    Location:
    San Diego
    • Informative x 1
  3. Soundchasr

    Soundchasr Member

    Joined:
    Mar 8, 2016
    Messages:
    246
    Location:
    Very close
    Excellent. Thanks.
     
  4. mrElbe

    mrElbe Member

    Joined:
    Aug 17, 2014
    Messages:
    849
    Location:
    Stouffville, ON Canada
    Try to keep any extension as short as possible. Line loss will reduce the Amps you can draw without tripping the breaker.
     
  5. kort677

    kort677 Active Member

    Joined:
    Sep 17, 2015
    Messages:
    1,858
    Location:
    florida.
    FWIW: I use a 65 ft 12g 15 amp cord that get the job done. you aren't going to be pulling more than 3-4 mile per hour regardless of length, it is wise not to keep the cord coiled when in use
     
  6. TexasEV

    TexasEV Active Member

    Joined:
    Jun 5, 2013
    Messages:
    3,770
    Location:
    Austin, TX
  7. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

    Joined:
    Mar 28, 2015
    Messages:
    531
    Location:
    Houston, TX
    No, current in amps is constant throughout the circuit (Kirchoff's current law). Amps at the circuit breaker = amps at the plug = amps at the car no matter how long the extension cord is.

    What will happen is that the longer the extension cord is, the more voltage drop it will produce, resulting in lower voltage at the car than at the outlet. This reduces total power available for charging, and therefore reduces the charging rate.

    e.g. On a dryer outlet, nominal voltage = 240V, circuit rated current = 30A, maximum continuous draw = 24A. In theoretical ideal conditions, power available at the car for charging = 240 * 24 = 5.76 kW.

    With long extension cord, voltage at outlet = 236V (4V drop due to the current draw through the building wiring), voltage at car = 226V (10V drop due to 100 foot extension cord), current = 24A. Power available at the car for charging = 226 * 24 = 5.424 kW.


    The reason that it works this way for the car chargers is that the chargers are regulating the current they draw. That is an unusual operating mode when compared to other devices.

    For example, an electric motor like a vacuum cleaner would behave differently. The motor is under a constant mechanical load, thus must produce an equal amount of mechanical power. A longer extension cord on the vacuum will cause the same voltage drop at the vacuum cleaner motor, reducing it's power output, which will cause it to slow down, which decreases the back-EMF, which then causes current to increase to bring produced mechanical power back to equilibrium with the shaft load. So yes, in this case, the total current draw with the extension cord will be higher than with a short cord.
     
    • Like x 1
  8. Zarwin

    Zarwin Member

    Joined:
    May 12, 2014
    Messages:
    406
    Location:
    Hillsborough, NC

Share This Page