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

Can I combine 30A and 50A 240V lines?

Discussion in 'Model S: Battery & Charging' started by Hometheatremaven, Mar 29, 2013.

  1. Hometheatremaven

    Joined:
    Dec 27, 2012
    Messages:
    215
    Location:
    La Jolla CA
    I am having an electrician run a new 50A 240V line to my garage to charge my soon-to-be-received Tesla S. He is doing this when he replaces my existing Zinsco box.
    I also have an existing 30A 240V dryer outlet that can be extended to the location of the Tesla plug.

    Is there anyway to combine those two power sources to charge quicker? If so, what adapter would I use on the mobile charging cord? Or is there a different way to go?

    Thanks.
     
  2. qwk

    qwk Model S P2681

    Joined:
    Dec 19, 2008
    Messages:
    2,817
    Only the HPWC charges at a greater speed than a 50A receptacle.
     
  3. Doug_G

    Doug_G Lead Moderator

    Joined:
    Apr 2, 2010
    Messages:
    15,852
    Location:
    Ottawa, Canada
    Uh, no. If you want faster charging you need a 100A circuit, an HPWC, and dual chargers in the car.

    Just stick with the 50A circuit. You will quickly find it's all you need.
     
  4. bluetinc

    bluetinc Member

    Joined:
    May 11, 2009
    Messages:
    682
    Location:
    MD
    Hey Hometheatremaven,

    Setting aside the issues directly related to combining the circuits, the how, and the costs, the bottom line in this case is that it won't help you very much anyway. When I combine two circuits, the current splits just about evenly. Because of this the smaller circuit will limit you at 80% of the rated current, or 24A. You would then be pulling 24A from both the 30A circuit and the 50A circuit, or 48A total. So, in the end, you might pick up that ability to charge 20% faster.

    Peter
     
  5. Lloyd

    Lloyd Active Member

    Joined:
    Jan 12, 2011
    Messages:
    4,885
    Location:
    San Luis Obispo, CA
    Ummm NO you can't do that. It is expressly against NEC at sizes < AWG 1/0. You can't guarantee conduction as you think on the two different conductors. One can overheat and start a fire. Setting aside the fact that you said there are issues, this needs to be clear.
     
  6. FlasherZ

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

    Joined:
    Jun 21, 2012
    Messages:
    7,019
    In theory, you *could* do it. It will be far too complex and impractical, though... read up on Ohm's Law and parallel circuits. As Lloyd points out, against the NEC which will invalidate your homeowner's insurance.

    50A is generally good enough for anyone, or you'll need to install a bigger circuit w/ HPWC.
     
  7. Hometheatremaven

    Joined:
    Dec 27, 2012
    Messages:
    215
    Location:
    La Jolla CA
    Thanks to everyone. Especially Flasher Z who shamed me into replacing my Zinsco box (fire hazard) with a new one ($2000) and running a new 50A line in conduit under the walkway and into the garage ($1000).
    Flasher, maybe I should tell the electrician to send you the bill for the new box :) Haha!
    Anyway the Tesla will charge faster with the new 50A line instead of the 30A dryer line (which would have cost < $100 to extend).
    Okay Flasher, I'll only have him bill you $1900 :)
     
  8. bluetinc

    bluetinc Member

    Joined:
    May 11, 2009
    Messages:
    682
    Location:
    MD
    Hey Flasher,

    I'm not sure why you quoted that line, it is what I do see when I do combine circuits. That said, no argument that doing so safely is very very complex and impractical, especially for home use, which I would NEVER recommend.

    Peter


     
  9. FlasherZ

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

    Joined:
    Jun 21, 2012
    Messages:
    7,019
    Yes, in hindsight, I can see the confusion on my quote choice. I meant to add on to what you were saying; namely, that in the absence of some complex calculations, specialized hardware and/or specific distances of wire, etc., current will try to divide equally based upon resistance of the conductors. Managing asymmetrical currents across parallel conductors is very very difficult.

    On top of that, if you have a failure of one of the conductors it can cause some problems too unless you size things appropriately.
     
  10. bluetinc

    bluetinc Member

    Joined:
    May 11, 2009
    Messages:
    682
    Location:
    MD
    Agreed!

     

Share This Page