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Two EVs. How I automated charging with a transfer switch.

Discussion in 'Model S: Battery & Charging' started by Jsvette56, May 7, 2013.

  1. Jsvette56

    Jsvette56 Member

    Joined:
    Feb 25, 2013
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    Location:
    Santa Clara
    Last week I took delivery of my new red Tesla at the factory. My wife already has a Leaf and uses our J1772 AVinc charger to top it off every time she takes a trip, so it's basically plugged in all the time when the car is in the garage requiring coordination as to who was going to get the one plug.

    To avoid arguments about whose car did or did not get charged up I added a separate NEMA 14-50 outlet so I could plug in the Tesla and because I only have power (50A circuit) to charge one of the EVs at a time I needed a method to transfer power to one or the other cars on some prearranged schedule. To solve this I went to the local electric supply store and bought two 50A contactors, and an electric timer control with NO and NC contacts. I wired the timer control to the contactors so that one or the other of the charger circuits are powered up. Then I set the timer so that the LEAF charger is on 20 hours a day as the Leaf has only a 3.3KW charger and slow and set the Tesla to be charged in the middle of the night.

    It seems to work pretty well and there is a manual switch to power one or the other up separately. Untitled.jpg
     

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  2. FlasherZ

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

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    Battery powered mechanical timer? I don't see a safety ground going to that plastic timer box, nor a neutral...
     
  3. Jsvette56

    Jsvette56 Member

    Joined:
    Feb 25, 2013
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    As I'm not an electrician I always look for advice on these kinds of projects, especially where safety is concerned. The timer had no internal ground connection and everything inside was plastic so I am not sure how I would ground it.
     
  4. mckemie

    mckemie Member

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    Location:
    Dale, Texas
    Unless you have a new Leaf, it will pull only 12-14 amps. Using only 40 amps of your 50 amp circuit, you would have 26-28 amps left to charge your Tesla concurrently with the Leaf. I have noted that my Tesla seems to remember the last used charger setting for each location. At one of my locations, a J1772, I limit current to about 20 amps to minimize voltage drop. So, I don't have to remember to set the charging current each time I start a charge at that location. At other J1772 locations, it starts at 30 amps.
     
  5. FlasherZ

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

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    By NEC rule you may not do this. Continuous loads, when added together, must operate over conductors and overcurrent protection devices that are rated at 125% of that load. This means that you are not permitted to "use up" the "leftover" 10 amps that the Model S doesn't use with another continuous load. You may use intermittent loads, but the Leaf doesn't qualify as one.

    - - - Updated - - -

    No worries... many timers do expect a ground connection, and many of them require a neutral to operate (as they're 120V).
     
  6. jomo25

    jomo25 P4398

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    He was talking about using the leftover 10 (50-40) but the leftover 28 (40-12). Not sure of that's ok, just pointing out for clarification.
     
  7. FlasherZ

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

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    Oh yeah. I passed math once, I think.

    My apologies for my inability to subtract.
     

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