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Anyway to combine 2x 32A 240V J1772 to 1x 64A 240V HPWC?

Discussion in 'Model S: Battery & Charging' started by redline0316, Mar 28, 2014.

  1. redline0316

    redline0316 Member

    Jan 31, 2014
    Bay Area
    There's a few places I want to charge with several J1772 available. I'm wondering if it is possible to build something that could combine the power into a portable HPWC? There would need to be some extra circuitry to protect against sudden loss of one/both of the J1772's...any ideas?
  2. Cosmacelf

    Cosmacelf Well-Known Member

    Mar 6, 2013
    San Diego
    If you do a search, you'll find someone who built a custom NEMA 14-50 combiner, to combine two 14-50 into one 80A feed. There are many issues with doing this. From what I remember, the person ended up having to use a microprocessor controller and fancy circuitry to ensure bad things didn't happen such as trying to draw too much current from one source (if the resistances are different, a simple combiner would attempt to draw more from one plug versus the other). For J1772 you have the added complexity of spoofing two J1772 protocols to each pedestal and then giving the right J1772 signal back to the car - again, requires some thought. Doable perhaps, but pretty involved...
  3. GSP

    GSP Member

    Dec 28, 2007
    One way to do this would be to build a "mini-supercharger" from two Tesla (or other brand) on vehicle chargers. Their inputs could be two J1772 or two 14-50, one for each charger. Combine the DC output and charge the car using the Supercharger protocol. The two liquid cooled chargers with electric pump, fan, and radiator, would be quite bulky and heavy. Not an easy project to do either.

    Another interesting method would be to modify a twin charger car with a second charging inlet, and re-wire the chargers to each have their own inlet. You might need to modify Tesla's software for this to work.

  4. linkster

    linkster Active Member

    Apr 22, 2013

    Here is a pic of said combiner:


    red, I will contact the owner to see if he wants to respond.
  5. FlasherZ

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

    Jun 21, 2012
    There are devices out there that will allow it to work. Not all of them are safe, and they all violate the NEC which could open you up to liability or insurance issues. That said, I know plenty of people who use them. I've seen them work well, and I've seen some of them fail. Many work safely when there are no other infrastructure failures, but have dangers under some failure scenarios.

    For example, the device pictured above has a potential problem with combining equipment grounding conductors. If this is used in a campground built before 2005 that uses 3-wire feeds to pedestals (most of them), and there is a neutral conductor failure between the service panel and a pedestal (a relatively common failure), this box becomes the return path for unbalanced loads from the pedestal with failed neutral. It may also create a situation where a human in contact with the car that's charging can become part of the return path (it won't be a significant amount of current, but you may feel it). It is a corner case, but could cause a shock.

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