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Can an adapter be made to combine 2 x NEMA 14-50 into a single HPWC connector?

Discussion in 'Model S: Battery & Charging' started by AmpedRealtor, Dec 21, 2013.

  1. AmpedRealtor

    AmpedRealtor Active Member

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    I was thinking about this while reading about camp and RV sites that have multiple NEMA 14-50 outlets. I don't know anything about how electricity works, so perhaps it's a silly question to begin with. But couldn't someone build a magic box with two NEMA 14-50 connectors/cables on one side and a Tesla HPWC connector/cable on the other? The magic box would have the circuitry to combine the two 40A feeds into a single 80A feed with a connector at the end telling the vehicle that it's an HPWC.
     
  2. mknox

    mknox Well-Known Member

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    Please don't do this. It is dangerous to try and parallel 2-240 volt circuits, especially when you note a lack of electrical knowledge. We are already starting to hear of garage fires and hooking up Frankencables like this will only exacerbate the problem, not to mention putting personal safety at risk.
     
  3. bluetinc

    bluetinc Member

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    #4 bluetinc, Dec 21, 2013
    Last edited: Feb 20, 2014
    Hi AmpedRealtor,

    I've created just what you are describing, a magic box that combines two of the 14-50's into one power feed for the car. It works well and the idea is solid.

    But, the devil is in the details and especially in this case. The core of the issues is that what is behind the outlets is not the same at every location in the country, or even at multiple plugs at the same location. Because you are dealing with a system that is combining these outlets, if something goes wrong you will surge tens of thousands of amps for a moment before something (or multiple things) fuse/melt. Add to this, that in practice, you have no visibility into the electrical system information that you need to know, and most of this is hidden underground.

    Needless to say, FlasherZ's warning should be taken very seriously. To manage this, I had to design a number of "sensors" along with a processor with custom code to manage all this. The amount of work was very significant and only now (a year later) have I managed to come up with viable autonomous solutions to all the issues I found along my cross country trip.

    I'm coming to the conclusion that simply using the SuperChargers and getting 80A J1772 systems installed elsewhere is the real solution.

    Peter
     
  4. pgiralt

    pgiralt Active Member

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    I will join in and say please don't do this. It may be technically possible under very specific circumstances, but there is a very good chance that the two outlets you are using are on different phases (at least a 50-50 chance of it being backwards) for each hot leg because the two hots will be wired randomly. In a 3 phase location, you have even more likelyhood of the two outlets being on different phases. This is above the fact that if one hot was loose, you would end up drawing too much current on the other and trip the breaker. If you connect to different phases, you will also trip the breaker after seeing sparks fly and burning out your frankenbox.
     
  5. bluetinc

    bluetinc Member

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    The kicker is that you are actually unlikely to fry the frankenbox, you will fry the upstream breakers, and potentially the meter, meaning that you will be destroying equipment that isn't yours.

    Peter

     
  6. yobigd20

    yobigd20 Well-Known Member

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    You'll burn your house down. Don't do it ::/
     
  7. Cosmacelf

    Cosmacelf Active Member

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    bluetinc is correct. There are many variables to contend with. Is the supply single phase, 2 legs, like residential wiring, or 3 phase commercial wiring? If you want to use this at an RV park, reports from the field indicate that many RV parks have trouble delivering 40A through their NEMA 14-50 receptacles, let alone attaching two together and expecting it to work. To do this right would require what bluetinc has built - actual software running on a CPU with sensors to detect things like out of balance current draws. I echo his sentiment and say that it isn't worth it.

    Use NEMA 14-50s for overnight charging, and 40 amps (or dialed down to 30 amps if the RV camp wiring isn't up to snuff) is fine for that.

    The one useful combiner is a dual-220V combiner for when you are overnight charging and all you have is 120V residential outlets. Even there, the box must be built correctly with relays to prevent shock hazards, and you are taking a chance with such a set up.
     
  8. dhrivnak

    dhrivnak Active Member

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    I tried something similar to join two J-1772 plugs and after several tripped breakers, quirky 3 phase wiring and stubborn ground fault loops I gave up. Not saying it can't be done but it can't be done easily or reliably.
     
  9. AmpedRealtor

    AmpedRealtor Active Member

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    Thanks everyone, I was not intending to do this. I was just curious as to whether it was possible. Just a mind experiment.
     
  10. N4HHE

    N4HHE Member

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    The Right Way To Do This™ would be on twin charger models for Tesla to put a 2nd charge port on the right side of the car. Then connect using two UMC's.

    Presumably the HPWC has intelligent communication with the car so the car would know to do the right thing if an HPWC was connected.
     
  11. AmpedRealtor

    AmpedRealtor Active Member

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    If the issues could be solved, this might make a good product to reduce charging time when more than one 14-50 outlet is available.
     
  12. FlasherZ

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

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    I'll just add to the voices here who talk about it being a bad idea.

    As mentioned, it's not a great idea because there is little margin for error. There's a reason that the NEC is very, very tight on its restrictions for paralleled conductors. The biggest issue to overcome is the giant variance in resistance along multiple paths that you'd find in the wild. Checking for phase alignment is required and easy; you'd also have to add a circuit to ensure there wasn't more than x% variance in current across the multiple paths (due to resistance differences) and shut the device down if there was. The question would be how many times in the wild the device would work vs. shut down due to current variance.

    - - - Updated - - -

    I've said it in other threads, and I'll just say it here for reference. It is very, very difficult to set up one of these devices safely. Not only do you have to contend with ensuring that both of the circuits you use are unloaded, the inputs are properly phased, and that the device's plugs don't get energized, but you also have to deal with failure scenarios that could create problems - e.g., the device becoming the return path for a broken neutral in the infrastructure, or a grounding problem that would result in the device's case being energized. I don't recommend this at all.
     
  13. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Concerning putting 2, 120V outlets together to make 1, 240V outlet, there are devices for sale that do that. See a repeat of a post that I made over a year ago. The problem is that they don't work with GFI outlets, so you have to run extension cords into the house to find two outlets on different phases. Its just too much trouble to fool with for me.

    ======================
    From Combining two 120V into a 240V connector - Page 2, #17:

    I actually bought a box that does this when I got my Roadster 3 years ago. You can find it at 220 240 Volts from 110 120 Volt Outlets - Catalog & Pricing. I got it to work in my home to test and verify. As has been said already, you have to find two 120 V. outlets that are on opposite sides (phases) of each other (red and black behind the wall).

    The second, more-annoying condition you need satisfy is that both outlets cannot be GFI outlets. If a 120V GFI outlet sees a current imbalance between the hot and neutral wires, it trips thinking the rest of the difference current is going to a ground fault. In the combiner box it is just going to the hot from the other outlet, but the GFI sees the imbalance and trips. GFI outlets are now required on all outside, bathroom, kitchen, and garage outlets in new construction. This means that you have to drag extension cords into the house or office. By the time I figured all of this out, and saw how many wires and extension cords that were needed, I decided that it was just too much overhead for the gain in charging speed.
     
  14. TonyWilliams

    TonyWilliams Active Member

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    Heres a graphic basic overview of what you want. Can it be done? Of course. Will it always work, meet regulation(s) or make the RV park happy? Probably not.

    There are folks who use these types of products at RV parks, where burning down your house won't happen. If you were to use 45 amp quick blow fuses in addition to the 50 amp circuit breakers, a cheap and simple (if inelegant) solution can be made to protect from load imbalances.

    As to having hot leads (yes, you could electrocute yourself just handling the plug), there are simple safeguards for that, too. I don't show that in the drawing below. An active computerized control is absolutely the best way to handle this, with breakers, fuses, relays, etc as mechanical backups.


    Quick240v100a.jpg
     

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