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Dual-circuit wall-plug charger

Discussion in 'Technical' started by KarenRei, Jul 22, 2017.

  1. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    Something I've been thinking about for a while... it seems to me that it should be possible to make a charger that charges from two ordinary wall plugs (where I am they're Schuko 220V 15A), so long as the plugs are plugged into different circuits in the building with different breakers.

    * We're all single phase here, so there should be no phase issues.
    * No power should flow to ground so there shouldn't be a ground fault.
    * Resistance should be the same on both circuits, both on the live and neutral, so current should be divided up evenly

    Am I missing something or would this be possible? Note that I don't think it would be possible (at least safely) in the US because if I'm not mistaken you guys have a split-phase approach to power, and not all of the phases in a house are the same - correct?

    Just curious.
     
  2. Tam

    Tam Active Member

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    #2 Tam, Jul 22, 2017
    Last edited: Jul 22, 2017
    This is what I understand.

    The US uses two phases.

    A regular breaker uses 1 hot line with 120V.

    [​IMG]

    To get 240V, the double-circuit breaker uses 2 different lines, each with 120V.

    Thus, your idea of using two separate lines from different phases, different wall outlets, different circuits should work.

    However, it's a violation of National Electrical Codes to do what you suggested. They want you to buy a double-circuit breaker and work from there.

    [​IMG]
     
  3. boaterva

    boaterva Supporting Member

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    Well, who knows what is 'code' in Iceland... :) In the US, there is a device (I don't have a link for it this second) that does exactly that, plugs into two outlets/circuits. The problem is that it can't use circuits on ground-fault breakers (as I recall), and most garage circuits are. So, you need to run extension cords everywhere.

    Somewhere with true two-phase and that doesn't have that requirement may have a better chance of doing something like that, but, local electrical code needs to be checked.

    Most locations in the US use two phases, 180 degrees out of sync, called split-phase. Either phase to neutral is a 'normal' 120 VAC circuit. The two 'hot' leads to each other is used to get 240 VAC for stoves, water heaters, Tesla Wall Connectors :D etc.
     
  4. KarenRei

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    True single phase, you mean. :) We're 220V live + neutral + ground rather than 120V live + out-of-sync 120V + neutral + ground. So all outlets are in phase.

    Because Tesla is yet to come to Iceland, our charging options limited, and our population density is low, being able to get 3 1/2 kW pretty much anywhere would be a big plus. Especially for an energy sipper like the Model 3. I just think "May I plug into a few outlets while I'm there" will go over a lot better than "May I do some improvised rewiring of your breaker box?" ;)
     
  5. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    #5 KarenRei, Jul 22, 2017
    Last edited: Jul 22, 2017
    Haha, well, I can think of a convoluted way to do it with this. Almost.

    Marinco Two 30 Amp Female to 50 Amp Y-Adapter

    Two Schuko to NEMA-30A adapters, one of those Y adapters, then a NEMA-50A to Tesla adapter ;) The only problem: that Y-adapter is designed for 120V.

    I could make something like that, though. 2+ 15A power cords, 1 30A power cord, one 30A to charger adapter. Female ends cut off the 15As, male end off the 30A, then wire nuts joining the cables together. I might try it out and have it run a few hair driers to see how it goes.
     
  6. FlatSix911

    FlatSix911 918 Hybrid

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  7. Randy Spencer

    Randy Spencer Member

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    This was what I thought I would do some day, so 15 years ago when I was having them put in a new 200 amp panel I asked them to run two circuits from the two sides of the panel and put them next to each other. Now that I have an electric car I was ready to take advantage of this and bought a nema 14-50 and wired it to the two outlets. I plugged the charger in to the 220 and immediately saw the test lights light up. Very happy I plugged in the car and quickly the power went out. Damn, this car has quite a draw that it can take two 20 amp circuits and blow. Oops, no. both breakers are fine, but there is no power at the outlet! What is going on?

    I discovered by plugging my stereo into each circuit that the GFCI had blown. Pushed it back on and all was well. Plugged the car in again and again, power went out. But this time the GFCI was fine, and the breakers were still on, but the stereo showed the other outlet was now dead. Oh, crap, the electrician 15 years ago put another GFCI on this leg too, but not next to each other. It was on the next outlet up the wall 10 feet away. Wow, code is a bitch!

    I was going to jury rig this, but the wife was having an electrician over to put in some cans so I had him wire ANOTHER breaker to that same garage location. 220v worked great on the charger, but it really didn't charge the car much faster, but this is a Mitsubishi iMiev, only got 22 kWh battery. The charger probably only handles 2000 watts, either 120 or 240 volts.

    -Randy
     
  8. KarenRei

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    #8 KarenRei, Jul 22, 2017
    Last edited: Jul 22, 2017
    NEMA 14-50 is split phase, is it not? You have two separate out-of-sync 120V phases, with a net 240V difference between the phases, power flowing from one live to the other during half the cycle and reversed on the other. So you have little to no power returning through the neutral line then; unless I'm mistaken, the neutral is only for dealing with imbalances, or when you want 120V and tap only one of the phases vs. the neutral. If you have little to no current flowing through the neutral, that's of course going to trigger GFCI.

    In my case however I'm talking single phase. Two live wires, in-phase, joined together, and two neutrals, joined together (and of course grounds joined). We don't do the whole split-phase thing to get 220V in Iceland :)
     
  9. Tam

    Tam Active Member

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    I guess Iceland uses EuroPlug for home wall outlet. Public chargers would have either J1772 or Mennekes (Type 2).

    If so what works in Europe should work in Iceland too (Tesla European standard Universal Mobile Connector, HPWC, Supercharger...)
     
  10. KarenRei

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    We use Schuko, which is the most common of the Europlug variants found across Europe (the base Europlug power pins are the same across all of the variants, but the shape of the casing and the location of the grounds vary). It's blue in this map:

    Schuko - Wikipedia

    So I have no concerns about being able to find a workable solution for plug charging in general (although I find it weird that they don't list European charging adapter options on their website... apparently even their CHAdeMO adapter on their site isn't valid for Europe). They wouldn't leave Europe unable to charge from a wall socket. The question is whether I'd be able to manage 30A (or more) with splices. But I'm pretty sure the answer is"Yes, although not in accordance with code".
     
  11. Randy Spencer

    Randy Spencer Member

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    Yes, that is why I kept blowing GFCIs, sorry if I wasn't clear. Oh, so 220v x 15 amps, like us plugging into a 110v outlet rated for 30 amps. I would think in that environment your solution would be practical, but maybe not something safe. If you had to run extension cords for example they could get very hot.

    I have a SUPER thick 10' power cord for my RV that I used to test my new air conditioner and after just 10s of minutes running, the cord was quite hot. If you are going to charge a Tesla at high power you will probably be better off running the correct solid core wire from the breakers to avoid any issues with heat. Remember you are paying for that electricity and any that is used to heat the wire is NOT going to charge the car.

    -Randy
     
  12. miimura

    miimura Active Member

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    You are missing something very basic. If you combine two different circuits on the same phase, you cannot add together the allowed current from each socket. The reason is that the resistance along each path will not be exactly equal and therefore the current will not be equal, overloading one circuit and leaving the other under-utilized. This is inherently unsafe. Please don't try it.
     
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  13. KarenRei

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    #13 KarenRei, Jul 28, 2017
    Last edited: Jul 28, 2017
    I didn't miss it, I just considered the difference in resistance to be small enough that just a slight rampdown from the combined capacity would be sufficient to account for it. How different could the resistance be, with two cables with the same rating and same length, connected securely with wire nuts, plugged into the wall in the same building? The only potential differentiating resistance I can see in that scenario is the length of the run in the walls (since they should be wired with the same gauge),

    If we're talking 220V, then to charge at, say, 25A means a total circuit resistance of 8,8 ohms. 12 AWG has a resistance of ~0,005 ohms per meter. So the resistance has to be overwhelmingly in the vehicle, not the wiring, meaning essentially equal for both paths. The difference in the length of the wiring runs in the wall should hardly even factor into the equation.
     
  14. GSP

    GSP Member

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    @KarenRei ,

    I am not an expert, but combining two AC plugs in parallel seems very unsafe to me. Resistance in the two paths can be significantly different with just one loose or corroded connection, overloading the other path, and there could be other issues.

    Please check with both a good local electrician and your power company before attempting something like this.

    A single 220 V schuko actually should work rather well for overnight charging with typical city commuting and errands. When faster charging is needed, apply your effort to getting proper blue 32A single phase, red 3-phase, and Type 2 outlets installed where you travel in Iceland.

    Good Luck,

    GSP
     
  15. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    Indeed, and if there was a corroded connection, a draw of too much current from the other circuit should throw a breaker and immediately cut it off, should it not? That's the whole point of circuit breakers.

    Like I have the assets to fund the construction of a nationwide charging network on my own.

    At least we're getting CHAdeMOs on the Ring Road. It's a start.
     
  16. miimura

    miimura Active Member

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    In theory, you could build a device that works like a GFI that would cut off the power if the two legs were passing different amounts of current. That would be much safer than relying on circuit breakers to protect you from unequal current overloading one circuit in the two parallel paths.

    There was someone in the Australia sub-forum who built a special device so that he could charge with higher currents at caravan parks. I don't recall if he was adding up parallel circuits on the same phase or if he was trying to re-assemble 3-phase from different single phase sockets. In any case, he had all the right detection and monitoring circuits in his box so that it was safe and would not fully activate until all the correct conditions were met.
     
  17. KarenRei

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    Could just wire in two <15A breakers, one on each leg. Then it would throw mine, not theirs. That'd actually be great in terms of avoiding bothering people by risking throwing their breakers.
     
  18. GSP

    GSP Member

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    The whole point of electrical codes, trained and licensed electricians, and inspections is to insure that you do not have an incident that requires protection from a circuit breaker. Circuit breakers usually work, but like anything else they are not 100% reliable. Please don't bet your life or your family's life on it.

    CADdeMO on the ring road will be a great start for Iceland. Much better than a bunch of L2 charging stations in the city, like my Midwest US location has. :)

    What I was suggesting, perhaps not too clearly, was to use Schuko outlets, and install proper high power connectors if you need them at home and maybe at relatives you visit, or wherever you would have needed the "two Schuko" solution.

    You could also try to talk hotels or restaurants or other businesses you frequent into installing outlets for their customers. The cost of installing a simple blue or red outlet is likely only a few hundred Euro. Many businesses already have these outlets and can be convinced to list them on plugshare.com for EV drivers to use.

    Be careful,

    GSP
     
  19. EchoDelta

    EchoDelta Member

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    I've known people who have done this (split current of the same phase through two wires, have done it myself for non-EV needs; and also in the US get 240v from different 120 outlets)
    but definitely it's the sort of thing you should do only if you have EE knowledge, in general, and about your specific setup... and can't fool-proof for others to "re-use". You seem to be informed enough to know how to tackle it.
     
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  20. EchoDelta

    EchoDelta Member

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    Check in the USA/northwest forum how different advocacy groups have crowdsourced the installation of high-amp L2 chargers on common travel circuits not served well by superchargers; for other models of summoning and aligning other's resources to this goal. Even just sitting with biz owners and helping them apply for Tesla destination chargers makes a diff.
     
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