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UMC vs SPC - how can SPC get away without the "box"?

Discussion in 'Roadster' started by smorgasbord, Jul 7, 2014.

  1. smorgasbord

    smorgasbord Active Member

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    The Spare Mobile Connector is just a wire and the connector:
    Screen Shot 2014-07-07 at 3.51.48 PM.png

    The Universal Mobile Connector has a big box along the wire:
    Screen Shot 2014-07-07 at 3.56.08 PM.png


    What technically is going on that the Spare Mobile Connector gets away without such a box?

    What are the limitations of the Spare Mobile Connector? Could I feed 20 amps through it at 110volts? Could I feed 15 amps through it at 220volts?

    What's driving this is that I stayed at a friend's beach house this past weekend, and they only have 110volt outlets. I was thinking about getting the Quick 220 thing to piece two 110volt out of phase outlets into a single 220volt outlet, but then I would have had to have brought my UMC, and then the total package was getting alot bigger than I had room for in the Roadster trunk. So, I paid a visit to the SLO 70 amp chargers and spent a couple hours at Starbucks doing work.
     
  2. stopcrazypp

    stopcrazypp Well-Known Member

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    #2 stopcrazypp, Jul 7, 2014
    Last edited: Jul 7, 2014
    The SPC is a completely dumb cable that's only for low power charging modes (where an EVSE is not required by the electrical code).

    The electrical code requires an EVSE for any EV charging connection except for 110V single phase sockets:
    http://www.madkatz.com/ev/nec1999Article625.html

    The Roadster seems to be the only EV that even supports 110V charging without a EVSE (the Model S doesn't seem to support this).

    So the box in the UMC serves as a mobile EVSE and also has logic inside to decode the various adapters and translate it into the proper J1772 current/voltage signaling on the car end.
     
  3. slcasner

    slcasner Member

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    The small pin in the Roadster's charging connector carries the pilot signal from the EVSE to the car telling how many amps the EVSE can provide. The signal is a square wave where the duty cycle indicates the maximum available current. With the SMC, there is no square wave on that pin, just a resistor to ground or maybe it is just open. The Roadster accepts that signal to mean that the current limit is 16A.

    The EVSE includes a circuit powered by the line voltage to generate the signal and also sequence through some handshake steps with the car (see https://code.google.com/p/open-evse/wiki/J1772Basics). So, the box has to include that circuit, plus its power supply, plus a GFCI big enough to handle the higher current. The wall-mounted HPC (at least the Roadster one, not sure about the Model S one) also has a big contactor (relay) that only closes to allow the line voltage through to the car connector pins after the handshake completes. The UMC and the older Roadster mobile cable don't have the contactor.

    Nope and nope. You may notice that when you have the SMC connected to the car the current adjustment in the car goes only to 16A. I tried an experiment where I connected 220 volts across the line and neutral pins of my SMC (on which the GFCI has been replaced with a good-quality plug), but the car would not charge. I assume the software only allows the null pilot signal when the voltage is 110.
     
  4. hcsharp

    hcsharp Active Member

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    It's easier to first answer what's going on in the UMC box. Your Roadster is capable of pulling 70A from power supply when you plug it in. If it did that every time you plugged it in, it would burn a lot of houses down. Or at least trip a lot of breakers. So it needs to know how many amps it is allowed to pull. The so-called pilot signal on the small pin lets it know how many amps are available. The UMC box contains a smart pilot signal generator. I say "smart" because it determines the number of amps to signal based on which adapter you are using with it. The UMC also contains a large relay to connect/disconnect all power. I won't bore you with the reasons for the large relay.

    Generally your roadster will not charge without a pilot signal letting it know how many amps it can pull. There is an exception to this, and that is charging at 115v, up to 16A. The EU exception will do 13A at 230v. If the roadster senses 110v and a grounded pilot signal, it will start charging at 15A (or is it 16?). That is what the SMC provides: 115v and a grounded pilot, so the roadster starts charging at 15A.

    Yes, and yes, but not legally and not without modifications. The modifications would require that you add a pilot signal generator to pull more than 16A at 120v. Or pull anything at 240v. But after the modifications you would essentially have the same thing as a UMC. The only point of this exercise would be to make yourself a low-powered UMC, and even then it would violate code if you pulled more than 16A.

    When I stay with friends/relatives on long trips without a dryer or stove outlet, I install a temporary 240v 50A breaker in their panel to a NEMA 14-50R. But I have a fair amount of electrical experience and know how to do this safely. It only takes me a few minutes. There are other options if I can't bring the right breakers for their panel. That discussion will wait for another day. I've even stayed at a number of Airbnb hosts this way. Of course I checked it out with them ahead of time and paid extra for the electricity and general special need.
     
  5. slcasner

    slcasner Member

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    Henry, I don't know if you read my post before writing yours, but I note that our posts are contradictory in a few places.

    I confess that I have never seen the inside of a UMC, so my statement that it does not contain a contactor was a guess. I do know that the original Roadster 30A 240V Mobile Cable with the large, rectangular box did not contain a contactor. It did contain a rather large 30A GFCI, which might be considered a relay, but the GFCI did not open to disconnect power unless there was a ground fault. Martin Eberhard's RFMC contains neither a contactor nor a GFCI. Since the UMC box is much smaller, I made the assumption that it does not contain a contactor either.

    You've clarified that the SMC pilot signal's "resistor to ground" is 0 ohms, AKA a wire. OK.

    Most interesting are our contradictory answers to the questions about extending the functionality of the SMC. I interpreted smorgasbord's questions to be about handling 20A/110V or 16A/220V without modifying the SMC (save perhaps replacing the GFCI plug with a 220V plug); that is, without adding a pilot signal generator that would require a box to contain it. Drawing 20A isn't allowed by the car's software so that is not possible unless the OVMS can override it. However, drawing 20A from a 20A circuit will cause the breaker to trip, so you'd really need to step up to a 30A outlet (which needs a different connector). For the second case, 16A/220V, I know that won't work without a pilot signal because I tried it.
     
  6. hcsharp

    hcsharp Active Member

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    #6 hcsharp, Jul 9, 2014
    Last edited: Jul 9, 2014
    Actually, I don't think we contradicted on much at all. The GFCI inside the original 30A mobile charger did contain a relay but like you said, it never interrupted current without a ground fault, so its operation as a relay could almost be ignored. By contrast, the UMC has a much bigger relay that turns on and off every time you plug in.

    My answer about using the SMC may have appeared to contradict yours, but I qualified it with "but not legally and not without modifications." So in the end I think we had pretty much the same answer to that. Considering that it would be a waste of time to make the modifications necessary, and there would be serious safety issues, I probably should have provided a response more like yours. I might have been influenced by a handful of Roadster owners who have actually modified their SMC to use it as a more compact mobile charger.
     
  7. smorgasbord

    smorgasbord Active Member

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    Thanks for all the info.

    My question was about using it with a Quick 220 in order to get something like 15 amps at 220 volts. As it stands, if I had to bring along my UMC and the Quick 220, I wouldn't - I need the trunk space for other things.
     
  8. hcsharp

    hcsharp Active Member

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    The OpenEVSE board is very small and I wouldn't be surprised if it fit in the Quick 220 box. Just a thought. You might also be able to find one of the original Juice Boxes. They weren't the best EVSE design but they were very small (the newer ones are better, but bigger). You could have it plug into the output of the Q220 and have it programmed to 15A.
     
  9. slcasner

    slcasner Member

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    There's no pilot wire in the SMC cable, though. You'd have to open up the Tesla connector (the car end) and hook in a new wire that goes to wherever you put the OpenEVSE board. If it was in the Q220 box at the other end of the SMC cable, that would mean you'd need to run a new wire along the length of the cable.
     
  10. hcsharp

    hcsharp Active Member

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    Darn I forgot about that. Yeah, the only reasonable option is use the SMC with 115v if he doesn't want to bring his UMC. Just stay longer at the beach house!
     
  11. TEG

    TEG TMC Moderator

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    Some vehicles, like LEAF and Volt I think, go through a test sequence before they start charging from an EVSE. This includes making sure the contractor works properly to disconnect the line current when signaled to do so. For that reason, EVSEs without a contactor (like the old RFMC) would not work to charge those vehicles. If the charging system in the car doesn't check much, you can get away with leaving off safety features on the EVSE and still have it work. Although the basic function of an EVSE is fairly simple, there are a surprising number of incompatibilities between different vehicles and different EVSEs. On Roadster, differences between 1.5 & 2.x charging systems had them behave differently with some EVSEs. In some cases there were differences in the amount of current leakage they would allow before the GFCI features would activate.

    Also, just because an EVSE has a small "box" doesn't mean it lacks a contactor / relay. For instance, the Model S UMC has a little tiny one.
     
  12. donauker

    donauker Member

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    I can say that one of these statements is not 100% correct. I modified my original Roadster 30A 240V Mobile large box EVSE by removing the Roadster connector and cable and replacing it with a J1772 connector and cable. This unit is being used to charge a 2014 Leaf on a daily basis.
     
  13. qwk

    qwk Model S P2681

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    If one knows what they are doing, they can modify/make another SMC to charge without a relay/contactor. Scott did that and used it at up to 60A 240V(pic below).

    image.jpg
     
  14. hcsharp

    hcsharp Active Member

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    I charged a Leaf once with a portable charger with no contactor/relay in it. I've also been told that not all Leafs are tolerant of this. Maybe the early years were different? Both the MS and Roadster will charge without a contactor. The Ford Focus Electric will not charge without a contactor/relay.

    - - - Updated - - -

    This is what I meant by "modifications" to the SMC. smorgasbord could do the same with his cable. That little control box could hang out of the roadster connector eliminating the need for the extra wire in the cable. Would it be worth his time? No. Although I don't know how often he would use it. I've heard from a couple other roadster owners who've converted their SMC this way. One of them used it at 24A with a TT30 outlet on a regular basis. It's a very compact charging solution, It's just not legal or necessarily safe.
     
  15. TEG

    TEG TMC Moderator

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    #15 TEG, Jul 14, 2014
    Last edited: Jul 14, 2014
    It was my understanding, from things I read on the forum, that the MC240 could turn the 240V on/off using the contactor in the GFI module:

    Extra wire on MC240 GFCI
    So the GFCI itself may have only turned off the 240v in case of a ground fault, but it sounds like there was an extra control line to let the pilot board switch it on/off too.

    - - - Updated - - -

    Yes, there have been a number of interoperability issues between different versions of different vehicles, and different types of J1772s EVSEs.
    Like I said, the basic operation is fairly simple, but the safety checks they do during initial handshake can something cause unintended failures.

    Here was a bit more about that:
    http://priuschat.com/threads/charging-pip-using-chevy-volt-110v-charge-cord.106366/
     
  16. donauker

    donauker Member

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    It has been a number of years since I personally used my MC240 but my fading memory would tend to agree with you on this. I believe there was a click from the box upon initiation of charge by the car. Just need to remember to test it out when it is no longer needed by its current user.
     

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