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Please explain differences in Models S and Roadster charging...

Discussion in 'Roadster' started by TOBASH, Aug 12, 2014.

  1. TOBASH

    TOBASH Member

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    Please don't leave replies like "They are just different". I would like to know the inner workings.

    What accounts for the Model S and Roadster differences in charging that allow the Model S to SuperCharge while the roadster cannot.

    What construction differences are there in the batteries?

    What signal differences are there in the charge currents themselves?

    What computer differences exist?

    Just trying to truly understand the inner workings of my vehicle.

    I don't just want to drive. I think all drivers should understand their vehicles. I feel it makes me a safer driver and car operator.

    Best,

    T
     
  2. Saghost

    Saghost Active Member

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    I'm not an expert in either car, but as I understand it, everything is different - voltages, connection schemes, cooling methods - I don't believe they have something in common beyond being electric cars based on small format battery cells.

    The Supercharging piece is the one easy specific question you asked. To Supercharge, the car allows high voltage DC power to be pushed directly into the battery pack, bypassing the car's built in charger.

    In most cars, this is done with a separate set of contacts for the high voltage DC power. The model S works differently: under the rear seats, between the two locations for the onboard chargers there is a set of high powered contactors which switch the connections at the charge port from going to the on board charger to being hooked directly to the battery pack.

    The Roadster has no similar mechanism for connecting the battery pack directly to the outside, so Supercharging it is impossible (it would also need programming to tell the Supercharger how much power to give it.)
    Walter
     
  3. supersnoop

    supersnoop Tesla Roadster #334

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    The Roadster's charging signal is based on the J1772 standard, but limited to 70A. If presented with an 80A charger, the latest software update will allow the car to negotiate and charge at 70A.

    The Roadster's charging system is primarily limited by it's ability to keep the batteries within proper temperature. Remember that Tesla's main technological advantage isn't the car or the motor, but the ability to maintain the batteries.

    And, as Saghost mentions, "Supercharging" is based on feeding DC power directly to the batteries. It's a path that doesn't exist in the Roadster.
     
  4. bonnie

    bonnie Oil is for sissies.

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    Most of that information is present, in great detail, in the Roadster technical forum. You can see the battery layout, actual pictures of the cells, etc. I'd start there & then ask further questions after reading the information available.
     
  5. hcsharp

    hcsharp Active Member

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    The first question was answered pretty well in this thread. The second is answered pretty well in some old Roadster threads. The design is similar to the Model S in terms of battery organization, function, and cooling/heating.

    Supercharging uses a serial communication protocol. The other signals (for current available, car connected, ready for power, etc) are mostly the same for each car.

    We're not allowed to tell.:biggrin:

    Agree. And you don't necessarily have to be a techie to understand your car.
     
  6. markwj

    markwj Moderator, Asia Pacific

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    Both the Roadster and model S have wiring from the charge port to the charger(s) for AC charging. There is only one charger in Roadster (part of the PEM), and up to two chargers (one optional) in the Model S. The chargers convert the incoming AC into DC to charge the batteries.

    The Model S has additional wiring and battery arrangement to allow direct DC connection from the charge port to the batteries for supercharging. The Roadster doesn't have any such DC connections. The Model S also has support for the supercharger protocol (which allows the car and supercharger to communicate to control the DC supercharge).

    Primarily layout: The Roadster's batteries are arranged in 11 sheets (vertical arrangements of cells) within one large block. The Model S batteries are arranged horizontally under the car. While the core design is the same (18650 cells with liquid cooling), the Model S design is more mature and uses a different battery chemistry.

    The AC charging signalling is pretty much the same. The Model S with dual chargers supports up to 80A, but the Roadster is limited to 70A.

    The DC charging signalling is only support for Model S and is based on supercharger protocol. Chademo is available via an adaptor (that presumably converts chademo protocol to supercharger protocol, but that is just a guess at the moment).

    At their core, very similar. Both vehicles have telematics, screens, and Linux computers. Model S seems to use ethernet networking to inter-connect the main user-interface computers, while Roadster uses CAN bus.

    Implementation-wise, completely different. For example; the Model S has a 17" touch screen, and the roadster has a 3.5" touch screen.
     
  7. TOBASH

    TOBASH Member

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    So... Why wouldn't a computer controlled current inverter allow the high DC current from a supercharger to convert to AC and charge a Roadster at 70 Amps? If a large DC amperage is required for the Supercharger to remain active, couldn't a parallel circuit passed through a large resistor act as an excess current dump?

    A computer might monitor the system and provide feedback to the supercharger to fool it into taking its time to charge a roadster.

    T
     
  8. markwj

    markwj Moderator, Asia Pacific

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    #8 markwj, Aug 13, 2014
    Last edited: Aug 13, 2014
    For DC charging the roadster:

    Firstly, the charge port has just 3 pins - AC neutral, live and earth.

    Secondly, even if it had DC pins, there are no DC cables from the charge port to the battery.

    The roadster charge port is J1772 signalling - AC only.

    For an inverter to convert to AC (as you suggest):

    Yes, possible, but a 240V 70A inverter is a big box.

    Also wasteful as input to superchargers is AC, so what you are suggesting is AC(mains)->DC(supercharger)->AC(inverter)->DC(car charger).

    But, the bigger issue is 240V 70A is 16.8kWh. The supercharger could charge 8 Model S cars in the time taken to charge 1 roadster. Not good for utilisation of superchargers.
     
  9. TOBASH

    TOBASH Member

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    You did not understand my statement:

    Use a DC to AC inverter with some type of current sump for extra current and a computer monitor to give signal to the supercharger.

    Basically insert an inverter between the supercharger and the roadster.
     
  10. markwj

    markwj Moderator, Asia Pacific

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    Sorry, I had a two-part reply but it got early-posted by tapatalk. I've updated my reply with the second part which answers your question.
     
  11. WarpedOne

    WarpedOne Supreme Premier

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    How is that better than mounting HPWC at supercharger locations?

    It acctually is much worse becase of all the conversions that would take place:
    AC mains => DC supercharger => AC converter => charger DC => battery

    Compared with
    AC main => supercharger => model S battery
    and
    AC mains => HPWC charger => roadster battery

    For ~2000 vehicles still out there in the wide whole world it ain't gonna happen.
     

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