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No CAN Bus, No 12V for Model Y

Discussion in 'Future Vehicles' started by Cosmacelf, May 3, 2017.

  1. Cosmacelf

    Cosmacelf Active Member

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    In today's 1Q conference call, Elon stated that Model Y will not use a CAN bus, and instead use a new high speed bus. He said that while Model S used 3 km of wiring, and the Model 3 uses 1.5 km of wiring, the Model Y will use 100m.

    He also said they will finally discard the legacy 12V power, which he derided as saying wasn't the right voltage for anything.
     
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  2. 11thIndian

    11thIndian Member

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    I honestly wasn't expecting this much Model Y news to come out of today.
     
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  3. Garlan Garner

    Garlan Garner Well-Known Member

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    I was shocked also. There is no way that talking about the Model Y at this point is a good idea. The Model 3 isn't even out yet.
     
  4. 11thIndian

    11thIndian Member

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    I don't know- at this point, a late 2019 production start at the earliest won't affect anyone's decision to buy a currently announced vehicle. That's all they need to worry about. But this will put them in the mix with other cSUVs slated for 2019/2020. I'd hoped they'd get the jump on them by 6months, but the announcement that the Model 3 and Model Y WILL NOT share a platform makes it easy to explain any "delay".
     
  5. Cosmacelf

    Cosmacelf Active Member

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    There were several interesting tidbits today. Elon ALMOST said that full autonomy might need a CPU board hardware upgrade from AP2, but that it would be OK since the board can be swapped out just fine, and the hard to swap wiring harness and sensor suite would stay the same. Uh, OK.
     
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  6. Saghost

    Saghost Active Member

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    I saw that in the elektrek article on the call. They seemed to be implying there wouldn't be a low voltage system, or at least no low voltage battery - which I was having a very hard time understanding.

    If what he's saying is that most of the electronics are really designed for 5V or 3V and are converting the 12V down and they don't really have any big 12V loads any more so they're going to build it with a 5V system and battery instead, I could see that (though lots of folks have 12V accessories...
     
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  7. Haxster

    Haxster Member

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    Years ago there was a push to replace 12V batteries with 48V batteries in all cars. These made sense for larger motors that drive A/C compressors, electric power steering, brake boost, heated elements within the cabin, and even smaller motors, etc. Thinner wires, less weight, less copper, cheaper motors, and a little more energy efficiency. I don't know what happened with this trend, but it would seem to make sense for electric cars. Maybe that's why Tesla may be going in that direction.

    Regarding the electronics, with modern voltage converters, it doesn't make much difference whether they convert down from 12V or 48V.

    And 48V is still low enough to not be much of a shock hazard in most situations.

    Still, it would seem in bad form to not provide at least one robust 12V outlet for accessories...and make the damn fuse easy to replace!
     
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  8. scottm

    scottm Active Member

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    This from Jalopnik

     
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  9. scottm

    scottm Active Member

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    And we can avoid a similar thread for model Y... as this one for model S, because ...no battery.

    The working theory in model S world is... if only Tesla had put the DC-to-DC converter inside the main pack... do away with the external 12v battery.
     
  10. scottm

    scottm Active Member

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    "High speed network" and reduced wiring length.

    Uhm... commodity ethernet with PoE ? And each node is also a hub, one port in, one port out... daisychain to next node in the car and few home-runs to the mother of all computers.

    CANbus ... expensive node cost per device, and too... you know, ..yesterday.
    LIN is not know for its speed.. but it's cheap.

    Some busses were just meant for cars, what will it be for model Y?
     
  11. Cosmacelf

    Cosmacelf Active Member

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    Yeah, in the early Model S days I kept asking why they didn't use a DC-DC converter instead of a 12V battery and the only answer I got back is that for safety reasons there has to be a mechanism to disconnect the HV battery pack from everything, and thus you need another low voltage battery to reconnect. I never really bought/understood the issue. I wonder what the Bolt does?
     
  12. scottm

    scottm Active Member

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    Another way to reduce half of the wiring for power is just use the chassis as the ground return. Don't even run a wire for negative / ground.

    One positive wire to things that need power... or, PoE to smart devices that need moderate power... and run no separate power lines.
     
  13. Cosmacelf

    Cosmacelf Active Member

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    To answer my own question, the new Bolt does indeed continue to have a 12V lead acid battery.
     
  14. Saghost

    Saghost Active Member

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    The issue is that 400V DC is fatal and so lots of precautions are taken.

    The 400V system is floating ground - neither side is connected to the vehicle's frame or the 12V system, and the computers are always watching to confirm that remains true - and will disconnect the pack immediately if either side connects.

    There's also a high voltage interlock circuit on most (all?) modern EVs. This is a 12V circuit with connections that physically block the 400V circuit, so that you have to break the 12V before you can touch the 400V.

    If the car detects a crash, the 400V is automatically disabled, just like the fuel pump inertial switch on an ICE car.

    All of these require the ability to isolate the 400V system on a moment's notice, and implicitly, they all require an independent 12V source to validate that the safety systems are operational before 400V power flows.

    On most EVs, 400V power is locked down completely when the car is off, except for during charging or when HVAC is on.

    Tesla chose a different route, and leaves the battery connected and computers on most of the time (which is why other cars don't have vampire drain - any computing they do while "off" comes from the 12V battery instead,) but they still need the safety systems and the ability to recover after the pack is isolated.
     
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  15. Cosmacelf

    Cosmacelf Active Member

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    OK, makes sense, but couldn't you still power the 12V bus with a 400V to 12V DC-DC converter? Surely there is enough isolation in such a converter to not pose any safety hazards? You can still disconnect the 400V battery to the rest of the car, but leave the connection to the DC-DC converter intact?

    Or is the concern the other way around - if the 400V battery develops a problem, then you want an independent, more reliable power source to handle emergency requirements (hazard lights, etc.).

    I'm just hoping there is a different architecture that could eliminate the 12V battery. While Elon didn't promise that, he did say the Model Y would eliminate the 12V bus, which could just mean using a 48V battery. OR it could mean making a different pack architecture which carves out some cells for a 48V (or whatever) auxiliiary battery, thus at least getting rid of lead acid.
     
  16. cdub

    cdub Future Model 3 owner / Current original Leaf owner

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    I'm sure they'll have a second smaller batter using a higher voltage but that is still safe and keep that system still separate from the main 400v battery.
     
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  17. Saghost

    Saghost Active Member

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    Maybe. You'd need very reliable isolation of both sides within the converter, in a fashion that can't fail under any sort of accident.

    Then you'd have to figure out what the first responder can cut to kill 12V power on the car safely.
     
  18. jbcarioca

    jbcarioca Active Member

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    There was much debate. So far Audi has gone to 48V for engine controls and supercharger actuation in at least one model, Delphi is promoting 48v for the same purpose. I suspect the giant moves will be coincident with the 2018-2023 models BEV coming from Germany. What will be the solution for BEVs I have no idea.
     
  19. scottm

    scottm Active Member

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    How about run a single wire loop through all pillars snaking it through the whole car... that could be cut anywhere... and it opens the circuit.

    Like a trip wire.. any disruption of power on this line unlatches it (opens a relay). Re-powering / re-connecting the wire after a disruption does nothing (it's supply power is latched out when the relay opened).
     
  20. dhanson865

    dhanson865 Active Member

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    Except then how to you do the HV disconnect during power off for first responders to cut into the car? The 12v is a safety system not just a power system.

    edit: I see the thread has covered this in later posts.
     

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