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The P85D battery

Discussion in 'Model S: Battery & Charging' started by Olle, Oct 16, 2014.

  1. Olle

    Olle Member

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    Since the P85D has more power than the P85 I am wondering if it has its own battery.

    Especially since a lot of people have been saying that the P85 power is battery limited I am now confused. I read that people have gotten up to 363 kW. If the battery power is limited, how can the P85D get 515 kW from a battery limited at lets say 363kW?

    Actually two questions come to mind:
    1. Does P85D have a more powerful battery or the same as the current cars use? Wasn't it power limited then??
    2. Does it have a front HV outlet or do the D cars have a cable in the actual car running from the rear HV outlet to the front DU?
     
  2. Johan

    Johan Took a TSLA bear test. Came back negative.

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    It's good that you made a new thread about this subject. I have the same questions but unfortunately not the answers. Keep in mind that even during full discharge the battery is only operating at 3.76C in a P85 which really isn't that much. At 515 kW in a P85D it would be 6C which isn't unreasonable at all, at least in shorter bursts.

    I'm guessing there is a direct front high voltage connection between battery and front motor. But we won't know for sure until Tesla tells us or someone takes a look!
     
  3. Saghost

    Saghost Active Member

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    I'm assuming they have a new battery pack. The discharge rate for 515 kW isn't terribly high for lithium cells (though higher than any other Tesla car,) but there are a bunch of other parts in the battery pack that are sized by power output, too, and would probably have to be changed to allow more current.

    We won't know until they tell us or we get pictures of a car's innards, but I would bet heavily on a cable to the front of the car. The modules are all wired in series, so the only place you can get the full 400V is at the end of the series stack where the current connection plugs are. That means they'd effectively have to run a cable from the back of the car to the front either way, you're just choosing between running the wires in the battery pack or outside of the pack in the car.

    For safety reasons, Tesla has to but a contactor across each connection that leaves the battery assembly, so they'd have to have extra parts if they made a separate set of connectors.
    Walter
     
  4. Olle

    Olle Member

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    Thanks for the insights Walter. Your assumption of a more powerful battery pack leads to another question: Will the P85 get more power too? The motor power is listed as 350 kW on the order page as opposed 310 for the old P85.
     
  5. Saghost

    Saghost Active Member

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    If it got the putative "E" pack, then I think it would get more power.

    Given this week's track record on the forum, though, Tesla would have a revolt on their hands if they gave those new packs with the extra power to the next production block without announcing it months in advance and charging extra for it. ;)

    (More seriously, the heavier duty components must cost something more, though likely not much. Tesla would have to decide if they think it makes sense to spend the extra money to deliver more power for the P85 only, and whether to change orders/charge more.)
    Walter
     
  6. Johan

    Johan Took a TSLA bear test. Came back negative.

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    You are probably correct about there being no sense in "compartmentalizing" the pack so yes, the cabling would all have to start from the end of the stack. And likely the inverter for the front motor is in close vicinity to the motor it self, just like in the rear? It would be the inverter/motor controllers that would "decide" how much current to draw from the pack at any given moment. The battery wouldn't really "know" if it's hooked up to one or two motors, only that at any given moment there is a certain draw from it. (Rather being requested from it by "opening the floodgates" i.e. electrically lowering resistance).

    So my best guess is that the pack that is in all S85s and P85s on the roads right now can tolerate a draw of 6C "cell-wise" but perhaps not "pack-wise" i.e. in the P85D cars the cell configuration is likely the same but there are probably upgraded wiring and contactors in different parts of the pack. Not to mention the big fuse, talket about in another thread.
     
  7. Saghost

    Saghost Active Member

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    That would be my guess as well.

    More speculatively, having a high current, high voltage cable running to the front of the car might be useful to Tesla otherwise. There's been a little discussion about that patent Tesla took out a while back for a battery system that integrated a conventional battery like they use now and an Aluminum-Air primary battery as a range extender.

    If they decided to offer a range extender battery for the Model S (some folks thought it was part of the Model 3 plan instead, and it might be,) they'd most likely put it in the Frunk - which would mean running cabling to the back. That used to be a serious barrier for installation/retrofit - but the front inverter is right by the Frunk, probably actually in "microwave" area of the RWD Model S's frunk. So it would be easy for them to create plugs there for a frunk mounted range extender system (they'd need contactors on both sides of the connection for safety, of course.)
    Walter
     
  8. Olle

    Olle Member

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    I agree too all said except the range extender. RWD won't have the cable and and AWD will only have space ahead of the microwave, which is the crumple zone.
     
  9. swegman

    swegman Member

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    Wouldn't having a different battery for the D version of the car complicate matters with the battery swap system? In order to simplify battery swapping, it would seem Tesla would want just one 85 type battery and one 60 type battery, and have the extra wiring harness external to the battery.
     
  10. Olle

    Olle Member

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    #10 Olle, Oct 16, 2014
    Last edited: Oct 16, 2014
    They already have the A battery with a different supercharging spec. From what I understand from @Saghost it doesn't make sense with an extra HV outlet up front even in the D, so all versions will probably all have the same physical fit. Just different performance characteristics. If the P85D in fact has a more powerful pack, you could still have full interchangeability in the swapping stations. Provided that the P85D customers accept the possibility of less power while driving the swapped pack. (given how intelligent these cars are we probably don't have to even mention the obvious fact that the car will automatically sense what pack it carries and adjust the max power draw and charging accordingly)
     
  11. wk057

    wk057 Senior Tinkerer

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    I'm willing to bet there is no new battery, at least not one with new connectors and such. Maybe... MAYBE there will be a revision with slightly larger internal wiring (the needed ~1500A is a bit high for the 2/0 wire in the "D" pack, IMO...) but I highly doubt it.

    The power needed for the 210HP front motor at full power is ~156kW, so about 500A worst case. That's pretty doable with just a cable running somewhere like the cabling for the DC-DC and AC compressor does.
     
  12. kennybobby

    kennybobby Member

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    There is a 100 Amp fuse in the High Voltage Junction Box under the rear seat that supplies power thru a cable to the dc-dc converter. The easiest solution would be to just increase the wire size and change to a class aR fuse (such as used in the battery) with a higher rating to cover the front inverter and motor loads. Those semiconductor class fuses can tolerate large overcurrents (e.g. 3x rating for 30 seconds) but will fuse open in the event of a short circuit event.

    My guess is that the factory has probably collected so much data from their entire fleet of computers-with-tires to have good confidence that the discharge rate can be increased and the thermal control system can handle the load such that the cells will not get overheated and damaged. All your cars are belong to us.
     
  13. HankLloydRight

    HankLloydRight Fluxing

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    Is everyone assuming there are two inverters, and therefor the need for 2 DC feeds? Has this been documented or proven any way, or just conjecture? Perhaps there's just one (possibly beefed up) inverter to drive both motors.
     
  14. miimura

    miimura Active Member

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    Distributing DC and having the inverter mounted directly to each motor is the only sensible way to do it. These are synchronous motors, the inverter has to commutate the motor correctly in order for the motor to produce the commanded torque. Using a single inverter for motors on each axle would be like having an ICE AWD system with no center differential and the axles locked together. Very bad idea.
     
  15. wk057

    wk057 Senior Tinkerer

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    Separate inverters are needed for precise motor control of the two motors.

    Also, Elon said in a video interview that the two setups would have the benefit of adding redundancy, which implies separate inverter hardware.
     
  16. Olle

    Olle Member

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    two invertes

    Two inverters is the only way to do it. Even if you had one inverter box for the two motors, it would in essence be two inverters in that box (unless you want the two motors to spin at the same speed, but then the car wouldn't be driveable).
    You would also need 3 heavy cables from inverter box to each motor. DC feed only needs 2 cables. If you look at the pictures on the ordering page, you see one inverter attached to each motor.
     

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