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Tesla Model 3 Battery Pack Architecture

Discussion in 'Tech Talk' started by garsh, Aug 24, 2017.

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  1. garsh

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    Full article:
    Tesla Model 3: Exclusive first look at Tesla’s new battery pack architecture

    So, the CAD drawing we were shown at the Model 3 reveal was NOT of the final design.
    The pack has four modules.
    50kWh battery: 31 cells per "brick", 23 bricks in outer modules, 25 bricks in inner modules.
    74kWh battery: 46 cells per "brick", 23 bricks in outer modules, 25 bricks in inner modules.

    [​IMG]
    Here's a diagram of the pack's electronics.
    [​IMG]
    1. Charge port connector
    2. Fast charge contactor assembly
    3. Coolant line to PCS
    4. PCS – Power Conversion System
    5. HVC – High Voltage Controller
    6. Low voltage connector to HVC from the vehicle
    7. 12V output from PCS
    8. Positive HV power switch
    9. Coolant line to PCS
    10. HV connector to cabin heater and compressor
    11. Cabin heater, compressor and PCS DC output fuse
    12. HV connector to rear drive unit
    13. HV pyro fuse
    14. ?
    15. HV connector to front drive unit
    16. Negative HV power switch
    17. Connector for 3 phase AC charging

    And diagrams of the assembled pack:
    [​IMG] [​IMG]
     
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    • KennethK

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      I just hope that the reliability of the system is high. Hopefully the components are still easily accessible and swap-able.

      So the Gigafactory is really assembling a large part of the vehicle if the whole battery assembly/ controls are one component.
       
    • KennethK

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      So the electronic assembly probably is located somewhere under the rear seat. I love seeing all these detailed drawings!

      I didn't know that the "powertrain" generated enough heat to warm the batteries.
       
    • garsh

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      It sounds like swapping a battery pack will be more involved than for an S or X.
      According to the article, the bolts are accessible from above instead of below, so parts of the interior would have to be removed.

      So, definitely no fast battery swapping stations for this car.
       
    • KennethK

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      The battery pack as a whole, yes, will be more time consuming than an S or X. But, I was referring to individual components, like the AC/DC charger or other components. Probably pop up the rear seat, unbolt a cover and pull out the components.
       
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      • TrevP

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        With this new design battery swapping is effectively dead. Tesla is putting all their efforts into Supercharging as if their network expansion wasn't proof enough ;)

        If find it very intriguing how they're using software to control the motor outpost to effectively 0 in order to generate heat for the battery pack thermal management system. Just goes to show how much effort was put into finding more efficient ways that will result in cost savings. If this works well, and it should if they're going into mass production of it, I can expect a lot of these new methods to eventually make its way into their other cars.

        It's all becoming more clear now what Elon meant during the last fainancial call that they're going to bring Model S and X up to the same tech level as Model 3 soon.
         
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        • Akilae

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          Also a good reason to keep away from CPOs right now and wait for the 3 (trying to convince myself right now :) ).
           
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          • garsh

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            I was thinking about those per-brick cell counts. It's strange that they don't have a common multiple.

            But then I remembered some talk about potentially having "extra" cells in the pack that only get used if a cell goes bad. Perhaps the cells are in groups of 15, and each brick has a single "spare" cell (30+1 and 45+1).

            Just thinking out-loud.
             
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            • garsh

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              • MelindaV

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                comments in the article are listing #14 as a pyro switch. I don't know what that is, but seems logical, being next to a pyro fuse ;)
                 
              • Skione65

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                @MelindaV,

                The PSS is a new safety system to 'quick-disconnect' and bypass either a faulty battery or especially in an accident or post accident for passenger safety. Also used occasionally 'in-line' in airbag systems. Here is a not too long read...10 pages on new design PSS's as they pertain to new generation EVs in particular. Auto-Aliv is one of the top manufacturers. Very interesting read. Enjoy!

                https://www-esv.nhtsa.dot.gov/Proceedings/24/files/24ESV-000163.PDF

                Ski
                 
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                • Model34mePlease

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                  What is the shape of the battery 'brick' that yields an odd number in each module? It is interesting that the picture shows 12 'repeats' along the smaller one and 13 'repeats' in the larger one. Is it possible that it is really 24 (2x12) bricks in the smaller and 26 (2x13) bricks in the larger? That would yield the same total number of bricks.

                  Also, what is the function of '17. Connector for 3 phase AC charging', as opposed to '1. Charge port connector' (which I would think goes to the SC port)?
                   
                • JimB

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                  #13 JimB, Aug 24, 2017
                  Last edited: Aug 24, 2017
                  I don’t know why, but I’m always interested in how the cells are interconnected and I have not seen any other post about it. Here’s my take on it.

                  I’ve seen the cell voltage as either 3.6v or 3.78v. Assume it is 3.78v.

                  So, if the cells in a brick are connected in parallel and the bricks are connected in series and the modules are connected in series. Then:
                  The output of the 23 brick module would be 3.78 x 23 = 87v
                  The 25 brick one would be 95v. Adding the 4 modules would be 364v. Sounds about right.

                  Also, going from 50 kWh to 74 kWh adds cells in the parallel connected brick, so the voltage does not change.

                  Maybe this is obvious.
                   
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                  • Tom Bodera

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                    Great discussion guys. I am curious on using the motor to generate heat with zero torque. Would that mean tryign to spin the motor one way and reverse very quickly to create countering torque to heat up the windings without moving?

                    "10. HV connector to cabin heater and compressor"
                    Also "HV - High Voltage" could they not have used the cabin heater to heat the battery pack through a loop?That way excess motor heat on the same loop could have been used to heat the cabin and cool the loop.

                    Lastly any thoughts on the compressor being AirCon only or heat pump?
                     
                  • garsh

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                    Probably not.

                    To make the motor spin, you need to send it an AC waveform. A magnetic field is created by a *changing* electrical field. If all you want to do is to generate heat, you could probably just provide a constant DC voltage, and have it (the stator of the motor) act like a resistive heater. Since the electrical field isn't changing, no magnetic field will be created, and the rotors won't move.

                    But, that's just a guess.
                     
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                    • John

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                      Gotta love that every Model 3 comes standard with An Explosive Guillotine.
                       
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                      • Roderick80

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                        sorry for the noob question, but how is the coolant dispersed through this particular battery pack and is it different than what occurs on the X/S? I can't tell from the diagram.
                         
                      • garsh

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                        I was also thinking that the inverter might not have been designed to deliver a DC voltage to the motor. So, another possibility would be to send a very high-frequency AC waveform to the motor. If the motor is sitting still, it will basically not have time to spin in one direction - the magnetic field will have moved and started pulling it in the other direction before it gets started. Combine that with a parking brake to keep things from "shuddering".

                        In other words @Tom Bodera , you might be right. :)
                        Well, mostly. It wouldn't _really_ be the inverter trying to spin it one way, then the other. The inverter would just be driving the AC waveform too fast for the rotor to start following along.

                        Here's a good video explaining the "start up problem" with synchronous motors.
                        Basically, Tesla could be making use of this "issue" to have the drive units generate heat w/o moving.
                        I've linked to 1:54, which describes startup. The whole video is interesting though.
                         
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                        • JWardell

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                          #14 is the pyro fuse, not 13. It is shown as the tallish black module in the first photo.
                          #13 appears to be a bus bar with small wire connector coming out of the top, most likely a current sense for overall current draw

                          I should also note I like the innovation of the pyro fuse.
                          Breaking very large currents is extremely difficult, and a normal switch or fuse will just cause the current to jump the gap. Typically this requires a large, heavy, and expensive contractor with giant contacts as well as magnets to guide the electric field. That's a lot of extra expense and weight for something that would only be used once during an emergency. Here Tesla uses pyrotechnics to blow a much larger gap than would occur with a fuse or breaker, not to mention has zero heat loss as there is no thin fuse wire to heat.
                           
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                          • Kizzy

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                            I'm slightly amused by the car having a kind of self-destruct mechanism. “Like a spaceship” indeed!
                             

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