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Ideal nominal voltage for a class 8 semitruck

Discussion in 'Technical' started by Rowan256, Sep 9, 2017.

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  1. Rowan256

    Rowan256 Member

    Joined:
    Sep 5, 2017
    Messages:
    128
    Location:
    Amsterdam
    Hello everyone, I was recently thinking about real longrange trucks with swappeble batteries and I was wondering how high the voltage of such a truck battery and swap battery should be. I think it should be significantly higher as a car battery because otherwise the cables would be too thick and the battery would struggle too much to handle the amps (high amps means bigger cables, high voltage means lower amps for the same amount of kW). But at the same time, the voltage shouldn't be too high, because when there comes a flood like currently with the hurricane in America, or if a driver accidentally drives into a lake, or a river, I guess it could make a battery extremely dangerous.

    My personal estimate would be around 900 volts (about 2,5 times as high as current Tesla cars), but is there anyone out there with good knowledge about things like this?

    Thanks beforehand for all info!
     
  2. arnis

    arnis Member

    Joined:
    Apr 13, 2015
    Messages:
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    Location:
    Estonia
    You are about right. Vehicles should not go over 1000V DC at 100% state of charge.
    Nominal voltage of 900V DC will result in 990V DC at 100% SOC.
    CCS plugs support up to 1000V. With integrated cooling up to 500A.
    This is 450-500kW charging current per one plug. Two plugs can also be used.

    It appears that some, slightly bigger passenger vehicles, might also prefer 600-800V packs.

    Flood-danger is not what matters when selecting appropriate voltage.
     
  3. GSP

    GSP Member

    Joined:
    Dec 28, 2007
    Messages:
    2,280
    IGBTs are available with 600 V and 1200 V ratings. FETs are available with 600 V ratings.

    The 600 V transistors are used for light duty cars and trucks. The can be safely operated with system voltages up to 400-450 V max.

    Heavy vehicles, such as electric buses, usually use 1200 V IGBTs. This allows max system voltage of 700-800 V. These IGBTs cost more, but since less current is required less of them are needed, and lower cost cables and connectors can be used.

    The trade off depends on many factors, but when power is above 200-300 kW (270-400 hp), the higher voltage usually is the less expensive option.

    Since Tesla will use Model 3 motors in their semi, they may buck this trend and stick with a 300-400 V system. Being able to just produce a few more motors and inverters from their very high volume assembly line likely will overwhelm the cost factors described above.

    GSP
     

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