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Car Battery 12 v

Discussion in 'Gen 2 Prius Technical Discussion' started by stevejackson, Aug 8, 2008.

  1. stevejackson

    stevejackson New Member

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    Hi all,

    I Understand that the Hybrid battery is 240 Volts, why is there a 12 volt battery?
    Can any one help me.

    Thanks in advance.
     
    #1 stevejackson, Aug 8, 2008
  2. efusco

    efusco Moderator Emeritus
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    The 12v powers up the computers and is the primary energy source for the accessories. There's a DC-DC inverter that charges up the 12v from the HV battery.

    Keeping the HV battery disengaged when the car is not in operation preserves it and protects the car. 12v accessories are cheaper as well.
     
    #2 efusco, Aug 8, 2008
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    2G has a battery with nominal voltage of 201.6V, while Classic has a battery with nominal voltage of 273.6V. This is because 2G has 28 battery modules while Classic has 38 modules. Each module has a nominal voltage rating of 7.2V.

    When the battery is in normal operation and being charged, the actual voltage will be 10% - 20% above nominal values.
     
    #3 Patrick Wong, Aug 8, 2008
  4. kohnen

    kohnen Grumpy, Cranky Senior Member

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    You don't _NEED_ another battery (from a physics point of view) but it is helpful to have a 12V battery (from an engineering point of view).

    By having a separate 12V battery, Toyota can use the standard 12V electrical system that (almost) every other on the planet uses.

    Many of those 12V systems need a small amount of current all the time (the clock, the radio to remember settings and the car remote receiver come to mind).

    One _COULD_ power them with an inverter off of the ~300V hybrid battery, but very low current 300V to 12V inverters tend to be inefficient. And, from a safety point of view, it's a smart idea to only have the high voltage system live when it HAS to.

    One more point: If you discharge the 12V battery to the point of destroying it, you're out a few hundred bucks. If you were to discharge the hybrid battery to the point of destroying it, you're out a few grand. This too makes it attractive to completely disconnect the hybrid battery when you're not using it.
     
    #4 kohnen, Aug 8, 2008
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