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Just what is that 12V battery for?

Discussion in 'Newbie Forum' started by GaryGarland, Jun 16, 2009.

  1. GaryGarland

    GaryGarland New Member

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    Hi all,
    I've tried doing my research but i'm getting more confused than ever - i'd appreciate any guidance or correction.
    in my 2009 prius,
    I THINK the 12V battery is soley for running the car accessories, and the air conditioner (okay, power steering, too)
    I THINK the traction battery is used to start the engine - though i'm not sure so i'd like correction.
    I THINK (okay, pretty sure) the ICE recharges the 12V battery
    Does the 12V battery do anything other than run the 12v accessories, power steering, air conditioning, and power the dome lights, smart key system, clock, radio memory?
    Thanks!!!!
     
    #1 GaryGarland, Jun 16, 2009
  2. EZW1

    EZW1 Active Member

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    Let me put it this way.... The traction battery powers MG1, MG2, and A/C Compressor via the Inverter. That is all. The 12V battery runs everything else in the car. The only tie between the two batteries is the fact the 12V battery is recharged by the traction battery via the Inverter.
     
    #2 EZW1, Jun 16, 2009
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  3. GaryGarland

    GaryGarland New Member

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    thanks, i stand corrected!
     
    #3 GaryGarland, Jun 16, 2009
  4. timberwolf

    timberwolf New Member

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    A DC-DC converter, converts the 201v DC to 12v DC to provide the 12v supply that is used to power the various 12v components and charge up the 12v battery when the car is in Ready mode.

    The inverter, is used to turn 201v DC into a high voltage AC, and this is used to power either MG1 and MG2 when neither is being used to generate power.

    The 12v battery is used to provide a 12v supply when the car is not in Ready mode. The primary purpose of the 12v battery, is to provide power to start up the various Prius computers (ECUs) and switch in three relays to reconnect the HV battery (traction). The secondary purpose is to provide a 12v supply when the Prius is in ACC or IGN-ON mode.

    The ICE is spun up to speed with the MG1 and the power for this is provided via the inverter from the HV battery (assuming the Prius isn't moving and providing some regeneration from MG2).

    Eeek, I hope I haven't got that too wrong, the Prius is a complicated piece of engineering :)
     
    #4 timberwolf, Jun 16, 2009
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  5. F8L

    F8L Protecting Habitat & AG Lands

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    HERE is a good description of how the Inverter works on a Prius.

    The next couple paragraphs talk about the A/C and the 12v battery but according to forum rules I shall not post the rest. Please click the link above for more info. :)
     
    #5 F8L, Jun 16, 2009
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  6. GaryGarland

    GaryGarland New Member

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    thanks all - i had thought it was the flux capacitator that created the gigawatts, now i realize it was the deflector dish :)
     
    #6 GaryGarland, Jun 17, 2009
  7. OZ132

    OZ132 Member

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    So how many Amper Hours are needed from the 12 volt battery, to provide for the few things it powers?
    And, since it does NOT provide "cranking" power, is it designed differently from the typical auto battery?
    Could it be replaced with a cheaper automotive type battery? (There is room in the compartment for a somewhat bigger [physically] battery.)
     
    #7 OZ132, Jun 17, 2009
  8. F8L

    F8L Protecting Habitat & AG Lands

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    It all depends on what you are trying to power. My car woudl be much different than someone without power hungry modifications.

    The stock 12v battery is fairly typical. You can exchange the stock battery for a deep cycle style battery as many people have done with great sucsess. The main benefit of this swap is that you will not harm the battery as significantly with repeated draining which is especially important for large stereo systems or people who tend to store their vehicles often.

    The typical deep cycle battery swap is done by purchasing the Optima Yellow-Top kit from eLearnAid.com.

    12 Volt (12v) Toyota Prius Auxilary Battery for 2004, 2005, 2006, 2007, 2008 and 2009 with installation kit and free shipping
     
    #8 F8L, Jun 17, 2009
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  9. GaryGarland

    GaryGarland New Member

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    after a bit more time thinking, i may be getting it -- or being overly thick.
    let's say i leave the dome light on and the wimpy 12v battery dies overnight -something i've read about.
    in theory, do i have enough juice in the traction battery to start the engine, and eventually have the inverter charge the 12v battery, OR, will i never get to that point because the electronics in the car won't get enough power, even though the traction battery is full?
     
    #9 GaryGarland, Jun 17, 2009
  10. F8L

    F8L Protecting Habitat & AG Lands

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    Depends on how drained the 12v battery is and what its overall condition is. In many cases the answer is no, you will not be able to start the car. You will have to put a charger on the 12v battery or jump start the car to get the system to boot up and then allow the traction battery to recharge the 12v battery. The 12v battery is required to "boot" up the car then the traction battery takes over to crank the engine. In laymans terms anyway. I'm sure someone could describe the exact sequence better. :)
     
    #10 F8L, Jun 17, 2009
  11. Celtic Blue

    Celtic Blue New Member

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    From what I understand that is a much more accurate description than the one that preceded yours.
     
    #11 Celtic Blue, Jun 17, 2009
  12. GaryGarland

    GaryGarland New Member

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    thanks again.
    so i wonder, is there an add-on or a method that would allow the traction battery, via inverter, to double as the 12v battery for the purposes of starting the systems and getting the ICE to run? it seems silly to me to need a jump start when there's a couple of hundred volts laying in wait...
     
    #12 GaryGarland, Jun 17, 2009
  13. richard schumacher

    richard schumacher shortbus driver

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    Safety. Toyota certainly could have done that, but they evidently decided that that would have made it more difficult to isolate the high voltage battery when needed.
     
    #13 richard schumacher, Jun 22, 2009
  14. GaryGarland

    GaryGarland New Member

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    I hear ya. i remember some devices out there that you attach to the car battery, and if the voltage gets too low it cuts out - sort of like creating a spare battery - i wonder why they couldn't isolate a certain voltage from the traction pack
    based on reading about the 12v battery dying easily (door left open, dome light, etc.) i just bought (waiting to get) a portable 12v pack - the shame is the non-always on 12v outlet - then you could get a cheapie weak pack and just power up the computer, etc. - instead, i got one that has aligator clips for the battery (fuse compartment) - as we don't need to actually juice up the engine, it has far more cold cranking amps than i believe the prius would need, as that juice comes from the traction battery (again, unless i'm mistaken)
    i know coastal has a 12v outlet mod - but i like the idea of my accessories powering down with the switch off.
     
    #14 GaryGarland, Jun 22, 2009
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