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Why a hotshot from a 12v battery?

Discussion in 'Gen II Prius Technical Discussion' started by genalex, May 5, 2006.

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  1. genalex

    genalex Member

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    I don't understand why a dead Prius should receive a hotshot from a car with a 12v battery.
    I thought the ICE gets spinned up by one of the motor/generators on the high voltage bus.
    Can someone please explain the process for me?

    Also, what functions does the 12v battery serve beyond operating the radio and other accessories?
    And how is the 12v battery recharged in operation?
  2. Frank Hudon

    Frank Hudon Senior Member

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    the 12 volt battery is used to boot up the computer that starts the car. When it's dead the computer won't send the 200 volts to MG1. 12 volts is used for every function other than starting and powering the main drive motor, MG2, and the A/C compressor. The 12 volt battery is charged via a D/C to D/C converter attached to the bottom of the inverter. This unit takes the 200 volts and drops it down to 13.8-13.9 volts to charge the battery and power the car when it's in Ready mode.
  3. eagle33199

    eagle33199 Platinum Member

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    I think i can answer your questions, but others feelf ree to correct me if i'm wrong.

    The 12V battery is involved in the initial start-up of the car. The way i understand it, the high voltage batteries are basically disconnected from the engine to prevent accidental draining, the the 12V battery reconnects tham (it's more or less a simple electrical switch). So if the 12V is dead, it can't flip that switch to connect the high voltage batteries.

    The 12V electrical system serves all the same purposes it does in a normal car. So it runs the radio, headlights, power steering, windows, and all the other electronic gadgets in the car.

    Tha 12V battery is recharged (and the 12V system powered) through a converter that sits between the high and low voltage batteries. This eleminates the need for additional equipment to convert mechanical energy into electrical.
  4. genalex

    genalex Member

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    <div class='quotetop'>QUOTE(Frank Hudon @ May 5 2006, 12:32 AM) [snapback]250072[/snapback]</div>

    Thanks. Makes sense. But isn't the high voltage in GenII Prius 500v?

    (I remember thinking when I read it that thats the voltage that street car and subway traction motors use.)
  5. Frank Hudon

    Frank Hudon Senior Member

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    <div class='quotetop'>QUOTE(genalex @ May 4 2006, 09:45 PM) [snapback]250082[/snapback]</div>

    the HV battery in the G2 Prius is 200 volts, that is the nominal voltage but in normal operation it runs any where from about 212 -247 volts depending on what the car is doing at the time. This viewed from CAN-view and the Classic is 273 nominal and is normally at 298 volts viewed with the Mini-Scanner.
  6. genalex

    genalex Member

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    <div class='quotetop'>QUOTE(Frank Hudon @ May 5 2006, 01:24 AM) [snapback]250098[/snapback]</div>

    OK, help dispell my confusion:

    The HV battery is ~200v. Is it then stepped up by the inverter to 500v ac? (Since the motor is described as synchronous in the manual and an inverter, by definition, changes dc to ac.

    I'm ashamed to admit, that despite my MS in EE, I haven't been able to assemble enough design info to get a comprehensive picture of the main electrical system.
  7. V8Cobrakid

    V8Cobrakid Green Handyman

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    how can you not picture the system. It almost seems normal to me... with the addition of a few High Voltage lines down the center of the car... well.. a tad to the driver side.

    It seems rather simple to me. *shrug* maybe i'm missing a few components.

    This little recharge system is pretty neat. The prius 12v battery is pretty small. no starter to power :) hehe

    I'll go over the seperate components again. Like i said i might be missing something. *shrug*.
  8. qbee42

    qbee42 My other car is a boat

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    <div class='quotetop'>QUOTE(genalex @ May 5 2006, 01:46 AM) [snapback]250101[/snapback]</div>

    Yes, the inverter/control steps up the voltage to around 500v. The high voltage reduces the resistive power losses in the wires and motors.

    Tom
  9. vincent1449p

    vincent1449p Active Member

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    <div class='quotetop'>QUOTE(genalex @ May 5 2006, 01:46 PM) [snapback]250101[/snapback]</div>

    It is actually stepped up by the boost converter up to a maximum of 500V DC. The inverter changes this to AC, providing its elevated power to the motor and generator. This boosted voltage is not fixed at any one voltage, it always varies between 200V ~ 500V depending on torque demand and the best electrical efficiency.
  10. hobbit

    hobbit Senior Member

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    For the basics [without the boost converter], look up US patent
    6131680. Brushless commutation in 3-phase half-bridges, with
    position and current feedback. The boost doubler simply sits
    between the battery supply and the inverter rails. I've got a
    diagram of that somewhere, but I've lost track of exactly where
    it came from. Probably the New Car Features off TIS. But grub
    around on Toyota's HSD site, there might be some info there.
    .
    _H*
  11. vincent1449p

    vincent1449p Active Member

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    Someone posted this diagram before.
    [attachmentid=3236]

    EDIT: Found the OP here.
    Thanks to kk6yb :)
  12. hobbit

    hobbit Senior Member

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    Yeah, that's about the one I was thinking of, although I've got a
    larger version someplace. I love how they call it a "reactor".
    Makes me wanna drop a pound of banana peels into "mr. fusion" and
    take a 200-mile joyride.
    .
    _H*
  13. genalex

    genalex Member

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    Thanks, guys. These are the details I was looking for.
  14. jayman

    jayman Senior Member

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    <div class='quotetop'>QUOTE(hobbit @ May 5 2006, 10:33 PM) [snapback]250632[/snapback]</div>

    I know what you mean. I do a lot of work in industrial automation and the term "line reactor" goes WAY back. For some odd reason the basic inductor is still called a "reactor."

    With 6-pulse Variable Frequency Drives, the line reactor minimizes harmonics to the line side. On the load side, a "reactor" is used to minimize corona and winding damage in motors not certified for VFD duty.

    Hint: spend the extra 3% and get the motor certified to VFD duty!

    Line reactors combined with capacitor banks can be used for power factor correction if an industrial plant has a lot of non-linear loads, eg motors. It's tricky to get the right balance of inductance/capacitance though, without introducing odd harmonics. Those are actually worse than leading or lagging PF.
  15. darelldd

    darelldd Prius is our Gas Guzzler

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    <div class='quotetop'>QUOTE(genalex @ May 4 2006, 09:25 PM) [snapback]250069[/snapback]</div>

    I'm still trying to figure out what a "hotshot" is? Is that Jersey-speak for a jump-start?

    And if it is... then I'll add to the fun. Even an EV with NO gasoline engine to turn over needs a "jump-start" when the 12V Aux battery goes dead - for the same reason as the Prius. If the computers can't power up, then the traction pack won't wake up, and nothing runs. Crazy to think that even with enough energy in the traction batteries to power your house for a few days... if the Aux is low, the car won't boot up. The first EV - the EV1 had a little self-jump button that would turn on the inverter and charge the Aux battery from the traction pack. Talk about a perfect, cheap fix that NOBODY else bothered to include!
  16. genalex

    genalex Member

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    <div class='quotetop'>QUOTE(darelldd @ May 9 2006, 09:50 PM) [snapback]252522[/snapback]</div>

    You have to cut me some slack on vernacular. I grew up in Philly so long ago I don't know if it's my age or my geography that's responsible for my odd terminology.

    Gene
  17. vincent1449p

    vincent1449p Active Member

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    <div class='quotetop'>QUOTE(darelldd @ May 10 2006, 09:50 AM) [snapback]252522[/snapback]</div>

    Prius has a small battery pack (1.3 kWh) as compared to EV1 (18.7 kWh Gen1 and 26.4 kWh Gen2). EV1 can afford to charge the Aux battery and still with plenty of charge left but if Prius were to charge the Aux battery and the HV battery gets below the critical SOC level, then even after the Aux battery is fully charged, system still would not get into [READY].

    However, if next gen Prius can be plug-in, then it will be a different story.
  18. jfschultz

    jfschultz Active Member

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    <div class='quotetop'>QUOTE(eagle33199 @ May 4 2006, 11:35 PM) [snapback]250073[/snapback]</div>

    There is a normaly open double pole relay at the HV battery pack. This is a safety feature in that the relay must be activated to get the high voltage out from the HV battery. Any number of detectable abnormal situations (such as airbag deployment) and shutting down will cut the control voltage to this relay and remove the high voltage even from the wires running under the car.
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