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EV mode with discharged 12 volt battery

Discussion in 'Gen 2 Prius Technical Discussion' started by statultra, Feb 7, 2008.

  1. statultra

    statultra uber-Senior Member

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    so i started my car this morning, engaged EV mode before the engine would startup, i had all bars but two green ones, so i thought i was good to go, so then i set out driving, quickly the bars dropped, all the way to 1 bar, it took about a good 5-10 miles before that 1 bar changed 2.

    My guess is that the battery didnt really have all blue bars to begin with, im guessing because my 12volt battery is low ( its not that good, it barely has power to start it ) my battery ECU didnt "realize" the real SOC from the Hv battery, i noticed when i disconnect the 12 volt battery with 2 bars on the MFD, and reconnect the MFD shows all blue bars, as if the battery ECU is calibrating itself or something. Im guessing that it would be detrimental to the HV battery to use EV mode with a low 12 volt battery to startup, because the ECU doesnt know the real charge and wouldnt react fast enough to combat a significant drop in SOC. Comments? this is just based on my experience today.
     
    #1 statultra, Feb 7, 2008
  2. Danny Hamilton

    Danny Hamilton Active Member

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    Hmm...

    Ok, so how do you know that the 12V battery barely has power to start it?

    How long did it take to drop to 1 bar? More importantly, how long did you expect it to take to drop to one bar?

    Once the car is in "Ready" mode, the 12V system is running off the HV battery, so the ECU shouldn't have a problem "knowing the real charge" or "reacting fast enough".

    It is however a bad idea to drive long distances with the EV mod activated. The HV battery is likely to last longer if you allow the ECU to keep it around 60% rather than forcing a discharge to one bar and then bringing the charge back up repetitively.
     
    #2 Danny Hamilton, Feb 7, 2008
  3. Danny Hamilton

    Danny Hamilton Active Member

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    You can disregard this question, I just found your other post where you state:

     
    #3 Danny Hamilton, Feb 7, 2008
  4. dogfriend

    dogfriend Human - Animal Hybrid

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    My thought is that you are probably pulling a lot of power from the HV battery as it uses the DC to DC converter to try to charge your 12V battery. Its not going to work right with a bad 12V battery.
     
    #4 dogfriend, Feb 7, 2008
  5. statultra

    statultra uber-Senior Member

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    well im thinking, if for say your battery has less than 40 % SOC where you would get MAIN +- on the MFD and your vehicle wouldnt start.

    so i was thinking, disconnecting the 12 volt battery and reconnecting it and starting it might actually start thinking it has 60 % SOC.

    well 3 years ago, i had my 2001 prius ( salvaged ), MAIN battery error, ( SOC below 40 %, the car was sitting for 2 years ), everytime i would disconnect the 12 volt battery and reconnect it would give it a tiny crank, until it realized the battery didnt have enough state of charge to perform the startup operation.

    My guess is on the 04-08 prius the battery ECU takes longer to realize the state of charge than the 01-03 ( again this is with lack of 12 volt power )

    sorry huge rant
     
    #5 statultra, Feb 7, 2008
  6. frosh

    frosh New Member

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    #6 frosh, Feb 8, 2008
  7. miscrms

    miscrms Plug Envious Member

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    I like the dc:dc converter theory. A weak 12V (particularly with a shorted cell as mentioned) seems likely to put a continuous drain on the HV system as it tries to bring the voltage up. Pair that with EV mode, and your HV battery is probably going to run down pretty fast. Again, it would be good to know how fast it ran down. Temps and terrain would also be good to know.

    You could be right though. If the voltage drops low enough on startup, it could lose track of its SOC. Since the SOC is determined by current flow history (coloumb counting) not voltage, if it forgets what happened yesterday it will be confused for a while.

    Might it be a good idea to replace the 12V instead of exploring all the things that can go wrong when you have a weak 12V? ;)

    Rob
     
    #7 miscrms, Feb 15, 2008
  8. Qlara

    Qlara New Member

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    Shouldn't the 12V battery also be charging by the ICE only?

    It's a bit hard to believe the 12V battery can be charged by the HV battery (alone) too. This seems to make the system a lot more complicated......assuming the ICE will take care of all (HV, 12V) charging already. (Remember the ICE will override the EV mode for charging, when the SOC is less than certain threshold no matter what.)
     
    #8 Qlara, Feb 15, 2008
  9. qbee42

    qbee42 My other car is a boat

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    No, the 12V battery is charged from the HV system through a DC to DC converter. If the ICE is running, then some or all of the HV may come from the ICE spinning the MGs, but in EV mode the ICE does not run, so all of the HV comes from the HV battery. It's not more complicated, it's actually simpler.

    Tom
     
    #9 qbee42, Feb 15, 2008
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