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12 Volt charge voltage in Ready mode changed today

Discussion in 'Gen 3 Prius Main Forum' started by DetPrius, Apr 1, 2010.

  1. DetPrius

    DetPrius Active Member

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    Location:
    Southeast Michigan
    Vehicle:
    2010 Prius
    Model:
    III
    I bought my SGII last fall when the weather had already cooled down in Michigan and I've had the voltage as one of my 4 gauges all winter and it has always read 14.7 - 14.8 while in Ready mode - until today.

    Today it was reading 13.5 for a 30 minute drive somewhere and also on the way home for another 30 minutes. The car then sat for 2 hours and I moved it out of the garage and found it back up to 14.7/8. Today was the first 70 degree day and that is all that I can think of that changed. Has anyone else noticed this? Could it be a sign of a problem? Could the voltage the inverter sends to the 12 volt battery vary on temperature or some other variable(s)?
     
    #1 DetPrius, Apr 1, 2010
  2. hobbit

    hobbit Senior Member

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    Two things. First of all, 14.7 is too high, and if your system
    really is trying to hold battery voltage there it's going to
    cook your battery dry in six months. Check it against a more
    accurate voltmeter, back at the battery itself. It should be
    right around 14.0, and maybe 13.2 in that "lower" state. I
    wouldn't trust the SG to be accurate on this, where its own
    measurement of the power supply rail is sort of a token gesture.
    .
    Second -- when the ambient temps are around 60 and above, the
    output voltage of the DC/DC *is* reduced a little when the car
    is in Drive. If this is happening you can both see a dip in
    voltage, and hear it in a slightly changed note of the inverter
    pump from under the hood, when switching between N and D. This
    is to adapt better to temperature conditions around the battery,
    and any good smart-charger will have a means of temperature
    compensation -- be it auto-sensing, or a manual setting before
    you start the charge cycle. Why it switches when the car is in
    D or not is a bit of a mystery, but that's how it works. This
    operation is governed by the VLO lead to the inverter.
    .
    _H*
     
    #2 hobbit, Apr 1, 2010
  3. qbee42

    qbee42 My other car is a boat

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    As an example of temperature sensing for chargers, the smart inverter/charger on my boat has a temperature sensor clamped to one of the battery posts on the big lead-acid house battery. The charge profile is changed depending on the temperature of the battery.

    Tom
     
    #3 qbee42, Apr 1, 2010
  4. DetPrius

    DetPrius Active Member

    Joined:
    Apr 24, 2009
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    Location:
    Southeast Michigan
    Vehicle:
    2010 Prius
    Model:
    III
    Can someone who has the technical manual tell us the acceptable voltage range? I've seen at least one other PC'er report the same 14.7 - 14.8 voltage from a SGII while in Ready mode.
     
    #4 DetPrius, Apr 1, 2010
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