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kWh - Measure by charge, or measure by display?

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by JF Coffin, Nov 22, 2018.

  1. JF Coffin

    JF Coffin Junior Member

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    Nov 22, 2018
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    Location:
    Santa Rosa, CA
    Vehicle:
    2015 Prius Plug-in
    Model:
    Plug-in Advanced
    Greetings, all
    Another measurement question.
    I track the kWh's drawn by my 2015 PiP, charge by charge, over time, through the use of a Kill-o-Watt meter, as well as the related EV miles driven between each of those charge sessions.
    Additionally, the vehicle has a readout, on one of the MID pages, relating EV miles driven and "kW hours".
    After adjusting for similar time/range periods, to boil the results down to an "apples to apples" comparison, I find these two kWh values never match, and do not progress uniformly over time.
    * Do we know what the MID is (theoretically) reporting? Is the kWh value reported supposed to represent the total kWh charged via the cable within any given time/range period? Or a statement of the total kWh used, related to the EV miles driven, which would also include an estimate of regenerated energy used by the vehicle?
    I'm reading a lot of great stuff from you all out there, and I greatly appreciate your perspective! Thank you!
    John
     
  2. KevinPluggedIn

    KevinPluggedIn Junior Member

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    2014 Prius Plug-in
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    N/A
    HI John - I have struggled with this as well. My impression is that the MID is reporting the output from the battery - Of course, rounded up/down (Although I always suspect down, at least based on the fuel gallons used reported on the same display). I monitor the usage at the wall via an Ensupra meter at the outlet.

    What I ultimately will be watching over time is 1) How many Kwh at the wall it requires to make 1 Kwh on the MID - There is a loss to resistance, heat, etch while charging, which appears to be about 25%. This may or may not get worse over time and with battery degradation. Only time and miles will tell. 2) How many actual miles am I getting per 1 Kwh at the wall. This is the equivalent to actual miles per gallon - ie, I don't care what the meter in the car says, I divide my HV miles on that tank by the actual readout on the pump when I fill up. (That can also be off by a certain % as well, but is generally well monitored in most states.).

    Hope that helps. Have a Happy Thanksgiving.
     
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  3. JF Coffin

    JF Coffin Junior Member

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    Nov 22, 2018
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    Location:
    Santa Rosa, CA
    Vehicle:
    2015 Prius Plug-in
    Model:
    Plug-in Advanced
    Hey Kevin, and many thanks for your thoughtful reply.
    Your conclusion regarding the meter is my inclination as well. Integrating a "use of regenerated energy" factor into the cal-key-lation, if that is indeed what the darling vehicle is doing, creates a variable influence with much more potential to confuse the results than clarify them.
    Appreciate your time, sir. Thanks again.
    John
     
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  4. jerrymildred

    jerrymildred Senior Member

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    2017 Prius
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    Two
    Welcome, John. I agree with @KevinPluggedIn.

    The Killawatt is showing the power put into the car, which is more than what's put into the battery. Some of that power also goes to heat loss, as Kevin said, and then there are the fans that run and the inverter coolant pump. There are LEDs on the EVSE cable, too. My cable draws a small amount of power even when it's not connected to the car.

    I am not sure if the kWh on the MID shows how much power goes into the motor/generators or if the total power leaving the battery. I tend to think it must be the total power leaving the battery since the MID also alters the remaining range estimate when you turn the air conditioner on or off. However, my manual says that it "Gives an indication of the amount of electricity that has been consumed by driving in" HV mode. I interpret that to mean power used by the MGs and also that it's a bit of an estimate, which fits well with it being whole numbers.
     
  5. JF Coffin

    JF Coffin Junior Member

    Joined:
    Nov 22, 2018
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    Location:
    Santa Rosa, CA
    Vehicle:
    2015 Prius Plug-in
    Model:
    Plug-in Advanced
    Hey, Jerry ... many thanks for your thoughts, sir.
     
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