SOC droop during IG-ON?

Discussion in 'Gen 2 Prius Technical Discussion' started by 2009Prius, Sep 18, 2012.

  1. 2009Prius

    2009Prius A Wimpy DIYer

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    I have seen SOC droop during IG-ON (not READY) but never collected the data until a few days ago. The car was turned off after a short drive, then IG-ON for ~13 minutes, then IG-READY to drive away. You can see the SOC steadily dropped from 50% down to 48% during IG-ON:
    [​IMG]
    while the HV battery temperatures and voltage remained constant. There was a small HV current reading fluctuating between 0 and 0.1A even though the relay was supposed to be open. Anyone knows what's going on?
     
  2. nh7o

    nh7o Off grid since 1980

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    Could the .1A fluctuation be just the random noise in the LSB that most measuring circuits exhibit near zero? I don't know what the resolution is, but I would think that some noise pickup will occur on this line.
     
  3. lamebums

    lamebums Member

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    Hi 2009Prius--

    I've noticed a slow and steady drop in SoC when the car is at Ready and not moving before. I've always surmised it was because the inverter was still pulling juice from the HV battery to keep the 12v topped off. I can only suppose that there's a similar condition for the IG-ON state?
     
  4. Britprius

    Britprius Senior Member

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    In ignition on mode the HV relay is closed running the 12v inverter and air con inverter if required the HV battery state of charge is also shown on the MFD, this would not be possible with the relay open.
     
  5. vincent1449p

    vincent1449p Active Member

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    The HV relay is closed only during [READY], not in ign-on. I don't believe you can turn on air con in ign-on.

    In ign-on, the Battery ECU is turned on so you can see the SOC on the MFD, nothing to do with the HV relay. There are also 14 sense wires connected to the Battery ECU to measure voltages and resistances so there should be small current flowing even though the relays are off.

    Vincent
     
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  6. Britprius

    Britprius Senior Member

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    Having checked the air con does work on my UK 2008 Prius in ignition on (not ready) but you are correct that the 12v inverter is not connected.
     
  7. qbee42

    qbee42 My other car is a boat

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    Ig-on draws power from the HV battery. Off and Accessory are the only modes where the relay disconnects the HV battery.

    Tom
     
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  8. vincent1449p

    vincent1449p Active Member

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    What you are seeing is the Fan does work in ig-on but no cold air coming out from the vent. The A/C compressor is powered by the HV Battery, so it only works in READY.

    Electric A-C Compressor.jpg

    Vincent
     
  9. vincent1449p

    vincent1449p Active Member

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    No, HV battery is not connected in Ig-on, only in READY.

    HV status by READY indicator.jpg

    Vincent
     
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  10. uart

    uart Senior Member

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    Thanks Vincent, that makes sense. We measure the 12V voltage at Ig-on and it always drops to lower than it's "acc" or off state voltage. So clearly the DC-DC converter is not operating in Ig-on mode.
     
  11. 2009Prius

    2009Prius A Wimpy DIYer

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    Recently I had two occasions that, after shutting the car off from the commute home, I turned it IG-ON for about 1/2 hour. The next morning the SOC dropped from 48.5% (right before car off and IG-ON) to 45.5% in one occasion and from 52.0% to 47.5% in the other. The only possible loss is through the sense circuitry as Vincent pointed out (quote above). It's amazing though how much current the sense circuitry takes to cause such a significant drop in SOC.
     
  12. qbee42

    qbee42 My other car is a boat

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    Remember that displayed SOC is just a calculated estimate. There is no way to directly measure SOC like you do with gas in the tank, so the Prius gives it it's best guess based on the previous SOC, voltage, temperature, and factors like that. Overnight changes in calculation factors will cause a big swing in displayed SOC without any real change.

    Another factor is the SOC of the 12V battery. If you run that down the DC to DC converter has to work hard the next startup to support the 12V bus and charge the 12V battery. This is a fairly significant draw that rapidly drops the SOC of the hybrid battery.

    Tom
     
  13. 2009Prius

    2009Prius A Wimpy DIYer

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    The SOC measured in the morning was in IG-ON mode, not READY, so the DC-DC converter is not turned on when the measurement was made.

    In more than a year of data collection comparing the morning SOC with the SOC the evening before, it has been almost always exactly the same, regardless of temperature and other factors. Very occasionally the SOC moves 0.5% overnight. We have to give Toyota credit for good compensation for factors that may affect the measurement. Now only when the car was turned to IG-ON for a period of time in between the two SOC measurements then they start to differ by a few %.
     
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