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SOC Battery"ology"

Discussion in 'Gen 2 Prius Main Forum' started by s3nfo, Sep 21, 2012.

  1. s3nfo

    s3nfo Member

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    Normally don't have to wait in line to get on base, but since thousands of people are now coming on base to work on the USS Vinson there've been lines to get on base recently. I've never had my traction battery go below half on my normal commute, but with the long lines now, I've had to inch forward in long lines, which means no regen and I've noticed a disturbing trend. I hit the bottom of the Coronado bridge and the SOC is 8 green bars, it takes like 10 minutes of inching forward to go from 8 bars to half, 4 bars, but then I go from 4 bars to 2 bars and engine running in 30 seconds. So, am I seeing the normal NiMH discharge knee, or do I have some bad modules/cells that only shows up at lower SOC's?
     
    #1 s3nfo, Sep 21, 2012
  2. uart

    uart Senior Member

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    Hi s3nfo. I think it's fairly normal for it to go down fairly slowly down to 5 bars and then much faster discharge after that. The reason is that the bars aren't really linear, bars 6 and 7 are much bigger than the others. See the attachment.
     

    Attached Files:

    #2 uart, Sep 21, 2012
    dorunron and usnavystgc like this.
  3. jdcollins5

    jdcollins5 Senior Member

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    Completely normal. The computers do an excellent job of protecting the HV battery and maintaining SOC between 40 and 80%. When you get to 2 bars, 40%, the ICE will kick in and charge back up to 4 bars. It will keep doing this until you get going again and after a few stops with regen braking it will charge back up to the 8 bars. The more accessories you have on, such as AC, the shorter the time between recharges.

    I have seen this a few times during accidents on the highway. No worries.
     
    #3 jdcollins5, Sep 21, 2012
  4. Britprius

    Britprius Senior Member

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    Uart came up with the same explanation as me only faster. In short normal.
     
    #4 Britprius, Sep 21, 2012
  5. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    Wow Uart. That's great info. I learned something new today. You guys never cease to amaze me...
     
    #5 usnavystgc, Sep 21, 2012
  6. s3nfo

    s3nfo Member

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    Uart,

    WOW, great information.
    So, with overlap, you can go from 4 bars at low (49%) to 2 bars high (47.5%) with only 1.5% usage. Allays my concerns.
    Thanks,

    Jerry
     
    #6 s3nfo, Sep 22, 2012
  7. uart

    uart Senior Member

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    Hi Jerry. The "overlap" is called hysteresis and it's designed to prevent rapid fluctuations between states. Basically it follows the upper thresholds while it's charging, but it follows the lower thresholds while discharging. So it would be more like from 49% to 44 or 45% to make that drop.
     
    #7 uart, Sep 22, 2012
  8. dorunron

    dorunron Senior Member

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    That would explain why it seems to take a long time to charge back up from 2 bars to the 3rd bar, but then picks up quicker after that due to the "hysteresis". I have noticed how it seems like a long time from the 2nd to the 3rd bar, but after that it seems to be a little quicker on the 4th bar, then slowing down some. The numbers seems to make sense to me after observations over time.

    Thanks for the info and the chart uart!

    Ron
     
    #8 dorunron, Sep 22, 2012
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