altanate battery charge/discharge at constant speed

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by harveygp, Jan 2, 2007.

  1. harveygp

    harveygp New Member

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    Can anyone explain why at constant speed (e.g. 60mph), according to the energy flow screen at least, the battery apparently flips from charge to discharge every couple of seconds.

    From an overall efficiency point of view, it seems a bad idea to convert energy unless strictly necessary.

    I would have thoght in this condition the ICE, MG1 and MG2 should operate as a plain CVT unit without any intereraction with the battery.

    Surely the kinetic energy of the car itself is a much more efficient repository for any short term imbalance between engine output and power-train demand?

    Any explanations?
     
    #1 harveygp, Jan 2, 2007
  2. efusco

    efusco Moderator Emeritus
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    The battery is as much a part of the "cvt unit" as the MGs and the ICE. The minor charge changes you see simply account for minor adjustments needed to maintain your speed without the need to vary the ICE rpm....thus, allowing it to stay within it's most fuel efficient operating range.
     
    #2 efusco, Jan 2, 2007
  3. DanMan32

    DanMan32 Senior Member

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    Also the vehicle itself takes a load on the 200V system, such as the DC-DC converter for the 12V, and the AC compressor.
     
    #3 DanMan32, Jan 2, 2007
  4. MattFL

    MattFL Member

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    2008 does it too

    I just noticed this same exact thing with my brand new 2008 Prius. Crusing on flat ground ~65mph and it flip-flops between charging and draining the battery. It switches randomly, but usually 3-5 seconds or so between switches. When you get to a up or down hill then it will stay one way or the other, but flat ground and it flip flops. Seems to run just fine so I'm assuming it's normal, I just didn't expect to see it.
     
    #4 MattFL, Dec 9, 2007
  5. qbee42

    qbee42 My other car is a boat

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    Keep in mind that the energy display only shows direction without any indication of magnitude. A very small current will show the same as a massive load. The display is also a slowed down snapshot of the actual activity. If you could see all the detail, you would see a small magnitude current swinging back and forth as the system compensates for minor load changes. You are correct in your assumption that the control system attempts to minimize electrical power conversion.

    Tom
     
    #5 qbee42, Dec 9, 2007
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