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A strange Behavior on my Prius III (with 8 full bars on HV)

Discussion in 'Gen 3 Prius Main Forum' started by iskoos, Jan 2, 2020.

  1. iskoos

    iskoos Active Member

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    I went to Atlanta area for the holidays. The terrain is much different over there (comparing to flat Florida:))
    Long hills on the country roads, it goes up then down constantly. I was able to fully charge my HV battery (full 8 bars) after a long time (In Florida, I generally cannot go pass 7 bars) by using regenerative braking when coming down the hills.

    Here is what happened. And this happened twice:

    I am at a traffic light after a long down-hill road, battery is fully charged to 8 bars with smooth and long regenerative braking. Engine stopped, temps in 70s outside (pretty warm for Atlanta area). No heater is running in the car. Engine is up to operating temps.
    And while waiting at the traffic light, foot on the brake, the ICE starts all of a sudden!..
    I look at the MFD and do not see any red or green arrows. So battery is NOT charging (nor does it need any charging). Engine is warm enough, but the ICE kicks in and keeps running for about a minute then stops

    When first happened, I didn't understand. I thought maybe the Catalytic Converters were too cold (though it was weird). But the second time it happened, I paid more attention but couldn't figure out the reason.

    Any ideas? (This never happened to me before)
     
  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    When (in the opinion of the computers) your Prius is over charged, it will move the engine as an airpump, absorbing energy from the battery.

    Perhaps that is happening.
     
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  3. iskoos

    iskoos Active Member

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    Himmm, you are saying HV battery never designed to reach to 8 bar level, and when it happens, computer will do whatever to bring the voltage down?

    I would think the computer could stop the regenerative braking temporarily to stop the over charge.
     
  4. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Correct, 8 bars is time to 'use up' electricity.
    It will use more battery to go down the road, but you are stationary.
    It will quit Regen, but you are stationary.
     
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  5. 3PriusMike

    3PriusMike Prius owner since 2000, Tesla M3 2018

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    It is more like you are at 8.1 bars and this happens.
    The car is reducing the battery SOC to allow for some headroom in case you are about to continue down a long steep road.

    Mike
     
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  6. dig4dirt

    dig4dirt MoonGlow

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    I know this may be a little off topic, but to put it in a different perspective,

    I went into the mountains over last summer and got to 8 bars and then some...
    And I was able to get up to 50+ mph in EV only in my "c" (normal is max of 43~44mph)
    I know this is not normal but it really wanted to drain that HV quickly.
    But maybe since I didnt come to a complete stop that the ICE didnt come on.

    I was driving pretty norms before and after, just lots of climbs and drops with braking
     
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  7. fuzzy1

    fuzzy1 Senior Member

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    It is designed to reach 8 bars under certain regeneration conditions, but it is not meant to stay there for very long. The charge extremes, both high and low, are less than ideal for battery longevity.

    In normal driving, the car can quickly burn off that very top charge by using it for propulsion, offsetting some fuel. But when not moving, it sometimes seems to get antsy about trimming the very top, so briefly spins the ICE (with electricity, not gasoline) the same way it does during engine braking.

    Very many Prius drivers have reported this. I haven't personally noticed it, despite hitting that charge peak and forced engine braking many many times, but my cases all have some flatter driving ahead to burn off part of this very top charge before rolling to a stop.
     
    #7 fuzzy1, Jan 2, 2020
    Last edited: Jan 2, 2020
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  8. ChapmanF

    ChapmanF Senior Member

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    I haven't personally noticed it myself either; I think my car usually just sits there at the stop light thinking hard about how fully charged it is, then avidly uses it up once I am moving again. So I can't directly confirm this explanation. But I have seen it a lot on PriusChat.
     
  9. Maarten28

    Maarten28 Active Member

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    "Not designed" is maybe a bit much, but 8 bars goes to 80% SOC and that is programmed by Toyota as the absolute maximum.

    I would think the computer could stop the regenerative braking temporarily to stop the over charge.[/QUOTE]
    It does, but since regenerative braking is much better than friction braking (you're not wearing out your brake pads), the Prius will want to help you braking by running the engine. And when the battery is completely full (80%) it will also try to run it down by running the engine.
    All in a bid to keep the car operating safely.

    From about 70% SOC the regenerative braking will be less and less and the car has to rely on friction braking more and more.
     
  10. iskoos

    iskoos Active Member

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    Thank you guys. That's plenty for me to believe why the car did what it did.

    So now there is only one question in my head:

    When this happened to me, was the ICE actually not running by burning gasoline? Was it spinning with the help of MG1 (like fuzzy1 stated above)?

    It really felt the engine was running on its own but I might be mistaken. It lasted about maybe 30-40 seconds and before the light turned green, everything was off. And I accelerated under the full electric power after that.

    I am not going to have this happen to me any time soon. I won't be able to check it again. But it was very interesting at the least.
     
  11. sam spade 2

    sam spade 2 Senior Member

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    This is defective logic.
    IF.....you will not have to STOP at the bottom of the hill, then purposely slowing the vehicle down more than you need to just to put charge into the battery......is wasting fuel when you then accelerate back up to speed.

    And I think you are fooling yourself here too.
    I do not think that it is possible to do any "real" acceleration with the basic hybrid models without running the ICE.
    My C certainly won't.
     
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  12. iskoos

    iskoos Active Member

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    I am having a hard time to understand what you are trying to do here Sam spade2...

    You are making some assumptions and telling me what I should or should not do but your assumptions are not correct.

    I know how to efficiently drive my car. I never (or just partially do) brake if I am not eventually going to stop. In both cases where I hit the 8 bars, I stopped at the bottom of the hills. So I hit the brake obviously and it was a smooth continuous braking for efficient charging.
    And you still BRAKE when going downhill even when you are not going to stop because there is something called "SPEED LIMIT" and if you do not want to obey the speed limits, then most of those country roads are single lane roads. There are other vehicles in front of you that obey the speed limit and you are required to keep a certain distance in between. So you brake even though you are not going to stop. Hope this answered your first comment. I never brake foolishly thinking that I will regenerate. I am well aware of the energy losses.

    And your second comment was even funnier. Yes. You can absolutely do real acceleration under full electric power up to certain speed on Prius. I cannot say about Prius C because I do no drive Prius C and we are not talking about Prius C on this thread.

    Thanks
     
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  13. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Regenerative Braking System this recovers some energy (30%?) and is limited by both the amount of kinetic energy it can convert to Electricity and by the capacity of the Battery. It does not work below 7 MPH. As speed rises, kinetic energy rises much faster than the rate of the inverter to make electricity

    Friction Braking System recovers 0% of the Kinetic Energy of the car, limited by the heat capacity of the rotors, and the boiling point of the brake fluid. (Neither is usually a problem unless you brake going down hill for miles)

    Engine Braking recovers 0% of the kinetic energy of the car, normally called into action when the HV battery is full, or when you choose B mode above 24 MPH.

    (Prime has different rules)
     
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  14. fuzzy1

    fuzzy1 Senior Member

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    The version I have often seen described here is definitely electric-only, no gas. To confirm, or to discover an exception where yours is doing something different, you'd need an OBDII engine monitor (ScanGauge-II, Torque app with BT dongle, Carista, etc.) to watch for additional details not shown on your dashboard.
    Speaking of defective logic ...

    Many of us travel hills where full coasting or gliding is prohibited by safety, speeds limits, or collision liability. Some braking is required.
    With a full-up battery, a Liftback can certainly achieve acceleration that is "real" enough for many of us. Other people may have different standards or requirements.
     
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  15. sam spade 2

    sam spade 2 Senior Member

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    I"m trying to get more details into the discussion.......which you now supplied........because some people reading your post might be mislead without those additional details.

    With my C, you can't make it hold EV mode above about 5 mph unless maybe you are coasting downhill.
    My guess is that the "standard models" won't really do much better than that.
    What IS the speed before it kicks out......10.....15 maybe 20.
    And that would be with REALLY light acceleration, right ??
     
  16. sam spade 2

    sam spade 2 Senior Member

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    I did say "more than you NEED to".
     
  17. fuzzy1

    fuzzy1 Senior Member

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    HE never said that he did.

    On a Liftback, normal EV mode is cancelled at 10 mph cold, ~25 warm, on a normal battery charge. But it can still go all-electric to higher speeds even after true EV mode has been cancelled, depending on conditions. The hard MG1-protection limit is 46 mph before the ICE must be fired.

    And when the traction battery is full and itching to burn off the top, it can go significantly faster than normal in all-electric before the ICE is fired up.
    Different people have different standards.
     
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  18. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Lets assume I am coming into town, so the car is warm and the battery is 80% 'full".
    I can slow to 35 and make it about 1 1/4 miles. It will climb over rail road tracks and a bridge over the river.
     
  19. dig4dirt

    dig4dirt MoonGlow

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    EV mode button= 9mph or less, hit 10mph and it auto cancels

    w/o EV button, just staying in EV range on the mfd=
    max of 43~44mph in a Prius "c" (2014)
    max of 45~46 in a Prius Gen3 (2015)

    I will admit that I have played around with my "c" much more than my Gen3 (and had a 2012c prior, since released in usa)
    but with EV button in my "c" I have experienced a few episodes where I pressed the EV button
    and have went over the 9 mph. I cannot remember the exact details, but
    I know I have for sure with testing. Had to be really gentle on the pedal.
    I just cant recall any episodes in the Gen3 but may have had them too.
     
  20. fuzzy1

    fuzzy1 Senior Member

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    For a Gen3 Liftback in the U.S., that is the cancel speed when the engine coolant is below 20C / 68F. Above that temperature, the EV mode cancel speed is much higher.

    Brain fart. Cancel the above.

    That 10 vs ~25 mph cancel speed is actually based on a higher engine temperature, somewhere above 100F. And might be different in ECO vs Normal.

    The 20C/68F threshold is for allowing EV mode at all. Below 20C / 68F, EV not allowed in the U.S. Rest of world (except the rest of North America??) that EV-or-not threshold seems to be 0C/32F.
     
    #20 fuzzy1, Jan 3, 2020
    Last edited: Jan 3, 2020
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