Is there room to charge a "full" battery?

Discussion in 'Prime Fuel Economy & EV Range' started by TJX, Oct 31, 2017.

  1. TJX

    TJX New Member

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    Hi all,

    Wife and I both got our new Primes last week, and still trying to figure everything out. This forum has been immensely helpful towards that end, so thank you all for your collective knowledge :)

    This morning when I got in my car, the battery was fully charged and indicated that my electric range was 26.9 miles. I have three different routes to work, and one of them begins with a 1.5 mile downhill stretch. Initially I avoided this route, because I believed that the regenerative energy produced breaking on a downhill would be wasted on a full battery. But this morning I took the route, just to see what would happen.

    What happened is this. My electric range continued to read 26.9 miles for the duration of the down hill stretch. Then when I leveled off and applied the excelerator, it didn't budge from 26.9 miles for a little while, even during a brief uphill portion of the drive. I can't recall exactly how much of the drive it lingered for, or even for how long. Tomorrow I'll pay closer attention. But in the meantime, has anyone had a comparable experience? Does anyone know from a technical angle whether the "full" battery charge has any headroom to accommodate situations like this?

    Thanks again everyone!
     
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  2. Elektroingenieur

    Elektroingenieur Senior Member

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    As on nearly all hybrid vehicles, to achieve a reasonable lifespan for the battery on the Prius Prime, Toyota has programmed the Hybrid Vehicle Control ECU to keep the battery state-of-charge in a limited range under most conditions, never allowing the battery to be completely charged or discharged. The meter indications you see are relative to this limited range, not to the true capacity of the battery.
     
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  3. bisco

    bisco cookie crumbler

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    is it possible that the engine came on and you didn't hear it?
     
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  4. TJX

    TJX New Member

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    Probably not. I keep it in EV Mode (not EV Auto), and I drive without listening to any music or the radio, so the cabin is pretty quiet. Although, you did ask if it's "possible" that I didn't hear the engine come on. So yes, I will admit that it is possible (if unlikely) since I wasn't specifically listening for it. Tomorrow I will rerun the experiment and be more vigilant.
     
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  5. bisco

    bisco cookie crumbler

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    most people report that starting with a full charge and immediately going downhill will start the engine.
     
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  6. TJX

    TJX New Member

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    That strikes me as odd. What function would that serve? Protecting the battery somehow?
     
  7. Elektroingenieur

    Elektroingenieur Senior Member

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    Yes: it allows engine braking to be used, if there is no more battery capacity available for regenerative braking.
     
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  8. TJX

    TJX New Member

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    OK, so tying this all together - Would it stand to reason that if the battery is reported as fully charged, and extended downhill breaking does not start the engine, then the battery is in fact being regenerated outside of its maximum plug-in charge range?

    And if this is the case, would we be well advised not to do this out of consideration for the battery's health?
     
  9. Elektroingenieur

    Elektroingenieur Senior Member

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    The HV ECU won’t allow charging under conditions Toyota considers unsuitable, and remember that they are making a warranty on the HV battery, in some markets, of up to 10 years or 150,000 miles.

    This view may provoke some vigorous discussion, but I think it’s reasonable to rely on the battery management and protection features designed into the plug-in hybrid system by Toyota’s engineers, who undoubtedly had access to extensive test data when developing and refining the system’s control strategies and parameters to balance vehicle performance, driving range, fuel economy, and battery lifespan.
     
  10. bisco

    bisco cookie crumbler

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    i agree with the above, but also the possibility that your car is defective, however unlikely. more testing and data is needed on your part, and please report your experiences here.
    also, you may want to invest in a scan gauge, which will give you real data, vs the toyota display which is just for interest.
     
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  11. TJX

    TJX New Member

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    Thank you both for the feedback. Unfortunately I was unable to take that route again this morning, but I will give it a go tomorrow and report what I find.

    Thanks again!
     
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  12. Lee Jay

    Lee Jay Senior Member

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    I've had it say 29.0 miles when I got in after charging complete and 29.3 when I got to the bottom of the hill near my house.
     
  13. JasonG

    JasonG Member

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    I've experienced something similar as I live near the top of a hill. Leaving in the morning on a full charge (100% battery indicated) the engine does not come on but the battery and range don't change. Also, the engine does not come on! This is <1 mile so I think that the maybe 2% regeneration is OK for the battery. As noted, it then takes more time to decrease from 100% than would be expected.

    I think if it was a longer hill the engine would come on to prevent excess charging. I've had this happen on longer downhills.
     
  14. joachimz

    joachimz Senior Member

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    I have a slight downhill in the mornings too and have also observed the EV range in creasing slightly (0.2) and ICE is definitely not running
     
  15. bisco

    bisco cookie crumbler

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    how are you folks determining that the ice is not spinning to burn of excessive charge?
     
  16. Lee Jay

    Lee Jay Senior Member

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    You can feel it if you're careful, or you can look at any of about three screens.
     
  17. bisco

    bisco cookie crumbler

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    not sure toyota's screens show when the ice is spinning to burn excess energy, or that it feels the same as combustion.
     
  18. joachimz

    joachimz Senior Member

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    couple thing for me, I would hear it and I also feel a ever so slight vibration when the ICE comes on.
     
  19. bisco

    bisco cookie crumbler

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    during combustion? or have you felt it on a downhill where it is freewheeling to burn off juice?
     
  20. Lee Jay

    Lee Jay Senior Member

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    Yeah, I have, and like I said you can feel it and you can see it on the screens in multiple ways.
     
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