Welcome to Our Community

Wanting to join the rest of our members? Feel free to sign up today.

Sign Up

Fully Charged HV Battery==No Regenerative Braking?

Discussion in 'Gen II Prius Technical Discussion' started by Oldwolf, Apr 27, 2011.

Social Buttons

  1. Oldwolf

    Oldwolf Prius Enthusiast

    Joined:
    Feb 15, 2011
    Messages:
    607
    Likes Received:
    58
    Location:
    NC
    Your Vehicle Year:
    2012 Prius c
    Model:
    Four
    I’ve searched for an answer to my question but have not found it yet.

    When the HV battery becomes fully charged, which might happen when driving down long mountain grades (that can continue for many miles), what happens? Does the computer just cut off regeneration so you “feel” a loss in regenerative braking?
  2. mikewithaprius

    mikewithaprius New Member

    Joined:
    Jan 5, 2011
    Messages:
    656
    Likes Received:
    100
    Location:
    Rhode Island
    Your Vehicle Year:
    2007 Prius
    Model:
    N/A
    You should switch into B mode (on the stick with D, R, N) for engine braking. This will help prevent overheating/overcharging of the battery pack (EDIT: last bit is wrong, see post #6) when it reaches the computer-imposed 80% state of charge limit. It will still feel like regen braking, but instead of taking that energy and putting into the battery, the engine throws it off as heat.

    You can still drive normally in B mode, too, accelerate, etc., just the braking is different.
  3. 2k1Toaster

    2k1Toaster HID Guru

    Joined:
    Feb 14, 2010
    Messages:
    3,892
    Likes Received:
    1,141
    Location:
    Rocky Mountains
    Your Vehicle Year:
    2006 Prius
    Model:
    Three


    When the battery is fully charged (80%), it then cuts to friction brakes. The transition is pretty seamless. When in B mode, it spins the engine as an air pump just to waste energy it captures from regen. That way it doesn't go into the battery.

    The car is extremely careful to protect itself. You cannot kill it. If the terminator was in a Cars movie, it would be a Prius. (With a slight personality change from "death to all" to "look at the fuzzy wabbit").

    I live on a mountain and every morning I start with low SOC and end up fully charged by the time I get to the town's elevation. I don't really notice the switch from regen to friction only when it fully fills up.
  4. firepa63

    firepa63 Former Prius Owner

    Joined:
    Jul 23, 2005
    Messages:
    1,762
    Likes Received:
    198
    Your Vehicle Year:
    Other Hybrid
    Model:
    N/A
    The ICE will also spin up to draw off energy when in D. You don't have to be in B, but it helps when going down a long hill.
  5. cwerdna

    cwerdna Senior Member

    Joined:
    Sep 4, 2005
    Messages:
    12,317
    Likes Received:
    1,925
    Location:
    SF Bay Area, CA
    Your Vehicle Year:
    2006 Prius
    Model:
    N/A




    Agreed w/firepa63. I frequently hit soc above 75% (as indicated by ScanGauge, looks like all bars filled on the MFD) while going downhill to get home and the ICE automatically turns on while in D, even at speeds <41 mph. Sometimes, the revving gets pretty high too, say over 3000 rpm.
  6. richard schumacher

    richard schumacher shortbus driver

    Joined:
    Mar 27, 2004
    Messages:
    7,652
    Likes Received:
    872
    Location:
    United States
    Your Vehicle Year:
    2004 Prius
    Model:
    N/A
    The reason to shift to "B" on a long downgrade is to save the friction brakes, not the battery. (The battery takes care of itself perfectly under all driving conditions.) And that's not just a matter of conserving the brake pads: it is possible to boil brake fluid, in which case you will have no brakes.

    Don't use "B" when not on a long downgrade because it will only reduce fuel economy.
    1 person likes this.
  7. billnchristy

    billnchristy Active Member

    Joined:
    Jul 18, 2009
    Messages:
    890
    Likes Received:
    95
    Location:
    GA
    Your Vehicle Year:
    2010 Prius
    Model:
    III
    We drive up and over Blood Mountain here in GA a few times a year and the first time you use B it can kind of freak you out when you are slowing down but the engine starts revving higher and higher.

    It works like a charm though, I love it.
  8. BAllanJ

    BAllanJ Active Member

    Joined:
    Dec 9, 2008
    Messages:
    658
    Likes Received:
    68
    Location:
    Kingston Ontario
    Your Vehicle Year:
    2009 Prius
    Model:
    N/A
    Is there any other way to use this energy productively rather than let the energy get thrown away spinning the engine?

    I was thinking that maybe if it was hot and you were using the ac minimally to improve mileage and you saw a full battery before a long downhill you could go to max ac and then you could reduce the ac later. Not sure if the ac uses enough to have an impact, but I'm just throwing this out there... wonder if there are any other possibilities?
  9. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    Messages:
    6,955
    Likes Received:
    1,748
    Location:
    Western Washington
    Your Vehicle Year:
    2012 Prius
    Model:
    Three
    Yes on the AC, because at this point, it is free. Just like going into 'B' mode, I switch it on before the battery fills.
  10. cwerdna

    cwerdna Senior Member

    Joined:
    Sep 4, 2005
    Messages:
    12,317
    Likes Received:
    1,925
    Location:
    SF Bay Area, CA
    Your Vehicle Year:
    2006 Prius
    Model:
    N/A


    Good idea... I think. Problem is, it's so cold in the Seattle area that AC is of no benefit other than to dehumidify.
  11. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    Messages:
    6,955
    Likes Received:
    1,748
    Location:
    Western Washington
    Your Vehicle Year:
    2012 Prius
    Model:
    Three
    Fortunately most of my long mountain descent experience has been in warmer seasons outside of Seattle.
  12. vincent1449p

    vincent1449p Active Member

    Joined:
    May 24, 2004
    Messages:
    862
    Likes Received:
    299
    Location:
    Singapore
    Your Vehicle Year:
    2012 Prius c


    Even in cold climate, the HV Battery gets heated up with frequent charging and discharging. So there is still benefit to use A/C for the longevity of battery life.
  13. cwerdna

    cwerdna Senior Member

    Joined:
    Sep 4, 2005
    Messages:
    12,317
    Likes Received:
    1,925
    Location:
    SF Bay Area, CA
    Your Vehicle Year:
    2006 Prius
    Model:
    N/A


    True... I do have HV battery temp XGauges set in my Scangauge so I'll check them more closely but err.. it's pretty cold for the driver already. I'm using the heater!

    Here's is our forecast:
    KING5.com | Seattle Weather Forecast Maps

    50 F = 10 C and 39 F = 3.9 C
  14. Oldwolf

    Oldwolf Prius Enthusiast

    Joined:
    Feb 15, 2011
    Messages:
    607
    Likes Received:
    58
    Location:
    NC
    Your Vehicle Year:
    2012 Prius c
    Model:
    Four
    To summarize:

    When the HV battery is full or nearly full and the car is descending a grade-
    1) The battery on the MFD turns a Salmon color.
    2) The computer starts to use the engine for a higher percentage of braking.
    3) When the engine cannot provide enough braking (RPM limited perhaps?) the friction brakes are utilized to some degree.

    Do I have the sequence correct? The automatic use of the friction brakes would requires some sort of temperature measurement to avoid overheating the rotors/drums. What am I missing?
  15. richard schumacher

    richard schumacher shortbus driver

    Joined:
    Mar 27, 2004
    Messages:
    7,652
    Likes Received:
    872
    Location:
    United States
    Your Vehicle Year:
    2004 Prius
    Model:
    N/A
    The car never automatically applies the friction brakes, that's up to the driver. The car will use more engine braking sooner when in "B" than in "D". Shifting is also the driver's responsibility, the car will not shift itself.
  16. uart

    uart Senior Member

    Joined:
    Sep 7, 2009
    Messages:
    3,603
    Likes Received:
    755
    Location:
    Australia
    Your Vehicle Year:
    2005 Prius
    Model:
    N/A


    Salmon Color? Mine just goes to full green. (8 bars.)

    What's with the Salmon thing, has anyone else seen that?
  17. Oldwolf

    Oldwolf Prius Enthusiast

    Joined:
    Feb 15, 2011
    Messages:
    607
    Likes Received:
    58
    Location:
    NC
    Your Vehicle Year:
    2012 Prius c
    Model:
    Four


    Sorry, I think that only applies to the GenIII's. I was reading this thread before and did not realize they were talking about a 2010>>http://priuschat.com/forums/gen-iii...66944-battery-never-fully-charged-8-bars.html
  18. uart

    uart Senior Member

    Joined:
    Sep 7, 2009
    Messages:
    3,603
    Likes Received:
    755
    Location:
    Australia
    Your Vehicle Year:
    2005 Prius
    Model:
    N/A
Similar Threads: Fully Charged
Forum Title Date
Prius, Hybrid, EV and Alt-Fuel News "FullyCharged" is back online Jan 11, 2014
Gen II Prius Care, Maintenance and Troubleshooting Hybrid Battery almost always fully charged on a long trip Mar 25, 2013
Toyota Prius Plug-in Fully Charged PIP in about 30min Dec 30, 2012
Toyota Prius Plug-in 12 miles EV after fully charged? Nov 21, 2012
Gen II Prius Main Forum battery never fully charged Oct 24, 2012