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Long Descents

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by markabele, Sep 17, 2014.

  1. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    Just got back from a trip to Rocky Mountain National Park. Was with some family in an RV, so we actually rented a car to use in the mountains. It was a Subaru Outback, which may be the perfect mountain vehicle. But anyway, a few of the roads had me thinking what my PiP would be doing if I was driving it. Seems like some of the downhills are so long and steep that it couldn't be good for the battery. Obviously it is great that we are able to recover that energy...but at what cost? That would have to be charging the car much faster than a Level 2 could.
     
  2. SageBrush

    SageBrush Senior Member

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    The car limits battery charging to around 30 kW IIRC, which is ballpark L2: 240V * 15 Amps
     
  3. roflwaffle

    roflwaffle Member

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  4. Maarten28

    Maarten28 Active Member

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    If the HV battery is full, it won't charge. The Prius will even turn the engine using MG1, thereby using electricity and braking the car. If you have adaptive cruisecontrol engaged it will do that automatically to keep the desired speed (normal CC will only brake a bit but will let the speed increase).
     
    #4 Maarten28, Sep 18, 2014
    Last edited: Sep 18, 2014
  5. gallde

    gallde Active Member

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    I discharge my full battery in 15 minutes twice a day on my drive to and from work, and range has not decreased in two years, so if the pack can take such a quick discharge, it can probably take a quick charge as well.
     
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  6. SageBrush

    SageBrush Senior Member

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    I cannot understand your post because you do not say what the capacity is of your battery or the fractional discharge, but a PiP battery that goes from 80% to 40% capacity in 15 minutes is averaging a discharge rate of 2/0.25 = 8 kW. That is less than L1 charging.
     
  7. GregP507

    GregP507 Senior Member

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    The condition of the electrodes is mainly the condition of the battery. If the charge state goes too low or two high, permanent damage can result to the structure of the electrodes. That's why Toyota's battery is protected from cycling too deeply.
     
  8. drash

    drash Senior Member

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  9. GregP507

    GregP507 Senior Member

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    When I was deep-cycling my lithium phone batteries; charging them once a day, they barely lasted a year. Since I started plugging in my phone everywhere I can; in the car, at work, and back at home, I seem to be getting much longer life out of them.

    Go figure...
     
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  10. drash

    drash Senior Member

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    Yeah I do a lot of "opportunistic charging" for most of my electronics. And yes, they seem to last much, much longer. I think that has something to do with better heat dissipation more than the amount of charge. Most of their research also appears around single cells which would have much better heat dissipation.
     
  11. iplug

    iplug Senior Member

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    Assuming you have a PiP. On a PiP you can discharge all usable battery capacity at near freeway/highway speeds in less than 15 minutes. It may not be the most efficient use of EV, but certainly there are many commuters who have to do this routinely.

    On long mountain descents the opposite is roughly true regarding regeneration. I can confirm that the PiP will protect itself and hold regeneration if this is happening too fast for more than a few minutes at a time.

    This is faster than level 2 charging in the PiP (3.3 kW) or even the more robust 6.6 kW charging level 2 limit of other plug-ins. So far, I am not aware of Toyota documenting any concerns about rapid discharge and regeneration as noted.
     
  12. SageBrush

    SageBrush Senior Member

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    There is a fellow PC'er from Santa Fe NM who set up a business reconditioning batteries for the folks with early battery problems. His main clientele were commuters to Los Alamos who deeply discharged their cars daily going up the mountain.
     
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  13. CaliforniaBear

    CaliforniaBear Clearwater Blue Metallic

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    I'm not sure what IIRC means but 240 volts * 15 amps = 3.6 kW. At that rate it will take just under 50 minutes to charge the battery from 20% SOC to 85% SOC. It doesn't actually charge at the full 15 amp capacity and slows down near full charge so it would be more like 1.2 hours for full charge. Its about 2.4 hours at 120 volts.

    The car will charge 150 Wh in 1 minute on a good 50 mph downhill with the appropriate amount of regeneration braking as seen on the energy display. That will provide 3 kWh in 20 minutes. I'm not sure the car will allow that rate of charge for that long (if you can find the right hill) but you could probably get a full charge in 30 minutes or so.
     
  14. SageBrush

    SageBrush Senior Member

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    Right you are -- my calc was off by a decimal.
    Thanks for the correction
     
  15. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    So if we all agree that charging the car in 20-30 minutes is bad...then I think we can agree that a long descent is bad on the battery...correct?
     
  16. The Electric Me

    The Electric Me Go Speed Go!

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    So you say you rented a Subaru Outback huh?
    Hey, I'm fine with that.
    Even if you PiP could of handled everything fine, you probably saved it some wear and tear. Even wear and tear that falls under acceptable normal parameters of operation.
    Plus sometimes it's fun to drive something different once in a while.
    Avoiding a debate over the minutia of battery charge/discharge and long mountaneous descents, I'd say you rented a good tool for the job. And now your Prius is ready for the work week.
     
  17. CaliforniaBear

    CaliforniaBear Clearwater Blue Metallic

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    Wrong. If the car will let you do it then it is okay. If the charge rate is too fast for too long the ICE will come on and take over enough braking to limit the charge rate. If its still too fast and long (unlikely) then it will add friction braking. You can always use the B mode but you will may lose some of the available regeneration charging. As they say "just drive it" the car will take care of itself.
     
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  18. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    That is an extremely simple, easy, and probably incorrect statement to make. Just because the car lets you do it doesn't mean it doesn't hurt it. Like most things, it's also not black and white (not simply ok or not ok), there are varying degrees as to actually how bad it might be for the car.
     
  19. markabele

    markabele owner of PiP, then Leaf, then Model 3

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    I agree. It was a great car for the job. It only cost $140 and we did almost 300 very hard miles in it (mild off road; hard turns, acceleration, and braking). There were also quite a few times where the high ground clearance of the Outback was really appreciated.
     
  20. CaliforniaBear

    CaliforniaBear Clearwater Blue Metallic

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    You said we can all agree "that a long descent is bad on the battery". Wrong, we don't all agree. The PiP is a fine car for mountain driving and provides great mileage due to its super regeneration capability.