Question regarding charging battery through regen on downhill slope

Discussion in 'Prime Plug-in Charging' started by SeattleHawaii, Jul 18, 2016.

  1. SeattleHawaii

    SeattleHawaii Member

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    Hi Folks -
    happy owner of a Prius Gen3...but...am considering the Prime once available in the US. Can anybody explain to me how the regen works for the EV part of the battery. E.g. if you went up a mountain pass and the EV part of the battery is exhausted and you are driving in regular HV mode but then get to the long downhill portion of the drive does the regen charge only the HV portion of the battery, or also the EV portion? or would you need to switch into EV drive to charge the EV portion of the battery (which might be an issue if EV is not available due to drained EV battery portion).

    Hope this makes sense...from what I read it sounds like there are two dedicated charge areas in the battery...I might be wrong.

    thanks much for any insight you can provide!

    Berndt
     
  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    In some very early prototypes, in the 2009 time frame, there were two parts to the HV battery.

    No production Prius battery has two parts, it is all one HV battery. (PHV, Liftback, v, Prime, Gen 1 to 4; all one HV battery)

    There are separate Fob batteries, and 12 v batteries, but all one HV battery.
     
  3. Trollbait

    Trollbait It's a D&D thing

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    It's all one battery, but there were some comments from Toyota that the car would only use a smaller portion of it while in hybrid mode. We have to wait for more details, but I expect that this is to keep the charge in the pack up if the driver puts it into hybrid mode in order to have EV mode available later. I don't see any advantage in not letting excessive regen charge be completely captured.
     
  4. bisco

    bisco cookie crumbler

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    the whole battery will charge as you come down the mountain while in ev mode, same way the pip works now.
    you don't have to switch anything.
     
  5. SeattleHawaii

    SeattleHawaii Member

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    Very cool - I was hoping that the whole battery would charge on downhill so that essentially you get more EV miles after you exhausted the EV battery partition. Saddle road on Hawai'i Island is a BIG hill and the battery should charge pretty much fully on the descent portion of the drive giving me another 22 miles on EV :)
     
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  6. bisco

    bisco cookie crumbler

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    nice! of course, the downside is the gas used to get up there, but it's still better than a gasser!

    it takes a LOT of downhill to put 22 miles into a battery.
     
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  7. SeattleHawaii

    SeattleHawaii Member

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    Don't have the exact numbers but believe that the downhill (<=8% grade) is probably around 15 miles. Even if it doesn't fully charge...any additional EV mile free is a good thing!

    That said - so what would be the most efficient approach with a charged Prime. Drive as far uphill as one can on EV then use HV for the flat part on the mountain and then recharge on the way down? Or, use the HV mode for the uphill portion and the EV mode for the flat portion before the downhill starts? Can't wait to try this all out later this year!!
     
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  8. bisco

    bisco cookie crumbler

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    phevs have two strikes against them when hill climbing. ev is very inefficient, and the ice isn't big enough to maintain speed. this is a problem for prius in very mountainous areas, and pip if you've used up the battery before the climb. toyota has copied gm's 'hill climbing mode', to allow the engine to charge the battery before the ascent, so you have both available.
     
  9. SeattleHawaii

    SeattleHawaii Member

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    thanks much for the info - didn't realize the new Prime will have a hill-climibing mode....I only hope the price of the Prime will be affordable :)
     
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  10. bisco

    bisco cookie crumbler

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    same here!(y)
     
  11. drash

    drash Senior Member

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    I'd probably use EV+ mode to get up the mountain which is similar but not exactly the same as "blended mode" in the PiP. There's a couple of places that have rather large hills at the beginning of stop light. I usually put the PiP in EV mode and press the accelerator enough to engage the ICE as I'm climbing. Efficiency loss while hill climbing is shared by both the battery and ICE but neither takes a huge hit.


    Unsupervised!
     
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  12. GT4Prius

    GT4Prius Active Member

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    Bisco - can you elaborate please?

    1. In what way is EV "very inefficient" - what kind of inefficiency are we talking about, and why is this the case?
    2. "The ICE isn't big enough to maintain speed" - surely this depends on how steep the Hill is? I live in a very hilly area and my Gen2 has never had a problem. I must be missing something, I don't understand what you're getting at.

    Thanks

    P.S. Can someone explain why the plug-ins with their bigger batteries aren't MORE efficient in hilly areas than non-plug-ins. That seems to be what the specs say, but there must be the potential to recover more energy on descents, more than offsetting the extra weight of the battery when climbing the hill?? My Gen2 certainly does sometimes seem to stop using regen braking when the battery is full. It doesn't tell me it has but I can feel the brakes change, and I don't think its fade happening that's making the change.
     
  13. Trollbait

    Trollbait It's a D&D thing

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    Hills suck for efficiency no matter the car or technology.
     
  14. bisco

    bisco cookie crumbler

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    generally speaking, you get more range in slower and flatter ev driving. i can't put a number on it, but it's just no fun using up all your ev on a big hill or high speed and then driving hv everywhere else.

    yes, steepness and length matter a lot, so you learn as you go. you won't regen coming down, nearly as much as you lose, so learning how much ev to use so you can refill is important.

    the prius engine wasn't designed to work by itself, so long ascents wear down the battery, then you have trouble maintaing speed. again, i'm talking about mountainous driving. colorado and etc.
     
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  15. GT4Prius

    GT4Prius Active Member

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    Thanks for the elaboration.

    As I suggested somewhere in Priuschat a few months ago, if the satnav was in use so the car knew where it was going and had topography data in its maps, it could send that data to the hybrid/ev control systems and optimise power and battery use for you. In fact I have an idea that one review of the Prime talked about the satnav "doing 3d chess" in a way that seemed to imply the Prime's Satnav may do this, but it wasn't clear.
     
  16. bisco

    bisco cookie crumbler

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    that would be fabulous. i'm sure it's coming, hopefully in prime.
     
  17. Redpoint5

    Redpoint5 Senior Member

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    The electric motor is always more efficient than the gasoline engine because the vast majority of the chemical energy in the battery is converted into mechanical energy to propel the vehicle. The conversion is something like 90% efficient.

    By comparison, the gasoline engine in the gen IV Prius has a peak efficiency of 40%, with most of the chemical energy in the gasoline wasted as heat instead of propelling the vehicle.

    Despite electric motor efficiency, the chemical energy stored in batteries is much less than the energy density of gasoline. In fact, gasoline has 47.5 MJ/Kg of energy compared to 0.3MJ/Kg for a lithium ion battery. That's over 100 times more energy per weight for gasoline!

    Gasoline engines are most efficient when operating at peak torque under heavy load and the efficiency drops off drastically at low loads, such as steady speed cruising on a flat road.

    So, when confronted with a large hill and a small amount of battery energy, it's best to use the vast reserves of gasoline energy to climb the hill, running the engine at peak efficiency, and saving the battery for relatively easy cruising.
     
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