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EV mode: input vs output

Discussion in 'Gen 2 Prius Accessories & Modifications' started by sseres, Feb 1, 2006.

  1. sseres

    sseres New Member

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    I love EV mode, and I think it's helping me and I'm not putting my car away for the night with a discharged battery.

    However, I was crusing down the boulevard today and noticed that it certainly a lot easier to discharge, then charge the hybrid battery. It got me thinking...

    is there a way to describe in layman's terms the basic ratio of how much electricity my Prius can generate for the battery (either from coasting or the ICE), versus the amount of energy that gets sucked out when I am driving in pure EV mode?
    :huh:
     
    #1 sseres, Feb 1, 2006
  2. efusco

    efusco Moderator Emeritus
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    Overall the ratio will always be 1:1 otherwise there would be a net gain or loss in charge.

    But I have a feeling you're trying to ask something else, I'm just not sure what. Are you looking for total available kW output of the battery? How many amps of output are possible vs. how many amps of input are possible in a given moment?

    Please try to clarify the question. Those of us with CAN-View are able to continuously monitor the charging and discharging of the battery and can probably shed a little light on the subject.
     
    #2 efusco, Feb 1, 2006
  3. sseres

    sseres New Member

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    Maybe something as simple as: for every turn of the tires that I push using EV mode (just the battery), how many more turns of the tires will it take to recap that battery energy expended.

    Does that make sense?
     
    #3 sseres, Feb 1, 2006
  4. gschoen

    gschoen Member

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    There is no fixed ratio, not even an approximate one. Both charge and discharge are variable.

    Your discharge energy varies based on vehicle load, acceleration, number of stops, speed, road grade, etc.

    Your charge energy is controlled by the computer and depends on a number of factors, including current SOC, engine temp, current engine load, etc.

    Charging can seem slower since the computer tries to optimize when to charge and keep the engine RPMs as efficient as possible. For example, charging the battery while the vehicle is stopped isn't very efficient, so it only would do so once your battery is low (2 bars and less for a warm engine).
     
    #4 gschoen, Feb 1, 2006
  5. KTPhil

    KTPhil Active Member

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    Going back to the original question, I think you are looking for the idea that it takes more bars to accelerate than get put back if you let up and use regen to charge it back up.

    There are conversion losses every time you convert from battery to motor to movement, then back to generator to battery again. Figures have been quoted here before, but I do not remember them. I would guess that there is less than 50% captured when all losses are considered. But whatever it is, that is more than you get with a non-hybrid!
     
    #5 KTPhil, Feb 1, 2006
  6. efusco

    efusco Moderator Emeritus
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    I'd say that the 50% number is probably fair. If I climbed a hill under all battery, turned around and went back down the hill trying to maximize regeneration I'd probably get ~25-50% back.

    All in all, though, it's said that regenerative braking ultimately only recaptures about 2-4% of all the energy used.
     
    #6 efusco, Feb 1, 2006
  7. sseres

    sseres New Member

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    that doesn't seem like much (all respect to the more-than-a-non-hybrid argument). It seems like the regenerative braking is what happens more often than actual disk braking, just from the sound of things when I stop. Really only 2-4%?
     
    #7 sseres, Feb 1, 2006
  8. efusco

    efusco Moderator Emeritus
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    If you drive your Prius from a stop up to 30mph, drive 5 miles the stop using maximal regenerative braking how much of the energy it took to get you from point a to point b do you think could possibly be recaptured?

    Think about it this way. On a highway trip of 100 miles regenerative braking will not recaputure any measurable amount of energy.

    In the city in stop and go traffic it will recapture a much higher percentage...at least measurable, but it still takes power to get up to speed, you can't recapture all that power even if you stop immediately and you can't recapture any of the cruising energy.
     
    #8 efusco, Feb 1, 2006
  9. viking31

    viking31 Member

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    See the attached pdf that is a synopsis of the energy used in a Prius. Some assumptions are made and I have not verified its overall accuracy, but it seems to be true in most respects.

    As to part of your question the section in the attached pdf regarding regenerative braking does state it is far from 100% efficient. Each green leaf car represents about 1/250 or so of a gallon of gas in the Prius equation. So, according to the author's assumptions if regenerative braking was 100% efficient in the Prius you would get about 3 green leafs for each stop from 60 mph.

    In the future I am confident we will see many more different methods that will be utilized in production autos that are more efficient than NiMH batteries in capturing the relatively large amounts of energy rapidly generated and consumed during braking and acceleration.

    Rick
     

    Attached Files:

    #9 viking31, Feb 2, 2006
  10. sseres

    sseres New Member

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    I'll read through it. Thanks everyone for your 2 cents about this most esoteric of threads.

    Not sure if it's been discussed before, but is there a *best* way to drive in EV mode? For example, is it better, once you're to speed, to leave your foot on the accelarator, then coast down like you do with the ICE, or pulse it to maintain speed and have the electric motor off as much as possible?
     
    #10 sseres, Feb 2, 2006
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