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Max Brake Regeneration technique

Discussion in 'Gen 2 Prius Technical Discussion' started by sebapisa, Apr 24, 2007.

  1. sebapisa

    sebapisa Junior Member

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    Does anyone know if it's more effective to let the Prius coast down to a complete stop or to lightly depress the brake pedal and stop in a shorter distance? Which way will regenerate more energy?
    Thanks for the information.
     
    #1 sebapisa, Apr 24, 2007
  2. efusco

    efusco Moderator Emeritus
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    This isn't the simple answer you would like. It's been asked and answered many times though...unfortunately our search engine here kinda sucks so it's not easy to find the prev.

    1)Maximal regeneration occurs at around 60amps--commonly we'll call this 60amp braking. It's a moderate to firm brake pressure.

    2)The key to "efficiency" isn't regeneration, it's distance. If you have a stop sign 1 mile away it's always most efficient to glide (no regen at all) to a stop...all energy used up to the point you began the glide is used and none wasted.

    Next best is to coast from say 1/2 mile away. Although you'll regenerate LESS than you could by 60 amp braking at say the 1/4 mile mark, overall energy conservation is bettery since you didn't use power to travel that extra 1/4 mile.

    Finally, 60amp braking will show the largest regenerative capture. Now, there are times to shoot for that 60amp capture rate...Highway traffic when a long slow coast/glide is not practical for instance...then you'd drive, under power, until the point where a steady 60amp braking would bring you to a stop...thus you get full advantage of your regen without creating a riot on the highway.
     
    #2 efusco, Apr 24, 2007
  3. sebapisa

    sebapisa Junior Member

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    <div class='quotetop'>QUOTE(efusco @ Apr 24 2007, 03:03 PM) [snapback]429279[/snapback]</div>
    It is simple enough, thanks for replying. I found a couple of threads but none of them really make the answer clear.
    Now my last question, and promise not to bother anymore :) If you don't touch the brakes you are not regenerating at all?
    Thanks
     
    #3 sebapisa, Apr 26, 2007
  4. ekpolk

    ekpolk What could possibly...

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    Evan's answer is probably as good or accurate as it's going to get, nevertheless, I'll add some perspective. I installed a CAN View about a month ago, and I'm still experimenting with best data presentations, and so forth. One of the items I typically keep up on my primary graphic screen (the one I drive around with) is the "charge" display. The bar moves up or down from center depending upon which way the juice is flowing. One dramatic thing I've noticed is that with just light brake pedal pressure, as compared to coasting, the charge leaps up substantially. As an example, if I'm coasting down the back side of the Crescent City Connection (the big twin bridges in New Orleans) at maybe 55 mph, I'll see charge levels fluctuating between approx 4.5-6.5 kW. If even lightly touch and hold the brake, that will immediately jump up to at least 10-12 kW, maybe more. Harder braking produces even larger increases.

    Of course, as soon as you apply the brake, you can assume that you're shortening the window of recapture (obviously you'll come to a stop sooner on the brake), so what works out to be "best" is hard to say for any given deceleration.
     
    #4 ekpolk, Apr 26, 2007
  5. alexstarfire

    alexstarfire New Member

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    Well, from the graph that someone, I don't remember who, gave us that showed the best regen capture was like 17% braking power. It took him like 22.5 seconds or so to slow down from 45 MPH to 5 MPH. Why he chose 5 I have no idea since I am under the impression that the regen stops at 7 MPH and you are using the brakes at that point.

    What I've always wondered, and what I also believe has yet to be answered, is whether it's constant deceleration that gives you the most regen, or whether it was just the amount of braking power applied, so you'd slow down a bit more when you started braking but less as your speed decreases?
     
    #5 alexstarfire, Apr 26, 2007
  6. priussoris

    priussoris New Member

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    <div class='quotetop'>QUOTE(ByWire @ Apr 26 2007, 02:37 PM) [snapback]430746[/snapback]</div>
    If you do not use the brakes at all you will still get some regeneration
     
    #6 priussoris, Apr 26, 2007
  7. sebapisa

    sebapisa Junior Member

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    Thank you guys so much for the information. This is an amazing car, no doubt, and at $3 bucks a gallon it's even greater.
     
    #7 sebapisa, Apr 27, 2007
  8. philmcneal

    philmcneal Taxi!

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    firm pedal feel is what you should experience

    as always, distance over time should yeild you the best regen amount, just take advantage of the braking distance and never hurry to finish it.

    but 17% braking is the sweet spot, its a firm feel and its when regen starts slowing you down by the single digits, just keep that brake feel CONSISTANT!
     
    #8 philmcneal, May 2, 2007
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