Rate of regeneration during deceleration

Discussion in 'Gen 3 Prius Main Forum' started by garyasta, Dec 1, 2020.

  1. garyasta

    garyasta Junior Member

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    Is it possible to change the rate of regeneration when decelerating so that a faster charging rate is achieved, similar to that of the braking rate? I have a 2010 Gen 3.
     
  2. ChapmanF

    ChapmanF Senior Member

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    Turn the cruise control on and set it for a significantly lower speed than you'll be driving. I do this for twisty mountain driving. I just use my foot on the go pedal to go faster, and when I lift it the car regens and slows aggressively.
     
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  3. Grit

    Grit Senior Member

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    Easy peasy, press-hold down the brake pedal harder.
     
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  4. BZzap!

    BZzap! Senior Member

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    Feather your brake pedal slightly going down hill and your charge rate will increase exponentially according to how much pressure you apply. Keep it within the speed limit and when your battery is at full charge you should use you “Brake” mode to avoid overcharging the traction battery. Applying the foot brake while in “Brake” mode will not charge the traction battery.
     
  5. garyasta

    garyasta Junior Member

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  6. garyasta

    garyasta Junior Member

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    Thanks for that ChapmanF, but I don't have cruise control to see if it works.
     
  7. ChapmanF

    ChapmanF Senior Member

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    I'm pretty sure if you don't have cruise control then it doesn't.

    I'm surprised though. I wonder if just adding the stalk and maybe the brake switch would be sufficient? That's how it was with Gen 1 in the US.
     
  8. Kramah313

    Kramah313 Active Member

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    The actual friction brakes don’t typically engage until the CHG bar on the hybrid monitor fills all the way up (there are exceptions, such as if you hit a large bump while braking). So you can achieve this with the brake pedal - just keep the braking amount from filling up the CHG bar and you’ll still be using regeneration only.
     
  9. garyasta

    garyasta Junior Member

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    Hi Kramah13
    I presume from your comment, that when coasting, and the CHG bar is only showing about 3mm into the graph, that there is no charging, as the bar is not filled up.
     
  10. Kramah313

    Kramah313 Active Member

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    The charging amount is linear - I have scangauges and can see this value as amps into the battery - when it’s got that 3mm it might be 5-10 amps, when it’s full it’s more like 80-100 (this also depends on speed somewhat, faster = more charging).

    If you see no bar at all, then there is typically not any regeneration being used.
     
  11. garyasta

    garyasta Junior Member

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    Hi Kramah313
    Obviously you are fairly tuned into how your Prius operates. Do you know if there is any way to increase the regenerative charging other than the higher rate during braking.
     
  12. garyasta

    garyasta Junior Member

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    Hi Grit
    I am referring to the coasting stage of slowing down, not the braking.
     
  13. ChapmanF

    ChapmanF Senior Member

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    Um, this is starting to sound as if there is some more specific question in your mind that you haven't quite put into the post.

    What is your use case for increasing the regenerative charging other than the higher rate during braking?
     
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  14. garyasta

    garyasta Junior Member

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    Apart from the higher regenerative charging when braking, I am presuming that a higher charging rate when coasting or slowing down would provide a quicker top-up to the batteries. This would then reduce the amount of time used operating the ICE.
    From most of the replies to my question, I infer that I would need to use the brake pedal (not good?) more often to increase regeneration and not rely on regeneration when coasting or slowing down.
     
  15. ChapmanF

    ChapmanF Senior Member

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    It's very common for new Prius owners to assume that regeneration is a better thing than it is. Some basics usually help:

    Unless you are driving one of the PHEV models (a PiP or a Prime), all of the energy to move and power your car comes from gasoline.

    The engine can convert that gasoline to useful work, at a shade under 40 percent efficiency. That's the best you can get; it happens when you're driving under typical conditions and the engine output is well mated to the demand, and not very much net flow either to or from the battery.

    When you brake, if you were in a car with no regen, you would be turning all of your kinetic energy into heat and losing it entirely. What makes regen braking nice is that it's not as wasteful as that. But that's a low bar. You are able to capture some of the energy you would otherwise have totally wasted, and then you can reuse some of that. You pay a conversion-inefficiency tax on both the capture and the reuse.

    If you have the choice between driving that captures lots of energy as regen and then spends it again, or just driving so that you're usually just letting the engine move the car and the battery fills in briefly for changes in demand, the second way will work out better.
     
  16. Kramah313

    Kramah313 Active Member

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    ChapmanF has the answer. And you have figured it out too but don’t realize it - you see the application of the brake pedal as wasteful. The brake pedal is the best way to get more regen out of the Prius, up to the point where it uses the actual friction brakes. The problem is that isn’t actually going to help fuel economy. The conversion of the kinetic energy of the moving vehicle into the stored energy of the battery involves some loss in the transfer. So does the conversion of the stored battery energy back to the kinetic energy to move the car.

    It’s more efficient to simply use the energy to move the car except in a couple of cases. The first is when the gas engine is turning but all of the power isn’t needed to move the car. During this case, the car will use some of the power from the gas engine to charge the battery. It may also do this if the battery charge is low, but you’ll notice the gas engine working harder to accelerate in that case. The second is when the car is slowing down. That energy is going to be wasted as the car stops anyways, so the Prius converts what it can back into the battery. You’re already pressing the brakes for more regeneration in that case anyways. The best thing you can do for fuel economy there is to leave enough time to slow down without filling the bar all the way. The friction brakes throw away 100% of that energy while regeneration at least captures some of it.

    Hopefully this info helps!
     
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  17. Mdv55

    Mdv55 Member

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    No one has mentioned the excess heat. If regen were turned up even more that also means more thermal stress on the battery and inverters etc... possibly reducing their life expectancy. Every thing is a balance.
     
  18. Grit

    Grit Senior Member

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    If we re going to go there, then bring in & break down gravity, wind, colder air molecule density vs hot molecule, brand make of tires & hv battery optimal temp
     
  19. Mdv55

    Mdv55 Member

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    You're overly minimizing the effect of regen on Temps. Have you ever watched inverter and battery temps spike? They go up fast, and the hybrid battery comes down very slow. Constantly adding more heat to it can easily mean the cooling fan can't keep up. More heat = less life.
     
  20. sam spade 2

    sam spade 2 Senior Member

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    Yes. Just press lightly on the brake pedal.
    Otherwise, no.
    You don't WANT too much deceleration without brake lights.
    And you can't get more regeneration without more deceleration.
     
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