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DaveEV
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Re: Leaf regen vs Prius regen

Wed Apr 06, 2011 2:41 pm

DaveinOlyWA wrote:As far as the Prius. At max regen we could fully charge in 90 seconds to cover SOC. From 40-80%.
At least that number matches up with your earlier stated 20 kW max regen in the Prius and 0.5 kWh usable capacity - that's a charge rate of 15C - that is only pushing the batteries about 8 times harder than the maximum allowable charge rate that Nissan allows (~50 kW during quick charge at lower SOC).

Would allowing another 30 kW of regen be useful on the Leaf? Sure would - but I suspect that Nissan thinks will wear the battery out too quickly, otherwise there's no reason to allow it. The motor / battery are capable of moving 80 kW+ when accelerating (though Nissan also cautions that frequent aggressive driving will also wear out the battery more quickly).

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Re: Leaf regen vs Prius regen

Wed Apr 06, 2011 2:51 pm

Any max value would be for short durations. Now if the Prius allows it on NiMH and the Leaf does not on Li, is there a difference in the capacity each type can take with minimal degradation?
its hard to argue with the Priuses already proven longevity concerning its battery management techniques
2011 SL; 44,598 mi, 87% SOH. 2013 S; 44,840 mi, 91% SOH. 2016 S30; 29,413 mi, 99% SOH. 2018 S; 25,185 mi, SOH 92.23%. 2019 S Plus; 11,333.1 mi, 93.73% SOH
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DaveEV
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Re: Leaf regen vs Prius regen

Wed Apr 06, 2011 3:14 pm

DaveinOlyWA wrote:Any max value would be for short durations. Now if the Prius allows it on NiMH and the Leaf does not on Li, is there a difference in the capacity each type can take with minimal degradation?
I'm sure that if you use AESC's "high power" cells instead of their "high energy" cells and only used 50% capacity instead of 90%, you could push the Lithium battery even harder than the NiMH battery with the same life expectancy (10 years, 150k miles).

In which case we'd be saying "Stupid Toyota - only 15C regen rate? Bah!" instead of "Stupid Nissan - only 1C regen rate? Bah!".

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evnow
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Re: Leaf regen vs Prius regen

Wed Apr 06, 2011 4:37 pm

Sorry guys. I still don't get it.

Leaf does have variable regen. You regen more by pressing the brake harder. What we don't have is the ability to change the amount of regen for a particular amount of brake press.

So, is the ask that Leaf should regen more for a given amount of brake press ?

I've to come down a fairly steep hill everyday. If I use Eco I don't need to use the brake at all to control the speed. Sounds like enough regen to me ...
planet4ever wrote:If I am slowing to a stop light or going down hill, and the regen is not heavy enough to do the job, I'm going to be using friction brakes. That efficiency is 0%.

That is assuming the regen is constant. Not the case, only if you floor the break, Leaf will use friction brake exclusively. As you press the brake harder, it regens more, but after a point it starts including friction brakes. The idea is to slow down such that you use mostly the regen portion of the brake.

Ofcourse, if you know you need to stop at a point, it makes more sense to reduce the speed slowly rather than go at a high speed till the last few yards and brake hard.
1st Leaf : 2/28/2011 to 5/6/2013
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Re: Leaf regen vs Prius regen

Thu Apr 07, 2011 6:14 pm

evnow wrote:
planet4ever wrote:If I am slowing to a stop light or going down hill, and the regen is not heavy enough to do the job, I'm going to be using friction brakes. That efficiency is 0%.

That is assuming the regen is constant. Not the case
No, I wasn't assuming constant regen. I was assuming, based on what others here had said, that the maximum regen possible on the LEAF was significantly less than on the Prius.
evnow wrote:I've to come down a fairly steep hill everyday. If I use Eco I don't need to use the brake at all to control the speed. Sounds like enough regen to me ...
Thank you! I was getting worried. I'll now (try to) wait patiently for my car so I can see for myself.

Ray
End of April 2013: Traded my 2011 SL for a 2013 S with charge pkg.

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Re: Leaf regen vs Prius regen

Thu Apr 07, 2011 6:36 pm

The Gen2 (NHW20) Prius tops out at about 21kw peak regen. The Leaf tops out at 30kW. The Leaf actually has more regen, but then again, it's a heavier car.

I find the ~20kW of regen in my Prius is more than adequate to stop the car with normal driving. Careful driving yields a bit more performance, and if you can stretch out your stops you get the most regen. This is because of the I2R losses. The battery charge efficiency goes up at lower rates.

Do not confuse the "simulated drag" regen, which I call "Pedal off" regen, with what happens when you hit the brake. The braking system first engages regen, and if pedal pressure is higher than what regen can handle alone, then the hydraulic brake modulator brings in some conventional friction braking to consume the difference.

Also, when the car gets below a certain low speed, the braking switches to friction, as regen is not able to hold the car once stopped.

-Phil
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Re: Leaf regen vs Prius regen

Thu Apr 07, 2011 9:53 pm

Another important thing to remember in this argument is that Nissan has programmed the Leaf to respond similarly to brake pressure no matter what the SOC of the car battery. In other words, at 90% SOC, light pressure on the brake might yield 1/5th the total possible regen but X amount of deceleration. Nissan had to make sure this same X amount of deceleration would be seen by applying the same amount of force on the brake even with a 20% SOC when the battery is looking to gobble up all the electrons it can take via full 30kW regen. I have little doubt that what you may feel is a "weak" regen is in some large measure Nissan's way of making sure that the car behaves identically no matter what the SOC. After all, it wouldn't do for a car with empty batteries to screetch to a halt via regen as soon as you ease off the gas yet have no regen effect at all when the car is at 100% SOC. That would feel like swapping back and forth from an exhaust-brake-equipped ICE with massive engine-braking forces to an electric car with no regen capabilities.

I personally had gotten quite used to the backwards throttle twist regen action on my Vectrix scooter, so I can certainly understand the desire for a user modulated regen, but to its detriment such a system lets you continuously pump regen back into the battery no matter what the SOC, severely shortening battery life for those not knowledgeable about a batteries' limitations to accept charge when near capacity and the associated battery heating. For now I'll content myself with popping in and out of ECO as needed...

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Re: Leaf regen vs Prius regen

Thu Apr 07, 2011 10:14 pm

DarkStar wrote:
gasmiser1 wrote:One note: I wish the regen was more powerful on steep downhills. Even with light braking I'd like more regen to slow the car down.
Were you rockin' ECO mode?
Remember, on the Prius it isn't the regen that really slows the car down on steep downhills. It's the engine braking. The Prius will continue to hold its speed even after the battery is completely topped off. The LEAF has no engine braking as it has no engine.

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Re: Leaf regen vs Prius regen

Thu Apr 07, 2011 11:03 pm

Come on, we've been around this argument several times already. The Prius does not use engine braking on a hill until the battery is full. There's a steep mountain pass I sometimes go down. The engine is silent until near the bottom, but when the battery is full the engine starts roaring very loudly. And when the next graph bar shows up (99mpg, of course) it has lots of regen cars stacked in it.

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Re: Leaf regen vs Prius regen

Fri Apr 08, 2011 12:23 am

LakeLeaf wrote:
DarkStar wrote:
gasmiser1 wrote:One note: I wish the regen was more powerful on steep downhills. Even with light braking I'd like more regen to slow the car down.
Were you rockin' ECO mode?
Remember, on the Prius it isn't the regen that really slows the car down on steep downhills. It's the engine braking. The Prius will continue to hold its speed even after the battery is completely topped off. The LEAF has no engine braking as it has no engine.
On the Prius this is not true, unless the battery is full, or you choose the "B" position on the shifter. The Prius does just like the Leaf; it simulates engine drag with regen when you take your foot off, but if you feather the pedal slightly it's effectively neutral and will coast. As you begin to hit the brake, the computer increases regen until it's at 21kW on the Prius, or 30kW on the Leaf, then brings in the friction brakes to "fill the gap".

Panic or really sudden stops (detected by the brake ECU by pedal velocity) automatically skip regen and bring in ABS only.

The Battery ECU on the Leaf will limit charge depending on battery SOC and temperature, so there are indeed times when regen will be less than 30kW. For instance, if you start at the top of a hill with a fully charge battery, you will not get any regen.

Also, just to be clear, "Engine braking" is indeed possible in an EV like the Leaf; all that has to happen is DC injection by the inverter. This will convert kinetic energy into heat in the motor windings. I don't think the Leaf does this, but it could be implemented as an emergency backup if the hydraulic braking system were to fail.

-Phil
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