learn me some Leaf regen and braking

[Nekota]

I do wish we had some indication of when the friction breaks are applied as it's awfully tempting to gently ride the breaks to come to a stop and I'm just not sure how much there is to gain from trying to stretch that out over a longer distance.

Yes - it would be awesome if there was a dial that indicated how much friction brake force was being applied to the car, even if only approximate.

The little gauge above the 'tree formation' seems like it shows when regeneration is maxed and pads begin to waste energy. Page 2-11 in the LEAF Owner's manual describes this gauge as the instant ECO driving level. When the regen energy panel shows max at 30KW applying additional braking force drops the instant eco meter.

 

[Rancher]

Before you head down a long hill, usually one does NOT charge their car to 100%. Since "re-generation" NEEDS to CHARGE the battery to work, the LEAF will NOT regen at all, in D or ECO, if the battery is ALREADY full. Any slowing will use just the mechanical disc brakes.

I have a property in North San Diego County and I live in South Orange County. Door to door is 64 miles, with about 75% driving on the "highway" (the "76") or freeway (the "5"). The last 10 miles (going to the Ranch) has some elevation (the property is at 2,100 feet, at the base of Mount Palomar, with (and I'm guessing) the last 5 miles going starting about 600 feet and ending up at 2,100 and the last mile starting at 1,500 then going straight up (source: Google Maps "Terrain").

I've done the drive once and "made it" with 3 bars to spare. What is "unfortunate" is that with a 100% charge, going back to Orange County I use the brakes as I need to leave the property full or I don't think I'll make it home (technically, I never did as I got a flat tire just as I got on the 5 north).

I would think that turning on the car would immediately start to use battery life and therefore "regen" would kick in. It seems I need to lose a bar before I can use econ mode and use the regen to slow me down. Not complaining, but it would be nice to have something so I don't need to ride the brakes as hard....

loving the car!!

 

[awiegel]

Why is it that you can only get serious regen by using ECO mode, which unaccepably nerfs the performance?

 

[kawh]

ok...thanks... but then how is "coasting" different from "regen." ??
sorry to be so slow (pardon the pun...)

I think the best way to get a feel for this is, as abasile just suggested, to watch the pie chart on the left side of the 'Energy Information' screen. [Push the 'Zero Emission', bottom right side of center console; then touch the 'Energy Info' option, top right corner of the menu.]

• When you see a pie slice going up into the positive numbers, energy from the battery is being used to drive the wheels. That only happens when you are pushing the accelerator (or letting Cruise Control push it for you).
• When you see a pie slice going down into the negative numbers, energy from slowing the car is being put back into the battery. That is regen. It can happen when you take your foot off the accelerator or when you touch the brake pedal lightly.
• If you are moving but don't see any pie slice at all, then you are coasting. That happens only if you put the car in neutral [move the shift lever straight left and hold it there for a couple of seconds] or if you are feathering the accelerator pedal very carefully.

Now, Gary makes it sound like a simple 1-2-3 choice among coast, regen, and disk brakes, but it's really much more complicated than that. The only way to make a car speed up is to add some energy to it, and the only way to slow down is to take some energy away from it (or away from what scientists like to call the car's momentum).

• With coasting the energy is being converted to heat rather slowly using friction - friction of the air against the car body, of the tires against the road, of the bearings in the wheels and gears and motor. But those things are always happening while the car is moving, so they are added to whatever else is being used to slow the car.
• With regen, part of the energy is being converted to electricity by making the motor work like a generator. But only part - the conversion process isn't perfect, and does generate heat. Besides, there is still the 'coasting' friction from above.
• With disk brakes, part of the energy is being converted into heat as the brake pads rub against the disks. But, again, only part of it. There is still the 'coasting' friction, and there is still the regen! (Well, unless you are in neutral.)

Ray

world-class answer. very clear. i totally get it. thanks.
kawh

 

[abasile]

I would think that turning on the car would immediately start to use battery life and therefore "regen" would kick in. It seems I need to lose a bar before I can use econ mode and use the regen to slow me down. Not complaining, but it would be nice to have something so I don't need to ride the brakes as hard....

At higher states of charge, the car limits the rate at which you can put energy back into the battery pack. This is to protect the long-term health of the pack. The closer you get to 100% charge, the more careful the car has to be about charging, including from regenerative braking.

If you want to mostly avoid having to use the friction brakes, perhaps you could charge to 80% before leaving your ranch, then do the remainder of the drive home more gently, at slower speeds.

When leaving our home at 6100' elevation, we manually limit our charge to 7 bars if we are about to descend the mountain on CA 330. We can thereby regen all the way down. Upon reaching the bottom of the mountain, the car indicates 8 bars, though we probably actually have the equivalent of 9 bars, still less than 80% charge. From there, we can drive the remaining 54 miles to Pasadena on the 210 freeway (70 miles total from home). Holding our speed down to 55 mph, we arrive in Pasadena with 2 full bars.

 

[thankyouOB]

with regard to the discussion about the TREE meter and its circle.
So far, I have not been able to fully dissect what is going on there.
It's response is not in line with the response on the energy screen in the center module.

It seems that eco and d have an effect on the meter surrounding the TREE, as does slowing the car by lifting off the accelerator, but adding ANY breaking to the mix immediately reduces the circle and the reported energy saving.
not sure why very minimal breaking would do that.
it remains mysterious to me, but I appreciate having it pointed out to me again, as I had written the tree meter off as froo-froo, as I dont go to the TREE competition website to see how I am doing compared to the world or region.

 

[planet4ever]

I would think that turning on the car would immediately start to use battery life and therefore "regen" would kick in. It seems I need to lose a bar before I can use econ mode and use the regen to slow me down. Not complaining, but it would be nice to have something so I don't need to ride the brakes as hard....

At higher states of charge, the car limits the rate at which you can put energy back into the battery pack. This is to protect the long-term health of the pack. The closer you get to 100% charge, the more careful the car has to be about charging, including from regenerative braking.

Just to underscore what abasile said, regen can charge the battery up to nine times as fast as the 240v charger can. So even if you reduced regen to "half a dot" you would still be pumping electricity in nearly as fast as the maximum rate from the charger, and the charger is throttled way back as the pack approaches 100%.

Ray

 

[DaveinOlyWA]

with regard to the discussion about the TREE meter and its circle.

the tree designates your level of efficient driving and does not correlate to any other gauge on the car and the reason why is that the actual efficiency is primarily dependent on driving condition and NOT driving skills. the tree ONLY gauges driving skills...ok, got it?

right, clear as mud!!

ok some facts

*it is possible to get very high numbers and not be an efficient driver if you are going slow enough or going down hill.

*no matter how skillful you are, you will get so-so numbers on the freeway. so the trees ignores the actual performance #'s and only bases your performance for the current conditions you are driving in.

even on the freeway, there is efficient ways to drive. CC is not one of them UNLESS you are driving on a road that is perfectly flat with no traffic impedance.

so trees is a reflection of your driving skills. to gain trees, minimize braking regen and sudden speed changes.

 

[thankyouOB]

with regard to the discussion about the TREE meter and its circle.

the tree designates your level of efficient driving and does not correlate to any other gauge on the car and the reason why is that the actual efficiency is primarily dependent on driving condition and NOT driving skills. the tree ONLY gauges driving skills...ok, got it?

right, clear as mud!!

ok some facts

*it is possible to get very high numbers and not be an efficient driver if you are going slow enough or going down hill.

*no matter how skillful you are, you will get so-so numbers on the freeway. so the trees ignores the actual performance #'s and only bases your performance for the current conditions you are driving in.
informative, and thanks,
but CC means?

even on the freeway, there is efficient ways to drive. CC is not one of them UNLESS you are driving on a road that is perfectly flat with no traffic impedance.

so trees is a reflection of your driving skills. to gain trees, minimize braking regen and sudden speed changes.

 

[jimad]

I live on top of a moderate hill, have been driving a LEAF for the last year, and the following is what I THINK I've figured out:

The amount of regen one can get is very dependent on a large number of factors including the following:

The number of double-circle bubbles to the left of "zero," which is highly variable depending on factors listed below.

If you battery is a little on the cold side, or hot side you will be limited.

You never get more than "5 bubbles" of regen in any case, which is not huge.

ECO mode lets you get more regen and less friction braking.

If you battery is 80% charged or more you are limited.

If the road is slippery, then obviously your regen will be limited.

I *think* you get more regen if you take your car out of 80% charge mode and put it into 100% charge mode before going down hills. I *think* Nissan does this because they take 80% charge mode to mean "please conserve my battery above all else" whereas 100% mode is taken to mean "please maximize my driving range even if that eventually reduces my battery longevity."

For example, since I live on top of a hill I routinely charge my LEAF to only 80% so I can get some useful regen while going down the hill -- and to conserve battery life in general.

 

[TomT]

Actually, it has no affect on the performance, it just remaps the pedal so that you have to tip further in. At full pedal, the performance is identical in both modes.

Why is it that you can only get serious regen by using ECO mode, which unaccepably nerfs the performance?

 

[TomT]

If you want to have a bit of fun, put the car in N and them mash the accelerator pedal and watch what the circle does... Great algorithm there... :lol:

with regard to the discussion about the TREE meter and its circle.
So far, I have not been able to fully dissect what is going on there.

 

[LEAFfan]

least to most wasted energy depends. regen would rank best because it recaptures some energy that can be re used.

No, garygid is correct. Coasting is best. If you use regen, it slows you down and even though you put some energy back, it isn't enough to start you going again. You will lose more than you gain when you regen except going down a steep hill where you can't keep it in N.

 

[LEAFfan]

The amount of regen one can get is very dependent on a large number of factors including the following:
The number of double-circle bubbles to the left of "zero," which is highly variable depending on factors listed below.
You never get more than "5 bubbles" of regen in any case, which is not huge.

The number of double-circle bubbles doesn't really tell how much regen/kW you actually get. If you look at the energy meter on the console, it shows it goes up to 30kW of regen, BUT that isn't the max...according to Ingineer, you can go as high as 50kW of regen. So when you peg (30kW) the regen meter, you have no idea how many actual Kw are going back into your pack.

 

[DaveEV]

least to most wasted energy depends. regen would rank best because it recaptures some energy that can be re used.

No, garygid is correct. Coasting is best. If you use regen, it slows you down and even though you put some energy back, it isn't enough to start you going again. You will lose more than you gain when you regen except going down a steep hill where you can't keep it in N.

No, it completely depends on the speeds involved, how long you regen and what speed is desired after the descent.

Go down a 1 mile hill and your options are hold a steady 60 mph with 5 kW of regen or hold a steady 70 mph in neutral and you have a target speed of 60 mph at the bottom of the hill, you'll definitely want to use regen to capture that energy instead of burning it up as wind resistance.

Go down a 100 yard hill at 30 mph and you might be better off putting it in neutral letting your car accelerate up to 40 mph and then coast up the other side until you get back down to 30 mph.

See a light turn red up ahead and your option is to put it in neutral and then use max regen as you close in to the light to stop or to max regen early and then coast in to the light, and using more regen early will capture more energy than coasting until the last second.

 

[LEAFfan]

See a light turn red up ahead and your option is to put it in neutral and then use max regen as you close in to the light to stop or to max regen early and then coast in to the light, and using more regen early will capture more energy than coasting until the last second.

I disagree with this. There is no need for regen if you time your distance to the light correctly. Coasting on flat terrain will always save more energy than using regen. So you left out the best and third option: Coast all the way toward the light, then resume speed as the light changes. How else do you think I've been able to achieve 8.4m/kW h on a 151 mile run?

 

[jimad]

The number of double-circle bubbles doesn't really tell how much regen/kW you actually get. If you look at the energy meter on the console, it shows it goes up to 30kW of regen, BUT that isn't the max...according to Ingineer, you can go as high as 50kW of regen. So when you peg (30kW) the regen meter, you have no idea how many actual Kw are going back into your pack.

Well, I've never been able to get my LEAF to regen more than 25kw down hill, but I'm going down the hill from my house starting off with an 80% charge, so, maybe that is limiting what I am seeing.

 

[planet4ever]

See a light turn red up ahead and your option is to put it in neutral and then use max regen as you close in to the light to stop or to max regen early and then coast in to the light, and using more regen early will capture more energy than coasting until the last second.

I disagree with this. There is no need for regen if you time your distance to the light correctly. Coasting on flat terrain will always save more energy than using regen. So you left out the best and third option: Coast all the way toward the light, then resume speed as the light changes. How else do you think I've been able to achieve 8.4m/kW h on a 151 mile run?

I don't see that you are disagreeing with drees. His assumption was that you had too much kinetic energy when you first saw the red light to be able to coast up to it. Your assumption was that you didn't. Obviously with your assumption you don't want to regen. Equally obviously with his you will have to use some combination of regen and friction braking.

My frustration with your claims, LEAFfan, is that I can rarely put them into practice. The lights around here are traffic-actuated and not synchronized, so you never know when they are going to turn red. If I see a green light some distance away and continue at speed, there is a very good chance it will turn red before I get to it. If I assume that is going to happen and start coasting immediately (ignoring how much I am upsetting the folks behind me) then I may miss an entire cycle. I have in fact increased the probability of that by my own actions, because I am creating a rolling blockade that will make the next green cycle very short. Likewise, if I see a red light several blocks ahead and start coasting there is a rather high probability that it will be red again by the time I get to it. But if I don't start coasting right away I will soon be stuck with the drees assumption, not yours.

Ray

 

[tamoora]

Hey Guys

Quick question, is there a way I can turn "off" regen braking? I am working on an experiment where I need to turn the regen "off" and let the vehicle coast down to stand still.

Thanks

 

[EVDRIVER]

See a light turn red up ahead and your option is to put it in neutral and then use max regen as you close in to the light to stop or to max regen early and then coast in to the light, and using more regen early will capture more energy than coasting until the last second.

I disagree with this. There is no need for regen if you time your distance to the light correctly. Coasting on flat terrain will always save more energy than using regen. So you left out the best and third option: Coast all the way toward the light, then resume speed as the light changes. How else do you think I've been able to achieve 8.4m/kW h on a 151 mile run?

But we live in the real world with short stops and for some of us actual steep hills which the poor regen on a LEAF can't even match under any conditions.