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Discussion Starter #21
So Mike, based on what you said, I’m assuming you use low regen for long highway trips? I had asked this question earlier in this thread and was asking if anyone had done controlled highway tests with regen on high and then low.


I’m actually surprised BEV reviews don’t go into this discussion. I haven’t even seen it discussed on the Tesla forum.

Thanks for the reply - Concerning coasting regen, it all boils down to exchanging momentum for energy or using the same momentum to coast to save battery energy. The later is more efficient, since the regen energy gained to hold the cars speed down, will take nearly two time that amount of energy to power the car back to the speed lost.

If you take two cars running at 55 mph and as we top the hill, one car uses regen brakes to maintain 55 mph and the other is allowed to coast to 65 mph, as these two cars reach the next hill, the coasting car has two advantages:

1) The coasting car will reach the next hill sooner since its traveling faster.

2) The coasting car will travel further up the hill since it has more kinetic energy stored from the higher speed.

When you consider the further distance the coasting car traveled, it would generally take almost twice the power you captured in regen to move the car to that distance.

It’s important to note, when you compare performance of an electric motor to its performance as a generator, its far from being 1 to 1 ratio, since the motor is primarily designed a motor first and a generator second.

Therefore, if you were to regen one mile at 55 mph, you would not store enough energy to travel the same mile you recuperated. While each car is different and effected by many variables such as; ratios, temperature, vehicles weight, BCM, motor size, etc., generally speaking, if you were regen down a long steep decent, most EV’s would have to regen around 3 miles to add back one mile of range.

For the most part, unless you enjoy experimenting as I do, you really don't have to be over-concerned with regen. In addition, if your live in Florida which is flat there is little to no advantage to coasting regen using the speed control. Where high coasting regen is useful in city traffic or rolling traffic on X-ways, as it allows the car to be driven somewhat like an I-3 using one pedal. I might mention the I-Pace has a very useful “Vehicle Creep” feature where the vehicle will "roll" like a conventional automatic trans or “hold” after you stop. This feature adds a whole new perspective to coasting and stopping the car with regen, be sure to give it a try.

Stay Safe - Mike

 

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Thanks for the reply - Concerning coasting regen, it all boils down to exchanging momentum for energy or using the same momentum to coast to save battery energy. The later is more efficient, since the regen energy gained to hold the cars speed down, will take nearly two time that amount of energy to power the car back to the speed lost.

If you take two cars running at 55 mph and as we top the hill, one car uses regen brakes to maintain 55 mph and the other is allowed to coast to 65 mph, as these two cars reach the next hill, the coasting car has two advantages:

1) The coasting car will reach the next hill sooner since its traveling faster.

2) The coasting car will travel further up the hill since it has more kinetic energy stored from the higher speed.

When you consider the further distance the coasting car traveled, it would generally take almost twice the power you captured in regen to move the car to that distance.

It’s important to note, when you compare performance of an electric motor to its performance as a generator, its far from being 1 to 1 ratio, since the motor is primarily designed a motor first and a generator second.

Therefore, if you were to regen one mile at 55 mph, you would not store enough energy to travel the same mile you recuperated. While each car is different and effected by many variables such as; ratios, temperature, vehicles weight, BCM, motor size, etc., generally speaking, if you were regen down a long steep decent, most EV’s would have to regen around 3 miles to add back one mile of range.
Your coasting car, which goes 18% faster at 65 vs 55, will encounter 40% (!) more wind resistance. So no, coasting faster will not save energy.

I have done the math and also measured the I-Pace's regen downhill vs energy used uphill. You get 90% (!) of the potential energy spent uphill back on the way down; it's uncanny how well regeneration works. That's why hybrids are so much more efficient than ICEs.
 

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I find this discussion regarding coasting down hills a little niave. Yes, considering an ICE, coasting down hills saves gas. (Hence all the truckers that have perfected that trick). However, the gain is because the potential energy that is converted into kinetic energy would otherwise be lost as heat in the braking system. If we assume that same energy is 90% reclaimed as stored battery energy, then the extra range would be minimal, at best a few percent. But factor in that coasting down the hills at elevated speeds leads to greater air resistance, and road resistance that increases as the square of the speed, then you have lost some or all of that minimal gain.
Yes, someone should try it, but I'm not wasting my time proving I gain 2-4 miles on a full charge. If my navigation criteria are that tight, then I am waiting for a disastrous road trip stuck in the middle of nowhere.
 

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I find this discussion regarding coasting down hills a little niave. Yes, considering an ICE, coasting down hills saves gas. (Hence all the truckers that have perfected that trick). However, the gain is because the potential energy that is converted into kinetic energy would otherwise be lost as heat in the braking system. If we assume that same energy is 90% reclaimed as stored battery energy, then the extra range would be minimal, at best a few percent. But factor in that coasting down the hills at elevated speeds leads to greater air resistance, and road resistance that increases as the square of the speed, then you have lost some or all of that minimal gain.
Yes, someone should try it, but I'm not wasting my time proving I gain 2-4 miles on a full charge. If my navigation criteria are that tight, then I am waiting for a disastrous road trip stuck in the middle of nowhere.
That's why I said this is a job for Bjorn. This is precisely the kind of thing he loves to do. ;)
 

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Discussion Starter #25
Your coasting car, which goes 18% faster at 65 vs 55, will encounter 40% (!) more wind resistance. So no, coasting faster will not save energy.

I have done the math and also measured the I-Pace's regen downhill vs energy used uphill. You get 90% (!) of the potential energy spent uphill back on the way down; it's uncanny how well regeneration works. That's why hybrids are so much more efficient than ICEs.
Sciencegeek your comments on drag are totally incorrect - Using my example - both cars used the same exact energy to climb the hill. However, the "Coasting Car" developed a much higher speed (regardless of drag) and also traveled further distance as well as higher up the next hill. These are indisputable facts why "free coasting" provides more range on an EV!

LOL - It's amazing that in only 1 year with your I-Pace you've become such an expert on recuperation, drag and coefficient abilities. I suggest you contact Porsche engineering to advise them they have been building the "coasting" Panamera Hybrid "wrong" for almost 10 years now. Also be sure to tell them they designed the new Taycan Electric backwards as well.

Stay Safe - Mike
 

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Discussion Starter #28
Hmm. Last time I checked, facts were facts and empirical measurements combined with basic theory mattered. They tend to have more explanatory power than some funny ideas. 🍺 🍺
Thanks for the reply - I surely would not post anything that was not researched or 100% factual. I encourage you to do a search on the benefits of coasting economy.

Coasting economy is nothing new - Many years ago, it was discovered that if you held the clutch in while going down a grade you could increase your fuel mileage considerable since it removed the drag of turning the engine over while coasting. While some users here might be too young to remember - years ago, different vendors offered an over-drive free-wheeling rear differential, which you could order for some cars. I had one on my 57 Ford. When engaged, it added an extra over-drive ratio, but more importantly, the over-drive unit would disengage the drive train from the engine for "free-wheeling fuel economy" any time you let off the gas pedal.

Coasting technology has been used for a decade now - On the Porsche Panamera hybrid. Porsche has been on the forefront with their amazing gas / electric technology. In fact they are the only sports car that offers both a an electric only or a sports car in the same car with 3.2 second performance. The Panamera’s dual clutch transmission offers two over-drive gears so at highway speeds the gas engine only turns around 1200 rpm. It also uses the same dual clutch transmission to decouple the gas engine and electric motors to allow the vehicle to free-coast for economy. The new Taycan electric uses many Panamera parts and technology as well. I have studied the Panamera Hybrid advancements since its inception nearly a decade now. It’s interesting to see how each year it has advanced.

This same coasting economy is offered on our I-Pace as well - Which is why Jaguar offered the driver the the menu option to either coast or regen. During highway travel in hilly terrain, you should always select the low regen setting for added fuel economy since this avoids baby-sitting the accelerator pedal to coast or putting the car in neutral.

Stay Safe Mike

 

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I'm just a guest here, but I've been driving regenerative braking cars since my 2000 Honda Insight. I think some of you are assuming efficiencies for regen that are much higher than reality. As a rule of thumb, I would go with 25% efficiency. Which is really not bad and obviously much better than just generating heat from friction brakes, but no where near the efficiency of coasting.
 

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The original question was whether having your I-Pace on low regen vs high regen setting makes a difference. If you change your driving behavior as a result of switching, then of course it makes a difference. But if you drive exactly the same way in both settings then it's not going to make a difference.

Regarding that article, it's good data and they tried to address the question of regen, but that was done a loooong time ago and they state:
"For one, we can document that electric regenerative brake systems are able to recover 55% of the vehicle's kinetic energy. I suspect it would be easy to get over 70% if we changed the gearing to improve efficiency."
Since then, regen efficiency in modern electric motors has gone up to about 90%. I'll post something when I get the chance that illustrates this with actual numbers from my I-Pace in real world conditions.
 

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The original question was whether having your I-Pace on low regen vs high regen setting makes a difference. If you change your driving behavior as a result of switching, then of course it makes a difference. But if you drive exactly the same way in both settings then it's not going to make a difference.
I think that is obvious. The issue is that it is more difficult to coast with high regen as opposed to low IMO.

Regarding that article, it's good data and they tried to address the question of regen, but that was done a loooong time ago and they state:
"For one, we can document that electric regenerative brake systems are able to recover 55% of the vehicle's kinetic energy. I suspect it would be easy to get over 70% if we changed the gearing to improve efficiency."
Since then, regen efficiency in modern electric motors has gone up to about 90%. I'll post something when I get the chance that illustrates this with actual numbers from my I-Pace in real world conditions.
The efficiency of electric motors has gone up, but not necessarily the regen efficiency. I think the Taycan is the only EV that I'm aware of that uses gears.
 

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Sciencegeek your comments on drag are totally incorrect - Using my example - both cars used the same exact energy to climb the hill. However, the "Coasting Car" developed a much higher speed (regardless of drag) and also traveled further distance as well as higher up the next hill. These are indisputable facts why "free coasting" provides more range on an EV!
Mike: these facts are indisputable. However, you forgot or ignored the energy still stored in the battery of the noncoasting car. As I pointed out earlier, and sciencegeek reaffirmed, the coasting car reaching 65mph will lose energy to drag at a much higher rate than the car doing 55mph. Drag is approximately proportional to speed squared, so the increased drag will be 40% of what ever energy is required to keep the vehicle at 55mph. If the potential energy is recaptured by regen even at an 75% rate, you will barely break even.
Part of the coasting idea is to use the kinetic energy built up to help the next uphill run and reduce the need to give the car more gas - as perfected my the modern trucker who is a thorough nuisance on the interstates around here.
If we are truly going to count Watts used in both styles of driving, maybe we should also factor in the "nervous energy" associated with oscillating between going faster than the average vehicle on the road downhill and then going slower than the average vehicle uphill. How about the extra distance travelled due to changing lanes?
 

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On a very different, regen related topic, I read an interesting tidbit that had me thinking if anyone had tried this.

A reviewer had stated (can’t even recall if it was an I-Pace review) that for long highway driving, it was best to have regen set to low for maximum range as the result of improved coasting.

Has anyone heard of this or tried it? I can’t even recall this ever being discussed on the Tesla forum. Intuitively it makes some sense, but I’m wondering why I’ve never seen it discussed.
I don't think that is true. Just come off the speeder less and it is the equivalent of low-regen. What does help is using the cruise control
 
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