Phoenix Range Test Sept 15, 2012 planning!

[TonyWilliams]

As a runner, I can tell you I don't want to run up and down a hill if there is a tunnel through it that's flat.

That's because a runner is like an ICE; you don't have regen . If a runner were more like an EV the choice of tunnel versus hill would less obvious. (Yes, you should still take the tunnel, but the difference in NET energy expenditure is significantly smaller in the case of the "regen runner". Unfortunately, no such thing as a human "regen runner", but the point is ... it's not a good analogy here.)

Stop this damn rational thought spewing!!!

:mrgreen:

 

[surfingslovak]

Who is who?

I'll 'out' myself, opossum on the far left, azdre hiding behind him.

Those of us who watched your local news video have seen both opossum and Scott Y previously, so when I saw the pics, I thought it was opossum, and then of course, you were the only female there, so I had to assume it was you since your car was one of the ones tested. Great work to all, many thanks for the hours and hours of work, the dedication to the cause, and the great amount of thought put into this range test. It is much appreciated.

I'm on the far right in that picture, right next to a former S10 driver. He has a wealth of EV experience, and I learned a thing or two from him. It was nice meeting everyone, and a privilege to be there helping. Tony did an amazing job organizing the event and opossum almost singlehandedly staged all the cars. I had trouble keeping up with him, and I nearly got fired for putting the wrong ID numbers on one of the cars

 

[DaveEV]

I would appreciate it if someone else would make a try at explaining the two different concepts, the recovery of ascent energy in descent, and the efficiency rate of regenerative braking. I've tried, at least a half dozen times, on various threads, and for over a year now, with little success.

I think what is being described is simply coasting. The thinking that you are simply trading kinetic energy (driving up some hill) for potential energy (being at a higher altitude), and coasting on the way down to trade the potential for kinetic energy (freewheeling down the hill). In theory, you'd have 100% recovery, but since there's rolling resistance, i^2 r losses in motor windings, air resistance, the climate control you forgot you left on, etc etc... YOU WILL NEVER HAVE 100% RECOVERY EVER IN THE REAL WORLD.

Coasting is the least loss though.

If we're talking about how much potential energy you can recover on the way down a hill after going up and comparing efficiency to driving the same distance on flat ground - the answer is a big "it depends".

What does it depend on? Mostly, it depends on the slope of the hill and how fast you are going.

I will tell you that rolling resistance, air resistance and climate control have nothing to do with it.

Say you're cruising at 60 mph on flat ground and pulling 15 kW out of the battery to maintain speed.

Now say you encounter a slight hill which increases power requirements to 20 kW going up. Coming back down the hill of the same slope and at the same speed will only require 10 kW.

Your average power requirements will be the same 15 kW as if you kept on flat ground - IF (and it's a fairly significant IF) one assumes that the efficiency curve of the motor is flat and that any increase in resistive losses between the motor and battery are minimal (which it should be at such a modest change in power).

So for a situation like that - you do get all your potential energy back.

But if the hill is steep enough that power requirements go negative and regen is required to maintain speed - now you end up having to add in the inefficiency of regen - which is probably around 70% efficient.

So for a case where power requirements go from 15 kW to 40 kW to climb the hill at 60 mph, coming back down you need 10 kW regen to maintain 60 mph, only about 7 kW of that 10 kW will be of use.

To get actual numbers, assume that you drive for an hour. Flat ground: 15 kW * 1h = 15 kWh. Hill: 40 kW * 0.5h - 7 kW * 0.5h = 16.5 kWh. So in this case the hill will take about 10% more energy.

NOTE: Number purely back-of-the-envelope but should be in the right ballpark!

 

[edatoakrun]

I would appreciate it if someone else would make a try at explaining the two different concepts, the recovery of ascent energy in descent, and the efficiency rate of regenerative braking. I've tried, at least a half dozen times, on various threads, and for over a year now, with little success.

I think what is being described is simply coasting. The thinking that you are simply trading kinetic energy (driving up some hill) for potential energy (being at a higher altitude), and coasting on the way down to trade the potential for kinetic energy (freewheeling down the hill). In theory, you'd have 100% recovery, but since there's rolling resistance, i^2 r losses in motor windings, air resistance, the climate control you forgot you left on, etc etc... YOU WILL NEVER HAVE 100% RECOVERY EVER IN THE REAL WORLD.

Coasting is the least loss though.

If we're talking about how much potential energy you can recover on the way down a hill after going up and comparing efficiency to driving the same distance on flat ground - the answer is a big "it depends".

What does it depend on? Mostly, it depends on the slope of the hill and how fast you are going.

I will tell you that rolling resistance, air resistance and climate control have nothing to do with it.

Say you're cruising at 60 mph on flat ground and pulling 15 kW out of the battery to maintain speed.

Now say you encounter a slight hill which increases power requirements to 20 kW going up. Coming back down the hill of the same slope and at the same speed will only require 10 kW.

Your average power requirements will be the same 15 kW as if you kept on flat ground - IF (and it's a fairly significant IF) one assumes that the efficiency curve of the motor is flat and that any increase in resistive losses between the motor and battery are minimal (which it should be at such a modest change in power)
So for a situation like that - you do get all your potential energy back.

But if the hill is steep enough that power requirements go negative and regen is required to maintain speed - now you end up having to add in the inefficiency of regen - which is probably around 70% efficient.

So for a case where power requirements go from 15 kW to 40 kW to climb the hill at 60 mph, coming back down you need 10 kW regen to maintain 60 mph, only about 7 kW of that 10 kW will be of use.

To get actual numbers, assume that you drive for an hour. Flat ground: 15 kW * 1h = 15 kWh. Hill: 40 kW * 0.5h - 7 kW * 0.5h = 16.5 kWh. So in this case the hill will take about 10% more energy.

NOTE: Number purely back-of-the-envelope but should be in the right ballpark!

Thank you for this explenation.

If anyone disputes this part of "drees" comment, can we try to resolve that issue, before moving on to the next question?

What amounts of regen are actually required in descents, and so, how much additional energy is required, and how much is the driving range of the LEAF reduced, due to ascents and descents, in real-world conditions?

 

[turbo2ltr]

This whole explanation is oversimplified and mixing and matching two different things.

You have the potential energy of the car. This has nothing to do with the battery.
You have battery energy which has nothing to do with potential energy.

If you go from 0ft to 100ft and back to 0ft elevation, you have regained 100% of your potential energy. This is true if you are in a Leaf, jumbo jet, or a skateboard. It in itself consumes no battery energy as it has nothing to do with battery energy.

As for the battery energy, there is always a net loss when traveling due to rolling resistance, aerodynamic drag and inefficiencies in the power electronics and battery energy delivery.

Putting THOSE losses aside (making this a theoretical conversation) ...

If you did not hit regen on the way down, I would agree that theoretically there is no net loss as compared to driving flat. Unfortunately in reality (you know, were we all live...well most of us), the drive gating higher power on the way up usually comes with an increase loss in efficiency. There are other losses in the energy delivery. How much? I don't know. I don't know if it would make a noticeable difference. Driving experience in the leaf says it does.

Now for the situation of hitting regen on the way down.
Regen is not 70% efficient. Most of that energy gets converted to heat in the batteries. Do I have data proving so? No, not on the leaf, but I do have for other vehicles I've worked on.
Once you hit regen, note that you are already dissipating a bunch of energy in the drag and rolling resistance before you even start recovering regen. So right there there is a huge loss of regen efficiency not included in your calculations.

 

[tbleakne]

Altitude doesn't "kill" range, though the effect is very significant on roads that require a lot of regen, to reduce your speed to the more efficient lower range required to rack up lots of miles. On mild ascents and descents, those that do not require regen or friction braking, the ascent energy is 100% recovered in the subsequent descent, though there is probably still a small loss of efficiency due to the more variable kW use, than on a otherwise comparable level route.

You are kidding, right ? There is never a 100% recovery - given the number of elements in between, even if each one is 95% efficient, you get to below 80% overall efficiency with regen.

...On mild ascents and descents, those that do not require regen or friction braking, the ascent energy is 100% recovered in the subsequent descent...

I would appreciate it if someone else would make a try at explaining the two different concepts, the recovery of ascent energy in descent, and the efficiency rate of regenerative braking. I've tried, at least a half dozen times, on various threads, and for over a year now, with little success.

The quotes in red are correct, but perhaps a detailed example may make it clearer.

Assume your car has reached the top of a hill and is about to descend the other side. At that point it has acquired some potential energy in addition to the energy currently in its battery. In acquiring that potential energy while climbing the hill, there were small amounts of energy conversion loss from the battery, the inverter, and the motor. To a good approximation the battery loss is proportional to the power level. If the ascent is gradual and the climbing speed is modest, such that the power level is 20 kW, then the battery loss is about 2%. 30 kW would be 3%. This can be seen by watching the battery voltage drop with the Gid meter. I have no way to measure the inverter loss, but 6% might be a good number, comparable to solar inverters. Nissan has published a color chart on the motor loss as a function of rpm and power, showing a loss range of 5-7%. The total loss in conversion from battery to potential energy is thus perhaps 13-16%.

For a given speed, the steeper the ascent, the more the loss. There is additional energy expended on rolling resistance and aerodynamic drag, but since these losses are always present, even on level ground, we can choose to ignore them for this discussion.

Now consider the car's descent. There are 3 cases, depending upon how steep the grade and how fast you go. For a given slope there is some equilibrium speed V* at which the car will coast in neutral, with no power going in or out of the motor. The steeper the slope, the higher V*.

In case 1, gentle slopes, your are driving at speeds of V* or greater, where the acquired potential energy is being expended on rolling resistance and aerodynamic drag with 100% efficiency because no electronics are involved. As usual, the faster you go, the higher the aerodynamic loss, and you may have your foot on the throttle to add more power, but the conversion efficiency of potential energy is still 100%.

In case 2, steeper slopes, V* is a higher speed than you want to go, and but you can achieve your desired safe speed using regeneration with either D or ECO mode. You may have your foot gently on the throttle to achieve the right amount of regeneration, but you don't have it on the brake. During regeneration the electrical system works in reverse. The motor acts like a generator, the power electronics act like a charger, and the battery accepts charge. Each of these 3 elements have losses similar to the losses of ascent that were not present in case 1. I believe the battery loss during charging is usually higher than the discharge loss, and the other losses may be higher also. Also consider that the net energy that does get back into the battery will be subjected to the normal losses when it is subsequently discharged.

Case 3 occurs when regeneration is not sufficient to keep the car at your desired speed, and you have to apply the brake, which imposes an additional frictional loss. On the LEAF applying the brake usually can increase the regeneration, at least temporarily, but the friction goes up in parallel.

The net result for descents is that if it is safe to let the car go a little faster to avoid regeneration, that will usually be the most efficient option, even though the aerodynamic drag increases.

 

[DaveinOlyWA]

hey, this is beginning to sound like first year physics all over again. the "perfect frictionless world" but i dont live there so...

i go with turbo. as stated before, i hesitate to provide this mostly because i have some doubts to my controls and data collection but when NOT leaving out things that i CANNOT leave out...iow; using REALITY i seem to have a regen efficiency that might be just over 50-60%.

once again, i hesitate to throw that out but there ya go. this led me to the conclusion that using neutral judiciously did allow me get more out of my LEAF which allows me to "slingshot" the ups and downs.

 

[pchilds]

I you coast down a hill at 70 mph, verses 60 mph with regen, you have wasted energy.

The power to overcome air resistance increases roughly with the cube of the speed, and thus the energy required per unit distance is roughly proportional to the square of speed. Because air resistance increases so rapidly with speed, above about 30 mph (48 km/h), it becomes a dominant limiting factor. Driving at 45 rather than 65 mph (72 rather than 105 km/h) requires about one-third the power to overcome wind resistance, or about one-half the energy per unit distance, and much greater fuel economy can be achieved.

 

[DaveinOlyWA]

I you coast down a hill at 70 mph, verses 60 mph with regen, you have wasted energy.

The power to overcome air resistance increases roughly with the cube of the speed, and thus the energy required per unit distance is roughly proportional to the square of speed. Because air resistance increases so rapidly with speed, above about 30 mph (48 km/h), it becomes a dominant limiting factor. Driving at 45 rather than 65 mph (72 rather than 105 km/h) requires about one-third the power to overcome wind resistance, or about one-half the energy per unit distance, and much greater fuel economy can be achieved.

i have tried several ways and i found that best thing (since regen level is based on speed) is to do combo coast/regen to keep speed within 5 mph +/- the speed limit until near bottom of hill then go to neutral and maybe get 10+ over, then power up hill when back down to speed limit.

naturally, hills are not created equally but one thing that is certain (talk to the performance king. there is a method to his "madness") there is no zero sum game when in gear. i feel a HUGE difference in potential momentum when in gear AND supposedly no power being transfered which tells me that the power consumption meter is not accurate and should be VERY loosely used as a guideline ONLY especially for those who think their A/C uses nothing. it does not use much granted. but i think it uses more than we are led to believe

 

[dgpcolorado]

I you coast down a hill at 70 mph, verses 60 mph with regen, you have wasted energy.

The power to overcome air resistance increases roughly with the cube of the speed, and thus the energy required per unit distance is roughly proportional to the square of speed. Because air resistance increases so rapidly with speed, above about 30 mph (48 km/h), it becomes a dominant limiting factor. Driving at 45 rather than 65 mph (72 rather than 105 km/h) requires about one-third the power to overcome wind resistance, or about one-half the energy per unit distance, and much greater fuel economy can be achieved.

i have tried several ways and i found that best thing (since regen level is based on speed) is to do combo coast/regen to keep speed within 5 mph +/- the speed limit until near bottom of hill then go to neutral and maybe get 10+ over, then power up hill when back down to speed limit.

I do much the same thing. I have to use max regen in Eco plus a little braking to get down my hill safely but near the bottom the road straightens out and if I don't see any Sheriff's officers around—speed limit 35 mph—I shift into neutral and let my speed build up so I can make the next rise. One thing I noticed the first time I tried it was that the heavy, fairly low Cd LEAF accelerates really quickly in neutral going downhill. It's not legal but it is more efficient than driving a constant speed. The trick is to remember to shift back into a "gear" before I approach the stop sign at the end or the regen braking is disabled and the remaining kinetic energy is wasted.

 

[DaveinOlyWA]

this is 1 thing I've always wondered about is how to drive the LEAF like the prius where you can have the feeling that little power is being used. I never get that feeling in the LEAF unless I an at 100% SOC or in neutral

 

[EricBayArea]

I LOVE that they all have their tow hooks in! :lol:

 

[edatoakrun]

Every discussion of ascent energy recovery always seems to lead to anecdotal testimonies, leading to lack of resolution, which has led to many believe that the incorrect range of estimates on the range chart, has some validity.

As posted yesterday:

="drees"
If we're talking about how much potential energy you can recover on the way down a hill after going up and comparing efficiency to driving the same distance on flat ground - the answer is a big "it depends".

What does it depend on? Mostly, it depends on the slope of the hill and how fast you are going.

I will tell you that rolling resistance, air resistance and climate control have nothing to do with it.

Say you're cruising at 60 mph on flat ground and pulling 15 kW out of the battery to maintain speed.

Now say you encounter a slight hill which increases power requirements to 20 kW going up. Coming back down the hill of the same slope and at the same speed will only require 10 kW.

Your average power requirements will be the same 15 kW as if you kept on flat ground - IF (and it's a fairly significant IF) one assumes that the efficiency curve of the motor is flat and that any increase in resistive losses between the motor and battery are minimal (which it should be at such a modest change in power)
So for a situation like that - you do get all your potential energy back.

But if the hill is steep enough that power requirements go negative and regen is required to maintain speed - now you end up having to add in the inefficiency of regen - which is probably around 70% efficient.

So for a case where power requirements go from 15 kW to 40 kW to climb the hill at 60 mph, coming back down you need 10 kW regen to maintain 60 mph, only about 7 kW of that 10 kW will be of use.

To get actual numbers, assume that you drive for an hour. Flat ground: 15 kW * 1h = 15 kWh. Hill: 40 kW * 0.5h - 7 kW * 0.5h = 16.5 kWh. So in this case the hill will take about 10% more energy.

NOTE: Number purely back-of-the-envelope but should be in the right ballpark!

edatoakrun:

Thank you for this explenation.

Does anyone dispute: this part of "drees" comment, can we try to resolve that issue, before moving on to the next question?

What amounts of regen are actually required in descents, and so, how much additional energy is required, and how much is the driving range of the LEAF reduced, due to ascents and descents, in real-world conditions?

I can't tell, from several of the comments since yesterday, whether there are objections to ...you do get all your potential energy back... in drees statement, or if you are just objecting to his assumption:

...IF (and it's a fairly significant IF) one assumes...

If that assumption was the only part of "drees'" comment above, that anyone actually objected to. Can we all please now discuss the same question, the validity of this assumption in "drees'" statement?

 

[TonyWilliams]

Every discussion of ascent energy recovery always seems to lead to anecdotal testimonies, leading to lack of resolution, which has led to many believe that the incorrect range of estimates on the range chart, has some validity.

Seriously, dude, put this in the appropriate thread. I've stipulated many times, the chart data for regen is median; obviously, regen can be 0%, and some number below 100%. The chart currently says 50%-75%.

Go over to the proper thread and you post EXACTLY how you think that should be changed (that will fit on one line in a chart).

Otherwise, you're the continual blow hard with no answers. Now, off like a bunny... hop, hop, hop, over to the other thread. I'll be right behind, but no peaking. Trust me... right there.

 

[edatoakrun]

Actually, moving the discussion to the range chart thread is not a bad idea, since the lack of understanding of the fundamental difference between energy recovery by regenerative braking and ascent energy recovery, as illustrated in Tony's comments like the one below, is what seems to have led to such confusion, and the widespread acceptance of extremely inaccurate range estimates in the first place.

I think you could find several of my previous comments on the same subject on the range chart thread, which have never seemed to have penetrated into Tony's consciousness.

Maybe someone else wants to give it a try?

Every discussion of ascent energy recovery always seems to lead to anecdotal testimonies, leading to lack of resolution, which has led to many believe that the incorrect range of estimates on the range chart, has some validity.

Seriously, dude, put this in the appropriate thread. I've stipulated many times, the chart data for regen is median; obviously, regen can be 0%, and some number below 100%. The chart currently says 50%-75%.

Go over to the proper thread and you post EXACTLY how you think that should be changed (that will fit on one line in a chart).

Otherwise, you're the continual blow hard with no answers. Now, off like a bunny... hop, hop, hop, over to the other thread. I'll be right behind, but no peaking. Trust me... right there.

 

[ztanos]

Actually, moving the discussion to the range chart thread is not a bad idea, since the lack of understanding of the fundamental difference between energy recovery by regenerative braking and ascent energy recovery, as illustrated in Tony's comments like the one below, is what seems to have led to such confusion, and the widespread acceptance of extremely inaccurate range estimates in the first place.

I think you could find several of my previous comments on the same subject on the range chart thread, which have never seemed to have penetrated into Tony's consciousness.

Maybe someone else wants to give it a try?

Every discussion of ascent energy recovery always seems to lead to anecdotal testimonies, leading to lack of resolution, which has led to many believe that the incorrect range of estimates on the range chart, has some validity.

Seriously, dude, put this in the appropriate thread. I've stipulated many times, the chart data for regen is median; obviously, regen can be 0%, and some number below 100%. The chart currently says 50%-75%.

Go over to the proper thread and you post EXACTLY how you think that should be changed (that will fit on one line in a chart).

Otherwise, you're the continual blow hard with no answers. Now, off like a bunny... hop, hop, hop, over to the other thread. I'll be right behind, but no peaking. Trust me... right there.

It seems to me that he has heard you, but since you haven't offered a better solution he has to stay with what he has.

 

[GerryAZ]

2:44am, just 25 minutes before I launched my car, "Black782", on the test course. Five of us stayed up all night, and one of those pictured doesn't even own a LEAF anymore!

Who is who?

I am the guy with the long sleeve shirt who happens to have his back toward the camera in all 3 daylight pictures.

Gerry