JoeS
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Re: Regen vs Neutral and speed for max range

Mon Nov 05, 2018 12:14 am

Aerowhatt wrote:
JoeS wrote:b) All other constraints aside, arriving a the bottom of the hill while continuously regenerating will result in a higher battery State of Charge than coasting down the hill exclusively in Neutral; ergo, in ideal conditions, I contend that we can go further regenerating instead of coasting in N.
I don't understand the intractable attachment to this idea. It simply cannot be quantitatively shown in practice...
Um, I had proposed that the way we would compare these two techniques was by reading the State of Charge at the bottom of the hill compared to SoC at the top of the hill. I submit that, all other things being equal, the vehicle with the higher State of Charge at the bottom of the hill will subsequently travel further.

Aerowhatt -
I take it you don't agree with this?
Would CaniOn Wh/km or mi/kWh over that distance be preferable?
What other measurable definition would you like to propose?

I see that in your subsequent discussion that you are including regeneration as part of your downhill driving to slow the car down (instead of simply aerodynamic drag). That is a change in the ground rules and is not the case we have on the table. If that's what you meant by "It simply cannot be quantitatively shown in practice...", then we might as well fall back and redefine our ground rules.

I thought that our basic bone of contention is energy loss due to aerodynamic drag for the higher-speed vehicle vs. regenerating inefficiency with drivetrain engaged for the lower-speed vehicle.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

Aerowhatt
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Re: Regen vs Neutral and speed for max range

Mon Nov 05, 2018 7:35 pm

I'm providing a proposed conclusion born of extensive data collection which all matches up well.

http://myimiev.com/forum/viewtopic.php?f=28&t=287&p=36475#p36475

You are putting forth a supposition based on your convictions only. I invite you to take it to the street and find this mythical hill which will give you the data that you wish to see. Bring back the screen shots for peer review and then there are grounds for a discussion. A discussion, which from my experience sussing out the most efficient way to drive the car in variable real world conditions. Would be purely academic since nobody seems to know of a road/hill that will get the result that you seek without risking safety, or a moving violation.
Personally I think you do a disservice to less tech savvy owners/drivers of the car persisting in presumably attempting to undermine the veracity of facts supported with accurate documented data.
Is anybody else regularly taking drives in this car that are 68 to 70 miles and have an elevation change spanning 5,000 ft (5,000ft up and 5000ft down) on a single charge and arriving back at the point of origin with range to spare?? The car has only seen turtle once when changing weather conditions and a long hike provided a moderate headwind for both directions of the trip.

Aerowhatt
2014 cool silver ES, acquired new 4/2015 (42.7ah at ~26K miles)
2014 Labrador Black Pearl ES, acquired new 3/2016 (41.5ah at ~15k miles)

JoeS
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Re: Regen vs Neutral and speed for max range

Wed Nov 07, 2018 8:00 am

Aerowhatt, I am saddened by the vehemence in your remarks because, like the man in the movie said, "what we have here is a failure to communicate".

Here's where we agree: on any downhill, be it a 5000-ft mountain drop or the backside of a highway overpass, judiciously alternating between N and D (or even E and B to avoid going too fast) will result in optimizing the car's distance traveled/charge.

You and I both do this, and we'll see who's first to wear out the shift lever.

On downhills, neither of us advocates leaving the car in "gear" continuously, be it D or E or B, and attempting to "feather" the gauge at the "zero-energy" point. I personally find it impossible to find and hold that "zero-energy" spot (somewhere between green and blue on our power meter).

You have aptly demonstrated this by showing the CaniOn data for the five-mile stretch, the metric of interest being miles/kWh, showing the differences among D-N, D, E, and B. I note that your average speed on these downhills is around 60mph, which is what I also usually hold the car to unless surrounding traffic dictates otherwise.

Once again, we are in complete agreement on the coasting technique, each of us having espoused and advocated it in numerous posts on this website for years.

So, what's all the fuss about?

What I've unsuccessfully been trying to convey is that we have an even more subtle subset within this advocacy discussion.

Specifically, on a steep downhill (say, >6% grade) where we can alternate between N and the other settings to maintain a constant speed during this downhill, all I'm saying is that we will get a better result by maintaining a lower speed. By "better result" I mean a lower Wh/mi or Wh/km or higher mi/kWh or km/kWh for that particular stretch of road.

My basis for this argument is that aerodynamic drag at the lower speed will be lower, thus allowing us to stuff a little more energy back in the battery at the lower speed than at the higher speed (since the car has a higher retarding force at the higher speed).

In an attempt to demonstrate this I tried to set up an extreme case whereby one car merely coasts while the other regens continuously and I thought that coasting would show no change in SoC whereas regenning would show an increase in the SoC at the bottom of the hill. Notably, as shown by your arguments and my own recent experience, this scenario is proving to be unrealistic - I haven't found a hill long enough and deserted enough around here to demonstrate this. I am sorry that this extreme example attempt on my part became misconstrued.

So, where are we?

Aerowhatt has shown data comparing the N-D (and E and B?) technique vs. leaving the car in D or B or E, at the same constant speed.

I would like to do the same, but using the N-D-E-B technique comparing two different constant speeds: say, 70mph vs. 50mph.

In real life, during the last 2-1/2 years and 60,000 miles that I've criss-crossed this country and made numerous West Coast trips in the Tesla I have often had the opportunity when facing a 6%, 7%, or even 9% downhill to select the cruise control speed at which to go down those grades and have actually slowed down a few times when I was running a bit low. Did it do any good? - I dunno. Hmmm, now that I think about it, I could do a controlled test in the Tesla even though it has a much lower Cd than the i-MiEV and the result might just be measurable, and it just might work... now, all I have to do is convince my wife that after we've gone down the hill that we're going to go back up and do it all over again! :roll:

To close this, once again, Aerowhatt - you and I are in violent agreement that coasting is superior to leaving the car "in gear". I'm simply trying to say that going downhill slower is ever-so-slightly better.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

PV1
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Re: Regen vs Neutral and speed for max range

Wed Nov 07, 2018 8:27 am

Joe, thanks for clearing up your talking points. After reading through the last few pages, it's been tough for me to even follow what was disputed. It will be interesting to see results of regenning down a hill at different speeds. Be careful out there.
:idea: :idea: :idea: :!: :!:

Dropbox maintenance in progress. If any of my links aren't working after November 17, please PM me and let me know which one isn't working.

Thanks.

Don
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Re: Regen vs Neutral and speed for max range

Wed Nov 07, 2018 9:19 am

It's pretty obvious to me that if you coast down the hill in N and the aero drag limits your speed to 75, that regenning just a little bit in D and using that to limit your speed to 70 will have you with more energy in the pack at the bottom of the hill than coasting. Instead of wasting energy to aero drag and using the car's quiescent 1.2 amps (or whatever it is) you're getting something back from regen and you're getting to the bottom of the hill at roughly the same time . . . . and maybe even avoiding a speeding ticket

It is nice to have a cruise control (like my Volt and your Tesla have) which makes this an 'automatic' exercise

Am I missing something? Why do we even need to try to 'prove' this??

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
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Aerowhatt
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Re: Regen vs Neutral and speed for max range

Wed Nov 07, 2018 12:23 pm

I'm sorry if my conviction level hit you wrong Joes. I get frustrated with supposition being held up against fact. For people who are not tech savvy, really can't see the difference. I appreciate your clarification of your viewpoint on the most efficient way to drive. Enclosed is a dizzying amount of information on this topic. I'm posting it because My wife asked me about my frustration and I told her that I was using our mountain trips as an example. She said I would be surprised if anyone believes that we take those drives. I wouldn't believe it if I wasn't right there with you and I drive the i miev every day too.

So hear we go. the following is screen shots of canion and GPS data of the drive to and from the 10K trial head in the Sandia mountains and back from our home.

10k Trail head up only.png
10k Trail head up only.png (994.8 KiB) Viewed 273 times


OK so that's the way up. canion screens at the house and at the trail head follow:

canion one.png
canion one.png (104.5 KiB) Viewed 273 times


canion two.png
canion two.png (122.18 KiB) Viewed 273 times


As we can see the trip so far has covered 35.9 miles and used 87.5% of the useable battery capacity. Notice the RR = 1
Last edited by Aerowhatt on Wed Nov 07, 2018 12:47 pm, edited 1 time in total.
2014 cool silver ES, acquired new 4/2015 (42.7ah at ~26K miles)
2014 Labrador Black Pearl ES, acquired new 3/2016 (41.5ah at ~15k miles)

Aerowhatt
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Re: Regen vs Neutral and speed for max range

Wed Nov 07, 2018 12:45 pm

The trip down and back home:

10k trail head down only .png
10k trail head down only .png (686.43 KiB) Viewed 269 times


canion three.png
canion three.png (125.32 KiB) Viewed 269 times


Interesting is the screen below which was grabbed at the bottom of the steep mountain road:

canion four.png
canion four.png (133.34 KiB) Viewed 269 times


It shows an SOC of 24.5% compared to the 12.5% at the top After 11miles and 3000ft of altitude descended 12% of SOC has been gained maximizing regen all the way and no friction braking whatsoever. This same stretch going up took the SOC from 54.5% at the base to 12.5% reducing it by 42%.

So 42% SOC to climb and 12% returned on the way down 12/42 = 28.6% of the power to climb was returned by the regen on the same mountain road. As you can see the speed on this stretch of road is quite low, average is certainly < 30mph. So regen is critical and also relatively less effective than we would like, at the same time. I point this out because I think it shows that regen is inefficient enough that it would take a pretty big difference in speed to do better with regen than coasting at a faster speed. It does go against "common sense" or expectations. If there is any advantage to going 30 mph in gear down a hill that will support a coasting speed of 60 mph, it would be small at best. One or two percent SOC increase for several miles of hill. The problem is that there are no hills where 30 mph or 60 mph on the same road are permissible, let alone safe. So what is the point of discussing it and muddying the waters of definitive range extending advice for others?? That's what is frustrating me. I'll make this my last word on the thread unless someone has questions, related to what I have posted.

Aerowhatt
2014 cool silver ES, acquired new 4/2015 (42.7ah at ~26K miles)
2014 Labrador Black Pearl ES, acquired new 3/2016 (41.5ah at ~15k miles)

jray3
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Re: Regen vs Neutral and speed for max range

Wed Nov 07, 2018 1:32 pm

Excellent. That was quite a trip.
2012 i-SE "MR BEAN" 94,000 miles
2000 Mazda Miata EV, 78 kW, 17 kWh
1983 Grumman Kurbwatt EV,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
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Don
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Re: Regen vs Neutral and speed for max range

Wed Nov 07, 2018 2:26 pm

Aerowhatt wrote:So 42% SOC to climb and 12% returned on the way down 12/42 = 28.6% of the power to climb was returned by the regen on the same mountain road. As you can see the speed on this stretch of road is quite low, average is certainly < 30mph. So regen is critical and also relatively less effective than we would like, at the same time. I point this out because I think it shows that regen is inefficient enough that it would take a pretty big difference in speed to do better with regen than coasting at a faster speed. It does go against "common sense" or expectations. If there is any advantage to going 30 mph in gear down a hill that will support a coasting speed of 60 mph, it would be small at best.

So . . . . now I'm completely lost . . . . but I get lost easy, so no worries there

You went up the hill and used X amount. You regenerated going down the hill at about the same speed and got a little less than 1/3rd of the amount of energy you used climbing the hill back by regenning. I understand that part and agree the return is certainly less than we would like . . . . but it is still something - Better than coasting and getting nothing, no??

But, where I get lost is . . . . you suggest that not regenning and coasting down the hill at twice the speed in N is going to be more or less just as efficient? You're not going to have that 1/3rd amount of energy you used going up the hill back in your pack . . . . are you? You'll get to the bottom sooner, but with less energy left to resume the drive home . . . . or, am I completely missing the point of this exercise?

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1979 Honda CBX six into six

Aerowhatt
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Re: Regen vs Neutral and speed for max range

Wed Nov 07, 2018 5:59 pm

Don wrote:
You went up the hill and used X amount. You regenerated going down the hill at about the same speed and got a little less than 1/3rd of the amount of energy you used climbing the hill back by regenning. I understand that part and agree the return is certainly less than we would like . . . . but it is still something - Better than coasting and getting nothing, no??

But, where I get lost is . . . . you suggest that not regenning and coasting down the hill at twice the speed in N is going to be more or less just as efficient? You're not going to have that 1/3rd amount of energy you used going up the hill back in your pack . . . . are you? You'll get to the bottom sooner, but with less energy left to resume the drive home . . . . or, am I completely missing the point of this exercise?

Don


OK so the point is that this grade starts out at -13.5 % I actually pull out of the parking area in N to avoid using any power. You must put the car in a drive gear within 150 ft or you will be going to fast for the first switchback corner. On a grade like that if all I can get from regen is a tad more than 1% SOC per mile then a lesser grade (one that you could coast down without exceeding 80 mph) is going to yeild much less power per mile. According to the math 6% grade would yield less than half of the SOC gain per mile. It's not worth talking about it, is the point. Regen when you need to for speed control otherwise coast coast coast.

Aerowhatt
Last edited by Aerowhatt on Wed Nov 07, 2018 6:34 pm, edited 1 time in total.
2014 cool silver ES, acquired new 4/2015 (42.7ah at ~26K miles)
2014 Labrador Black Pearl ES, acquired new 3/2016 (41.5ah at ~15k miles)

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