Pier
Posts: 51
Joined: Tue Nov 15, 2011 9:01 am
Location: St-Aubert, Qc,

Regen vs Neutral and speed for max range

Sun Jul 14, 2013 4:56 am

Under certain conditions, I beleive regen is better than neutral for maximum range. I know it has been discussed many times, and I agree that most of times it is better to put the shifter in neutral ( or the needle at zero energy use). Neutral seems better mostly at medium to low speed.

I recently went on a 105 km mountain journey, let's say 6000 feet ups and 4500 feet downs in many short ups and downs.( and the opposite going back). The longuest was around 15 km at energy use of 4.5 km per bar and the steepest was 5 km at 3 km per bar. I had to maintain some energy for the last pass before arrival. I arrive with 2 bars left and 20 km RR.

Here is the main subject. I had two choices : going down in neutral at 120 kmh or go down on regen at 60. It seemed to me that the latest was more efficient for the long run. I beleive the reason is : what % we loose in regen we gain a superior % by not fighting against the wind at 120, but I have no numbers to prove it.

WHat do you think about it ?

JoeS
Site Moderator
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Joined: Thu Dec 15, 2011 5:47 am
Location: Los Altos Hills, California

Re: Regen vs Neutral and speed for max range

Sun Jul 14, 2013 8:01 am

Pier, I agree, for the situation you described! Thank you for your post.

As you know, I am a huge proponent of N as a significant hypermiling technique; however, when going downhill if the hill is steep enough that keeping the vehicle in one of the drive modes still allows it to keep going with the flow of traffic, then by all means regen is a significant benefit, the only sacrifice being speed and time-to-destination. Another example of driving slower improving range.

On your trip, did you actually see your Fuel Gauge go up any bars (in addition to your RR increasing)? I proved that it does happen, see the graph here. :ugeek: Has anyone ever seen an ICE gas gauge go up while driving? :lol:

In case anyone is interested, we have a number of places where coasting in N is discussed:

http://myimiev.com/forum/viewtopic.php?p=1210#p1210

http://myimiev.com/forum/viewtopic.php?f=28&t=1189

http://myimiev.com/forum/viewtopic.php?f=28&t=354

http://myimiev.com/forum/viewtopic.php?f=28&t=292

Maybe we should combine a few of those into one Topic?
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

Llecentaur
Posts: 239
Joined: Thu Dec 27, 2012 7:56 am

Re: Regen vs Neutral and speed for max range

Sun Jul 14, 2013 8:14 am

Yes, I would say that from 60km/h speed and higher, it is beneficial to regen gently than coast down in N. of course there is a margins of error, traffic condition and how pressed you are to save. If you have no choice because you have to regen to get home, then one could argue to put the hazard lights on and regen as low as 40km/h as an ICE driver would do IFGP has a mechanical failure. If you are in a hurry or traffic does not allow going so slowly, then up to about 85km/h the loss due to the wind is acceptable, then it becomes a major factor if 100km/h or more.

Don
Site Moderator
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Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: Regen vs Neutral and speed for max range

Sun Jul 14, 2013 3:50 pm

Careful modulation of the 'go pedal' keeping the red needle between the 'Eco' range and the blue 'Charge' area is essentially the same thing as shifting it to neutral . . . . with the added advantage that you have instant regen available when you need to slow . . . . all without fiddling with the shifter

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1994 Miata 60K miles - Soon to be sold
1979 Honda CBX six into six

JoeS
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Joined: Thu Dec 15, 2011 5:47 am
Location: Los Altos Hills, California

Re: Regen vs Neutral and speed for max range

Sun Jul 14, 2013 6:34 pm

Don wrote:Careful modulation of the 'go pedal' keeping the red needle between the 'Eco' range and the blue 'Charge' area is essentially the same thing as shifting it to neutral . . . . with the added advantage that you have instant regen available when you need to slow . . . . all without fiddling with the shifter...
I find it way too much trouble to concentrate keeping the needle positioned in EXACTLY the zero drive energy spot ... besides, having driven a stick shift all my life, it gives my idle right hand something to do. :roll:

Actually, I could swear that there seems to be less drag with the car in N as compared to having it in one of the drive modes and 'balancing' at that zero drive energy spot. Incidentally, that zero drive energy spot varies, depending on whether the heater or aircon are on. :geek:
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

Llecentaur
Posts: 239
Joined: Thu Dec 27, 2012 7:56 am

Re: Regen vs Neutral and speed for max range

Sun Jul 14, 2013 10:36 pm

Plus on EU Czero models, the car is always in B mode (called D) therefore it is that much more difficult to keep it in the neutral Zone for a long stretch.

Anyone knows what equivalent KW is sent back to the batteries when the needle is near to the max regen ? The engine being an AC, I am wondering if it is not limited to 3300 that the charger can handle or is there another AC-DC converter for regen ?

Don
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Location: Biloxi MS

Re: Regen vs Neutral and speed for max range

Mon Jul 15, 2013 6:21 am

I don't spend hardly any time looking at the needle, so I'm sure I'm not keeping it EXACTLY centered either. Generally, I try to gradually lose a little speed going up hills and gradually gain a little going down the other side. It's pretty flat around here, so no long hills to deal with - The only 'major' ones for me are overpasses over the freeway and steep entrance ramps. I never take it out of B and I run the A/C most of the time and I usually have RR's in the 75 to 80 mile range after a recharge, so it seems to be working pretty well

Could I gain another 3% or 4% by frequently shifting it into N? I kinda doubt it since I have no major hills to go down, but since N and B are not easy to shift between, I gave up on that option the first month we had the car. Since I've never owned a car with an auto-trans, I'm used to keeping a very steady foot on the go-pedal. It just comes naturally to me, so no big effort or concentration needed to make it work

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1994 Miata 60K miles - Soon to be sold
1979 Honda CBX six into six

Barbagris
Posts: 225
Joined: Wed Feb 20, 2013 8:34 am
Location: Bilbao, Spain

Re: Regen vs Neutral and speed for max range

Mon Jul 15, 2013 7:00 am

Llecentaur wrote:Anyone knows what equivalent KW is sent back to the batteries when the needle is near to the max regen ? The engine being an AC, I am wondering if it is not limited to 3300 that the charger can handle or is there another AC-DC converter for regen ?


Near 50A, 16 kW or so.

Image

viewtopic.php?f=22&t=288

but can be bigger:

JoeS wrote:Regeneration (blue zone):

Seems to be linear, with max tick mark reading ~50A
Regen continues on up despite the needle being pegged, with a maximum reading seen of 104A when letting off the go pedal in "B" at around 65mph. I didn't try also applying the brakes to see if it would further increase.
...learning...

Llecentaur
Posts: 239
Joined: Thu Dec 27, 2012 7:56 am

Re: Regen vs Neutral and speed for max range

Mon Jul 15, 2013 10:30 am

Thank you for the information.

Wonder if that would mean pulling the car while regenerating would actually pump up the battery really quickly :)

Pier
Posts: 51
Joined: Tue Nov 15, 2011 9:01 am
Location: St-Aubert, Qc,

Re: Regen vs Neutral and speed for max range

Mon Jul 15, 2013 12:50 pm

Joes said: On your trip, did you actually see your Fuel Gauge go up any bars (in addition to your RR increasing)?

Yes it did once. Here is a part of my log...
16 bar , rr: 139km, at the start.
15 bars, rr:130 at 8,6 km hilly.
14 bars, rr:118, at 12 km, steep up road for 5 km.
15 bars, rr:125, at 15.5 km, downhill for 5 km.
14 bars, rr:117, at 20.4 km, hilly. And then 13b at 25.5 and 12b at 35 lightly down.

On that mountain trip, the worst efficiency I have seen was 3km to the bar on steep uphill and the best was 23 km/b, on long 15km light downhill, but without gaining a bar.

The trip was 106 km, from St-Jean (SJ) to St-Magloire (SM) at 1500 feet altitude, but having to go up 6000 feet and down 4500 to go and the reverse on the way back. I have a formula to calculate the total distance I could have done on a charge ( from 16 bars to 0 before the reserve), going the same speed and same conditions. I call it DTa and DTb. Distance Theorical according to RR or to bars. So ...

DTa : SJ to SM was 132 km and SM to SJ : 161 km.
DTb : SJ to SM was 129 km and SM to SJ : 153 km.

Another way to calculate the efficiency is the average number of km for one bar. So
SJ to SM (more up): 7.8 km / bar. Going slow first 30km on the flat to preserve energy.
SM to SJ (more down): 9.6 km / bar. Help from back wind last 30 km. Oh I forgot, also 20 kmh faster with back wind, and all the way down SM to SJ at 10 kmh faster.
Last edited by Pier on Mon Jul 15, 2013 4:37 pm, edited 1 time in total.

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