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TonyWilliams
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Re: Low battery warning not early enough

Sun Jun 26, 2011 1:14 am

LEAFfan wrote: My low warning usually shows up at around 11 miles left, which means at 38Mph I actually have 22 miles. Most of the time I'm in town, so I can get even more at a lesser speed.

Grasshopper, when you can take the pebble from my hand, it will be time for you to leave. But, there is much to learn.

38mph is the IDEAL speed for the absolute highest miles per unit of stored battery power. Going faster, OR SLOWER, will decrease your range.

Think of 38mph as X in the center of the bell curve. Any speed to the left or right of X results in a lower range.

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JRP3
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Re: Low battery warning not early enough

Sun Jun 26, 2011 6:40 am

I'm surprised at that, 38 mph is high enough that aerodynamic forces start to come into play, I'd expect a lower speed to be ideal. I think the Tesla Roadster ideal speed is around 25 mph. How did you, come up with the 38 mph figure? Is that from Nissan?

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TomT
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Re: Low battery warning not early enough

Sun Jun 26, 2011 6:51 am

According to Nissan, the drop-off in motor system efficiency below 38 is more than the aerodynamic gain of the slower speed.
JRP3 wrote:I'm surprised at that, 38 mph is high enough that aerodynamic forces start to come into play, I'd expect a lower speed to be ideal. I think the Tesla Roadster ideal speed is around 25 mph. How did you, come up with the 38 mph figure? Is that from Nissan?
Leaf SL 2011 to 2016, Volt Premier 2016 to 2019, and now:
2019 Model 3; LR, RWD, FSD, 19" Sport Wheels, silver/black; built 3/17/19, delivered 3/29/19.

JRP3
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Re: Low battery warning not early enough

Sun Jun 26, 2011 7:35 am

Interesting. That seems to relate to Tesla's choice of AC induction for better variable speed efficiency over PM's peak efficiency.
http://www.teslamotors.com/blog/inducti ... ess-motors
In contrast, induction machines have no magnets and B fields are “adjustable,” since B is proportionate to V/f (voltage to frequency). This means that at light loads the inverter can reduce voltage such that magnetic losses are reduced and efficiency is maximized.

edatoakrun
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Re: Low battery warning not early enough

Sun Jun 26, 2011 7:42 am

Nissan does report lower power train efficiency below 38 mph, but if you look at the efficiency curve on p 17 here:

http://www.electricauto.org/resource/re ... e_2_11.pdf

You will see that efficiency is above 85% at all rpm levels. So the loss of range below 38 mph is probably negligible, at least down to 20 mph or so. The much more significant loss of range, due to wind resistance at higher speeds, is compounded by drive train efficiency lose. So the resulting range curve is highly asymmetric, rather than bell-shaped, declining only slightly at lower speeds, and dropping off rapidly at higher speeds.

I believe there is really little reason to speed up to increase range. I frequently drive on narrow winding roads, at less than 38 mph. If I increase my speed to 38 mph, I figure I'm wasting much more energy (and tread) scrubbing the tires, than I am saving by speeding up to the car's "most efficient" 38 mph.
no condition is permanent

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TonyWilliams
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Re: Low battery warning not early enough

Sun Jun 26, 2011 8:32 am

edatoakrun wrote:So the resulting range curve is highly asymmetric, rather than bell-shaped, declining only slightly at lower speeds, and dropping off rapidly at higher speeds.

I didn't find an asymmetric jpg in my quick internet search !!! :-)

From one of the articles in the above quote links, "the information panels show downtown New York in traffic jam where average speed is 15mph (24 km/h) at an ambient temperature of -10C (+14F) [pretty cold!] where the car may attain a 62 (100-km) range."

It's difficult to say how much the range is impacted by the slow speed, or the cold battery, but my point was that really slow is not super efficient.
Last edited by TonyWilliams on Sun Jun 26, 2011 8:56 am, edited 1 time in total.

LEAFfan
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Re: Low battery warning not early enough

Sun Jun 26, 2011 8:40 am

The reason I said I could go a lower speed to get more miles is because of that utube video of those guys running the LEAF around the track at 17Mph and they obtained a high number of miles...140? I can't remember the miles they achieved.
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TomT
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Re: Low battery warning not early enough

Sun Jun 26, 2011 11:23 am

It's unclear from that article and graph whether or not the efficiency stated is the motor only or the entire inverter/motor/power train... If it is the motor only, there may be other factors at work at slower speeds that affect efficiency as well that make 38mph the sweet spot. Certainly parasitic loses would be a consideration since they are essential constant and thus contribute more to total power consumption at slower speeds.
edatoakrun wrote:Nissan does report lower power train efficiency below 38 mph, but if you look at the efficiency curve on p 17 here:

http://www.electricauto.org/resource/re ... e_2_11.pdf

You will see that efficiency is above 85% at all rpm levels. So the loss of range below 38 mph is probably negligible, at least down to 20 mph or so. The much more significant loss of range, due to wind resistance at higher speeds, is compounded by drive train efficiency lose. So the resulting range curve is highly asymmetric, rather than bell-shaped, declining only slightly at lower speeds, and dropping off rapidly at higher speeds.

I believe there is really little reason to speed up to increase range. I frequently drive on narrow winding roads, at less than 38 mph. If I increase my speed to 38 mph, I figure I'm wasting much more energy (and tread) scrubbing the tires, than I am saving by speeding up to the car's "most efficient" 38 mph.
Leaf SL 2011 to 2016, Volt Premier 2016 to 2019, and now:
2019 Model 3; LR, RWD, FSD, 19" Sport Wheels, silver/black; built 3/17/19, delivered 3/29/19.

91040
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Re: Low battery warning not early enough

Sun Jun 26, 2011 11:32 am

If 38 mph is the sweet spot for a flat road, does that sweet spot become a lower speed as the grade increases?
1st Capacity Bar loss 30k mi 16.25mo
2nd- 49k mi 25.5mo 51.5Ah
3rd- 73k mi 36.5mo 46.9Ah
4th- 86.5k mi 43mo 42.61Ah
5th- 101k mi 50.5mo 38.38Ah, end 36.13Ah
New Battery 9/28/15 104k mi 66.14Ah
1st- 160.5k mi 34mo 54.02Ah

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TonyWilliams
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Re: Low battery warning not early enough

Sun Jun 26, 2011 11:43 am

LEAFfan wrote:The reason I said I could go a lower speed to get more miles is because of that utube video of those guys running the LEAF around the track at 17Mph and they obtained a high number of miles...140? I can't remember the miles they achieved.
I think they were actually going 35mph.

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