Speed Threshold vs Battery Life

[Cube_]

Hey forum,

I purchased a 2021 Mach-E Premium AWD Extended Range and have been driving it for almost a year now. I drive a lot and I'm always looking for ways to conserve range (ie minimize use of temperature controls, drive at speed limits).

The question I have is - is there a 1:1 ratio in speed vs range consumption? Or does the ratio change based on how slow/fast I go?

Ie: if im driving at 30mph to get from point a to point b, will I have more battery range left than if I drove at 60mph to get to the same point?

I've noticed that if im driving at slower speeds in the city I use less battery range, but on the highway at 70mph I use more. However im not sure if it only appears this way because im getting to my destination faster.

Thanks

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[SnBGC]

I've noticed that if im driving at slower speeds in the city I use less battery range, but on the highway at 70mph I use more. However im not sure if it only appears this way because im getting to my destination faster.

Thanks

Your observation is correct. The faster you drive, the more energy consumed per mile.
All else being equal.....for the same amount of energy, you can travel further at 60 mph compared to 80 mph.

 

[SprManKalEl]

Also, consider regenerative braking. In stop and go traffic, you'll regenerate more energy than on a highway trip with no stopping/slowing down.

I do mostly highway driving and drive 40 miles one way to the office. I am also definitely not being careful on acceleration or speed. I am not unhappy with the efficiency.

 

[HondaRacer]

At highway speeds, drag due to wind resistance increases with velocity squared. You have an exponential effect on range.

 

[ctenidae]

At highway speeds, drag due to wind resistance increases with velocity squared. You have an exponential effect on range.

This.

There's probably a blip in that curve at whatever speed the MME is the most slippery and has the lowest coefficient of drag.

Entirely observational, but I seem to get the most anomalous high efficiency numbers on trips that have a lot of 60-65 highway in them.

 

[Sam2084]

Also, consider regenerative braking. In stop and go traffic, you'll regenerate more energy than on a highway trip with no stopping/slowing down.

I do mostly highway driving and drive 40 miles one way to the office. I am also definitely not being careful on acceleration or speed. I am not unhappy with the efficiency.

I don’t think regenerative breaking is the positive you think it is, sure, you get some energy back, but it’s not a 100% efficient process so you don’t the energy you put in to get you to a given speed. You would go farther not stopping at all than stop and go with regen. It’s all about drag here.

 

[ctenidae]

Also, consider regenerative braking. In stop and go traffic, you'll regenerate more energy than on a highway trip with no stopping/slowing down.

I think that's backwards. It makes logical sense that more regen events = more power regened. But, when you take into account losses at each end of the cycle as the system switches from discharge to charge and back, and that it's not 100% efficient generation so you don't get back everything you put in, you're actually better off doing 1 long regen event, from 60 to 0 for instance. Only 1 switching cycle, and you recapture as much as the system's efficiency allows of the energy you put in to get to 60 in the first place (though, none of the energy used to stay there).

Of course, that means that stop and go, where you're constantly either expending or collecting angry pixies, could be more efficient than a long time at speed and then just one long regen stop. If you're cruising for 10 miles, that energy is lost, but if you're constantly changing speed you're always getting something back over the whole 10 miles.

I have no idea where switching losses and efficiency set the equilibrium between the two, though.

 

[SprManKalEl]

I think that's backwards. It makes logical sense that more regen events = more power regened. But, when you take into account losses at each end of the cycle as the system switches from discharge to charge and back, and that it's not 100% efficient generation so you don't get back everything you put in, you're actually better off doing 1 long regen event, from 60 to 0 for instance. Only 1 switching cycle, and you recapture as much as the system's efficiency allows of the energy you put in to get to 60 in the first place (though, none of the energy used to stay there).

Of course, that means that stop and go, where you're constantly either expending or collecting angry pixies, could be more efficient than a long time at speed and then just one long regen stop. If you're cruising for 10 miles, that energy is lost, but if you're constantly changing speed you're always getting something back over the whole 10 miles.

I have no idea where switching losses and efficiency set the equilibrium between the two, though.

I can see the logic here. Maybe the whole thing is somewhere in the middle.

 

[Mach-Lee]

Hey forum,

I purchased a 2021 Mach-E Premium AWD Extended Range and have been driving it for almost a year now. I drive a lot and I'm always looking for ways to conserve range (ie minimize use of temperature controls, drive at speed limits).

The question I have is - is there a 1:1 ratio in speed vs range consumption? Or does the ratio change based on how slow/fast I go?

Ie: if im driving at 30mph to get from point a to point b, will I have more battery range left than if I drove at 60mph to get to the same point?

I've noticed that if im driving at slower speeds in the city I use less battery range, but on the highway at 70mph I use more. However im not sure if it only appears this way because im getting to my destination faster.

Thanks

Not 1:1, drag is proportional to velocity squared. So 60 mph would have 4x as much drag as 30 mph. Drag is about 70% of your energy consumption on the highway so speed makes a huge difference. Remember the V^2 thing next time you’re running low, slowing down 10 mph can save a lot of energy.

 

[HuntingPudel]

This.

There's probably a blip in that curve at whatever speed the MME is the most slippery and has the lowest coefficient of drag.
<SNIP>

As someone with just a little Aero education I have to say, Coefficient of Drag (CD) does not change with speed. It’s the same at zero relative wind speed as it is at any other relative wind speed. Further, since an EV does not have to deal with the inefficiency curves of an ICE, fuel consumption vs. speed should be relatively predictable at moderate speeds where airflow is laminar. Once turbulence is induced, raw drag will increase, adding to fuel consumption. At anything approaching terminal velocity, raw drag will be extremely high and fuel consumption will be insane. ??

 

[ctenidae]

As someone with just a little Aero education I have to say, Coefficient of Drag (CD) does not change with speed. It’s the same at zero relative wind speed as it is at any other relative wind speed. Further, since an EV does not have to deal with the inefficiency curves of an ICE, fuel consumption vs. speed should be relatively predictable at moderate speeds where airflow is laminar. Once turbulence is induced, raw drag will increase, adding to fuel consumption. At anything approaching terminal velocity, raw drag will be extremely high and fuel consumption will be insane. ??

Yep. I knew CoD was too specific a thing, the point being there is probably some speed where everything fits just as well as it's going to -laminar flow, drag, turbulence all balanced as well as they're going to be. Might be a really small blip, but some point along the curve is the "most efficient." I guess that's the speed where you'd want to stay as much as possible.

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