Another interesting article, enjoy.


http://my.apnicommunity.com/blog/view/id_5261

It's starting to look like the EPA testing cycles need to be made more rigorous to more closely approximate real world conditions. Buying a car with a supposed 100 mile range and at best getting 60 or 70 will generate a lot of bad press for electric cars in the general population.

This is a Wall Street Journal article:
http://online.wsj.com/article/SB10001424052748703561604575282491734663452.html?m od=WSJ_auto_LeadStoryCollection

If the Nissan Leaf does not have the range of a Toyota RAV4 Electric or EV1 with NiMH batteries, Nissan deserves to go bankrupt. Actual users of these 10 year old cars reported ranges of over 100 miles.

Your mileage will vary, those same RV4 users will probably get 175 miles of range using a LEAF.

At 95% SoC and average speed of 20mph.

It's starting to look like the EPA testing cycles need to be made more rigorous to more closely approximate real world conditions. Buying a car with a supposed 100 mile range and at best getting 60 or 70 will generate a lot of bad press for electric cars in the general population.
60 or 70 at best? That's not what I read:


"If you were going 70 [mph] the whole time, you'd probably get a range of 60 or 70 miles," Mr. Boyer said.
Well, duh! Everybody knows it takes a lot more fuel to drive 70 than to drive 35. The air resistance laws aren't changed just because your fuel is electricity rather than gasoline.

Why do I mention 35? because there is only one fairly short section of the LA4 test cycle that goes much over 35 MPH (about 2 minutes out of 14 1/2 minutes). And it only goes up to about 57 MPH. The average speed of LA4 is under 20 MPH.

So anybody who thinks they are going to go anywhere close to 100 miles in a Leaf at 70 MPH is off their rocker. Anybody who thinks a Volt will have a 40 mile AER at that speed has a similar malady.

last I heard, a steady 56mph on a level hwy simulates the LA-4 cycle.. but thats probably apples and oranges. Lots and lots of stop and go in the LA-4

at 70 MPH my little calc shows a range of 66 miles which seems to agree with the article. This assumes the same Cd as the Volt and a usable battery capacity of 24 kwhx0.8=19.2 kwh.

Question:

Is the Leaf's usable battery capacity really 80%??

I think Prowler said in the Tesla you can select a mode that allows closer to 90 or 100% capacity??

Also, the Leaf's CD is not quite as good as the Volt.

Anybody remember how much worse it is??

I'm just saying your average person who drives their car anywhere but the city or heavily congested highways is going to be pissed when their 100 mile range is actually 60 or 70 miles. They need to at also show it in a more demanding interstate highway environment to show what a realistic expectation of range will be.

I'm just saying your average person who drives their car anywhere but the city or heavily congested highways is going to be pissed when their 100 mile range is actually 60 or 70 miles. They need to at also show it in a more demanding interstate highway environment to show what a realistic expectation of range will be.

I'm sure Nissan will make this part of their training program for new adopters. It's not much different than calculating MPG and range. They will supply simple tables that owners can use that tell them their expected miles depending on vehicle velocity and elevation change. There will also be telemetrics on board the vehicle to keep the operator informed of remaining range. Most EV drivers know exactly how far their vehicles will go and plan accordingly.

at 70 MPH my little calc shows a range of 66 miles which seems to agree with the article. This assumes the same Cd as the Volt and a usable battery capacity of 24 kwhx0.8=19.2 kwh.

Question:

Is the Leaf's usable battery capacity really 80%??

I think Prowler said in the Tesla you can select a mode that allows closer to 90 or 100% capacity??

Also, the Leaf's CD is not quite as good as the Volt.

Anybody remember how much worse it is??
I seem to remember seeing a semi-official statement somewhere of .29 CD for the Leaf compared with .28 for the Volt. Do those numbers make any sense? (I don't know anything about that sort of stuff.) I've also been getting the general impression from several sources that DOD will be greater than 80%, maybe as much as 90%, but that Nissan expects the total capacity of the pack to degrade noticeably over its "usable lifetime". So you might start out getting 80-90 miles at 70 MPH but get only 60-70 miles five (or possibly ten) years later.

That sounds like a rough life for a battery, but a PR bonus for the ramp-up period. (If I was a battery, I'd want to be in a Volt.)

I seem to remember seeing a semi-official statement somewhere of .29 CD for the Leaf compared with .28 for the Volt. Do those numbers make any sense? (I don't know anything about that sort of stuff.) I've also been getting the general impression from several sources that DOD will be greater than 80%, maybe as much as 90%, but that Nissan expects the total capacity of the pack to degrade noticeably over its "usable lifetime". So you might start out getting 80-90 miles at 70 MPH but get only 60-70 miles five (or possibly ten) years later.

That sounds like a rough life for a battery, but a PR bonus for the ramp-up period. (If I was a battery, I'd want to be in a Volt.)

I think you are right on the Cd, that's what I remember. I will update the curve fit in my program to reflect this 3.6 % increase. It will have a lot more effect than the increase in wt of the Leaf from 3000 to 3500 lb.

I seem to remember seeing a semi-official statement somewhere of .29 CD for the Leaf compared with .28 for the Volt. Do those numbers make any sense?


Yes they do, Cd is a non-dimensional value. FYI--the equation to calculate drag is:

Fd = 1/2 x ρ x V^2 x Cd x A

where:

Fd = the force of drag in lbm,
ρ = the air density (= 0.074887 lbm/ft^3 on a standard day @ sea lvl)
V = the speed of the car relative to the air in Ft/sec
A = the frontal area of the car in Ft^2
Cd = the drag coefficient (i.e., .28 or .29)

The power required to overcome the aerodynamic drag is given by:

P = Fd X V

Where Fd is calculated using the equation above, and V is the speed of the car in ft/sec.

You can read more here if your curious: http://en.wikipedia.org/wiki/Drag_(physics)

“P = Fd X V” – Rooster

Yes, we must notice that in Fd there is already V^2, which means power requirement increases at the rate of the cube of the rate of speed change. BTW, tire hysteresis loss or rolling resistance increases in direct proportion to the speed. All in all, slow down if you want to maximize your EV range. Road rage might be a real problem as many EV’s start sharing the road with high-power ICE driven vehicles.

I'm just saying your average person who drives their car anywhere but the city or heavily congested highways is going to be pissed when their 100 mile range is actually 60 or 70 miles. They need to at also show it in a more demanding interstate highway environment to show what a realistic expectation of range will be.

A range of ranges will probably be published in the sticker.. in any case I hope Nissan uses a sophisticated display that constantly recalculates remaining range by analyzing how you are driving the car. Battery charge level determination is not an easy thing to do. The driver needs accurate information but there will always be an error, probably Nissan will under-estimate the remaining range.

How does Tesla do the range display?

“P = Fd X V” – Rooster

Yes, we must notice that in Fd there is already V^2, which means power requirement increases at the rate of the cube of the rate of speed change. BTW, tire hysteresis loss or rolling resistance increases in direct proportion to the speed. All in all, slow down if you want to maximize your EV range. Road rage might be a real problem as many EV’s start sharing the road with high-power ICE driven vehicles.

Interestingly, the wh/mile consumed can be approximated as linear in a speed range of 50-75 MPH.

An interesting curve check it out:

http://www.teslamotors.com/blog4/?p=70

George, thank you for the Tesla Motors graph. Very informative. The fact the maximum range is obtained at around 18mph means that the effect of constant power consumers such as lights, HVAC and entertainment plays an important role in overall range expectation.

- When running at a reasonable constant speed, power requirement to move a vehicle is rather low… 15HP to 25HP.

- The effect of V^3 turns into V^2 since time to reach the destination is in inverse proportion to V. In other words, by doubling the speed the vehicle consumes 8 times more power to win over the wind, but it reaches the destination in half the time making the actual energy consumption 4 times.

- The effect of rolling resistance loss is a wash since it is linear to the speed. But, of course, the lower the resistance, the longer the range.

- Power consumption of lights, HVAC and other devices cannot be ignored since it can be as much as half of the total power requirement, thence the range peak at around 18mph.

George, thank you for the Tesla Motors graph. Very informative. .

You're welcome.

I've known for a long time that air resistance predominates at high speeds, but somehow I had never thought to ask the logical follow-on question. How do dynamometer tests manage to simulate wind resistance?

The only thing I can think of is by adding additional drag based on speed, but the Tesla graphs show that is not a linear function, yet nowhere close to exponential or the perhaps theoretical cubic. It obviously relates to the vehicle's CD, but how can it be accurately mapped from that CD? Especially since I would expect that real vehicles in real wind situations develop vortexes or eddies or whatever at specific wind speeds.

On second thought, the aerodynamic curve in the Wh/Mile graph could in theory be a graph of a cubic equation with a lot of the curve missing on the left end, except that I can't find any coefficients that come close to fitting.