Let's talk about range

[daniel]

I've been range-testing my new EV Porsche (and posting results along with other discussion in this thread) and it has forced me to calculate two separate numbers: full-pack range, and the range I can actually drive without depleting my batteries to a harmful level.

I have never driven to dead empty, and probably never will if I can help it, so I log how many amp-hours (ah) I use for a given distance at a given speed in a given gear, and then calculate my range based on the specs I've been given for my pack: 200 ah, 28 kWh. As an example, yesterday's test run at 55 mph (the slowest I would drive on the freeway, and to date the best efficiency I've seen, since surface roads, though slower, involve some stopping) was 25 miles using 58.8 ah. This works out to 85 total pack miles, or 68 miles without over-stressing the batteries, since LiFePO4 can go down to 80% depth of discharge (DoD).

So do I advertise that my electric Porsche can go 85 miles on a charge, or do I say 68 miles on a charge, or must I give both numbers and laboriously explain about the need to leave some charge in the battery pack?

The Prius maintains the state of charge of its traction battery within safe levels, so it's not an issue when talking about its range in electric mode. I do not know whether the Tesla does something similar. The Volt, if they ever build it, would start its engine when the computer decides the battery has reached its minimum safe level. But Xebra owners typically state the range as how far they can drive before the car stops, even though doing this regularly leads to premature battery failure. And the EV field is so full of exaggeration and empty promises that I think it's fair to say that companies promising EVs "real soon now" are stating full pack range, not safe range.

So which is it? Should people be stating range as how far they can go without over-stressing their batteries? Or is it legitimate to state range as how far they can go until the car stops, even though this would lead to premature battery failure if they did it regularly?

[Matt Herring]

Originally Posted by daniel

I've been range-testing my new EV Porsche (and posting results along with other discussion in this thread) and it has forced me to calculate two separate numbers: full-pack range, and the range I can actually drive without depleting my batteries to a harmful level.

I have never driven to dead empty, and probably never will if I can help it, so I log how many amp-hours (ah) I use for a given distance at a given speed in a given gear, and then calculate my range based on the specs I've been given for my pack: 200 ah, 28 kWh. As an example, yesterday's test run at 55 mph (the slowest I would drive on the freeway, and to date the best efficiency I've seen, since surface roads, though slower, involve some stopping) was 25 miles using 58.8 ah. This works out to 85 total pack miles, or 68 miles without over-stressing the batteries, since LiFePO4 can go down to 80% depth of discharge (DoD).

So do I advertise that my electric Porsche can go 85 miles on a charge, or do I say 68 miles on a charge, or must I give both numbers and laboriously explain about the need to leave some charge in the battery pack?

The Prius maintains the state of charge of its traction battery within safe levels, so it's not an issue when talking about its range in electric mode. I do not know whether the Tesla does something similar. The Volt, if they ever build it, would start its engine when the computer decides the battery has reached its minimum safe level. But Xebra owners typically state the range as how far they can drive before the car stops, even though doing this regularly leads to premature battery failure. And the EV field is so full of exaggeration and empty promises that I think it's fair to say that companies promising EVs "real soon now" are stating full pack range, not safe range.

So which is it? Should people be stating range as how far they can go without over-stressing their batteries? Or is it legitimate to state range as how far they can go until the car stops, even though this would lead to premature battery failure if they did it regularly?

I guess it depends "who" is asking about your range. If it's the avg. driver who is just "peeking" at your car then I'd tell them max. range until the battery is dead...they are not likely to ever buy one and really just need the bullet points of the car. If it's someone with some general knowledge of EV's then I'd tell them both range figures and you could probably get into more finer point of the vehicle with them.

When I'm out and about with my Prius I get approached with mpg questions all the time...and I consider my audience before answering.

Typical question: "How many miles per gallon do you get in that car?" My answer: "60 miles per gallon."

If their follow-up question is "How do you do it" I know they have an actual interest in hypermiling or how the car works and I might go into more fine details including city vs. highway mpg, how EV mode works, some hypermiling techniques, my grill block, etc.

If their follow-up question is "Does is have alot of cupholders" I'm pretty safe in assuming they have no interest in "how" the car works and I just answer their question with a smile and end with "It's a great car."

I like talking to people about mpg in my Prius but I also don't want to turn someone off from the car by muddling their mind with alot of details that may make it sound too complicated to drive it. So, I keep it basic until I know what information they are looking for...basic vs. detailed. Either way, it's nice to know someone is interested in your vehicle and what you have to say about it.

[daniel]

Thanks. Good answer.

[JRitt]

And you should tell them how many watts/mile you use for city/highway so they can compare this to the cost of driving thier own car.

[Rybold]

When regarding the EV industry and manufacturers advertising their cars, it is only responsible, good public relations, and avoids lawsuits if they print ALL of the numbers on their literature. If you just want to paint a fancy decal on your car for style and getting the word out to the public that there is an EV on the road, I would use the maximum number.
For people in parking lots, I agree with Matt.

[daniel]

Answering my own question five months later, when people ask me about the Xebra's range (that being the car I drive daily these days) I generally tell them both numbers: range to dead empty and range to a level that does not stress the batteries. Unfortunately, big car companies have no compunctions about full disclosure, and will likely state the range to dead empty under the most ideal conditions and slow driving.

[Allannde]

You know, I came to the same conclusion but not by thinking out. It just kind of happened. Almost everyone asks me how far my EV will travel on a charge. My answer has developed: "Thirty miles before it would stop for lack of power, but I limit it to 15 miles because I have never needed more and because the batteries are happier (last longer) that way."

It is a dilemma. I want to be honest but I also want to present EVs as desirable. When push comes to shove, honesty trumps desire, in my thinking. Is that good for EVs?

I hope so.