Learning to manage battery on long drives

I just tailgate greyhound buses to get great range on long trips, lol.

yobigd20 said:

I just tailgate greyhound buses to get great range on long trips, lol.

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And Walmart trucks. They're everywhere.

I've been surprised by the efficiency of my P85.

I'm going to use 34,020Wh as the energy content of a gallon of gasoline, per this page:
Miles per gallon gasoline equivalent - Wikipedia, the free encyclopedia

Over 11,198 miles in the six months I've had it, it has averaged 358Wh/mile, or about 95MPG. That includes everything I've every done in it - all the dogging and gunning I've ever did in it to impress myself as well as friends and anyone else getting a demo - and all the heating I had to do during the unusually cold winter we just had.
I just happened to reset a tripmeter 3,089 miles ago. Over that distance it has averaged 331Wh/mile, or about 103MPG. This has been through warm weather, and while continually gunning the car is just as fun as it ever was, I just don't do it as much as I used to
I started to notice that driving by myself was less efficient than driving my dog around, or my girlfriend, or both. Having both in the car got better efficiency! For the simple reason - that I drive more gently when they're in the car.
So lately, I have tried to drive as efficiently as possible. Prior to this I might see daily commutes in the low-400's to mid-300's depending on weather and various factors.
Today I drove my usual commute and managed it using 287Wh/mile, or about 118MPG. Yesterday I did the same commute and drove around town a little, and used 272Wh/mile or 124MPG.
My all-time record is driving back from the San Marcos Supercharger to my house in Austin, when I drove at the "prescribed" 55mph all along IH35 which made me pretty unpopular. Though it was around midnight so I was probably OK It's a pretty level trip, and I made it home using only 241Wh/mile - or 141MPG by that calculation. Anyhow the "Ideal Range" was shorter than the range I was actually getting! I was able to drive 10 miles and only see 9 miles drop off the range-o-meter.

I can totally believe the Florida guy that got 400+ miles in one charge. I am very confident that with gentle driving and not going over 55mph, you can really trust the range-o-meter in your car.

One does not realise how incredibly efficient this car is (and especially considering the available performance) until you calculate that a BMW M5 that is averaging 17 MPG is consuming 1,982Wh/mile. :|

Speed makes the biggest difference because double the speed means 4 times the air drag. 55 vs 65 sounds like a small difference in speed. It's only 18% faster but requires 40% more energy in terms of air drag. Going at 65 is 76% higher air drag.
Going at 62 vs 65 reduces air drag by 10%. There are other losses that are not speed dependent so the result in actual energy usage is not only measured by that. But the faster you go the bigger the part that air drag plays. So staying away from high speeds is the best for getting more range.

David99 said:

Speed makes the biggest difference because double the speed means 4 times the air drag. 55 vs 65 sounds like a small difference in speed. It's only 18% faster but requires 40% more energy in terms of air drag. Going at 65 is 76% higher air drag.
Going at 62 vs 65 reduces air drag by 10%. There are other losses that are not speed dependent so the result in actual energy usage is not only measured by that. But the faster you go the bigger the part that air drag plays. So staying away from high speeds is the best for getting more range.

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That's why I follow big bus's. I can do 75-80mph while still getting below 300Wh/mi.

MartinAustin said:

I've been surprised by the efficiency of my P85.

I'm going to use 34,020Wh as the energy content of a gallon of gasoline, per this page:
Miles per gallon gasoline equivalent - Wikipedia, the free encyclopedia

Over 11,198 miles in the six months I've had it, it has averaged 358Wh/mile, or about 95MPG. That includes everything I've every done in it - all the dogging and gunning I've ever did in it to impress myself as well as friends and anyone else getting a demo - and all the heating I had to do during the unusually cold winter we just had.
I just happened to reset a tripmeter 3,089 miles ago. Over that distance it has averaged 331Wh/mile, or about 103MPG. This has been through warm weather, and while continually gunning the car is just as fun as it ever was, I just don't do it as much as I used to
I started to notice that driving by myself was less efficient than driving my dog around, or my girlfriend, or both. Having both in the car got better efficiency! For the simple reason - that I drive more gently when they're in the car.
So lately, I have tried to drive as efficiently as possible. Prior to this I might see daily commutes in the low-400's to mid-300's depending on weather and various factors.
Today I drove my usual commute and managed it using 287Wh/mile, or about 118MPG. Yesterday I did the same commute and drove around town a little, and used 272Wh/mile or 124MPG.
...

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This is a very interesting thread which got me thinking about what my cost per mile is to drive.

For the past 4 years, I have driven a Prius which I bought largely to see if I really could get 50mpg. Like MartinAustin, I have learned how to efficiently drive the vehicle with my best mileage being 63mpg over 58 miles (some downhills on a oneway trip). My average over 76,000 miles including cold winters was 48.3mpg. So at $4/ga my cost is $0.0828/mi.

Here in CT, I pay $0.16/kWh for electricity. This includes $0.0099/kWh for 100% renewable replacement of kWh used. So using MartinAustin's 358 Wh/mi average, the cost per mile will be (.16/1000*358) or $0.05728/mi.

This represents a ~30% fuel cost savings from driving the Prius (one of the most efficient ICE cars). That despite electricity costing more per gallon in CT (34,020/1000*0.16) or $5.44/GGE.

But like with the Prius - I was intrigued by the Tesla technology. Can I really drive all electric? So I've sold the Prius and bought a Model S and am now eagerly awaiting it's arrival. Mid-Sept is the current estimate.

artsci said:

After a year with the car I've gained enough driving experience to learn how to manage battery consumption on a long drive so that even minor range anxiety is gone. Today I drove about 210 miles with a start charge of 250. Ended up with about 15 miles of range left. I avoided my usual highly aggressive driving style, kept the speed under 70 (closer to an average of 55), and chose a route that took me off interstates onto two lane back country roads (with max 55 mph speed limits) that not only saved distance abut also range. And I arrived at my destination with time to spare.

On such a long trip I do a standard overnight charge to full range. Then in the morning I switch to a Max Range charge about 75 minutes before my departure time. That way the battery is not at Max Range level for more than a few minutes.

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All that knowledge goes to waste in the winter.
I for one hate not driving at my normal speed or how I'd drive an ICE car.

EdA said:

All that knowledge goes to waste in the winter.
I for one hate not driving at my normal speed or how I'd drive an ICE car.

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The thread was for long trips (without stopping to charge) when you need to manage range. It's good to have the knowledge in case you need it. When traveling long distance from Supercharger to Supercharger you can go as fast as you want.

I drive pretty normal, go with the flow on all roads and my lifetime average after 11k miles is 302 kWh/mile (AC running 90%).

yobigd20 said:

That's why I follow big bus's. I can do 75-80mph while still getting below 300Wh/mi.

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+1

I am always surprised how much better range I get on I-5 driving really fast(80-90) vs highway 101 in the hills driving under 60 mph!
and in the southern heat the car is amazing compared to moist coastal air

Humid air is actually less dense than dry air at the same temperature. The heat may be boosting your range, because it sure isn't the low humidity.

stevezzzz said:

Humid air is actually less dense than dry air at the same temperature. The heat may be boosting your range, because it sure isn't the low humidity.

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thanks. my brain is melted. physics has leaked out of it this week. today feels like north Kauai weather, almost - upper 60's, super sunny and it feels waaay hot out.
the heat and not driving in hills helps a lot

brianman said:

And Walmart trucks. They're everywhere.

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Just don't follow the one that has been driving for 13.5 hours and is traveling 65 in a 45 zone!

They are governed to max 65mph!