# Amp hours per mile.



## Bowser330 (Jun 15, 2008)

gojo said:


> Got my insurance today, and took the RX7 out on the road. According to the Cycle Analyst I averaged 2.7 amp hours per mile with my 120 volt pack. This was with a mix of back roads at around 30 MPH, and mostly 45 to 50MPH highway.
> 
> 
> Would this be typical?


120 * 2.7 = 324wh/mile, yes that is typical....whats your battery pack? LA or Li? Whats your overall weight? have you done any aerodynamic improvements to the RX7? e.g. grill block, underbody panel, smaller mirrors, lowered...etc?


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## gojo (Feb 1, 2011)

Bowser330 said:


> 120 * 2.7 = 324wh/mile, yes that is typical....whats your battery pack? LA or Li? Whats your overall weight? have you done any aerodynamic improvements to the RX7? e.g. grill block, underbody panel, smaller mirrors, lowered...etc?


The car is about 2750#s with 10, 150ah LA's. I am hoping the pack lasts until they come out with some PBcarbons I can replace the LA's with.

I am planning on putting a sheet of aluminum over the grill block to both improve aerodynamics, and keep water out. I put 175 racing springs in the back, and I have to put some heavier springs up front. The springs of course bring up the car, and will add some to the drag, but it is nice to not bottom out. 

I have an Impulse 9 motor, and Curtis 1231.


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## Guest (Jul 7, 2011)

Yes that is typical. I am getting around 2.5 AH per mile. It also depends upon how fast and how hard I push it. Mine is calculated at full freeway speed of 55 to 60 mph with very little in town stop and go and then the stop and go is hard acceleration. I think I could if I were only driving in town get that much lower but my car is also quite light. So I think yours is right in the range of normal. 

Pete


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## EV-propulsion.com (Jun 1, 2009)

Also, correct wheel alignment and tire pressure can make a big difference in rolling resistance.


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## dtbaker (Jan 5, 2008)

Bowser330 said:


> 120 * 2.7 = 324wh/mile,


sounds a little high for an aero car like a rx7 unless there are a lots of stops/starts included... getting lead moving takes way more than keeping it rolling.

check brake drag, tire pressure (go 5# or 10# over recommended), alignment, and if you get new tires make sure you go with the narrow higher profile rather than more sporty wider low profile given the stock diameter.


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## tomofreno (Mar 3, 2009)

> sounds a little high for an aero car like a rx7 unless there are a lots of stops/starts included... getting lead moving takes way more than keeping it rolling.


 Actually acceleration usually doesn't require that much energy. It takes about 90 Wh to accelerate my car from 0 to 50 mph, and requires a bit under 200Wh/mile to maintain that speed of 50 mph on level ground (about 5% more "from the wall"- including losses during charging). Suzuki Swift, 2250 lb.


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## dtbaker (Jan 5, 2008)

tomofreno said:


> Actually acceleration usually doesn't require that much energy. It takes about 90 Wh to accelerate my car from 0 to 50 mph, and requires a bit under 200Wh/mile to maintain that speed of 50 mph on level ground (about 5% more "from the wall"- including losses during charging). Suzuki Swift, 2250 lb.


thats right around what my Swift gets too.... right around 200Wh/mile average use measured w/ CA, and close to 300 Whr/mile 'at the wall' average total use with all loss from rolling, aero, motor, controller and charger. My Swift weighs in at 2020# now with 38 x 100ah cells (120v).

I would expect an Rx7 to be not much more?!


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## Ziggythewiz (May 16, 2010)

tomofreno said:


> Actually acceleration usually doesn't require that much energy. It takes about 90 Wh to accelerate my car from 0 to 50 mph, and requires a bit under 200Wh/mile to maintain that speed


So 1 acceleration takes nearly the same power as 1/2 mile. So if you have to stop 10 times, that's 5 miles less range. Sounds like a lot to me.


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## GerhardRP (Nov 17, 2009)

Ziggythewiz said:


> So 1 acceleration takes nearly the same power as 1/2 mile. So if you have to stop 10 times, that's 5 miles less range. Sounds like a lot to me.


Actually, acceleration gives you kinetic energy that you can recover by coasting to a stop. It is braking that dissipates good quality energy into heat along with other losses.
Gerhard


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## tomofreno (Mar 3, 2009)

> So 1 acceleration takes nearly the same power as 1/2 mile. So if you have to stop 10 times, that's 5 miles less range. Sounds like a lot to me.


I stop with regenerative braking. Hardly use my mechanical brakes, so I get back a good part of that acceleration energy. A typical drive for me would be about 20 miles, mostly on highway, a couple stop lights and maybe 2 or 3 stop signs, so acceleration is a small part of the energy used. If you drive in heavy traffic stopping and accelerating a lot, yes, you would use more. But you likely would only be accelerating to maybe 30 mph which takes a little over 30Wh, so about 6.5 stops per mile. That 200 Wh/mile is at 50 mph. At 35 to 45 mph I use more like 185Wh/mile.


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## PTCruisin (Nov 19, 2009)

Here is some more data:

I see an average of 320Wh/mi over the same daily commute of 20 miles round trip. About 10 miles is on surface streets at max speed of 40mph and the other 10 miles is at highway speed of 55-65mph.

The car weighs 3100lbs, has a drag coeff. of 0.38 and is powered by 120V, 100Ah LiPO4 pack.

If I use secondary roads and surface streets (no highway) I see about 280Wh/mi, with an average speed of 30mph.

This has been fairly consistent over the past 10 months with some temperature-dependent variation. Colder batteries = higher Wh/mi.


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## Beemer (Jun 2, 2011)

You'll find on a car if you divide the weight in pounds by 10 you'll have the average WH/mile.

So, i.e. A one tonne car, (2200lbs)/10 = ~220WH/mile.

It's no good using AH/mile or V/mile for exactly the same reason. Watts is power. If you run double the voltage you'll require half the current for the same effort of work.

Regenerative braking is extremely lossy at cell level unless you are holding your EV's speed down a very, very long hill. Only super capacitors are immediate but too expensive to consider.

It's far more efficient free rolling your speed down, using hyper mileage tricks etc.


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## gojo (Feb 1, 2011)

Beemer said:


> You'll find on a car if you divide the weight in pounds by 10 you'll have the average WH/mile.
> 
> So, i.e. A one tonne car, (2200lbs)/10 = ~220WH/mile.
> 
> ...


Pretty close. My RX7 weighs 2700 pounds, and I got 2.7 amp hours per mile. My last trip averaged 2.4 ahrs per mile, so maybe fewer stops and starts, or maybe less head wind. What I like about keeping tract of the ah's is I have a good idea of when to start heading back to the barn.


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## spdas (Nov 28, 2009)

Aloha, just to throw a confusing wrench into the calculations. I get 2.1 miles per 200amp Calb cell, running 46 cells @ 60mph. Kinda hypermiling (almost never use the brakes), but have fat 195/50/15 tires. 

Francis


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## Beemer (Jun 2, 2011)

gojo said:


> Pretty close. My RX7 weighs 2700 pounds, and I got 2.7 amp hours per mile. My last trip averaged 2.4 ahrs per mile, so maybe fewer stops and starts, or maybe less head wind. What I like about keeping tract of the ah's is I have a good idea of when to start heading back to the barn.


I think WH is preferred for accuracy if such a meter is fitted. It must balance a bit against harder driving which makes the voltage drop and the cells in turn lose energy as heat.

I know there are many potential variables as *spdas* shows, can I guess if your car has circa 120V pack?


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## Beemer (Jun 2, 2011)

spdas said:


> Aloha, just to throw a confusing wrench into the calculations. I get 2.1 miles per 200amp Calb cell, running 46 cells @ 60mph. Kinda hypermiling (almost never use the brakes), but have fat 195/50/15 tires.
> 
> Francis


200AH Calbs?
>100miles for >30,000WH on the maths would be say around 270WH? Respectable enough for any car. Does it weigh say, 2700lbs?

A bit of food for thought:
I had a standard petrol nissan tino and my dad has a similar ford c-max. both similar shape size and weight "midi mpv's". I have cheap tyres and it free wheels far less well than my dad's car which has the wide sporty tyres of a good brand. Wouldn't put it past the nissan to be out of alignment too.

They say you can get 3-5% better mileage with "eco" tyres. Anyone can get that blowing the tyres hard!

Try both, lol


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## spdas (Nov 28, 2009)

I am looking for considerably better WH/mi. Car weighs about 2300#. (will be scaling it soon), and I the tires are dragging me a lot more. They are reallly wide, even though I have them at 40-42 psi., I am expecting more when I go to some LRR 195-70's. Also will be skinning the underside. but one step at a time so I can see the difference the changes make. I don't see how some EV Yaris owners with basically the same setup CLAIM to get 150+ per charge. 


Francis


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## Beemer (Jun 2, 2011)

spdas said:


> I am looking for considerably better WH/mi. Car weighs about 2300#. (will be scaling it soon), and I the tires are dragging me a lot more. They are reallly wide, even though I have them at 40-42 psi., I am expecting more when I go to some LRR 195-70's. Also will be skinning the underside. but one step at a time so I can see the difference the changes make. I don't see how some Yaris with basically the same setup can get 150 per charge.
> 
> 
> Francis


This is where diyelectriccar meets ecomodder 
Good luck with it all Francis, don't forget to post us what you find.

Andy


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## spdas (Nov 28, 2009)

Beemer said:


> This is where diyelectriccar meets ecomodder
> Good luck with it all Francis, don't forget to post us what you find.
> 
> Andy


200ah calbs you ask? Well they are 180s and came in at 196ah and my newer ones came in at 204ah. Improvements at the factory, but does not say too much for helping me balance my pack

Francis


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## Guest (Jul 26, 2011)

spdas said:


> I am looking for considerably better WH/mi. Car weighs about 2300#. (will be scaling it soon), and I the tires are dragging me a lot more. They are reallly wide, even though I have them at 40-42 psi., I am expecting more when I go to some LRR 195-70's. Also will be skinning the underside. but one step at a time so I can see the difference the changes make. I don't see how some EV Yaris owners with basically the same setup CLAIM to get 150+ per charge.
> 
> 
> Francis



They claim 150 miles but fail to mention it was at 35 mph for the entire run. I have a Leaf and get a real 75 miles at 55 to 65 mph. I do this daily. It is my commute car. I'd say you should get about 80+ miles if your easy on your car at freeway speeds of 55 to 65 mph. That is real world. If your getting that your doing just fine. Many claim this sort of mileage with lead acid too. Just makes me laugh. At slow golf cart speed I can see that but not at freeway speeds.


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## spdas (Nov 28, 2009)

gottdi said:


> They claim 150 miles but fail to mention it was at 35 mph for the entire run. I have a Leaf and get a real 75 miles at 55 to 65 mph. I do this daily. It is my commute car. I'd say you should get about 80+ miles if your easy on your car at freeway speeds of 55 to 65 mph. That is real world. If your getting that your doing just fine. Many claim this sort of mileage with lead acid too. Just makes me laugh. At slow golf cart speed I can see that but not at freeway speeds.


Yeah, I don't "hypermile" but I also don't quite as aggressively as in my Diesel Previa. Almost never use the brakes and hold a steady 55-60 mph and 50 (200amps) up the steep pass over H3. So not really needing to use brakes, I suppose regen is a non-starter for me. Don't want to loose the wide 195/50 tires, but that will be the next thing to go once I get familiar with the ACTUAL range. 

Francis


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## Beemer (Jun 2, 2011)

spdas said:


> 200ah calbs you ask? Well they are 180s and came in at 196ah and my newer ones came in at 204ah. Improvements at the factory, but does not say too much for helping me balance my pack
> 
> Francis


A bit off topic but that's not bad!
The golden rule: Cells die quicker at the top and the bottom of their charges. Don't go there matey.

Bottom balance and don't over charge. There's nothing but trouble and tears beyond the knee of the charge curve.


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