# need mileage estimate



## mizlplix (May 1, 2011)

Sorry, guys: I really suck at math and I guess I suck at forum searches too...

Can anyone do the math for me?

I need an estimate of what mileage to expect from my car as built.

2,500Lbs.(maybe 500 Lbs lighter, no scaled weight as yet)
AC50 (forget regen issue for this.)
6.14:1 axle ratio
32" diameter tire
2-gears, 1.75:1 and 1:1
24" X 48" car frontal area, (generally flat)
130 AH pack at 125 VDC (average)
Area is flat, no hills 
I usually commute city streets, @ 45MPH.
My plan is to utilize the pack 3.4-3.0 volts
The ambient temperature stays between 45 Deg and 108 deg F. (Almost never freezes)

I just need an average mileage per charge. 

TYVM, Miz


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## Ziggythewiz (May 16, 2010)

Using 300 wh/mile as estimate, you'll get 38 miles at 70% DOD and 43 at 80%.


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## mizlplix (May 1, 2011)

Whoa, that is a little less than I had guessed.

My Son's Jet Electrica is 3,400Lbs and does 42 miles per charge at 45 MPH and another 5 miles at 25 MPH. all with 20 GC6-FLA batteries.

My car was built to drive to work, 18 miles to and 18 miles back, flat -no hills.

I guess I'm OK for that.

Miz


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## Ziggythewiz (May 16, 2010)

Well, it is just an estimate...you'll be in good shape for your commute, and with the regen should have enough for an errand or two as well.

What do you have counting the AHs?


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## mizlplix (May 1, 2011)

I have a ZEVA coil running my Autometer Fuel gauge. 

Last year I loaned my truck to my son, he left me his Electrica. It had 6 month old batteries.

I drove it for two weeks, home-work-home.

Other than being a pain in the ass to stop, it drove fine. I had a space to charge it at work, but many times did not. It drove OK in either event.

It has a 500 amp curtis controller while mine had the old 400 amp controller. Boy, what a difference that made, that and the 4 extra batteries in the back seat area. It left the total at 20- 6volt GC batteries, for a 124 volt pack.

It could peg 400 amps for a few seconds, then settle down to 250 amps or so for a couple of minutes.

The cruise was 100 amps or so at 45 MPH.

BTW: It did pull 75 MPH once while I was following it with my truck.

My old Electra with 16 batteries and the 400 Amp controller would only do 57-60. 

Those were good "learner cars". We both learned a lot during the reconditioning. 

Miz


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## dougingraham (Jul 26, 2011)

At 2500 lbs drop dead range of about 65 miles. 80% range is 52 miles. 70% range is 46 miles.

At 2000 lbs drop dead range of about 81 miles. 80% range is 65 miles. 70% range is 57 miles.

Just estimates and of course your mileage may vary.


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## somanywelps (Jan 25, 2012)

The weight is no where near as important as the wind and rolling (depending on speed) resistance.


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## Ziggythewiz (May 16, 2010)

somanywelps said:


> The weight is no where near as important as the wind and rolling (depending on speed) resistance.


That's true for highway. OP said city and max 45 mph (exactly my commute). Wind resistance doesn't even matter under 35. Weight, and luck at the lights, matter much more.


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## tomofreno (Mar 3, 2009)

mizlplix said:


> Sorry, guys: I really suck at math and I guess I suck at forum searches too...
> 
> Can anyone do the math for me?
> 
> ...


How many cells? 125V average seems high. If you use the standard 3.2V per cell, 38 cells would be 122V. Small cross section of only 16 ft^2. My little Swift is about 19 ft^2. I use around 190Wh/mile at 45 mph, in a car about 300 lb lighter than yours, so figure around 200-220 Wh/mile for yours. Assuming 38 cells and 0.8*15.8kWh = 12.7kWh, you should get around 60 miles range at 45 mph and 80% DoD in warm temperatures.


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## dougingraham (Jul 26, 2011)

somanywelps said:


> The weight is no where near as important as the wind and rolling (depending on speed) resistance.


Of course they the rolling resistance and wind resistance are the determining factors. For a rough estimate and a generally car shaped object you can use the weight because a heavier car shaped object will have both higher rolling resistance and higher Cd. With Lithium batteries with their almost non-existent Peukert effect and over a normal range of car sizes (1000 lbs to 5000 lbs) and typical speeds up to 65 mph dividing the weight by 10 gives a reasonable estimate of watt hours per mile. With his 45mph speed the air drag is almost unimportant.

2000 lbs / 10 = 200 wh per mile.

130AH * 125volts = 16250 wh sized battery pack.

16250 wh / 200 wh per mile = 81.25 miles.

Reduce to 80% gives 65 miles.

Or reduce to 70% gives 56.88 miles.

Still works with lead acid but Peukert makes the estimate wildly optimistic. You change the reduction to 50% and then expect it to be half that again initially.

You can go crazy trying to get better estimates but adding more parameters that you cant measure accurately until the car is complete (if then) tends to decrease the accuracy of the estimate rather than improve it.


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## batterytang (Nov 17, 2011)

As I know a good motor would be helpful improving the driving distance...


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## mizlplix (May 1, 2011)

> How many cells? 125V average seems high. If you use the standard 3.2V per cell, 38 cells would be 122V. Small cross section of only 16 ft^2. My little Swift is about 19 ft^2. I use around 190Wh/mile at 45 mph, in a car about 300 lb lighter than yours, so figure around 200-220 Wh/mile for yours. Assuming 38 cells and 0.8*15.8kWh = 12.7kWh, you should get around 60 miles range at 45 mph and 80% DoD in warm temperatures.


60 miles is what I originally "Fingered" out, but I wanted to get someone elses opinions because it seems that everyone has their own way to calculate the requirements/mile.

To add to this, I have rock hard/skinny tires. It is fairly open terrain with only a few stop lights per mile.

I cant wait to weigh it, that has been guesses up till now.

Miz.


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## Ziggythewiz (May 16, 2010)

Yup, just measure it with a good meter and you know. No guessing required. My bug uses way more than 'typical' and much more than when I started. He needs to lose some weight.


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## tomofreno (Mar 3, 2009)

mizlplix said:


> 60 miles is what I originally "Fingered" out, but I wanted to get someone elses opinions because it seems that everyone has their own way to calculate the requirements/mile.
> 
> To add to this, I have rock hard/skinny tires. It is fairly open terrain with only a few stop lights per mile.
> 
> ...


 That estimate should be pretty good since I have been writing down the Ah used, miles traveled, and energy consumed from the wall for the charge, each time I have recharged for over 2 1/2 years now. Yours isn't very aerodynamic, but has very small xsect, and at 45 mph air drag shouldn't be too bad (I estimate it to be a bit higher than the estimated rolling resistance force for my car at that speed - drag coeff 0.32). Yeah, those tires should make a significant difference.


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## JRue (Jun 1, 2011)

I like Jack's formula of :
Estimated Wh/mi = (vehicle weight) / 10. 

Get a good weight estimate!

This has held up (as far as I know) pretty well for general driving. I don't put much stock in freeway vs. city driving differences in range calculations. In my experience it all washes out in the end BUT your results may vary depending on the type of driving you do most. I still collect of lot of trip data and when I compare say a 50 mile freeway trip to a 50 mile in town trip I don't see a striking difference in energy used. 

I like things simple and it doesn't get much simpler than that especially when sizing. 

FWIW my car (AC50 motor 650A Curtis controller) weighs 2500 lbs and gets right about 250 Wh/mi.

At 2500 lbs 65 mile range
At 2000 lbs 80 mile range!


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## tomofreno (Mar 3, 2009)

JRue said:


> I like Jack's formula of :
> Estimated Wh/mi = (vehicle weight) / 10.
> 
> Get a good weight estimate!
> ...


 Lets see, my car weighs 2260 lb and it uses about 190 Wh/mile at 35 mph and about 250 Wh/mile at 60 mph. If I average the two that's about 220 Wh/mile, so the 226 estimate is close to the average. Of course if I were planning a conversion to commute on mainly highway at 60 - 70 mph I would under size the pack using it.


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## JRue (Jun 1, 2011)

tomofreno said:


> Lets see, my car weighs 2260 lb and it uses about 190 Wh/mile at 35 mph and about 250 Wh/mile at 60 mph. If I average the two that's about 220 Wh/mile, so the 226 estimate is close to the average. Of course if I were planning a conversion to commute on mainly highway at 60 - 70 mph I would under size the pack using it.


Very interesting and I completely agree about adjusting the estimate based on your typical commute. If there isn't one already it would be interesting to start a thread collecting measured weights and energy usage stats. 

What I loved most about building my own EV was setting up a car specifically for me and my needs. My build might not suit everyone but it fits me perfectly and that is so cool!


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## Ziggythewiz (May 16, 2010)

tomofreno said:


> Lets see, my car weighs 2260 lb and it uses about 190 Wh/mile at 35 mph and about 250 Wh/mile at 60 mph.


But if you use 190 Wh/mile at 35 mph (which is really high), your average Wh/mile would actually be around 300-400. As JRue said, there isn't much of a difference in highway usage vs city usage (at reasonable speeds) because while it takes more power to cruise at higher speeds, it takes much less power to cruise than to start and stop frequently. That lets the 1 Wh/m/lb/10 rule apply as a fair approximation in most scenarios.


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## tomofreno (Mar 3, 2009)

Ziggythewiz said:


> But if you use 190 Wh/mile at 35 mph (which is really high), your average Wh/mile would actually be around 300-400. As JRue said, there isn't much of a difference in highway usage vs city usage (at reasonable speeds) because while it takes more power to cruise at higher speeds, it takes much less power to cruise than to start and stop frequently. That lets the 1 Wh/m/lb/10 rule apply as a fair approximation in most scenarios.


How do you get my average would be 300 to 400? I gave the actual usage at two speeds and the average of those two. No, 190 is not high, it is lower than most conversions - that's driving around town, not cruising at constant speed. Clearly I use considerably more energy/mile at high speed than lower. The "rule" works ok to get a rough estimate, but like I said, I wouldn't base my pack size on it if I planned a lot of highway driving, where many drive at 65 - 70 mph, maybe unreasonable speeds to you.


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