Rough Idea of Expected Range

9172 Views 18 Replies 9 Participants Last post by O'Zeeke, May 17, 2008

O'Zeeke

Discussion Starter · May 14, 2008

I think I read this in one of Electro Automotive's publications, its a way to get a rough idea of your EV's expected range.

Multiply your vehicles actual GAS mileage by the weight of your battery pack. For my Mustang it's 20mpg(if I drive it nice) x 1152 = 23040

Divide that # by 420 for carburated cars and 450 for fuel injection
23040/450 = 51 miles. That works for me.

This takes into account traffic, terrain, chassis weight and driving style so it supposed to be fairly accurate.

I haven't got mine on the road yet (almost) so we will see how it compares when I do.

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Qer

· #2 · May 14, 2008

Nice formula, but two questions:

1. The weight is in what? As a Europe I'd expect kg, but it's lbs or something like that, right?
2. We're talking wet led now, or is it applicable on gel-batteries too?

O'Zeeke

Discussion Starter · #3 · May 14, 2008

Qer said:
Nice formula, but two questions:

1. The weight is in what? As a Europe I'd expect kg, but it's lbs or something like that, right?
2. We're talking wet led now, or is it applicable on gel-batteries too?

Weight is Lbs. and I believe it refers to flooded lead/acid but if someone has gel in their EV let us know

Qer

· #4 · May 14, 2008

Hmm. That'd mean I would only have a range of depressingly low 50 km (a little more than 30 miles) both with the S-10 and Opel Calibra (the higher max load on the S-10 is pretty much evened out by the lower mpg) if I want to bring a passenger and some food from the grocery store without hauling more than legal. That's not much.

I wonder if that can be because of tax reasons? In Sweden you pay car tax depending on the weight of the car, so maybe they've registered a too low total weight on the car to lower that cost. I better investigate if it'd be possible to raise the numbers...

TheSGC

· #5 · May 14, 2008

Those numbers sound pretty accurate to me. I just used it to estimate my range, and if I am nice to it I would get 40 miles, and if I drive it like NASCAR I would get 32 miles. Not bad, and almost dead on to my other calculations.

1996 Civic LX- 38 MPG if I am nice, 30 MPG if I have the need for speed.
And I am using a rather small 480 LBs of flooded lead and I have no plans to drive freeway once its an EV.

O'Zeeke

Discussion Starter · #6 · May 14, 2008

Hi SGC, what voltage and batteries are you using?

kixGas

· #7 · May 14, 2008

What does the gas mileage of your car with an ICE have to do with it? That is meaningless. If I had a V8 that got 10 mpg then I swapped in a 4 cylinder and got 22 mpg then I did a EV conversion I instantly increase my range according to that calculation.
Or is this intended to be one of those unsubstantiated conclusions like how as the populations of Pirates have decreased since 1800 the frequency of natural disasters and effects of global warming have increased?

TheSGC

· #8 · May 14, 2008

kixGas said:
What does the gas mileage of your car with an ICE have to do with it? That is meaningless. If I had a V8 that got 10 mpg then I swapped in a 4 cylinder and got 22 mpg then I did a EV conversion I instantly increase my range according to that calculation.
Or is this intended to be one of those unsubstantiated conclusions like how as the populations of Pirates have decreased since 1800 the frequency of natural disasters and effects of global warming have increased?

Actually, I think it has to do more with aerodynamics than engine size. I can't pluck my 4 cyl Civic engine in a F150 and expect to still get 30-38 MPG, hell it probably couldn't even drive the thing. Of course it won't be perfect, there is absolutely no way to calculate the true range because every conversion is different, everyone drivers differently and terrain is always different.

I have compared this to some cars on the EV Album, voltage range 72 to 120, flooded batteries in the 12 volt variety and they are very close.
I am going to be using a 96 volt system using 12 volt 125 Ah batteries.

kixGas

· #9 · May 14, 2008

That is my point. The calculation uses a variable that has nothing to do with it. For example, a Camry can come in a 4 cyl or a V6- both have different MPG yet the body and rolling chassis is the same. If you converted a 4 cyl Camry and a 6cyl Camry to an EV, and all else being the same, you should expect similar performance in each. Similar comparisons can be made with a Mustang, Charger, GTI, any Jeep etc etc. Might as well throw in there your cholesterol level as a variable in the calculation.
Cd is a major contributor. I thought I saw a formula somewhere that uses Cd as a variable.

Fatboy

· #10 · May 14, 2008

I've got to agree that this formula is a little shady. There's just too many variables involved to just pick one or two and come up with an answer.

FatBoy

T3Tech

· #11 · May 14, 2008

I would still say that using the EV Calculator would give one a better idea on expected range. There's too many variables unaccounted for in simply comparing the MPG of an ICE to battery weight to arrive at a reliable range estimate me thinks.

It may be ok for a *very* rough guess, like saying that the ball will most likely land somewhere in the ballfield for any given batter but it may go over the fence or into the stands - it's not necessarily going to be down the third base line.

X1/9jm

· #12 · May 15, 2008

On the calculator, when they list 'inital curb weight' for the vehilce, is that before the motor and batteries are installed or the completed EV?

O'Zeeke

Discussion Starter · #13 · May 15, 2008 (Edited)

kixGas said:
What does the gas mileage of your car with an ICE have to do with it? That is meaningless. If I had a V8 that got 10 mpg then I swapped in a 4 cylinder and got 22 mpg then I did a EV conversion I instantly increase my range according to that calculation.
Or is this intended to be one of those unsubstantiated conclusions like how as the populations of Pirates have decreased since 1800 the frequency of natural disasters and effects of global warming have increased?

Pirates? What the hell do pirates have to do with energy consumption and range estimates that we are discussing here?
I didn't come up with the formula so don't shoot the messenger. However, in defense of the formula, the gas mileage is used only as a value for energy consumed by that vehicle, unique to it's driver habits, gear ratios, weight, aerodynamics, etc compared to the energy value by weight of lead. A 10 mpg Hummer wont get 22 mpg with a 4 cyl, much less even move it unless you got rid of more than half the weight. As it says, its a "rough " estimate, and most EV'ers using flooded lead that I know have confirmed that it is fairly accurate, as The SGC has concurred previousely in this thread. Why don't we keep the discussion to EV's and forgo the superflous mention of pirates, natural disasters, etc.

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T3Tech

· #14 · May 15, 2008

X1/9jm said:
On the calculator, when they list 'inital curb weight' for the vehilce, is that before the motor and batteries are installed or the completed EV?

That would be the initial curb weight of the vehicle in it's pre-conversion state.
The weight of the ICE components is estimated (though an actual figure, if known, could be plugged in IIRC) and subtracted while the weights of motor, batteries, etc. are added back in based on selection to arrive at the vehicle weight used in the final calculations. As I recall, all the variables can be manually edited from the defaults provided under the detail drop downs.

MrCrabs

· #15 · May 15, 2008 (Edited)

It looks like formula is based of comparing the energy density of Gasoline to Lead Acid batteries....

gasoline ~ 45 Mega Joules / kg
Pb A ~ .1 Mega Joules / kg.

45/.1 = 450.... where do we see the number

This seems like a rule of thumb estimate for Lead Acid batteries.
Another rule of thumb estimate I have seen is that for each % of total weight that is made up of batteries, you get 2 miles of range.
Range = Battery weight/total weight * 100 * 2

Here are some numbers for my planned conversion. For the sake of argument lets say I can get down to a 2000 lb vehicle without the batteries.

Code:

Total    Battery        MPG        percent        mpg
Weight  Weight                estimate    estimate
2500     500         28         40             31
3000     1000         28         67             62
3500     1500         28         86             93
2500     500         22         40             24
3000     1000         22         67             49
3500     1500         22         86             73

I like the way this formula takes driving style into account, but is really only useful as a rule of thumb when looking at doner car choices.

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O'Zeeke

Discussion Starter · #16 · May 15, 2008 (Edited)

Thank you Mr Crabbs for clearly pointing out the energy relationship between gasoline and Pb/A

kixGas

· #17 · May 16, 2008

O'Zeeke said:
Pirates? What the hell do pirates have to do with energy consumption and range estimates that we are discussing here?
I didn't come up with the formula so don't shoot the messenger. However, in defense of the formula, the gas mileage is used only as a value for energy consumed by that vehicle, unique to it's driver habits, gear ratios, weight, aerodynamics, etc compared to the energy value by weight of lead. A 10 mpg Hummer wont get 22 mpg with a 4 cyl, much less even move it unless you got rid of more than half the weight. As it says, its a "rough " estimate, and most EV'ers using flooded lead that I know have confirmed that it is fairly accurate, as The SGC has concurred previousely in this thread. Why don't we keep the discussion to EV's and forgo the superflous mention of pirates, natural disasters, etc.

I guess I lost you- my point was that using gas mileage as a variable in calculating the range of an EV is stretch. So many factors play into was the gas mileage of a car such as displacement, fuel type, timing, driving habits, design of the car, how well tuned it is, forced induction etc. When the ICE comes out of the car you are left with essentially the coefficient of drag and driving habits as remaining factors to your range.
I am not talking about putting a 4 cylinder in a hummer to get 22 mpg. But take my wife's daily driver for example (Grand Cherokee). Depending on what engine you choose from the factory whether it is a 3.7l V6 or the 6.1L V8 your mpg range will vary from 11-20 mpg. Similar comparisons can be made with other cars which have different engine options. But when it comes down to the range of a converted EV the coefficient of drag and driving habits are remaining factors to your range.

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helixev

· #18 · May 16, 2008

Doing it backwards for my toyota pickup

(based on my range)

7mpg * 1365 (battery pack weight in lbs)
equals - 9555

9555 / 450 (engine was fuel injected v6)
equals - 21.233333333333333 (my range if I drive nice)

O'Zeeke

Discussion Starter · #19 · May 17, 2008 (Edited)

kixGas said:
I guess I lost you- my point was that using gas mileage as a variable in calculating the range of an EV is stretch. So many factors play into was the gas mileage of a car such as displacement, fuel type, timing, driving habits, design of the car, how well tuned it is, forced induction etc. When the ICE comes out of the car you are left with essentially the coefficient of drag and driving habits as remaining factors to your range.
I am not talking about putting a 4 cylinder in a hummer to get 22 mpg. But take my wife's daily driver for example (Grand Cherokee). Depending on what engine you choose from the factory whether it is a 3.7l V6 or the 6.1L V8 your mpg range will vary from 11-20 mpg. Similar comparisons can be made with other cars which have different engine options. But when it comes down to the range of a converted EV the coefficient of drag and driving habits are remaining factors to your range.

The point is:
1) is that most people do a combination highway and city driving, and you want your average mpg. Using your Grand Cherokee as an example http://db.theautochannel.com/db/new...=2008-Jeep-Grand-Cherokee-Laredo-4X2&id=23617 you will see that the 3.7L combined mileage is 17 (14 city -19 hwy)
the Hemi V8 combined is 15 mpg(13city -18 hwy)
There is a difference if all you drive is city with the Hemi and Hwy with the 3.7L (5mpg) but for the average driving the difference is only 2mpg
2) that this combined mpg number is used to derive an energy value in megaJoules/ weight of gasoline which reflects all the variables from your type of driving (city, hwy) aerodynamics, weight, style of driving, terrain, gear ratios etc. of what THAT car currently gets, and compares that number to the megaJoule/weight of lead/acid. That is why mpg of your ICE has EVERYTHING to do with this, all the variables have been averaged out for you by that mpg value.
3) that this as I have said is a "rough" estimate, based on a formula from the 1990's from Electro Auto using Pb/a, DC, and probably assuming you will drive your EV pretty much the same as you did as ICE

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