# Knowing the battery size



## dtbaker (Jan 5, 2008)

otmezger said:


> My question is: Do you think, knowing the size of the battery will save you money for your DIY conversion?


I really don't think it requires an app.... its pretty simple. The problem is that most people don't know how many miles they drive per day, and/or are unwilling to live within a reasonable limit (to control the cost of the build).

I think what we are seeing in our group is pretty great data for small cars, and small trucks with 50/75/100 mile range being realistic, but hardly any DIY has done large SUVs or large trucks.... which may be better suited for bio-diesel anyway.


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## piotrsko (Dec 9, 2007)

if you are asking what physical size the battery array needs to be, then: no it won't matter to me. I have a space that is 2 meters by 2.5 meters by almost 1 meter high.

if you are asking how many Ampere hours needs to be for this commute, then YES, put that into the app.


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## Ziggythewiz (May 16, 2010)

dtbaker said:


> I really don't think it requires an app


I'd have to agree; the only difficulty involved is knowing the weight and aerodynamic characteristics of your donor, so unless the app includes all that it can't help much. 

Not everything in the world needs an app; if you can't plug a few numbers into a relatively simple formula you probably shouldn't be building an electric car.


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## tomofreno (Mar 3, 2009)

From the link you gave, it seems you are creating an app to predict vehicle range for different battery packs. There are some "ev calculators" around that estimate expected range as a function of vehicle speed by estimating rolling resistance force, drag force, and some rough estimate of things like frictional losses and inertia of rotating parts. They also account for the efficiency of the motor and motor controller. Equations for these can be found, for example, in "Build Your Own Electric Vehicle" by Bob Brant. Of course the actual range a person gets depends on what kind of roads they drive on (highway, city, secondary roads) at what speeds, which may vary considerably from day to day. Maybe the app could give estimated ranges based on "what ifs" for various combinations of driving conditions. That would be very useful to a person trying to decide if an ev will meet most of their driving needs, or a person who just purchased an ev and is trying to calibrate themselves to how far they can drive under different conditions. The EPA estimates are of course an example of this, but it would be more useful if the person could input their expected conditions to get an estimate.


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## WaWa (Oct 8, 2012)

Hi there,

The only straight answer I can give you is: 15 kWh for 65 miles in EV at highway speeds. For example 78 LifePo4 60 Ah batteries for 250 V.
It is a late answer, but I am new to this site. Maybe it is a death threat?
Kind regards, ||| Walter


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