Battery sizing in an electric vehicle

  • Thread starter Vibhav
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i am working on a developemnt of electric vehicle as my final year project..i have calculated the max. power required by 800 kg vehicle is 30 kw..
so i am using 30 kw 3 phase AC induction motor..
now can you please help me out in sizing my battery pack..

weight : 800kg
max. velocity : 80 km/h
range : 100 km


Insights Author
Gold Member

The simplest calculation ignores efficiency and use data. Just multiply power times time. 30 kw for one hour means a 30 kwh battery. So how many hours do you need? The hours of use, or the distance range are requirements. One of the first things to learn in your project is that nothing can be designed without first defining the requirements.

What was the requirement that led you to the 30kw number for the motor?

The next step, is to recognize that the vehicle is not driven at maximum power all the time. (Think of a conventional auto. You do not (or should not) drive with the gas pedal all the way to the floor all the time.) So, 30 kw is the maximum power, what is your estimate for the average power? Multiply that by hours to get a better estimate of battery capacity.

Then, make a guess about efficiency. Perhaps 80% is a good number. Divide the battery capacity estimate by 0.8.

These answers are very general. You must provide numbers for averages and efficiency for your own project. Ask your project adviser what proof you need that those numbers are correct.


Science Advisor
Homework Helper
Gold Member

Governments specify the test conditions/driving profile under which range is assessed. I know its different for Europe and the USA because the range quoted for the Nissan Leaf is quite a bit different in different jurisdictions.

So ideally you need to work out how the weight of the car affects the energy used while driving to one of these standards. Although I'm not sure how easy that is to calculate.
I've never built an electric vehicle, but I've thought about it occasionally, and I've spent some time browsing this forum that I thing is good.


Gold Member
weight : 800kg
max. velocity : 80 km/h
range : 100 km
You are making a vehicle that weighs almost 1 ton and you want it to go 50 mph?

in comparison here are the approximate specs for the 2017 nissan leaf...
motor: 80 KW
Weight: 1500 kg
Battery: 30 kWh
range: 160 km
max speed: 150 km/hr

Your car will be about 1/2 the weight, with 38% the motor strength, which is fine. Its just a note of the scale of your project

This is quite the project. I hope you are doing this with a team, because it will be a lot of work.
What are you using for a motor. Do you plan on using a high voltage battery? Low voltage will increase your current and could cause heating problems in cabling and the battery. High voltage will cause a bunch of other problems as well, as well as special considerations in designing it.

To give you perspective if you use a 600V nominal battery pack, you'll expect about 50 Amps of current at peak load. You will need to size your cables for this

What type of controller do you plan on buying/making?

Keep us posted on your progress!!!!
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