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how to calculate the battery capacity
pratik r. sonawane
November 16, 2021
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To find “battery capacity for electric vehicle”
First, you must need some basic information about motor like how much load you can put on a vehicle
Always remember, in the electric vehicle the weight (kg) is an important aspect.
Because if you want to design a vehicle in such a way that can handle more people on the vehicle rather than accessories then you must care about not taking any extra load on the vehicle except basic components.
So let’s begin our calculation
Before calculation, we need the following parameters
Motor voltage (V)
Motor power rating (W)
Motor peak power rating (W)
motor maximum loading capacity (kg)
On the other hand, your valuable wishes like
Wish #1 How much distance do you want to cover in a single charge?
Wish #2 How much weight do you want to carry with your vehicle?
Wish #3 What will be the speed of the vehicle when the vehicle is “loaded”?
So first you have to put your extra activities aside for the next 15 minutes. It is really a simple calculation.
Let’s do our first calculation
Now you may think, “Is it a hard calculation?” Ha-ha, it’s not.
My work is to explain it deeply and your work is to understand it carefully. Now let’s get back to the topic.
We find our first answer that how much current does the motor need to work at full efficiency. Next, calculate motor peak current rating. Do the same calculation as above.
Now, we got two parameters that will help us to find the battery’s “C rating”. The third parameter will help us to find how much “load current” does require to motor for performance.
To calculate Max. Power to weight ratio, As we know what is the peak power rating of the motor and what is the maximum loading capacity of the motor. Both the parameters are important to know the motor limitations.
Therefore,
Now multiply the max. P/W ratio with how much weight you want to carry with your vehicle (wish #2)
It will show, how much power does the motor consume under load condition.
Now from “motor power under load condition” we can calculate motor “load current”.
If you observe that we have three nature of current,
- Motor rated current
- Motor peak current
- Motor load current
Always remember for Ev’s the basic technical statement is, “Nature of current flowing through the system of the electric vehicle under various circumstances is always show a variation in magnitude during acceleration or deceleration”.
hence to calculate a precise value for battery capacity we have to calculate the “average value”.
The “average current” is equal to require battery capacity, which is obviously a minimum requirement.
For example,
If your vehicle consumes “average current” 18A (battery capacity 18Ah) and you are getting an average speed of 45km/hr.
So theoretically, the vehicle can run only 45 km because it has a battery backup of 1 hour.
Now let’s calculate the battery capacity as per your wishes.
Remember, you have two wishes left!!
Now wish #1: How much distance do you want to cover in a single charge
Example. Say 1000 km!!! Or do you want to ride to the moon? Let’s hope this is not your wish because then you have to make a battery that is bigger than the size of a rocket! ha-ha.
So 1000km is enough for us.
How much distance do you want to cover in a single charge: 1000km
Next wish #3: What will be the speed of the vehicle when the vehicle is “loaded”?
Example 100km/hr and average current 50Ah
Good, this is it!!
You got your answer!
Now, I am sure you understand the calculations. Share it with your friends and family because “Sharing Is Caring”.
calculate your battery capacity by using "battery capacity calculator"
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