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how to calculate the range of electric vehicles?
pratik r. sonawane
april 22, 2021
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the range of electric vehicles is difficult to find but not so difficult to predict.
yes, we can predict the range of electric vehicles but for that, we need to consider lots of stuff, like how much load is on the vehicle, battery capacity, motor wattage, power to weight ratio, and many more.
In this article, we will solve the problem of finding the range of electric vehicles but we are not considering losses during the run
like rolling resistance, friction, aerodynamics.
what we are going to calculate will provide an answer, which is closer to the actual answer.
first,
why it is so much difficult to find out the range of the electric vehicle.
the answer is pretty much simple but a little bit unsatisfied. which is related to the one term. “A variable current consumption”
you know in electric vehicles, the nature of current flowing through a system is different. it shows variable characteristics.
why?
because in the case of motor the load is variable hence as a result “current consumption” also shows variation in magnitude.
the motors, which are used in electric vehicle applications goes under various conditions like climbing, acceleration, deceleration, braking, and so on.
this kind of situation produces different kinds of results. which will affects motor “current demand”.
now in the case of the battery,
for example:
the capacity of the battery is 10Ah and the load current demand is 1 Ampere then we have to calculate how much time does battery is required to drain completely?
the question is easy to answer because the battery is draining a constant current or steady current
the answer is 10 hours or 600 minutes. right!!
formulae :
but as we discussed the current demand for electric vehicles is variable in nature hence it becomes complicated to calculate the exact kilometer or mile range of the Ev’s.
therefore, we have to calculate motor current demand at various conditions.
types of “current demand” in electric motors:
- rated current rating
- peak current rating
- load current rating
note: please be sure before doing a calculation you must have all datasheets and specifications for motor and battery.
now let’s start our calculation with an example,
calculate the rated current demand for the motor.
ex. motor voltage: 60V
motor wattage: 1000W
the motor rated current is 16.66A.
now, calculate peak current demand for motor
as given,
motor voltage: 60
peak motor power: 1500W
motor peak current demand is 25A.
thereafter, we need to calculate the load current which will tell us motor current demand when the load is applied on it.
(assume, the load is vehicle plus driving person and luggage weight)
now, calculate the power to weight ratio requirement.
ex.
motor maximum loading capacity: 350 kg
peak power: 1500W
from calculation power to weight ratio : 4.28 W/Kg
consider,
the bike load (including all-electric accessories) is 150 kg and Mr. Musk is driving it and you know Mr. musk is a healthy person so maybe his weight is around 75kg. suppose Mr. musk doesn’t know how many miles his car can cover! therefore, let’s help him to find out the range of his vehicle.
so the total weight of the vehicle will be 230 kg.
to find motor power consumption during load,
multiply P/W ratio with vehicle total weight.
power consumption under load condition is 984.9 Watt. now we need to find out the current demand under load condition as given,
motor voltage: 60V
motor wattage: 984.9W
from the calculation,
the current demand under load condition is 16.40A
did you notice we got three nature of current?
- rated current
- peak current
- load current
these three natures of current are nothing but a result that came from different situations or circumstances.
“rated current” is flowing through a system when the motor is working under its full efficiency.
“peak current” is flowing through a system when the motor is under acceleration or initial pick-up.
“load current” is flowing through a system when the motor is working under load conditions.
now, we have to find the value of the average current.
average current demand will be 19.35A
this is it!
the above answer can help us to understand the nominal current demand for vehicles.
this is an average current demand for electric vehicle motors.
let’s assume you design a Lithium-ion battery pack of 60 volts with a capacity of 100Ah.
Also, read | How To Calculate Battery capacity for an electric vehicle.
divide that batter capacity by average current demand.
hence battery backup will be 5.17 hours.
consider, your electric vehicle average speed is 45 km/h
then the range of the vehicle will be 232.65 kilometers or 144.78 miles!!
but this is not an exact answer. during the run, there is an instantaneous rate of change of current consumption. hence 233 ± 10 kilometers (145 ± 6.21 miles) is always better to assume.
this is one of the ways we can find out the range of the electric vehicle. hopefully, you found your answer in the article.
Note: the range of the electric vehicle may vary with surrounding situations or circumstances.
calculate your range of the vehicle by using "range calculator"
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