Project 4
Battery pack capacity calculation for
EVs as per our required range.
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Battery pack is the motive source in electric vehicles. Designing of
battery pack is one the important section in EV Designing and battery
pack calculation depends on several factors. Normally range of the
vehicle and Motor specfications directly influences the battery pack
capacity.
In this we can get an idea of how to Design/ Calculate battery
pack for EV as per your range requirementFor battery pack capacityBefore designing a battery pack, Let's look the basic parameters of
battery.
Cell voltage - potential difference between the cell terminals. It is
differentiated into Max voltage, Min voltage and Nominal voltage.
Usually nominal voltage is taken for calculation and design as it is
mid range between maximum and minimum voltage.
Amp hour rating - Amp hour rating of a cell/battery is how much
amperage a battery/cell can provide for exactly one hour. The
C rating tells you how many amp hours the battery/cell can provide
for a very specific period of time.
C rate - Charging and Discharging rate of cell/battery. Usually it is
the rating of the battery capacity. If 100 Ah battery pack has c rate
1C, meaning that a fully charged battery rated at 100 Ah should
provide 100 A for one hour. Same battery discharging at 2C, it
delivers 200 A for 30 minutes.
Let's consider, we are using a BLDC motor, it draws different amount of
current from the battery depending on the speed. Factors we need to
consider while designing a battery
Given- Vehicle weight=300kg
Motor Rating= 1200w,65v
Range=225km
Max speed= 60kmph
First we have to calculate Motor Current
P= V*I
1200=65*I
I=18.46A
Current withdrawm by Motor 18..46amp
Assure current loss 1-10%
After loss new motor current 18.46*1.05=19.38amp
Now calculate the power required at max speed
At 60kmph power = voltage*current;Power=65*19.38; power=1260w
Then we have to calculate travel factor
Travel factor = Total Range/Total speed'Travel factor=225/60=3.75
To calculate power based on power factor
Power required = Power*Travel factor;power required =1260*3.75=4.7kw
Then we have to calculate Battery pac capacity based of efficiency
we take battery efficiency85-95%
we take 90%
Required battery pck capacity=4.7/0.9=5.23kw
Then we calculate battery pack efficency based on motor efficiency
Total Battery pack efficiency= 5.23/0.9=5.812kwh
Now we have find how muh connection comes in series and parallel
Series connection
Motor Voltage= 65v
Cell Voltage = 3.7v
no of series cells= 65/3.7=18
18 cells in series
Parallel connection
Motor current = 19.38A
cell current=2.8A
No of parallel cells 19.38/2.8=7
7 cells in parallel
calculation part done
Now we see how to developed battery pack
First we have to select cells types then size of cells