# C RATING

C RATING

C rate of the battery is the rate at which the capacity of the battery is charged or discharged to the load. C rating is important in applications which draw high amounts of current.

Maximum Current Draw = Capacity (Ah) x C-Rate

Example, a 3S 2.5Ah 5C LiPo battery pack will draw a maximum safe current of

2500mAh x 5C = 12.5A

Discharging a battery too quickly is not good considering the health of the battery. Due to which internal resistance (IR) will increase than discharging within the battery’s limit.

The battery capacity is generally rated at 1C, which means that the fully charged battery rated at 2Ah must provide 2A for 1 hour. The same battery if rated at 0.5C should provide 1A for 2 hours. Same battery rated at 2C should provide 4A for 30 minutes.

C/10 = C10 = which means C amount of discharge current flowing for 10 hours

C/5 = C5

C/0.5 = C0.5 = 2C

20C = The discharge current the battery is capable of discharging is 20 times C

The higher quality batteries are capable of handling higher charge rates with minimum or no degradation but the lower quality batteries have higher possibility of getting overheat at higher charge rates. It’s always suggested to charge at 1C or follow the recommendations from battery manufacturer regarding high performance and long battery life.

Lets go through some of the mathematical calculations

• Average Battery Current

IB=C/N

IB = Average battery current

C= Capacity in Ah

N= No of hours of discharge

Example:

For 10Ah of battery and 10hours of discharge

IB=30Ah/10h = 3A

It means that 30Ah of battery is capable of supplying 3Ah of average current to the load up-to 10hours. Though due to losses 30Ah battery can supply 3A average current for less than 10 hours.

• Continuous Discharge

2500mah battery with 5C rating

Continuous Discharge Amperage = (mAh/1000) x C Rate)

= (2500 /1000) x5=12.5A

• Run Time for Safe Continuous Discharge

2500mah battery with 5C rating

Run Time = (60min/C-Rate) = (60min/5) = 12min

Therefore, Discharge 25A for 12min

C rating of a battery is very important factor as the energy stored in a battery is dependent on the speed of charging and discharging current.