Drone LiPo Battery Calculations


It can be difficult to find the right battery for your drone. There are so many things to take in account for such as voltage supplied,

LiPo batteries can have multiple cells. Usually, the one cells delivers approximately 3.7 Volts. The number of cells in a battery is denoted by the “S” letter. A 4S LiPo Battery has 4 cells therefore delivers a 14.8 V.

The battery capacity is the next important LiPo battery characteristic. It is denoted on the LiPo battery as “mAh“. mAh stands for milli-Ampere per hour. A 2000mAh LiPo can deliver 2 Ampere ( 2000mA/1000 = 2A ) for 1 hour or 2mA for 1000 hours.

Lastly, discharge rating is denoted on the LiPo battery as “C“. Some batteries have two discharge rates: nominal discharge and burst discharge rate. It is recommended to stay on or below the nominal discharge level to preserve battery life. For more information, check battery supplier for max peak discharge rate.

LiPo Voltage Supply Calculations

Based on what PDB (power distribution board) and ESCs (electronic speed controller) you use for your drone, there will be a suggested voltage supply rating for each of these components. In the “Drone Build From Amazon”, the PDB voltage supply rating is between 2S – 6S, and the ESCs voltage suppy rating is between 2S – 4S. Since the ESCs get power from the PDB, the max voltage supply should come from a 4S LiPo battery. The calculation for the how much voltage a LiPo supplies is the following:

( # of cells ) x ( 3.7 Volts) = Voltage Supply

LiPo Max Current Discharge Rate Calculations

In combination with battery capacity and the discharge rate, we can determine the max current discharge rate can handle. Like before, we only going to use the nominal discharge rating on the battery. It will set the maximum current continuous discharge rate of the LiPo battery. The calculation of the max current discharge rate looks like this:

( Capacity/1000 ) x ( Discharge Rating  ) = Max. Current Continuous Discharge Rate

Max Flying Time from LiPo

This calculation takes in consideration of the current draw from the motors, ESCs, receiver, video transmitter, etc. of the drone. The current draw also depends on the way you fly and external factors such as weight, resistance and wind. However, always use a LiPo low battery warner on your RC device to get a more accurate reading. The approximate amount of minutes you should fly your drone is done by the following calculation:

[( Capacity/1000 ) / ( Current Draw )] x 60 = Approx. Max. Fly Time

Drone Power Consumption Calculations

The current drawn from the drone’s system depends on the components. The ESC has a continuous current draw of 20 A but has a burst rate 25 A. There are 4 ESCs on a drone. Receiver has a current draw of 30 mA. Flight controller has a current draw of 100 mA. The total current draw from the drone’s system is 86 A. That calculation looks like this:

( 20 + 20 + 20 + 20 + 0.03 + 0.1) A = 80.13 A

Thus, the battery brought for the “Drone Build From Amazon” is a 3S 2300mAh 45C LiPo battery. The battery needs to compensate for the current draw by the drone’s system. The battery is able to be continuous discharge at 103.5 A. The calculations should look like this:

( 2300mAh / 1000 ) x ( 45 C ) = 103.5 A

It is a good rule of thumb the battery max current discharge rate should be greater than current drawn from the drone’s system. That comparison solution should look like this:

Max. Current Continuous Discharge Rate > Current Draw 

If we were to use the burst rate current, the current draw would be 100.13 A. In this scenario, the LiPo battery would be able to handle the current draw. This will give you the extra power at the high end. If you do reach that amount of max. current discharge rate, you should get other ESCs that draw less current or buy propellers that reduce motor’s current draw on the system.

Conclusion

We have used formulas to determine the right LiPo battery for our drone. By calculating parameters like Current Draw, Max. Current Continuous Discharge Rate, and  Approx. Max. Flying Time, we can determine number of cells, discharge rate and battery capacity we will need from our drone.

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