Batteries

Hobby King Zippy 11.1v 30C 3000mAh LiPo Battery

LiPo batteries (short for “Lithium Polymer”) are the latest and greatest when it comes to battery technology.  When considering power to weight ratio, LiPos are far superior compared to NiCad (Nickel-Cadmium) or NiMH (Nickel-Metal Hydride) batteries.

There are several options when choosing a LiPo battery.  The first is the voltage level that the propulsion system runs at.  A single cell LiPo battery outputs 3.7 volts.  To increase the overall voltage, LiPo cells are connected in serial.  Connecting the LiPo cells in serial, cumulatively adds to the overall voltage.  For example, two 3.7 volt LiPo cells will output 7.4 volts and a three LiPo cells will output 11.1 volts and so on.  For Scout, the motors and Electronic Speed Controllers that I have chosen run at 11.1 volts and so I chose 11.1 volt battery.

The second option is capacity.  Capacity is how much power the battery can hold measured in milliamp hours (mAh).  For example, a LiPo battery rated at 1000 mAh will discharge in one hour with a 1000 milliamp load placed on it.  If the same battery had a 4000 milliamp load placed on it, the battery will discharge in 15 minutes.  The higher the capacity of a battery, the longer the flight time, but also the bigger and heavier the battery will be.

The third option is discharge rate.  Discharge rate is how many amps can be discharged at a time.  The discharge rate is multiple of the total capacity of the battery and represented as the “C” rating.  For example, a battery with a capacity of 2000 mAh and a discharge rate of 10C is capable of withstanding 20,000 milliamp or 20 amp loads.

 

Battery Charger

LiPo charger needs to be capable of charging a 3-cell battery.  A battery charger capable of balance charging the battery is also recommended.  Balance charging reads the voltage of the individual cells of the battery and charges each cell equally to the other cells.   This feature will increase charging time but will prolong the life of the battery and provide slighter longer flight times.

 

Calculate Flight Time of LiPo Battery

Before we can calculate flight time, we need to know the average amperage the quadcopter will draw.  Once we have the average amperage draw we can then calculate flight.

To calculate flight time, take the battery’s capacity in amp hours, then divide that into the average amp draw of the quadcopter and then multiply it by 60.  The total is the flight time in minutes.

For Scout, I chose a 11.1 volt 30C 3000 mAh LiPo battery.  I calculated the average amp draw of Scout to be around 20 amps.  This will give me a flight time of 9 minutes.

Flight Time Calculator

Battery Capacity: mAh
Average Amp Draw: A
Flight Time: Minutes

Connectors

Power connectors come in various of shapes and sizes.   Choosing a power connector is dictated by power requirements and compatibility.   The most common power connectors are XT-60, Deans Ultra Plugs and EC3 and EC5 Bullet Connectors.

I use the Deans Ultra connectors but I found they can lose contact when fully plugged in.  This is an inherent design flaw with the T type connector.  I would choose the XT-60 connector if I was not so invested in the Deans connector.  I favor the XT-60 because they are easier to solder and connect and disconnect with ease.