When you plan to build a mini quadcopter, how do you choose your battery voltage? 3S lipo battery or 4S lipo battery? Maybe for newbie, you don’t know the difference between 3s an 4s lipo, even though you may don’t know what’s the mean of 3S lipo and 4S lipo (you can read these articles: RC Lipo battery knowledge or The analysis of lipo battery parameters); so I wrote this article to tell you the difference between 3S and 4S for mini quadcopter.
It’s kind of obvious, the main difference is voltage that powers the motors. In my experience with cobra motors, the speed of my quad goes up a lot because of the extra 1S.
Let’s say we have a 2300KV motor, when powered under 3S lipo (12.6V), RPM (rotation per minute) is 2300 x 12.6 = 28900 (in theory). That means the motor spins 28,900 times a minute with no load. When you power the same motor with 4S lipo (16.4V), the RPM is 2300 x 16.4 = 37720, a huge increase in RPM.
Increase in RPM means more thrust, more power, and your quadcopter flies faster. However, the relationship of motor thrust and voltage is not linear due to efficiency loss. Some motors perform well in 3S, but not as good as expected in 4S where most energy just transforms into heat. Apart from thrust, we also need to consider other aspects such as torque, current draw etc. The easiest way to determine if your motor is suitable for 4S is to search for thrust data table, or test it yourself. Some motors rated for 3S simply cannot run on 4S, where the high voltage/current could damage and burn the wires.
Some might ask if a 3S quadcopter can out perform a 4S quad, the answer is definitely yes. Many factors come into play that can determine the speed of a quadcopter: combination of motors and propellers, weight, etc. But under the same condition, a multirotor that runs on higher cell count battery should have more power thus faster.
Also note that 4S setup are usually a little heavier than 3S, because of the additional weight of the voltage regulator, and heavier batteries. Like many high capacity batteries are all heavier than low capacity batteries.
Have you knew the difference between 3S lipo and 4S lipo?