I often see people saying they are going to run a certain battery but the battery they are saying is undersized or way over size for their aircraft or requirement so I figured I would post up an article to show you how to properly. In this article we are focusing on miniquad motors and requirements but the formulas are the same for larger quads and hex copters.
So lets break this down.. I will use the Airbot Micro Titan 2204 2300kva motor in this example because I know the specs and has done my own testing so I know what they actually are pulling.
I always base my battery requirements based off the maximum power that the motor can pull since this would be worst case. (or best depending on how you fly)
Airbot’s pull a maximum of 12 amps on 3S batteries with 5×3 props. So we take the amperage that they pull and times that by the number of motors on your quad or hex. I run a quad so it would be times four.
12(amps)x4(motors)=48amps(max load amperage)
So we have a max load of 48 amps at any given time. So we need to get a battery that is at least capable of providing 48 amps of power.
So lets find the correct battery.. 1300mah, 1500mah and 1800mah batteries seem to be the sweet spot for miniquad batteries so we will use these in our example.
First convert the milliamps per hour to amps per hour. All you do to do that is move the decimal point. a 1500mah is 1.5 amps per hour, 1800mah is 1.8, etc.
So we take our max amperage requirement and divide it by the amps per hour the battery can provide and this will give us our needed C rating.
So that shows us that we need a minimum of 32C for a 1500mah battery to operate properly and not voltage sag our battery due to pulling too much current. I usually round this number up to the next highest C rating so that I know I have a bit of reserve if needed. So in this case we would go with a 35C rated battery.
Here are a few more based off of the three most popular sizes.
48(amps)/1.3(amps/h)=36(minimum required C rating)
48(amps)/1.5(amps/h)=32(minimum required C rating)
48(amps)/1.8(amps/h)=26(minimum required C rating)
As you can see the lower mah batteries require a higher C rating to be able to provide the power required due to the lower sized battery.
I hope this helps someone in choosing the correct battery for their build. This will be posted on ModifiedRC.com also if you want to link back to it.