How to choose battery?


#1

While I wait for parts of my quadcopter to turn up I have been looking at its power source and need some help with the batteries.

The motors, EMAX MT2213, can run with 3-4S battery packs. Playing with the calculator on eCalc.ch I am not sure what to go for. As it stands using a 3S pack would give me 6 mins flight and 11 hover. But if I add another battery I would get an increase in flight time (practically double) but to hover the throttle is an estimated 71%. Worse if I go to 4S as the current in flight goes over the rated Max of the motors.

I admit I am having to make assumptions about the craft (weight being one of them but calculated from the data I can find about the parts) and it is possible I am using the calculator all wrong. It has left me confused as to what to do. Basically I would like about 15 mins flight time overall.

Can I call on the more experienced guys to point me in the right direction?


#2

No expert but if you go to 4s then you may need to change prop size to get within motor current rating and efficiency.

I have had similar questions myself, where according to ecalc I get say 8 mins with one battery, but only 11 minutes with two - if that is the case then I would just land and swap batteries because I have no means to charge at the field so the batteries I take is my flying time limit.


#3

Your right about the prop, it would have to go down to an 8" which would mean hover is using a very large throttle. Like you I guess I will have to have two batteries and just swap out when power gets low!

I am planning on getting a charger that can run off of a car so at least I can, in some cases, recharge if needed.


#4

unfortunately no car, so unless I drag a car battery with me (not happening) I am stuck with the batteries I have. I have 6 x 3s 4ah I think so about an hours flight which is actually a lot longer that it seems - The most I have used with the iris in a single session was 4 batteries, and when I used to fly IC planes I don’t think I ever had more that 6 x 15 minute flights in a day at the field.


#5

You may need to look at alternative motors so you can swing a bigger prop - the larger the prop the more efficient it is.

Unfortunately the larger the prop the more vibration so more jelly video likely, I went with the 880kv motors and 12" props for my hex build. I think that should theoretically give me enough lift to take over 2kg of payload with a 75% hover but of course that would drop flight times to something insanely short.


#6

For now I’ll stick with my current plans as they should work. Later I’ll look at upgrading.

Maybe you could make a small pull-a-long truck for a car battery… :smiley: lol Really though your right, easier to have several batteries to use.


#7

In general the difference between 3S battery, and 4S battery will largely depend on your motors, but for MT2213 I think you will get better flight times with 3S battery. Many posts on the internet seem to suggest 4S = longer flight automatically which is not always true.

For longer flight times as loise suggested, the bigger the propeller the more efficient it is, thats why most quadcopters with long endurance have very low KV motors driving large props. A slow spinning prop is much more efficient than a fast one.due to air turbulence.

So for your motors with 10inch props I would suggest that you go for the biggest 3S battery you can comfortably lift (you should be able to hover at less than 75% throttle, ideally 50%)

Also I just posted a video that talks about choosing the best motors/props/ESC for your quad.


#8

I managed to use a 4s battery with those motors and use the supplied props (even went to 12" at one point), however they got very hot, hotter than I could touch, it was risky but oh well they still work. :smiley: My only gripe about these motors is that you should use loctite with them (for the props) and check the prop nut regularly.