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3S 11.1V 2100mAh LiPo Questions

#1
I use Venom 3S 11.1V 2100mAh 20C LiPo batteries in 3 of my planes. I want more power/speed and I am confused to what would give me that. In my the planes there are 2 40 Amp ESCs, and a 30 Amp ESC. I have thought about buying a 4S version of the same battery (4S 14.8V 2100mAh 20C), would this give me the added power or would I need to get a higher mAh or C rating? I am just unsure what would give me more power without hurting the ESC. Any help or clarification would be awesome!! Thanks.

Payton
 

Christopher14

Driftin' with the wind...
#2
If you want to run a 4s battery you will first have to look at the ESC and see if it is rated for 4s. If isn't you will need a ESC that is rated for 4s, then you will need a smaller prop, if you stay with the prop you have and use 4s the motor will get hot due to the increased amp draw. The way to determine the correct prop is this:

First get the ratio of voltage change, in your case it is 3s to 4s, so divide 4 by 3 and you get 1.33333333.

Now to get the prop loading, diameter times the diameter of the prop times the pitch of the prop. So for an example lets say the prop your plane is using is a 10x5, So 10 x 10 x 5 = 500.

Now you divide 500 by 1.33333333 and you get 375.0000009375. Lets just round it down to 375 shall we.

Now you know that the prop you can run safely is a prop with a prop loading of 375 or below, in this case a 9x4 would be good choice. it has a prop loading of 324.

Hope this helps! If you have any more questions just ask away!
 

joshuabardwell

Senior Member
Mentor
#3
If paytonC11 wants to invest a little money in an eCalc.ch login, he can check out different scenarios with more granularity. For example, I fly a SunnySky 2212 kv980 motor on my quad, on 3S, with a 10x4.7 prop. For that combination, eCalc predicts 923 grams of static thrust, pulling 14 amps, with a pitch speed of 38 mph. The prop loading is 470.

If I were to go to 4S, with a 9" prop, a pitch of 6" would give a prop loading of 486, which is pretty close. eCalc predicts 19 amps with 1461 grams of thrust, and a pitch speed of 63 mph. This is a clear performance upgrade from 3S, but I'm pulling 33% more current.

With a 9x5 prop, the loading is 405. eCalc predicts 17 amps, 1289 grams of thrust, pitch speed of 54 mph. Still an increase in current, but only about 20%. Perhaps more than I would expect given that the prop loading is so much lower, though.

If patyonC11 can provide full details of his power system (battery, motor model and kv rating, prop size/pitch, and ESC rating), I will run up some scenarios in eCalc for him, if he wants.
 

Epitaph

Ebil Filleh Pega-Bat ^.^
Mentor
#5
Hi

Have you looked to see how much current draw you are having? It might be the 30A ESC is maxing out before it gets to the maximum the motor can take (depends on the case), and some ESCs just burn out, where as others limit at (in this case) 30A and won't allow more to pass through eventhough the motor can take more.