What is the difference between 3s and 4s lipo battery with same ampere and c rating?

ArduCopter Copter 4.0
1

Hello everyone!

I am having the following doubts.

For example,

  1. I am having 3s and 4S lipo battery with 5000 mah. Will I get the same flight duration from both of them or diffrent one?

  2. If same that is okay. If not same, Then how can I calculate the flight duration for both the battries where the ampere’s are same?

Please let me know.

Thanks.

2

The voltage is different. Use E-calc software to calculate that.

3

3S and 4S are in regards to the battery voltage. Low voltage = lower thrust = might not fly.

4

Please read my 1 st question and try to answer.

Thanks.

5

Please answer the first question.
Will I get the same flight duration?

Thanks

6

What you fail to account for is the weight of each battery. If they are both the same C then obviously the 4S battery will be heavier. Your question is too simplistic. Take @amilcarlucas advise and invest a whopping $2.99 in eCalc and you can look at many scenarios.
.

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7

E-Calc is great in terms of the computations and taking into account nuances!

If you want to understand more about batteries I will give a quick, but not complete summary.

1.) No, you will not get the same duration of flight out of a 3S 5000 mAh vs 4S 5000 mAh. The total energy stored in each battery is different as one has higher potential.
To compute: 3S (cells) * Nominal Voltage (V) * 5 (A-h) = 3 cells * 3.6 (V/Cell) * 5 (A-h) = 54 W-h

For 4S 5000 mAh -> Energy stored = 72 W-h

Note: I used 3.6V/cell for the nominal voltage but this is dependent on cell chemistry.

Generally, for flying vehicles an important metric is the gravimetric energy density.

IE: 72 (W-h) / battery_weight (g) : “just get more Ah” has finite returns due to weight

Next you find your thrust vs power curve given the propeller, motor, and voltage combo. You will see this info. for example here in the “Specifications” tab https://store-en.tmotor.com/goods.php?id=341

So for example if at 50% throttle gives you the thrust you need to hover with power use of 31W per motor.
A rough estimate of flight time is: 72W-h / (4 motors * 31W) = 0.58 hours

There are other consequences to a higher voltage as well:

  • All electrical components must be able to accept that higher voltage (motors, ESC, BECs, sensors, etc.)

  • At higher voltage things run more efficiently as to get the same power out you need lower current (A) and resistive losses are I^2*R dependent

  • However, the same motor will turn faster with 4S vs 3S which yes is more thrust… But this isn’t just as simple as “now I get more thrust and linear amount longer flight time.” You now could be operating your motor and propeller with far less efficiency and we didn’t take in account efficiency into anything above…

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8

Thanks Dave,

That means, manual flight calculation can not be done, since its involve with both ampere and c ratings, correct?

9

You can. Josh posted some good info above. There are several factors to consider as he noted. Also, there is diminishing returns with adding more capacity all else being equal. So the Flight time vs. capacity is not a linear relationship. And if the thrust/weight ratio is diminished then Flight Stability can be compromised.

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10

Dave,
Please check this link and let me know whether is correct or not?

Thanks.

11

Sorry, not going to watch some guys YouTube video…

I’m going to enter the info here and have an answer in 30 seconds.

ecalc
ecalc2322×914 223 KB

1 Like
12

I too sorry to asked you to watch
Thanks

13

So I just quickly was perusing what I could find related to quadcopters,

This seemed ok from glancing at their process, equations, etc. (Don’t fault me for bad info in it :slight_smile: )

Looking at their references or type in to google scholar “quad copter flight endurance”

Unfortunately, most material I have is related to fixed-wing which is far more complicated.

14

Big thanks Josh.

I will fly and test, then come back to you with the practical result.

Thanks again.

15

#1. No.

#2 Use the attached spread sheet.

Multirotor Flight Time.zip (7.5 KB)

Change the file extension to .xls and open with Excel or OpenOffice Calc.

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