3s vs 4s batteries?

[fotophanatic]

What is the main difference (outside of voltage) of a 6000mah 3s and 6000mah 4s? The 3s 6000mah that we are looking at weigh 583g each and the 4s 6000mah weigh in at 723g each. Going to be running parallel on a 950mm quad that weighs about 6-8 lbs loaded w/batteries. Has OS 3825-750 motors and not sure on the esc's and has 12x6 APS props. Trying to get the best flight times possible. We are using 2 6000mah 4s batteries currently and getting about 8 minutes of flight time. The 3s batteries would weigh about 520g less than the 4s which are right at 723g each. The whole battery thing has got me seeing cross-eyed!

 

[KopterX]

The ESCs will draw more AMPs from the 3S batteries because of the lower voltage, and the flight time will be shorter even with that 520grams less on total weight. 8 minutes is a good time for you built and changing the number of cells or mAh is not the answer for longer flights. Just get more batteries with you on the field. About 4-6 pairs of batteries and a fast charger will keep you fly most of the day.

 

[ChrisViperM]

One of the main differences between 3S and 4S (apart from other factors) is the change in RPM of the Motor. If your motor has a rating of 700 RPM/V, it means your motor spins at 700 turns per minute for 1 Volt applied (without propeller). With that formula, your motor will do 7700 RPM's on 3S (11,1 V) and 10360 RPM's on 4S (14,8 V).

Chris

 

[KopterX]

One of the main differences between 3S and 4S (apart from other factors) is the change in RPM of the Motor. If your motor has a rating of 700 RPM/V, it means your motor spins at 700 turns per minute for 1 Volt applied. With that formula, your motor will do
7700 RPM's on 3S (11,1 V) and 10360 RPM's on 4S (14,8 V).

Chris

...a very accurate statement, but not so relevant in hovering flight, where the voltage output to motors is regulated by the ESCs to achieve the RPM necessary to hover. The only relevant difference from this point of wiev is the maximum RPM. The 4S will have about 20-25% headroom of maximum RPM compared with a 3S. In more simple words, you need bigger S number for heavier builds or speedy builds.

 

[ChrisViperM]

...a very accurate statement, but not so relevant in hovering flight, where the voltage output to motors is regulated by the ESCs to achieve the RPM necessary to hover. The only relevant difference from this point of wiev is the maximum RPM. The 4S will have about 20-25% headroom of maximum RPM compared with a 3S. In more simple words, you need bigger S number for heavier builds or speedy builds.

+1 ...agreed