DTB

My Feedback: (15)

On any given setup, which Li-poly do you prefer?

3S or 4S?

3S pulls less Amps, but has less power.
4S pulls more amps, but has more power.

Matt Kirsch

My Feedback: (21)

Actually, on a given setup, you'll draw about 33% more current. Not exactly what I'd call "slightly more." In fact, that extra cell gives you about 76% more power.

The question you're really asking here is, "Do you prefer a 200 horsepower engine or a 350 horsepower engine?" Knee-jerk reaction, you're gonna say "350 Horses! R-R-R!" Of course, the answer is going to depend on many factors, especially the plane and how you want it to fly. A 4S pack may be overkill for the needs of the plane, or even too much for the power system. A 3S might leave the plane underpowered.

NOW, if you're really asking, "For the same amount of power, which do you prefer? 3S or 4S?" That's a different question entirely. First, you have to re-tune the rest of your power system such that as you increase Volts with the additional cell, you DECREASE Amps by changing the motor wind or reducing prop size. That way, you have the same amount of power for both, so you can make a valid comparison.

Advantages of the 3S setup include the fact that the components will be less expensive. It'll be lighter, due to the lower number of cells, the (probably) smaller motor, and the fact that a 3S setup doesn't require a separate battery pack or UBEC to run the servos. A disadvantage is that run time will be shorter due to the increased Amps.

Advantages of the 4S setup include increased run time, and less stress on the components due to the fact that you're running at a lower current. In most cases, the motor, ESC, and battery are far from being maxxed out, so there's always the possibility for more power. Disadvantages are that you need a separate receiver pack or UBEC to run the servos, and the setup will be heavier as well as more expensive.

Bevo

The 3 cells are less money and lighter batteries. If I needed a 4 cell pack I'd buy two 2 cell batteries and put them in parallel. This way when I do my big electric airplanes I can make a 5 cell or 6 cell out of the batteries I have.


Bevo

Matt Kirsch

My Feedback: (21)

Series, actually, and that's a great idea. I do the same thing, constructing bigger packs from smaller packs.

I noticed that the same thread is running over at Wattflyer, with a whole lot more "play" than it's getting on here...

slsh9615

Dear MAtt Kirsch,

I like your idea, can u show me how you group smaller pack to make bigger pack, I have 4, 3s pack, and 2, 2s pack 2250mah lipo.

I wanted it to be 6s4p, i have tried to do " Y " harness to assemble the pack, but both the 6s pack and 4p pack become very hot, right after i connect them to the Y harness, eventhought all the pack is newly charge.

Is it something wrong with my homemade Y harness, can u show me how to make a y harness step by step and the maetrial that i need for it.

tq in the advance for anybody that can help me to solve this problem.

MAKODS

A 4 cell pack makes a big difference when flying off a grass strip with a 5lb plane, the 3 cell just wasn't enough umph!