Battery capacity question

Hi everyone. I'm new to multirotors and have a question regarding batteries. I've built the 3DR Arducopter kit with APM 2.5. I've been using 3 cell, 11.1v 2200mAh lipo batteries. I am able to get 9-11 minutes of flight time per battery. I'd love to be able to get more flight time.

I've read several sites about batteries and understand them this way - lipos have 3.7 volts per cell, thus a 3 cell has 11.1 volts. Capacity is measured in mAh. The higher the number the higher the capacity.

So here's my question - as long as I stay with a 3 cell 11.1 volt battery, can I upgrade the mAh number? I saw some 5000+mAh batteries that were 11.1 volts and assumed that one of these would give a longer flight time. True?

Also, I've come across some cables that let you run 2 batteries in parallel. Obviously this adds more weight, but is this another good option for increasing flight time?

Thanks.

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T3Permalink Reply by Richard Boyhan on June 7, 2013 at 3:24am
The simple answer to both questions is yes. You can also fly 4S batteries. If you fly 4S you will have more power. Your copter will fly like a rocket. You also will need to tune some of PIDs down for stability.
Good luck and fly safe.
Permalink Reply by CyberCrash on June 7, 2013 at 5:29am

Once you've tried 4S, never go back.

Permalink Reply by Ty on June 7, 2013 at 6:29am

Thanks for the replies. I just didn't want to overpower and burn something up. Since my post, I've looked at what I have plugged in on my Arducopter - The APM Power Module says it has an 18V max input. I'm assuming that the little circuit board on the Power Module is what regulates the power going to the APM 2.5, so as long as I stay under 18V I'm good. The ESCs in my kit specify "2-4 LiPO, 5-12 NIHM/NiCd" in the battery section.

Starting to understand this stuff more and more each day, thanks to this forum!

Permalink Reply by Euan Ramsay on June 7, 2013 at 7:25am
Once you've tried 4S, never go back.

But once you 6S, you never go back 4S...:-)

(Caveat: I run 3S and 6S. Logic would dictate a 9S or even 12S monster next...:-)

T3Permalink Reply by Richard Boyhan on June 7, 2013 at 2:36pm
Be careful. To high a cell count and the dc volts from your battery can kill you. Not kidding.

ModeratorPermalink Reply by Dwgsparky on June 7, 2013 at 4:52pm
Not just kill but burn, maim and destroy, it's the current that kills you , 50ma can be deadly, 24volts can push over 100ma through your body in perfect conditions, more volts=more current. Electric cars are especially deadly. A 24v (6s) battery can push 240amps into a 0.1 ohm short circuit or nearly 6kw of pure heat, think serious smoke and flames. Treat electricity with great respect, it bites.

AdminPermalink Reply by Morli on June 9, 2013 at 12:42am

The heavier the airframe , the more power you need to burn. More capacity also means more weight.

Permalink Reply by Ty on June 12, 2013 at 6:06am

The ESCs that I have are rated for 2-4 LiPO, if I use a 6 I'll kill them, right?

Permalink Reply by Andrew Sommer on September 24, 2013 at 10:53pm

I'm sold. I just tried my quad that I had been using 3s batteries and decided to try a 4s. WOW it went from being a well tuned but somewhat sluggish stable ship to being a tight as a drum locked in "Top Gear" super quad. I'll have to up grade the ESCs since I've kept the same props


T3Permalink Reply by Richard Boyhan on September 25, 2013 at 4:59am
Hey Andrew nice-looking ship, what size FEV are you running, what's the wattage?
Permalink Reply by Andrew Sommer on September 25, 2013 at 8:48am

Right now with 4s I'm over powered for ESCs as they are GetFPV Lumenier 30 amp ESC with SimonK Firmware at  I was running 5000ma 3s with 13 x 4 props on NTM 3536 910kv.

eCalc has the NTM 3536 910kvs rated at 520 watts vs the specs on HK at 350 watts so I'm kinda wondering....with the 3s I was getting a safe 291 watts max power, with the 4s same 13 x 4 props I'm at 473 watts max power but definitely over the ESC limits at 38-40amp at full power. I have some Turnigy Trust 45s with SimonK I'll switch to today. Then my only real question is what the actual rating of the motors is. Hover on 4s is only 102 watts and my type of flying for video should keep me well below even the 350 watt HK spec.

With the 4s 5800ma batteries the eCal it says I should drop down to 10 x 6 to be below 30 amp max power ESC limit but brings me back to a < 8 min safe flight time. But puts the hover throttle back at 51% and the max watts at a very acceptable 362 watts. I may decide to compromise and go with 12 x 3.8 carbon props for more reserve power.

The other new issue after the switch to 4s with the same props is my hover throttle is now 32% so in Loiter it climbs so I will need to adjust the hover throttle setting in the APM once I decide on the prop ESC combo. I already tried 10 x 4.5 props but the PIDS were off with the quad twitching a lot,  I didn't want to have to redo them an I have a lot of 13 x 4 props I've invested in all ready.

Specs:

  • Tarot 650 Quad with cheap plastic landing gear (notice wire holding the spread.)
  • APM 2.5 3.1 with old integrated compass Ubox GPS. with Moongel mount
  • NTM 3536 910kv with 13 x 4 HI carbon props -
  •     plan to upgrade to Tiger Motor MN3510 -13 700 kv for longer flight times
  • Luminier 30 amp esc with SimonK
  • Turnigy 9x v2 mode 2
    RCTimer brushless gimbal with AlexMos control board...still tweeking settings 
  • Fatshark 250 millwatt FTP with CCD killer Cmos cam (cam is ok not great)
  • Foxtech 32 channel diversity monitor - LOVE IT!
  • Flight Gross Weight 90 oz / 2550 grams 

The orange ball is Styrofoam from craft store with 1/2 balsa tail boom. This feature has been a HUGE success in orientation!


*** If anyone knows about the actual Hobbyking NTM 3536 910kv max watt rating please chime in. 


Also I need a step down transformer to power the Fatshark FPV anyone know a good light weight unit?

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