I am building a flamewheel 550 with dji 2212-920kv motors and 30A opto esc,and APM 2.6....I have the choice of 3 or 4 cell lipo....what will give me the longest flight-time of 5000mah 3c and 3800mah 4c (ca same weight)?

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5000mah 3c w/ 10.45 props

I use 4c 35-70discharge ratings 5000mAh and i wish i had larger capacity like 8000mAh
On dji550 with rc timer motors 2212-1000kv with gimbal and camera , telemetry and fpv. total weight 2.7kg
On 10x45 props.
Forgot to add my flight time on 50% batteries when they discharge to 3.7v is 5min. At 10min they are empty. 5000mAh gone. I usually fly 5-7min tops.

Assuming you are correct that they have EXACTLY the same weight the 3800mah 4 cell has an 1.3% advantage. So almost nothing. Comes down then to what you have and or which has a cost advantage. If they are not the same weight, I would go with the lightest.

let's make an assumption that your motor has a fairly flat efficiency curve (thrust per watt) when holding watts constant but varying voltage by +17%.  if so, then it's simple math.  it's all about watts in the battery at that point.

3 cell (a proportional number to voltage) x 5000 = 15000

4 cell                                                  x 3800 = 15200 so a 1% edge.  [if you want the numbers in watts, multiply by 3.7]

but let's say that the response isn't flat and that the rotor (motor+prop) responds more efficiently at lower rpm ... say about 2% more efficient (likely).  then the 1% gain is lost and the 3S wins by 1%.

then let's say you decide to size your wires going out to the motors.  the lower amp system (the one using the higher volts) can use smaller wires, so you save a few grams and extend flight time.  now the 4S fights back.

then let's say that the batteries, because of wrapping the battery surface area and wire lengths used to connect the cells, that the 3S is more efficient (likely in your case) ... 

this is adding up to at least a 1% difference (lost track though of which way), which is huge because in a 10 minute flight we are talking a whopping 6 seconds ... oh ... so don't worry about it.  look at cost instead and just go fly.

if you really want to pursue this because you want every possible drop of blood out of the turnip, Hugues is hosting a thread on batteries as we speak.  tune in there. we are about to do some tests because we, like you, are hoping that the blood in the turnip runs deep.

P.S.  in reality, if you tested the two system you would see up to a 7% difference, but you won't know until you tested both.

For the price you cant beat these:

http://www.hobbyking.com/hobbyking/store/__21370__ZIPPY_Compact_500...

5000mAH for 27$??? if you sit on that page you can get them for ~25$!!!

This is what I use.

zippy zipped here ... just arrived are the Zippy 25C 3S 5000 (blue) and the Zippy 25C 3S 5000 Compact (yellow; hey, in the above photo).

So somethings fishy in China (or was that Belgium? :-).  The compact zippity has a volume that is 14% less than the zippidy-doo-dah (same with weight).  maybe part of the yeller one lives in a worm hole or they add helium to it?

Oh something tells me that this will be a revealing test.  I'm waiting for a larger scale and the resisters to arrive before I start the tests.     

My 4 x 25C Zippy Compact's all puffed before 25 cycles, they then lasted barely 35 flights before capacity dropped below 60%, so cost per flight was very high. Unless they've changed the chemistry I'd seriously avoid the 25C's, rather choose the 35C versions which (I've heard) last longer.

http://www.rcgroups.com/forums/showthread.php?t=1607931

I have a Flamewheel f550, stock motors, I really like the 4S 30C AGA Power Batteries (4200, 5200 and 6200)

I have tried others but these seem to give me a couple more minutes and not as heavy as some of the others.

I have 10" props, I found them at Hobby Town USA

http://www.aga-power.com/list-10-1.html

Have you flown 3s?

Hi

What do you think your flight times would increase to if you added another 5000ma battery parallel ?

Do you fly aggressively to use up the battery or just light hovering and way point flying ?

You gotta love a company that next to their weights puts +5% and then proceeds to even list some of the weights in 10ths of a gram.  Impressive!  But the I noticed that the weight for the 6200 30C is clearly wrong at 413 grams because that is the same weight as listed for the 5200 30C.

Do you have a gram scale where you could weigh your batteries?  I'm trying to figure out if their weights include or exclude the wires.  If it includes the wires and the capacities are on par with other advertised batteries, then these batteries are about 8% better (per their claim) and worth testing.

I'm about to order the AGA 4500/25C for test, which per their data is their most efficient battery.  But wanted to see if you have actual weight data so I can figure out if their weights include the wires (a significant component in choosing their most efficient battery to test).

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