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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Hi friend, 

            Flight time will be more in 5000mah 3c ....in 4c the thrust will be more (you can add more payload)....


Regards,
UNMANNEDENGINEERIA

Forrest ---- Xian06 & Mangus pointed out laptop packs and 18650's, here is a thread for you to read: http://diydrones.com/profiles/blogs/my-97minute-06second-record-qua...

There are others experimenting who have been playing with the Panasonic laptop 18650 type cells/packs for a couple of years. Also, Tesla Auto will have a big bundle of them to energize their car.

My 18650 pack (See attached photo.):

I made a small 3S 5000mAh battery pack ~ 2" X 3" x 1/2" (50mm X 70mm X 12 mm) at 129 grams. The cells are cheap Chinese advertised as 5000mAh with protection circuitry. They have NO protection circuitry or protection other than a vent. I know - I tore one apart. The 3S battery pack is likely 1C to 2C and easily lifts my 450mm Flamewheel clone outfitted with HK 1000kv bldc motors, 30A ESCs and 10 x 4.7 props. Approx weight? Heavy - I've got junk on board. When the quad is powered quickly it will cause the low battery LED to flash but, the copter will fly.

I'm a noob and do not fly well so, I've fallen back to using a Turnigy 3S 2200mAh 30C. The 18650s do not supply enough current with my poor flying skills jamming on the throttle which starves the quad for power and constantly triggers the on board battery alarm. The over power draw without ample supply causes the quad to drop or falter in flight which as you would realize causes more issues I just can't learn through.  ;-)  But, hey --- the battery pack will fly the quad.

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Hi Forrest and other experts,
Noob question regarding batterry:
If i put batteries A + B in parallel, the total mAh will be (A+B)mAh right.
What about the C rating, is it (A+B) or stay the same?

Thanks.

(A+B).

In series C rating will stay the same.

C is the same, but potential continuous output is doubled.

Thanks everyone for all the links to LiIon.  I'm working through the numbers.  First blush is that the X2 Black Momba needs another diet.

5ah @ 30C = 150a
x2
10ah @ 30C = 300a
Thanks Graham and Dronedroid.
I understand now.

All true -- the higher voltage allows lower gauge wire or less resistive power loss, and higher voltage means more RPM on-tap.

There are downsides.. the 4S batteries (as a generalization) have less energy/gr because of the added cell (packing, bonding, conductors).  I'm going to try it, but need to find a buck/boost regulator for the 12v lighting.  If I add a regulator, 3S won't work, and if I don't 4S will fry the LEDs, so hmm.. any small 3S/4S regulators for 12v?  (needs 1A or so).

I looked at those HK links, but they appear to be drop-down regulators only, and need about 1v higher going in than out.  The 11.1v 3S pack would get dropped low enough to fail the LED lights @ 12v.

The buck/boost regulators generally cost more, and they ones I've seen are larger/heavier.

Is about $6.00 OK for Step up/Step down switching supplies? A range of devices are at


http://www.pololu.com/catalog/category/133

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