[daddyrabbit1954]

Originally Posted by kyleservicetech

With a model with 11 servos, IMHO, you definitely need primary and backup power to your receiver and servos.

What I did on my 7 Hitec 645MG servo'd model was use a Castle Creations 10 Amp Switching BEC on the receiver's battery input. That CC BEC was programmed to 6.6 Volts DC.

And, as a backup, a two cell 2300 Mah A123 battery pack, with two series 9 ampere silicon diodes in series in the battery packs red wire. This drops the voltage of the A123 pack to less than the 6.6 VDC programmed into the CC BEC. As a result, the A123 cells are just "Floating", unless the Castle Creations BEC looses voltage due to an overload. (These switching BEC's generally just lower their voltage when overloaded, with no damage to them)

After a days worth of flying, the A123 pack was topped off with a Cellpro Powerlab 8 charger. Only about 20 milliampere hours was required to top the A123's off, so that indicates the CC BEC was handling most of the load. If you go this route, just make one flight, then top off the A123 battery. If it takes more than perhaps 500 mah or 1000 mah, you may need to go to the Castle Creations 20 Ampere BEC, or just go with the 20 Amp unit right away.

And, you do not need to worry about loading down the A123 cells, they will put out 40 amperes without issue, enough to melt your servo wires. (I accidentally shorted the servo sized battery leads on a two cell 2300 Mah A123 pack. Burned the copper wires right out of the insulation of the wires. Didn't harm the battery, at all, I could swear that battery was laughing at me.)

The A123 pack was plugged into a battery switch, that connects to an unused channel on my receiver, as a dual battery input to the receiver.

Since the A123 pack weighs in at about 4 1/2 ounces, that provides a little extra security at a reasonable weight.

Dennis

Until you mentioned them in your post, I had never heard about A123 batteries. I did some research and from what I can tell, you are talking about using two 2300 Mah A123 cells? I found these:
http://www.dealextreme.com/p/trustfire-protected-18650-lithium-battery-2400mah-2-pack-gray-5776

Would these be suitable? Don't know for sure if these are considered as A123 cells.