I have joined the Power Expander club. Now I need to know which "C" rating 2S battery I need to buy. It will be powering 8 Futaba BLS 172 servos and one throttle servo and a Electro Dynamics ignition kill switch.

Since most servo lead connecters are only rated for about 3amps continuous with momentary bursts of around 5 amps, I would have to say you would not be wrong with a battery that can push around 45 amps continuously. So, your C rating will depend on your mA rating of the battery i.e. mA * C = amp output and I came up with 45 amp by (8 power drinking sevos + 1 so so servo + ignition kill) *( approximately 5 amps )= 45 amps.
hope that helps. This is just my thinking of it and in no way is the only way of approximating power usage.

Which battery would you purchase on this page?
http://www.aircraft-world.com/shopdi...Ah+%7E+4000mAh

Hi,
Anything over a 6C battery is acceptable for a flight system. The size battery you want depends on the flying time you want. General rule of thumbs I use is:

50cc planes: use 2 1600mAH packs or more
100cc planes: use 2 2600mAH packs or more.
150cc planes: use 2 4000mAH packs or more.

Originally Posted by japan3d

I have joined the Power Expander club. Now I need to know which "C" rating 2S battery I need to buy. It will be powering 8 Futaba BLS 172 servos and one throttle servo and a Electro Dynamics ignition kill switch.

Cool, im keeping it light with 2 2200's!


; p

Originally Posted by japan3d

Which battery would you purchase on this page?
http://www.aircraft-world.com/shopdi...Ah+%7E+4000mAh

The 2500 or the 3300 would be plenty. Just keep an eye on your loaded power until you get a feel for how many flights you can safely get out of them before having to charge.

Originally Posted by funboy

Cool, im keeping it light with 2 2200's!


; p

Me too. I have the exact same servo and PowerExpander setup in my plane as the OP. I'm running a pair of 2500 mAh A123 batteries into the Competition 12 with no regulators. Lots of amp delivery and a quick recharge at the end of the day while I'm cleaning the plane.

I run 2 - A123's 2500mah on my 50cc

I was going to run A123's, but thought the servo power would be low. I am using A123's to setup up the plane, but will use the Lipos at first to see what response I get from the servos.