Samanth what camera equiment you are planning to put into your FPV plane?
Also your power system?

@azhaguvel -  FPV system (i've thought of , but still havent purchased) I have chosen a 1000mw video Tx and Rx.  But I still havent chosen the FPV camera... 
                    For on board video recording, i'll use my Canon SD900. It delives 1024x768 at 30FPS which is good. 
               
                              Power system - 1660kv motor with a 50amp ESC and 4amp BEC, 10x7 APC thin electric prop., 4 x metal geared servos from HK similiar to hitec HS-65MG,  2800mAh + 1500mAh (both 3S, 30C) in parallel, Spektrum DX6i and AR6200.

Putting two different mah battery in parallel. Is that a good idea? I guess no

links of the power system in HK would be a great and a clear cut of your power sytem

That is a good idea i guess....i've seen many people on youtube put a 2 x 2200mAh packs in parallel and the results are great !

Yes putting two battery packs of same mah is ofcourse a good idea. I am not sure about this, putting 2800mAh + 1500mAh in parallel the 1500 mAh may get drained before 2800 and the 1500 batteries might go dead(below 3.7) when 2800 mAh goes to 3.7 volts. I might be wrong.

OH ! yeah !!! thanks for telling me that...wow..i never thought of that. makes sense.

Welcome . But wait for some confirmation from the seniors (I am just 5 months old  in this hobby)

Since I am planning to buy the same plane looking forward for you plane pics and thread of the build log . All the best 

oh, thank you !   haha i couldnt help notice, but this is my 100th post

What Azhaguvel said is right.The 1500 will lose power before the 2800 one.Not advisable at all.

Which plane have you decided for the fpv which takes 10x7 prop? Are you building one?

The Problem is of 'Total Internal Resistance' between different cells. You should not just avoid different mAH Lipos to mix match also of Different C. infact, its advice able to join only same Ah/C/Make/Model Lipos. If these cell internal resistance (measurable by high end Balancer like Hyperion/iCharger) are dissimilar, they would go in a self-discharge cycle.

Putting a High-Amp Diode on between the Lipos is one of the solution, then High Amp Diaode are bulky, lossy and costly.

This one:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14465

Alright, I've found a solution to this. I'll just buy a new 4000mAh Lipo...

Please help me choose between Turnigy, Turnigy-Nanotech , and Rhino.

Is it ok to use the same battery to power up both the ESC and the video unit using a Y-connector(xt60). Wont it burn the video unit since the ESC is pulling more amps.

I dont think it would burn the video unit just because the esc is pulling more current(amps).
I am sure it would be convenient to use another battery for the Video unit.

I dont have enough space inside my AXN floater for another battery .

hmm...well then, use a Linear Voltage Regulator. And dont use a Y connector. Make sure the ESC and Video unit are in Parallel.
I am guessing that the input for your video unit is 9V.
Then go to your local electronics store and get an LM7809 Linear Voltage Regulator. It hardly costs 10 rupees.
It'll look something like this -

I would suggest Instead of using a LDO like 78xx, which would result in loss in energy and unwanted interference from motor. Instead, use a DC-DC Step-down converter is a better choice. I guarantees a constant voltage (settable by Pot)  till the input voltage drops considerably.
http://cgi.ebay.com/DC-DC-StepDown-Adjustable-Power-Supply-Module-LM2596-/330574414294?pt=LH_DefaultDomain_0&hash=item4cf7c541d6


I have one concern  though. Why do you need 9volt ? most of the DC-DC converters needs a minimal 3 volt differential between I/P and o/p. i.e if you have 12v input, you can have output of 1v-9v. better use a 2S Lipo and put a DC-DC Boost converter and get 12v Constant o/p:

http://cgi.ebay.com/LM2577-DC-DC-Power-Boost-Step-up-Adjustable-Module-3A-/260757400857?pt=LH_DefaultDomain_0&hash=item3cb65a2d19

any dc to dc booster/regulator will cause rf interference. More details here http://www.rcgroups.com/forums/showthread.php?t=1361685
Better go with separate battery and video transmitters wont lose strength till 8.5-9v. You would always drain your main motor battery before the vtx/cam battery however good your setup be.

What is the current draw of your Camera + Tx assembly ? Consider your flighttime. Calculate mAh required with safety factor 1.5. Add that amount of battery.

Let 1.2 watt power draw from 9 volt.
.: current = 133mA.

You expect 15 min of Flight-time. (4Ah / 50A = 4.8 min, avarage = 3*4.8 = 14.4 min)
.............................................(Your ESC is 1.5 times max capacity than motor and
...............................................you fly at an avarage throttle of 50%.)

Your camera battery requirement = 133mA X 0.25 hour x 2 as Safety factor
= 66mAH.


So, a 90mAH 3 cell lipo pack can be utilised.
or you may make your own by using Bluetooth headset battery.
This must not take space more than 4CC of space incl LM7809. Use TO220 Package for less weight.
Simply you may use NiMH 9Volt rechargable battery (250mAh min costs Rs.300).

You may use more low cost Li-Ion 200mAH cell costs nearly Rs.60/- per cell as current discharge rate is <1C.

If discharge rate >20% of C capacity, don't make parallel cell witthout hardware (Electronics).

e. g. If battery is 25C, dont parallel where load demand may go up 5C.
....(If battery is 45C, dont parallel where load demand may go up 9C)

So, your flight time > 10 min with single pack eligible for paralleling (6.5 min for 45C).
Then better replace and fly with lesser weight and can get more flight time with same 2 combination battery pack.

Hope I explane a  little bit simple.

Thanks


Thanks

CCD Cameras need constant power supply. They are usually either 5V or 12v. None of the regular Lipo/Nixx supply exact voltage in constant manner (4.8v,6v 7.2v/ 11.2v) you may peak charge these batteries above 5/12v, but they would soon drop down to unacceptable level for CCD. Many people blame Antenna/Distance for decrease in video quality, if they don't provide a constant voltage to CCD.

As a matter of fact, my comparison was with LDO like LM78xx. A proper DC-DC converter with a LC filter circuit is better than one LDO and 2 pair Caps to filter noise.