a weirdo topic about the C rating of a batt. pack
 

My understanding is that it is determined by the cell chemistry.  Basically, what chemical composition is used.

Prateek ,
The C Rating of the Battery is the capacity to discharge .
Every battery has an MAH capacity  : x mah
the C rating  : y

Hence the  Maximum  theoretical current the battery can discharge = xy amps

Eg
 suppose  you have a 1000 mah battery  rated for 15 C  then the max amps the battery can deliver = 15 x 1amp ( 1000 ma )  = 15 amps

This important   as this is what determines  the motor on which this battery can be used .

Eg if the motor draws more than 15 amps  at the peak then you cannot use this battery with it and if you do then the  battery will be damaged.

This is a simple explanation I am sure there are many more out here on the forum who can give you a detailed technical one.

The  higher the C  the heavier the battery and so the price  so it is direct material content  which determines the C rating
rgds
sai  

ok 

If our motor draws max current of 15A means can we use a 40c battery (I mean higher c battery) ? 

you can use no problem but it will add more weight to the plane
for 3d foam planes weight is a crucial factor



 

If your motor draws a MAX current of 15A, then the product of the capacity of the battery (i.e in mAh, like 1000 mAh) and the discharge C should be more than 15.

eg: if you are using a 100 mAh battery , then it should be MIN 15 C so that the product is atleast 1500mAh or 15A.
if you are using a 300 mAh battery, then it should be MIN 5C so that the product is atleast 1500mAh or 15A

Thank you for ur kind replies buddies!

Saurabh,
1500 mah is not 15A, it is 1.5A ? 1000mah is equal to 1 amp,

1000 mAh = 1 Ah.

Its acutally 1000 mah or to make it simple 1 Ah X 15C that makes 15 Amps. or 3000 mah or in other words 3 Ah X 5C = 15 Amps. Though One should consider some head room for the battery. Say if you want to use 15 amps then its better to have atleast 20 + Amps rated battery. Like 1 Ah (or 1000 mAh) X 20 C. If I were to use a motor of 15 Amps max, then I would use a 1300 mah 20 C to be on the safer side. though 1000 mAh still suffices.

Thanks for the correction.  MY BAD !!!

Nice Topic. So, If 20C,1800mah is used on a motor with 15A max. current, it will be safe and run longer, but weight increases. 1.8*20= 36A.
Am I right?

So when do you have an ESC blowing, considering that C is the rate of discharge based on the capacity of the Batt...
So if i have a Motor that has a max load of 20amps then my ESC and my Batt have to balanced based on the batt cap (mah) and its discharge (c)
wow!
I thought I read something more on this on another thread... coulnt find it...
please post it if anybody does..

I am not correct we have been deviating from the real topic : What Makes (causes) the C Rating of a LiPo'  and only Anwar has answered in the right direction.

The 'C' rating is the Max Discharge current (and charge) the LiPO could sustain. Now that depends on 'Total Internal Resistance' of the LiPO (the reason newer chargers like iCharger have this facility to measure). From the classic theorem , this is when

Total Internal Resistance(TIR) = External (Load) Resistance
http://en.wikipedia.org/wiki/Internal_resistance


Now as you more and more current load by putting larger BL Motor, the ESC would pose much lower resistance to the load line, thus to deliver higher current, the TIR of the LiPO should be lower.

As Anwar already said, the TIR depends on

1. The Chemistry of the Cell (higher conductive chemical)
2. Material of electrodes

And also the physics:

1. Total surface area of the Cell Electrolytes
2. Total Surface area of the Electrodes
3. Distance between the electrodes (this is a limiting factor)

As Ujwaana has said, the topic has veered. But to answer:
1. The ESC blows when it is overloaded. In short, if you use it with a motor that demands more current than its maximum rating. For your 20A motor the ESC rating should be a MINIMUM of 25A, with 30A preferred.
2. The ESC rating as above with a battery of 1500 mAH/20C, 2000mAH/15C (again minimum) and so on.