Thread: C Discharge????
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Old 04-19-2014, 05:17 AM   #4
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Originally Posted by garyp1029 View Post
I have read "Everything you Want To Know . . ." as well as several other posts concerning C discharge and I still don't get it. I understand that C is a discharge rate of drawing a certain quantity in a specified time period, BUT EXACTLY HOW does it affect real life choices? Using a plane I have ordered (Electrifly Super Sportster rxr) as a specific example---It has a motor of unknown details, an ESC of 18 amps, and a recommended 3-cell battery of 1300A and 30C discharge rate. QUESTION----Assuming weight is NOT a factor, can I safely use a 1300A 20C??? A 1500A 20C??? How about a 1800A 20C??? What would be the UNQUESTIONABLE result of reducing the C from 30 to 20? Are these figures cast in stone or are they wild estimates?
Is there a simple method of converting one of these to the other?
Your input would be greatly appreciated. Thanks. Gary
That "C" term is a general term that describes just how fast your battery can be discharged. The same thing applies to how fast you can recharge your battery.

If the battery mfg is honest in their specs, the higher the "C" rating, the better the battery will put out high currents without the battery voltage sagging to much. Kind of like an old lead acid car battery that can barely turn over your engine, as compared to a brand new battery.

IMHO, any C rating above perhaps 60 or so leads to diminishing returns. If you actually discharged a battery at 60C for the entire flight, your flight time would be less than one minute.

If you discharge your battery at a rate of 30C, that indicates a flight time of two minutes assuming full power for the entire flight. And, 20C would be three minutes.

Now, you've got the batteries MAXIMUM current capability, defined as per example, 30C. With a 1300 Mah battery, that is 1.3 Amp Hours. So, 30C would be 30C times 1.3 Amp Hours, or a maximum current of 39 Amps.

And, you've got "Flight" "C" which is how hard you are actually operating your battery. If you're pulling 22 Amps on a 1.3 Amp Hour battery, the value of C would be 22/1.3 or C= 16.92. Flight time would be 60 minutes/16.92 or about 3 1/2 minutes at full throttle for the entire flight.

Problem is, most battery mfg's don't indicate how long your battery will last running it at maximum C. We've had some guys in my club that only got 5 flights before the battery was junk.

Flight time is equal to 60 minutes divided by the "C" value actually being used while in flight.

And as Pizzano indicated, I've got a thread on this subject:

"C" and what it is
http://www.wattflyer.com/forums/showthread.php?t=65869

Hope that helps

DennyV
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