E-Flight Power Sources Ask questions or read about power sources as they specifically relate to e-flight including Lithium-ion, Li-Poly, Nimh and Nicad battery packs.

"C" rating

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Old 06-19-2012, 09:31 AM
  #1
skatsrc
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Default "C" rating

I'm going to fly a new type of plane at full throttle most of the time. Is it better to have a higher or lower C rating (ie: 25 C or 35 C)
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Old 06-19-2012, 01:29 PM
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Default RE: RE:

It depends what result you want and how close to the actual "C" rating you are.

If you want max power and/or if you are operating very close to the max "C" then use the highest actual "C" , if you want lower performance, long flight time and soggy performance and are operating well below the max "C" rating then choose the lowest "C" rating acceptable.

Probably the answer is simply to use the highest "C" rating , it won't hurt anything to go too high in "C" number. I know you already said you'd use WOT , but another thing to consider is that using a higher "C" rated pack may allow you to use LESS throttle to get the same power.
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Old 06-22-2012, 01:35 PM
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Default RE:

The only downside to a higher C rating is some added weight.  The C rating has nothing to do with flight time.  The prop and motor will try to draw all they need.  If they can't get it, then some of the power is lost in heat.  If they can get it, then the power will go to the prop.  More is better and more is also heavier.
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Old 06-22-2012, 11:33 PM
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Default RE:

The higher the "C" rating, the lower the battery's internal resistance. If you have a speed control and motor that can draw 60A, then the lipo ideally should be capable of delivering close to twice that current.
So, a 3300mah battery rated at say 20C can supposedly provide a maximum current of 66A, and is less than recommended for a 60A motor and speed controller. A 30-35C battery is much better. (99-115)
A 25C 3300mah battery can deliver 82A.
Remember that the C rating should not be considered a continuous rating if you plan on using the battery more than a few times.
The typical (for me) use - -
Take off 4s 3300mah Lipo Max current is limited to either 60A due to the speed control, or up to about 80A (battery & speed control combo)
As soon as the plane is in the air and stable, power is reduced, to just above 1/2 throttle for normal flying. This usually results in 5 to 6 minute flying times without overly discharging the battery.
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Old 06-28-2012, 10:32 AM
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Thanks for all the useful info, guys.
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Old 06-28-2012, 12:25 PM
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Okay that clears some things up for me. The plane comes with a 55 amp ESC so doubled it can handle 110 a. According to an earlier post the zippy 4000/25C (100a) will work good in the plane for both the w/b and output. I would also like to try a 3600/30C (108a) and a 3300/35C (115a). The extra 5a won't cook anything will it?
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Old 06-28-2012, 02:03 PM
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It seems as though you are thinking that the battery forces 100 amps thru to the esc and motor. It doesn't work that way , but rather the motor pulls whatever it requires from the battery. So, it is impossible to size the battery too big. Put a 1000 amp capable battery on and the motor may only pull 50 amps or whatever it wants.
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Old 06-28-2012, 05:23 PM
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That sheds some more light where needed. Thanks, Guver
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