C-rating: what you need to know & why

Apr 06, 2012 17 Comments by

Ever wonder what the right LiPo C-rating is for your various models?  How is C-rating actually rated?  We asked Lee Estingoy from Castle Creations this question and he gave us an insider’s view of this misapplied and understood rating.

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About the author

West Coast senior editor About me: I’ve been involved with RC aircraft since high school and have flown just about everything. I started my RC career with scratch-building, but now like many pilots I rely on ARFs to get me in the air. My main focus is on pylon racing, aerobats, combat and scale warbirds.

17 Responses to “C-rating: what you need to know & why”

  1. r.Mordred - ( says:

    I really did not get an answer to yhe question o had which is if i have a 35 amp controller calling gor a 20 c batt and put in a 35 c batt will ot destrpy my esc?

  2. RCFlyer44 says:

    Starts out great, but get a little confusing and off track there towards the end.

  3. jim wilkinson says:

    could not follow his explanation about the -C rating and the ESC,being new to elecrtic .
    it would be better if put on a chaulk board and have the motor,esc and the C RATING .AS i BUILD MORE ELECTRICS
    I FIND ALL THE INFORMATION ABOUT THE SIZE OF THE BATTERY AND C RATING,I ASSUME THAT INFORMATION GIVES YOU THE RIGHT EQUIPMENT

  4. RO Porter says:

    You show a thunderpower 65c battery but you make no comment about it. Is this a conservative battery or a dud. If I understand you could discharge tho full amp rating in a little less than a minute. If you cut back on the esc power requirement will you get more flight time?

  5. David Kosowski says:

    Talks about c rating but never really explains it.

  6. James Manley says:

    I did understand his explanation, but versus what my testing shows, it seems his explanation is incorrect. In my electrics I have noticed in my packs is, the C rating relates to how long i can sustain amperage for given throttle position before the battery starts to drop off and deliver less. For example using a 20 C pack 6cell 4000mah I pull say 50 amps for 1 minute. Before the amp draw begins to decrease. With a 30C 6cell same mah I pull 52 amps for 1 1/2 minutes before the amp draw begins to decrease. Overall the battery run time is seems to last a little longer also.

  7. Richard says:

    They missed one other important factor related to the “C” rating, an increased charging rate that will not overheat – and “puff” the battery.

    And for me, one of the important factors of a higher C rating is the battery has a lower internal resistance. This is an impedance that limits the current flow in the motor circuit. The higher C rating results in a lower total motor circuit impedance; and thus higher motor current! So watch out not to overload your ESC when moving to a higher C rated battery!

  8. Paul says:

    C rating allows you to calculate the maximum continuous current (amps) the battery is capable of supplying at it’s rated voltage. To get max Amps you multiply C rating by the capacity of the battery (Amp-hours). In my experience most battery manufacturers overstate the C rating, some by a lot!
    ex. 2000 mAh 11.1V 20C
    max continuous current = 20 (C) X 2 (Ah) = 40 Amps
    max continous power = 11.1V X 40A = 444W

  9. Nitrocharged says:

    If you stop watching it at 1:52 that’s all you need to know about C rating.

  10. Greg says:

    He did not want to really answer because he does not know or he really does not want to dive head first in to it. I have purchased cheap lipos and expensive ones. Usually the brand names work better. That does not mean the cheap ones are not good for certain applications. You need a brand name for a High performance EDF and can use a cheap brand for a park zone plane. A 35c 2200mah lipo pack can provide 77 amps constant. To figure it out you times the c rate by the mah so 35c times 2.2mah will give you the answer of 77 amps constant. You have to move the decimal point from the mah if the battery is not labeled as a 2.2 to get the answer. The brand name battery’s are rated under what they can put out. The cheaper Chinese battery’s are not always as good as they say and a 35c cheap battery may only be good for 30c or less in some cases. That is why the cheap battery’s get hot while you use them. I have over 75 lipos and have had good ones and great ones..

  11. Bob says:

    Well if I wasn’t confused before I am now??

  12. David Burns says:

    I would suggest that everyone enjoying the electric side of this hobby gain a working knowledge of ohms law.

    He did explain that the C rating is an arbitrary rating that has no universally accepted means to determine. At best we should be able to understand that a 30C rating from one manufacturer will be able to discharge at a faster rate than a 20C from that same manufacturer provided all other ratings are the same.

    See: http://en.wikipedia.org/wiki/Ampere-hour
    http://en.wikipedia.org/wiki/Ohms_law
    http://en.wikipedia.org/wiki/Lithium-ion_polymer_battery

  13. Jim says:

    He doesn’t really know either.

  14. Van Baugh says:

    I will have to admit that I do not know much about Lipos and their current rating. I do agree that the brand name Lipos seem to have a better current rating than the cheaper Lipos.
    For example, I have an Eflight Blade mCX2. I noticed that the 1 cell Lipos did not give me very good flite time. Maybe about 3 minutes. I purchased some 1 cell 3.7v 150mah 25c batteries.
    The batteries that came with the heli were 1 cell 3.7v 150mah 12c. The heli flew, on the 25c batteries, 5 to 7 minutes longer.
    So, I believe that the higher the rating the longer the battery can produce power. Greg has a good formula for determining the amp rating.

  15. Brett says:

    He missed a big point…CHARGE RATE. One of the things I love about gas/nitro is the lack of having to wait for batteries to recharge as often, you can land, refuel, fly… The higher C rating batteries really enhance my enjoyment of electric flying because you can charge them faster and fly more.

  16. Robert Lundstrom says:

    The first two minutes is all you need to know without graphs. How about a magazine article by MAN where they test several batteries for internal resistance, amp draw, and other real world flying applications?

  17. Gary Gullikson says:

    My take is that lipos start out at a certain actual internal resistance per cell and resistance rises as cells are used and stressed. as shown on my Cell Pro 10S charger’s IR per-cell display,.I you let them “loaf” they will perform well longer.I notice that High C -rated packs are usually thicker/heavier than, say,10C packs. A good high C-rated pack should retain good performance, run cooler and not “puff” when stressed, longer than a low c-rated pack.
    It would be interesting to compare cell resistance in T-Power vs Hobby King, etc., low price lipos, all rated at 25C, Some cheapies perform well for many cyckles, some develop hig h resisance in on or more cells early on.

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