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LiPo C-Ratings and What They Mean

This MaxAmps pack has a whopping 150C charge rate, so it can be charged very quickly.

What do charge rates mean, and is there a noticeable performance difference between high and low rated packs?

Charge rates are just what they sound like. It is the amp rate at which you are capable of charging a specific battery pack. Most commonly you will see this at 1C, 2C, and all the way up to 5C. Well what is “C” in this scenario? It is the amp hour of the battery packs. While most are familiar with the milliamps, the amp hour is that number divided by 1000. So for a 5000mAh battery, 1C would be 1(5) or a 5 amp rate, 2C would be 2(5) or a 10 amp rate, and 5C would be a 25 amp rate. A 1C charge or discharge should be an hour long process. 2C cuts that time to about 30 minutes. Balancing can extend the overall time but this gives you a ballpark in terms of the time it will take at any of these rates.
Your charge rate used to make a big difference in overall performance in the days of NiMH and NiCad cells. The faster you charged the more punch you would get. This also tended to lead to less cycle life. With LiPos the difference really isn’t that obvious. It’s not a night and day performance difference charging at a faster rate. Opposed to charging packs at faster rate you would see more benefit from charging your packs just before use because you would maximize capacity. The main reason to charge at a rate that’s higher than 1C at this point is to reduce charge time: 1C = 1 hour, 2C = 30 minutes, and 5C =12 minutes. Balancing tends to be an equalizer here, though. At a 5C charge rate, it is more likely for cells to get out of balance. The farther they are out of balance the longer it takes to balance at the end of a charge cycle. This can, in turn, increase overall charge times.
Higher grade batteries can handle these rates at little to no degradation but lower grade cells have a much higher probability of failure at higher charge rates. Make sure to charge your battery according to manufacturer recommendations to ensure long life and great performance.
Joshua Barker, MaxAmps

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13 Comments

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  1. Great Article!!!!!! Thanks!!!!!

  2. I only see where you discussed the C rating as it relates to charging. What about a 45C rated battery? Or even a 65C rating battery? I didn’t see any remarks on those ratings. Thanks.

  3. If I use a .60 glo motor with pneumatic retracts with Dectrum radio (+RXC7 rX) what kind of battery pack do I need to use?

    1. David,

      Since you are running a nitro motor and your retracts are pneumatic, the majority of the current draw will be from the servos. Your radio manual should tell you what voltage your equipment is rated for and you will probably use either a NiCd or NiNH pack of the appropriate voltage. The capacity of the pack (number of milliamp-hours) will be determined by the number and type of servos that you are using; i.e., analog servos versus digital servos. The guys at RC Groups can probably help you pick the right pack.

  4. I agree with “day” can you explain the higher ratings as mentioned?

  5. Love the fro bro!

  6. some people say that if you use a 30C battery and switch to a 60C (exemple) you can burn the motor and esc. This is true ?

    1. Andre,

      Not true. A higher C rating will not damage anything. The only thing that might damage your equipment is switching to a higher voltage battery, that is, one with more cells. For example, changing from a 3-cell to a 4-cell might damage something.

  7. Completely agree with “day” above. I have a basic understanding of the math of charge amps versus time to charge, but I’d love to see a little more meat on the nameplate ratings. Also things like if a given item recommends 45C, for example, what if a higher or lower C was installed just because I happened to have one on the bench? Would it work at all? Possible (heaven forbid) fire? Etc?

    Great start, but please flesh out a little more, or modify article title to more accurately reflect the actual topic being discussed. Great info, though, so please don’t take this as criticism at all!

    1. Using a battery with a higher C rating might improve performance somewhat because the battery with a higher C rating will probably have a lower internal resistance and will result in slightly higher working voltage.

      Using a battery with a LOWER C rating could be a problem, because you will be pulling more current than the battery is rated for. This might cause the battery to overheat, or damage it in other ways.

  8. The c rating on the back is the charge rate as mentioned.
    The higher value rating on the front is the discharge rate. So it’s the capacity multiplied by this number.
    Example a 5000mah 40C is 5×40=200A
    Manufacturers tend to exaggerate these figures sometimes I’ve found

  9. A LiPo battery has two “C” ratings, one for charge and one for discharge. These are the “absolute maximum ratings” of the battery, supposedly how fast you can charge and/or discharge without doing damage. In practice, the closer you come to these limits the shorter the life of your pack. Getting closer to the limit on discharge tends to accelerate failure more than pushing the charge rate. This is primarily because of heat. A 45C discharge of a 2000mAh battery is 90A of current. If the same battery can take a 5C charge, that’s only 10A. Power dissipation goes up with the square of current, so the 45C discharge generates a lot more heat than the 5C charge. And heat is what kills a LiPo.

    The charge “C” rate simply dictates how quickly you can charge your battery. 1C means it takes 1 hour to charge. You’d think 5C would mean the battery would charge in 12 minutes. But there are non-linearities in the charge cycle, so it will probably take closer to 20 minutes. There is no advantage to faster charging except that it takes less time to charge. You don’t get any more power in to the battery than if you charged it slow. In fact, I’ve seen some studies that show you end up with slightly less capacity at a higher charge rate.

    The discharge “C” rate is important for two reasons. First, you don’t want to discharge the battery at anything close to its “C” if you want the battery to last. I usually “derate” my packs by 50%. So if I have a motor/prop that’s going to pull 45A from a 2000mAh pack, I use a 45C rated pack which is good for 90A, 2x what I expect to pull from the battery. Higher C discharge is also important because “C” rate and internal resistance are highly correlated. A higher “C” battery has a lower IR. This means higher performance and maybe even a little longer flying time. A 20C pack might have an IR of 100mOhms where the same size 40C pack might be 50mOhms. If the motor pulls 20A from the pack, the 20C pack is going to show a voltage drop (“IR Loss”) of 20*0.1 = 2V. The 40C pack will show a 1V drop because its IR is 1/2 as much. If this is a 3S battery with a nominal voltage of 11.1V, the motor sees 9.1V on the 20C pack and 10.1V on the 40C pack. You get almost 10% more voltage from the 40C pack than the 20C pack. Since electric motor speed is proportional to voltage, this means you get almost 10% higher prop speed from the 40C pack. So higher “C” discharge rates mean less voltage drop due to the battery’s internal resistance which means more voltage gets to your motor which means you get better performance.

    Higher “C” discharge rate comes at a cost (more expensive). And it makes the battery heavier. Not a lot, but it could matter depending on what you’re flying. For most models, though, higher “C” discharge will provide better performance in spite of a small weight gain.

    I buy the highest “C” discharge rate I can afford. I don’t spend money on higher “C” charge rates. I spend that money on more packs. I do all my charging before I go fly, charge rate isn’t a factor, I just start charging earlier if I want more packs when I go flying…

    1. I got more info out of Randy’s comment to the article than I did the article. I still wonder though why these batteries can’t simply have Amperage ratings? Having these silly “C” ratings simply make it look as if modelers are either “elitists” who need their own terminology rather than using existing electrical characteristic nomenclature, or the makers of the battery, motor and components think modelers are to simple minded to understand basic electronics. I however am left with the question of if “C” rating x mAh rating = max output current, what do the “C” ratings on ESC’s mean?

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