What is "C" rate of lipo? - RC Groups
Feb 27, 2012, 03:54 PM
Registered User
Discussion

# What is "C" rate of lipo?

What is "C" rate? Is it abt discharge rate?
What is the advantage of that "C" more or less? Plain english pls
 Feb 27, 2012, 04:49 PM Space Coast USA As plain as can be. http://sites.google.com/site/tjinguy...arging-how-tos
 Feb 27, 2012, 05:03 PM Registered User Holy not searching for your answers in the 10 million posts this has already been explained in, but hey I'm all ears for this new one. I need some lessons on Li-Po too.. come on experts chime in any time now.
 Feb 27, 2012, 05:13 PM RIP Azarr - "Old age is not for sissies" Doesn't get much better than the link hoppy posted. Or, you can scroll down to the bottom and see similar threads. Azarr
 Feb 27, 2012, 05:34 PM Southern Pride
 Feb 28, 2012, 04:01 AM Registered User I must take issue with the link in hoppy's post: It starts off good by saying that C is a variable (I prefer to call it a constant), but then it goes on to say, "Figuring out what C is for a particular pack is simple, just take the capacity of the pack in mAh, divide it by 1000 to get Ah and then drop the "h", that is C." That is completely wrong, C is not simply the Ah without the h. C is quite simply a number that the manufacturer has determined, hopefully by design backed up by experiment. It is a constant for any particular pack, and can be used to calculate safe discharge amp rates. So, for a 2200mAh 20C pack, for instance, it should be okay to discharge it at anything up to 20 x 2200/1000 = 44 amps. Note that the headline C rating is not used to calculate charge rate: Usually it will say in the small print on the pack what C it can be charged at. It may be 1C, 2C, or maybe up to 5C or more. If it says nothing, you should assume a 1C rate for charging which, in the case of the 2200mAh pack would be 1 x 2200/1000 = 2.2 amps.
 Feb 28, 2012, 04:13 AM Southern Pride C does in fact stand for Capacity and not only that but capacity stated in Ah or mAh. Ever notice on the HK site number on thier nano tech LiPolys such as 2.2 or 3.3. That would be 2.2Ah or 3.3 Ah. The C45 indictaes it can be discharged at C X 45 or 2.2 X 45 or 3.3 X 45. C when used a statement of Capacity in Ah is often fairly accurate however when used with a multiplier such as 20 - 65 for stating possible discharge rates it is often just a bunch of hot air , marketing hype, used car salesmanship, fairy tales, etc... Charles
 Feb 28, 2012, 05:25 AM Registered User I see we are still managing to get confused over the difference between the C rate and the C-rating. The C rate for a battery is not actually capacity, it is (and always used to be known as) the 1 hour discharge rate. It is therefore the CURRENT which will discharge the battery in one hour. By a bit of good luck it is the same NUMBER as the capacity but because it's a current it is stated in mA or A not mAh or Ah . The C-rating is a multiplier which, when applied to the C rate, gives the (theoretical) maximum current the battery should be able to supply. So 20C means 20 times the 1 hour discharge current. Thus a 3000mAh capacity battery has a C rate of 3000mA (or 3A). If it has a C-rating of 25, usually stated as 3000mAh 25C, it should be able to deliver 25 x3 = 75A. If it has a C-rating of 40 it can in theory deliver 40 x 3 = 120A maximum. We could really have done with some clearer terminology. Using C for a current just tempts far too many people into thinking it means capacity and from there they go on to get even more confused . Steve
Feb 28, 2012, 05:52 AM
Southern Pride
Quote:
 The C rate for a battery is not actually capacity, it is (and always used to be known as) the 1 hour discharge rate
IMO that is a direct contradiction.

More correctly the Standard charge rate for LiPolys for years ,years ago was 1C.

In order to charge a battery in 1 hour it must be charged at 1C ,C being the capacity of the battery in Ah.

1Ah (1,000 mAh) charged at 1A rate is a 1C charge / one hour charge.

C used as a unit of capacity makes C charging rates and discharge rates much simplier for the masses to understand.

2.2Ah charged at 1C = 2.2A / charged at 5C = 11A

Discharged at 10C = 22 Amps. ( 10 X 2.2 ) / discharged at 10C = 6 minutes (60 min . / 10 ).

Long before LiPolys and their 1C charge rates came along Nicads were commonly charged at C/10 ( 1/10 C ).
To get the charge rate for a 1,000 mAh Nicad one divided the capacity of 1,000 by 10 which equals 100 mA whic is thus a C/10 or 1/10 C charge rate.

http://www.camlight.com/techinfo/techtips.html

Snip:

Quote:
 Maximizing NiCd/NiMH cell life The life of your cells can be increased by following these tips: Condition your new packs by gently cycling them, at least twice. Charge at a 0.1C rate (or less)

Charles
Last edited by everydayflyer; Feb 28, 2012 at 06:07 AM.
 Feb 28, 2012, 07:09 AM Registered User C can indeed mean "capacity", and I can see a logic for it being so in what we're discussing -- i.e. you take the capacity and multiply it by 25, or 0.1, or whatever the appropriate number is. But, if that's the case, what do we call that number itself -- the "discharge factor" or something like that would seem to make more sense than just referring to the "C-rating".
Feb 28, 2012, 08:21 AM
Registered User
Quote:
 Originally Posted by everydayflyer IMO that is a direct contradiction. More correctly the Standard charge rate for LiPolys for years ,years ago was 1C. In order to charge a battery in 1 hour it must be charged at 1C ,C being the capacity of the battery in Ah.
Sorry but it's annoying when people such as you who really should know better insist on referring to things charging at 1C where C is in Ah. You charge at a CURRENT measured in A or mA. You can't measure currents in Ah.

BTW it has never been possible to charge a battery in one hour using the C rate. It ALWAYS takes longer than one hour because charging is never 100% efficient. That's why it's sensibly called a DISCHARGE rate NOT a charge rate, because you can fully discharge a battery in one hour at that rate.

But you're right it has existed for many years, well before Lipos. Indeed the capacity of NiCds was usually specified at a DISCHARGE CURRENT of 0.2C. And the same value (the current C) was used to describe the charging CURRENT as in 0.1C or for some of the better NiCds anything up to 5C. But C has always been a measure of CURRENT it's never been a measure of capacity.

Fortunately the calculations using it are simple enough that most people manage to get them right even it they don't quite understand what it is they're doing .

Steve
Feb 28, 2012, 09:19 AM
Southern Pride
I posted

Quote:
 2.2Ah charged at 1C = 2.2A / charged at 5C = 11A
Which is correct.

Quote:
 I posted In order to charge a battery in 1 hour it must be charged at 1C ,C being the capacity of the battery in Ah.
Which you seem to want to iinterpret as me stating charging as a Ah rate.

Let me explain in very simple terms.

C being the Capacity of the battrery in Ah thus a 2.2 Ah (2200 mAh) is charged at 1C obtained by taking the capacity in Ahs and multiplying by 1.

Charles
 Feb 28, 2012, 10:35 AM Space Coast USA The problem is that C and C-Rate are being confused and used interchangeably. A 25C 3s1000mah pack is really a 25C-Rate 3s1000mah pack.
 Feb 28, 2012, 01:41 PM Registered User Whoops, double post.
Feb 28, 2012, 01:42 PM
Registered User
Quote:
 Originally Posted by everydayflyer Let me explain in very simple terms. C being the Capacity of the battrery in Ah thus a 2.2 Ah (2200 mAh) is charged at 1C obtained by taking the capacity in Ahs and multiplying by 1.
Let me explain the way multiplication works, in very simple terms if you like.

If you multiply a value in Ah by 1 you still have a value in Ah. 2.2Ah times 1 = 2.2Ah. You can't just suddenly ignore the "h" and pretend it's gone away. And talking about a charging current of 2.2Ah is as wrong as saying "The voltage of a 3S pack is 11.1 watts". Completely the wrong units.

But never mind, we've probably completely confused the OP by now so I'll let you carry on with your misleading information. As I say the numbers still work out right even if you don't quite understand what you're doing.

Steve