Apart from the few re-chargeable AAs in my stuff, none of the cells I have give an mAh value. The re-chargeable ones I have, do give mAh, but no C rating.
So, is there a reliable table anywhere that gives typical (ie in the absence of makers' specifics) values of mAh and C for the different battery technologies and standard sizes?
I don't think so. There are too many differences.
For Li-ion cells I use the rule of thumb to use 1/3 C. So it would take 3 hours to unload. But I think for good Li-ion cells 2C should not be a problem.
Some Lipo cells can do even perhaps 10C.
There is also the temperature dependance and how full they are loaded and unloaded. I read that for militairy applicatons the Li-ion cells are loaded up to 3.95V, and for consumers 4.20V. Consumers need longer lasting devices and military need high reliability.
I agree with Erdin
The C rating is highly dependent on the usage.
To give an example:
In my RC-planes I use LiPo's with C-rating
45C discharge and 5C charge
In my RC transmitter the LiPo is rated
3C discharge and 1C charge
Most portable batteries are rated at 1C, meaning that a 1,000mAh battery that is discharged at 1C rate should under ideal conditions provide a current of 1,000mA for one hour.
Yep I know what the C-rating means, was asking for some typical numbers if maker didn't stick one on the cell.
If you go to the manufacturer's site you can usually download what you want by brand. Outside that, here are some ROUGH numbers off the top of my head for some decent quality alkalines:
D - 15000mAh
C - ~7800mAh
AA - ~2800mAh
AAA - ~1100mAh
Carbon batteries would be good for about half that and NiCd batteries only for about 30% of the alkaline capacity.
Oh I thought this was a problem ...
The re-chargeable ones I have, do give mAh, but no C rating.
... so mAh and C are the same thing.
Re other cells, such as alkaline, you can usually find mAh ratings if you track down the
manufacturers datasheet for the part. It's just not printed on the batteries themselves.
With alkaline, a lot of them are labelled as heavy-duty, and from my experience, this
generally means "total-crap" as a battery. The better ones are labelled long life or such,
but they may deliver lower max currents than the heavy-duty ones. In any case, we should
all be using rechargeables anymore.
so mAh and C are the same thing.
No they're not... as this explains
For starters, the C in C Rating stands for capacity. To break it down to its simplest terms, the C rating is the maximum safe continuous discharge rate of a pack. If you see 10C on your battery, it means it can be discharged at 10 times that pack's capacity. Capacity refers to the milliamp-hour rating of the battery, which will be listed as a number followed by mAh (2000mAh, for example).
This is very poorly written. If you read that carefully, you'll see the 1st and last sentences
actually indicate the C rating is the stated capacity in mAh.
Then, onto completely different matters in between, the 2nd sentence says C is the
"maximum safe" discharge rate, but then sentence 3 says if the battery is stamped as
10C, that's the actual rate it can be discharged at - [although being 10X the "safe"
value, the battery apparently won't actually explode, and destroy your $500 R/C car
in the process]. Do you really want to trust your car to a guy who flunked English
101?
I think the guy who wrote the
page actually passed English 101.
Maybe it's poor writing, but C and mAh are NOT the same regardless of how that's written.
mAh is the energy contained; C is how quickly that may be used up. One is energy, one is power.
A 1000mAh battery might be able to provide 1A (thereby lasting an hour), but won't necessarily be able to provide 10A for 1/10 of an hour, since it might not be able to provide 10A at all. It might be able to give say 5A though, thereby lasting 1Ah/5A = .2 of an hour... you can't deduce the maximum current from the mAh value, just because you can do some simple arithmetic and say Cool!- this 1000mAh cell can provide 10A for .1h just because 1Ah/10A = 0.1 h
So the C value indicates what that maximum draw may be- you could have 2 x 1000mAh cells with different C ratings (say 8 and 10) which would both contain the same energy but deliver different power.
The maths is straightforward, the problem is the nomenclature. It would help if
someone would actually put units on C. And how do you rationalize these two
sentences?
the C rating is the maximum safe continuous discharge rate of a pack. If you see 10C on your battery, it means it can be discharged at 10 times that pack's capacity.
oric_dan:
The maths is straightforward, the problem is the nomenclature. It would help if
someone would actually put units on C. And how do you rationalize these two
sentences?the C rating is the maximum safe continuous discharge rate of a pack. If you see 10C on your battery, it means it can be discharged at 10 times that pack's capacity.
Lets say I have 2500mAh pack in helicopter. If I could charge it at 4C, then I could put 10A into it when charging. If I could discharge it at 20C, then I could draw 50A for about 3 minutes. I think that's what they mean.
Why is everyone assuming LiPo batteries? The question is about rechargable AA's which are usually NiMH.
Consult the manufacturer's data for the cells in question - I'm afraid all batteries are different and the only
reliable answers are in datasheets - this is one of the many reasons to avoid unbranded batteries!
C ratings are usually only used in the RC-model world, normally a battery datasheet gives typical charge and discharge
curves showing the variation of capacity and voltage with current - its not too hard to interpolate between a set of such
curves to get a good estimate of performance.
Alas all rechargable batteries degrade with time and usage, so in practice you'll be wise to choose battery
capacity and power ratings conservatively so they continue to function for a long lifetime (this is usually of no concern
in RC models world where things like a 30C LiPo really means "unlikely to catch fire if discharged at 30x capacity" and
the fact the number of useful recharging cycles is severed reduced by such abuse is immaterial since the overriding
concern is battery weight.
Alas all rechargable batteries degrade with time and usage, so in practice you'll be wise to choose battery
capacity and power ratings conservatively so they continue to function for a long lifetime
I have dozens of NiMH AA-cells, and have used many of them for almost 10 years now.
The ones that didn't last very long were the 2500 mAh Energizer cells that were sold with
a 15-min charger, so this would perform charging at a 4C "rate". Even with a fan in the
charger, the batteries would get too hot to touch, a sure sign of early death in the offing.
Of about 20 batteries, roughly 1/4 of them failed, and would not deliver the same energy
as the others, meaning they would quickly discharge and even reverse their polarities when
used in a pack.
My other 3 or 4 chargers charge in anywheres between 4 and 12 hours, and treat the
batteries in a much kinder fashion.
As I see it, you have to distinquish between energy capacity C in mAh, and charge/discharge
"rate", meaning n*C in amps. The terminology leaves a lot to be desired.
As I see it, you have to distinquish between energy capacity C in mAh, and charge/discharge
"rate", meaning n*C in amps. The terminology leaves a lot to be desired.
I agree. The R/C hobby battery suppliers seemed to have originally come up with this xC rating as a way to define how high a continuous current one could draw or force charge into or out of a cell in the shortest possible time frame, and was not something mainstream battery manufactures usually specified at the time. The competitive R/C contester types would often try and select cells from large batches such that they could consume the whole battery discharge in a short 5-10 min discharge into their electric motors and would select the cells that supplied the highest current. This is very hard on such cells and does result in pretty short lifetimes, but in the world of competitive contesting such is/was needed to remain competitive.
Lefty
Apparently, the R/C suppliers hand pick cells to match each other as closely as possible
in terms of similar characteristics.
When my Energizer cells started experiencing premature failure 5 or 6 years ago, I built
a jig to measure the voltage of each cell separately, and which displayed a representation
of same using Led light intensity, and could watch the bad cells in a series pack going flat
in double-time. Also shows what happens when you use different capacity cells in the same
series pack.
In both cases, the better cells overwhelm and actually discharge the other cells. Makes you
a believer in regards the problems with using poorly matched cells in a series pack.