What do all those numbers mean on your LiPo batteries? Wonder no more.
In the beginning we used nitro-methane based fossil fuels. They worked well enough but required a bit of tinkering with the carburetor, external starting equipment, a fuel pump and a glow-plug. I got tired of all that and switched to electric. But what a learning curve! Here's what I know:
LiPo batteries (Lithium Polymer) or packs are composed of multiple cells wired together. Each cell is 3.7v and can have various capacities (mAh ratings). Generally the bigger the cell is physically, the more the capacity as measured in milliamps per hour (mAh). By wiring these cells together in series (S) or parallel (P) we can get different voltages and capacities. (mAh is the measure of how many milliamps can be drawn from the battery over one hour. A 2200 mAh battery should give you the rated voltage at a draw of 2200 mAh for one hour.)
Voltage and Amperage
The most common LiPo battery is the 3S1P (or just 3S). Huh? That's 3 cells (3) wired in series (S) and 1 cell in parallel (P) for 3S1P (the 1P is generally assumed so it is left off for 1P style). Each cell is the same- typically 3.7v/2200mAh. So that 3S means it's an 11.1v battery with 2200mAh capacity.
The 1P means there is one grouping of cells. Some batteries will have a 2P, meaning that there are two groups of cells wired in parallel to increase capacity without increasing voltage. For example if you have a 3S2P battery it will have 6 cells at 11.1v/2200mAh per cell and since there are two groupings of 3 cells in parallel the whole battery would be 11.1v/4400mAh. Got it?
Quick review- the S rating increases voltage and the P rating increases capacity (mAh). The S rating tells you the voltage and the P rating tells you how many groups of cells there are.
Ok, that was the easy part....There is another rating system used for LiPo- the C rating.
The C rating
The C rating is the maximum discharge rate as well as an indication of the batteries internal resistance (higher C lower resistance- more power). As I mentioned earlier my example 3S pack rated at 2200mAh (or 2.2 Amps) could theoretically be discharged at 2200mAh (2.2 A) for one hour (1C). That's really not much of a draw. Most motors want upwards of 40 Amps (40,000mAh or 20C).
The C rating for my example battery is 25C continuous, 35C "climb outs" and 50C max bursts. This is derived from how many amps the battery can supply on demand. So this 25C pack would be 25 x 2200/1000 for a discharge rate of 50 Amps. So technically this battery can supply 50Amps continuously, 77Amps for a short period and a max short burst of 110Amps.
What does the C rating mean in practical terms?
It means that your battery will discharge at the given amperage. If your motor needs more power (amps) than the battery can produce you'll see an apparent loss of power. Let me give you a real world example:
I fly a 50 sized Hirobo Sceadu Evolution that I converted to electric. I started out using 4 11.1v/2200mAh 20C batteries in series and parallel for a 6S2P configuration (22.2v/4400mAh 20C). The heli flew perfectly. Power when I needed it, no hesitation, perfect. The only trouble was flight times...the batteries were of varying ages and I got maybe 4 to 7 minutes flight time.
I was now on a search for bigger better batteries. 22.2v batteries at 4000mAh aren't cheap. Especially with a 20C+ rating. So I headed to Ebay...
I purchased some cheap batteries on Ebay. They were a pair of 6S1P 22.2v 4000mAh 15C rated batteries. I used the batteries in parallel for a total of 8000mAh/15C.
Well, my flights were nice and lasted up to 16 minutes (more mAh). BUT, when I needed extra power for flying with a fuselage or I wanted to jump altitudes quickly there was no power (still only 15C). The motor slowed and I had to land to let the motor speed back up. After lots of testing I realized that the batteries couldn't supply the power needed! Crap! I got what I paid for...I realized just why the high end 6S1P batteries are upwards of $200 each. They can supply the power needed!
I later purchased some 6S1P 30C batteries. What a difference! Twice the C rating and lots more power.
Putting it all together
So now you know the numbers. The bottom line is that your typical 450 size heli is going to be fine with a 3S battery rated at 20C or so.
More mAh means longer flight times. More C means more more power on demand (depending on how you fly...).
Really the C rating can tell you a lot about the battery. It can be misleading unless you understand it!
Happy Flying!