From a RC flight site:
An Introduction to LiPo batteries
A LiPo battery (can) consists of multipe cells (as indicated by an "S" you see next to the number on a LiPo) These cells deliver approx. 3.7 Volts per cell.
A 1S LiPo would therefore supply 3.7V (3.7V * 1 cell)
A 2S LiPo would therefore supply 7.4V (3.7V * 2 cells)
A 3S LiPo would therefore supply 11.1V (3.7V * 3 cells)
A 4S LiPo would therefore supply 14.8V (3.7V * 4 cells)
A 5S LiPo would therefore supply 18.5V (3.7V * 5 cells)
A 6S LiPo would therefore supply 22.2V (3.7V * 6 cells).
There are higher voltage / cell batteries availble.
Capacity
- The battery's capacity (sometimes refered to as it's "gas tank size") is defined in mAh (milli-Ampere per hour). A battery with a 1000mAh capacity can deliver 1 Ampere (1000mA/1000) for 1 hour. Or 1mA for 1000 hours. The larger the mA the longer your run time.
The battery capacity, together with the LiPo battery's discharge rate will define its maximum current output Amps. This important to keep in mind, when choosing a LiPo battery. The combination of capacity and discharge rate is what you will need.
It's important to remember that the battery cell count dosen't count for maximum current draw, ONLY the voltage(V) of your LiPo.
Discharge Rate
- All LiPo cells have a discharge rate and is defined by the letter 'C', this is called the C-Rating. Most batteries manufacturers say something like "25C to 40C" discharge rate. This means that 25C is the nominal discharge rate and 40C is the maximum burst discharge rate. Depending on throttle position. You fly full throttle and are near the 40C end your flight time will be less than if you are flying quarter throttle and closer to the 25C. It's advisable to stay near or below nominal discharge level to preserve battery future life, that's not to say you cann run it wide open but the over all battery life may suffer. Not all brands will list the peak discharge rate on the battery. Always check with the manufacturer / instructions on their recomendations.
- Example of a discharge rate:
A 3S (11.1V) 2200maH 40C LiPo will result in the following:
2200mAh x 40C = 88,000 mAh discharge rate
88,000 mAh / 1000 = 88 Amp constant discharge rate.
So in theory, a 2200mAh at 40C LiPo can only handle an max Amp draw of 88A.
- Example of Max. Flying/Drive Time:
Using the example from above...
A constant current draw of 88Amps from a 2200mAh LiPo will yield:
(2200mAh/1000)/88A = 0.025 x 60 = 1.5 minutes flying time.
This is why the combination of LiPo Capacity and Discharge Rate is so important for selecting the right LiPo for your application.
Also note that current draw depends on how you fly, and external factors such as air resistance, weight and wind speed.
We always recommend using a LiPo low battery indicator, better known as a "LiPo Screamer". These are easily configured, and simply plug into the ballance port on your LiPo battery, and will warn you when the battery is near empty. A average of an $15.00 investment will save you hundreds in plane parts, batteries. LiPo's DO NOT like to be complety discharged. If this does happen you have just ruined your LiPo.
You can also use the "Screamer" on your rc cars as well, honestly in any application where a LiPo is involved it is recommended to use one.
Charge Rates
- Most LiPo vendors will tell you what the maximum charge rate of the battery is, usually in C rating. If they do not, then please use this rule, ONLY charge it at a maximum charge rate of 1C. So, a 2200mAh LiPo can be charged at a maximum rate of 2200mAh / 1000 = 2.2A. ONLY use a LiPo charge to charge LiPo batteries, any other charger could over charge the battery and cause it to swell, rupture, explode and or cause a fire. Never leave a LiPo unattended when charging it.
