What Are LiPo Battery Ratings?
Posted by on 03 August 2012 02:20 AM
There are three things that you should pay attention to when buying your battery. The Voltage, the Capacity (mAh), and the C Rating (C). Here is a quick overview of how each is indicated.
LiPo Batteries are rated at 3.7 Volts per cell, which is a key difference from the NiCad and NiMH only having a rating of 1.2 Volts. Because LiPo batteries are higher in Volts per cell, this allows battery packs to be smaller in size; especially helpful in cases of smaller RC vehicles.
Most RC LiPo battery packs will have two or more cells linked up in a series to provide higher voltages and each cell added will increase 3.7 Volts to the pack. You will only find battery packs in 3.7 increments. Each pack that is added to the Series is marked by an (S).
A lot of battery packs will have battery cells hooked up in Parallel to increase the capacity of the battery. Each Parallel series is marked by a (P).
Confused? Lets take a look at an example below.
You'll notice that this battery is at 2S and 1P. Where did i find this? The very top right corner, 3800mAh-25C-7.4V-2S1P. What this tells me is that the battery is running on 2 Series and 1 Parallel. Because it is a 2 Series battery, this battery is at 7.4Volts (also stated on the battery).
Most motor/speed controllers will show you what voltage is required for proper operation. This number should be followed in most cases since a change in voltage means that there is a change in RPM and will require changing the gearing. If a model calls for a battery at 7.4 Volts, then you should get a battery that is rated at 7.4 Volts, or 2S.
Capacity indicates how much power the battery can hold. This is indicated in milliamp hours (mAh) allowing the user to know how much load or drain (in milliamps) can be put on the battery for 1 hour at which the battery will reach LiPo cutoff. Keep in mind that LiPo batteries do not fully discharge, but will reach LiPo cutoff when the ESC (electronic speed controller) notices the voltage cell has dropped to its minimum. Unlike NiMH batteries which fully discharge, LiPo batteries typically cannot discharge to a rate of 3.0Volts per cell, any lower and the cell can potentially die and will no longer take charge.
EXAMPLE: A LiPo battery that is rated at 3800 mAh would be completely discharged in one hour with a 3800 milliamp load placed on it. If this same battery had a 1900 milliamp load placed on it, it would take 2 hours to drain down. If the load was increased to around 15,200 milliamps (15.2 amps), the time to drain the battery would be around 4 minutes.
For an RC model with that a high current draw, the higher the mAh is, the longer the battery will last.
Remember, the higher the mAh, the longer your play time will be. (Keep in mind that the higher the mAh, the larger the battery typically tends to be.)
Discharge rate is how fast a battery can be discharged safely. This is called the (C) Rating.
A battery with a discharge rating of 10C means that you can safely discharge it at a rate 10 times more than the capacity of the pack. A 15C pack = 15 times more. A 20C pack = 20 times more, and so on.
If a battery was rated at 10C and it has 1000mAh, this means that you could pull a maximum sustained load of 10,000 milliamps off that battery. If you draw continually from the battery at this pace, this battery will be done in about 6 minutes.
Some LiPo Batteries will indicate the continuous C Rating as well as the burst rating. A burst rating indicates the battery discharge rate for short bursts of extended power and is always twice the amount of the standard discharge rate. An example might be something like “Discharge continuos rate = 20C where burst rate = 40c”. The higher the C Rating, the more power you will get out of your battery.