In the last post we covered how RC lipo batteries are configured with the #s#p convention. Basically #s is for the number of cells in series and #p is for the number of cells in parallel. The more cells in series the higher the voltage. The more cells in parallel the higher the milliampere-hour (mAh). This post will take a look at the C rating that batteries come with.
In the picture we can see C being referenced in a few places – charge rate, discharge rate, and max burst rate. So, what is C?
C is related to the battery’s capacity and is referenced in terms of charge and discharge rates. For example let’s look at the battery we have. The capacity of the pack is 5000mAh or 5 Ah. 1 C for this battery is 5 Amperes. Basically C is the unit for a given battery’s capacity. This is nice but we do not often refer to a battery with this value alone.
The C value is often used to represent charge and discharge rates for a battery pack. In our example, and for many LiPos, the charge rate for the pack is recommended to be 1C or 1xC – in our case this means the recommended charge rate for the battery is 5 Amperes. Some batteries can sustain a higher charge rate, say 2C or more. If our battery could be charge charged at 2C it would be able to accept a charge rate of 10 Amperes (2C = 2x5A = 10A).
In addition to the charge rate C is also used with the discharge rate. Here it indicates what can be expected from the battery when it comes to discharging. There are two types of discharge rates – continuous and burst. The continuous rate is what the battery is rated for being able to sustain over a long period of time (until the pack is drained ofcourse ). The burst rate is a rating given for what can be expected from the battery in short bursts. This rate cannot be sustained for prolonged periods.
The continuous rate is the normal rate at which the pack can be drawn – the case when the motor is spinning freely. The burst rate is how much current can be delivered in a short period. Say your truck is at a full stop and you pull the throttle all the way. At that instant, the motor draws much more current than it normally would (to get moving from a stop). Having a higher burst rate means that you will be able to supply that hungry motor the juice it needs to get moving. Once the truck is moving, the continuous rate is what is needed to maintain speed.
When picking a battery pack, select a pack with a continuous discharge rate more than what your equipment needs. For instance if you have a motor that requires 50Amps choose a battery pack that has a continuous rate of more than 50A. If you use a pack that is not capable of delivering what the motor needs, your motor will underperform and the battery pack may be damaged from being discharged at too high a rate.
So, C is a multiplier of the battery’s capacity and is used to represent charge and discharge rates.