The basic knowledge of RC battery internal resistance
This entry was posted on February 3, 2017.
Battery is necessary accessories of RC plane. Different type battery has a different internal resistance. The use in different chemistry materials in same types of batteries, will also lead to different internal resistance. Normally internal resistance is very small that we are measuring with milliohms. It's a very important standard in measuring battery's performance. Normally, batteries with very low internal resistance have higher discharge power, vice versa.
From discharge circuit principle point of view, we can consider a battery and its internal resistance as two separate parts. A power string that has no internal resistance and a resistance comes in very low value. In this case if the battery was connecting to a light power device, then the voltages that can be assigned to the resistance can be very low, vice versa. At the same time some of the power will be consumed by the resistance. They might be converted to heat, or other complicated reverse electrochemical reaction. IR of a rechargeable battery can be really small when first out of the factory. After long period of use, electrolytic solution becomes exhausted, internal chemical material turns inactive, which causes the increase of internal resistance. When the internal resistance reaches a certain level that power cannot be released anymore, and then it comes to the end of batteries' life. Reason of batteries' power exhausted is mostly caused by the raise of internal resistance. Therefore discharged power volume should be in more consideration rather than charged power volume.
1. IR is not a fixed value.
It's difficult to measure the value of internal resistance since it is not staying the same under different circumstances. From the technical point of view, we will separate it into two different categories whilst discussing battery's IR: Charged and discharged.
A: Charged internal resistance stands for the IR value that is tested while a battery is fully charged.
B: Discharged IR stands for the IR value that is tested while a battery is totally discharged. In normal circumstances, IR is not staying the same during the discharge process, moreover the tested value will be much higher then it's actual value. However IR value is relatively more stable during charging process hence charged IR is more close to the actual value. IR value that tested during charging process is normally the standard value.
2. Internal resistance cannot be measured in the usual method.
In practice, the IR calculation equation cannot be applied in measuring RC batteries IR since the actual value is way too small to be precisely measured. IR of RC batteries are normally count in micro or milliohms ohms. However tolerance we required are 5%, since professional equipment are required in measuring RC batteries' internal resistance.