When you are looking to purchase a LiPo battery for your RC car, no one explains what exactly is required. Sure, you may know exactly what voltage you need as represented by the amount of LiPo cells in series. You may also know the capacity that you need as represented by the “mAh” of the pack. However what about the required C rating of the battery?
Quick Review of the C Rating
The C rating of a pack is a multiplier used to determine the maximum continuous discharge current of the battery. Typical numbers are 25,35,45 and so on. It is this Continuous rated C rating that is multiplied by the capacity of the battery pack in amp hours (Ah) to determine the maximum continuous rated current of the battery pack. A higher C rating tells us that the battery is able to provide higher current output performance.
Example:
4000mAh at 25C continuous. The maximum continuous discharge current of this battery would be 25 x 4 = 100 Amps
4000mAh at 45C continuous. The maximum continuous discharge current of this battery would be 45 x 4 = 180 Amps.
Can the C Rating Destroy your Motor or ESC ?
Now that we understand the idea behind the C rating, we can figure out if too high of a C rating can destroy your ESC or brushless motor. In the above examples we have determined that the battery pack with a C rating of 45 can deliver 80A more in comparison to the 25C rated pack. What does this mean for our brushless motor and ESC?
When it comes to battery packs and motors, the biggest concept to understand is that a battery does not “push” power to the motor. Just because the 45C rated battery can deliver 180A of continuous power doesn’t mean it will. In fact, the load placed on the motor determines how much power is going to be drawn through the motor, ESC and battery.
A higher C rating should not ever destroy any RC component. However, this does not fully mean that it is impossible. If the power system in your RC vehicle has not been correctly selected, it is possible that a component within your RC can fail. We discuss this further below.
Performance Benefit of Higher C rating
Having a higher C rated battery allows the battery to have a lower voltage drop under load. When the battery is able to maintain higher overall voltages, it is expected that the current increases as well. This increase in current is what can lead to failure within an electrical component. Power systems that fail purely due to an increase in C rating are 1) not selected correctly and 2) already operating near its thermal limits.
Here is an article that talks about choosing the best C rating for your power system. In short, it is best to select the highest C rating possible for maximum reliability within the ESC. Visit the ripple voltage page to learn more. Next we will look at how to confirm that using a higher C rated battery will not damage your RC car.
Confirming too high of a C Rating Does Not Cause Damage
There are a couple scenarios where higher or “too high” of a C rating can cause damage to RC’s and we can identify them beforehand.
Scenario 1 – Some Ready to Run vehicles use brushed motors. Brushed motors have a narrow performance range by nature and manufactures try to get the most out of these inexpensive motors. In addition, NiMh batteries are also commonly used in these setups. If your brushed motor is operating at case temperatures above 150F while on a factory setup, there is a very good change that using a LiPo battery at any c rating (NiMh batteries have a very low C rating) can cause thermal damage. It would be best to swap out the power system to a brushless setup prior to switching to LiPo batteries. If you are willing to try LiPo or a higher C rated battery, just be certain temp limits are not exceeded.
Scenario 2 – If your setup is operating near its thermal threshold, chances are significantly increasing the C rating of your pack will heat things up further. Use a temp gun to measure the temperature of each of the components within your power system. Confirm that the temperatures are within the maximum specified ranges. If you are operating within a safe temperature range on all components, try out the higher C rated battery. Measure the temperatures yet again of all components. If temps are still within spec, your system is good to go.
Conclusion
A higher C rated battery in the vast majority of setups will be best suited. Not only does a higher C rating provide better performance but it also provides higher reliability for ESC’s. Simply monitoring temperature (should be doing this already) upon any change in your setup and confirming it is within spec will guarantee reliability.
With correctly selected power system, there should never be such thing as “too high” of a C rating.