The ESC in a radio controlled vehicle is responsible for delivering power from the battery pack to the motor. Input power to the ESC is in the form of direct current. Output power is in the form of alternating current that is in perfect synchronization with the motor. The complex process of converting DC to AC power at the time a motor coil requires it, while managing motor speed is all handled by the ESC. However, the ESC is not perfect and in some cases requires help. Ripple voltage is one area that can get out of hand within your ESC. In this article we will understand what ripple voltage is, what would be an acceptable amount of ripple voltage and how it can be improved.
What is Ripple Voltage?
Ripple voltage is best defined as varying voltage at the source of power. Variation in voltage is measured at the battery input side of the ESC. It is possible to log ripple voltage within the ESC, however, not all ESC’s have this data logging capability.
You may have noticed that on the input side of the ESC are large capacitors. It is the job of these capacitors to smooth out any ripple voltage at the ESC. If the capacitors are unable to smooth out variations in voltage, the variation in voltage is felt by components further down in the circuit. FET’s also known as Field Effect Transistors are the components sensitive to ripple voltage. If it gets out of hand, these will burn up and render the ESC completely useless.
What Creates Ripple Voltage
During partial throttle usage, the ESC switches on and off the power that is sent to the motor. As the ESC goes through this cycle battery power is pulled at the same rate. The rate that the ESC is switching power on and off during partial throttle is the PWM rate. In many ESC’s, this value is programmable. The standard value or typical value that you would see is 12,000 Hz.
When the battery pack is loaded with an on cycle of the ESC, voltage sags. The amount of voltage sag that the ESC experiences depends on a few factors. One of those factors is the batteries ability to dump power quickly. As this process repeats itself multiple times per second the voltage bounces between the unloaded voltage and loaded voltage. In conclusion, it is this exact difference in voltage that is known as ripple voltage.
What is an Acceptable amount of Ripple Voltage
Now on to the important stuff. An acceptable amount of ripple voltage is less than 5-6% of the battery packs nominal voltage. Around 7-9% is OK. Around 10% is where you can get in to some permanent ESC damage which ultimately means that the lifespan of the ESC is reduced. Above 10% and your ESC is at risk. To determine the ripple voltage review a data log of your ESC while recording ripple voltage. Determine where the peaks are occurring within your run. Take the highest ripple voltage value that occurs as a peak within your run.
To calculate ripple voltage as a percentage, divide the ripple voltage by the nominal battery voltage (# cells x 3.7v/cell) and then multiple by 100.
Example:
Ripple Voltage – 1.27v / 6s Nominal 22.2v % Ripple Voltage = ( 1.27 / 22.2 ) x 100% = 5.72% This would fall in the category of good and acceptable
How to Improve or Reduce Ripple Voltage
There are a few different ways to improve ripple voltage. Let’s take a look at them.
The first area of concern is to check if the ESC to Battery leads have been extended. Having extended leads can “lead” to higher ripple voltage created within the ESC. It is important to not extend the leads of the ESC without compensating for this.
The second way to reduce ripple voltage is to add a capacitor bank. A capacitor bank is able to compensate for extending the leads on the battery side of an ESC. The capacitor bank AKA cap pack is also able to help for those beast of a power system. Cap packs are highly recommended for high powered EDF jets, high powered boats and speed run cars. You can read more on capacitor packs by visiting the Why Use a Cap Pack on an RC Car page.
One of the easiest ways to improve ripple voltage is if you are using undersized battery connectors. Check the rating of the connectors and make certain that the connectors are rated for the amount of power you plan to draw.
Lastly, using the highest rated C rating and battery pack capacity as possible will make significant improvements. The improvement comes from the batteries ability to dump more current. (amps) Under load a battery that can deliver more power will have less voltage sag. With less voltage sag there will be less ripple voltage.
Conclusion
The ESC is a very complex component found within our RC power system. However, when driven too hard or over any of its limits, the ESC can respond by turning in to a bunch of smoke. To avoid this it is highly recommended to monitor by using data logs the performance of your ESC. If you notice concerning data it is best to take action using the methods described above. Therefore, doing so will maintain maximum reliability within your power system.