Ripple Voltage in an ESC Explained and How to Improve it

In an RC vehicle, the ESC controls the flow of electricity from the battery to the motor. It converts the battery’s DC power into AC, perfectly timed to match the motor’s needs, while also regulating speed. Essentially, the ESC orchestrates the complex task of delivering power exactly when and where the motor requires it.

What is Ripple Voltage?

Ripple voltage refers to fluctuations in the power supply voltage. These variations are typically measured at the ESC’s battery input and represent small, rapid changes in electrical energy. It is possible to log ripple voltage within the ESC, however, not all ESC’s have this data logging capability.

Large capacitors are positioned on the ESC’s input side to smooth out voltage fluctuations. They act like tiny buffers, ensuring the ESC receives steady power even when the input varies. If the capacitors are unable to smooth out variations in voltage, the variation in voltage is felt by components further down in the circuit. Field Effect Transistors (FETs) are particularly sensitive to ripple voltage. Excessive fluctuations can damage them, potentially causing the ESC to fail entirely.

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 frequency at which the ESC switches power on and off during partial throttle is called the PWM (Pulse Width Modulation) rate. In many ESC’s, this value is programmable. The standard value or typical value that you would see is 12,000 Hz.

Applying load to the battery through the ESC causes the voltage to dip momentarily, a phenomenon known as voltage sag. 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

Tips for Maintaining a Stable Power System

There are a few different ways to improve ripple voltage. Let’s take a look at them.

First, inspect the ESC-to-battery wires. Extending these leads can increase ripple voltage if not properly compensated. 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.