PCB RC snubber for speed controllers
Optional PCB snubber to limit voltage feedback to the speed controller.
This option for the RC snubber consists of the componants pre-attached to a board; includes 1x .1uf 630V capacitor, 1x 3W 15Ohm resistor, and 1x 210pF 470V varistor.
Although our own speed controllers have on-board voltage protection (heavy duty 1200V diodes, the ones we don't build have a lot simpler protection) so if you plan to use those on a motor that feeds power BACK into the controller, you NEED a way to control the power feeding BACK into the controller, or you'll kill the controller. Its that simple.
Large DC motors, especially those controlled by Pulse Width Modulation (PWM) techniques, can generate substantial electrical noise and voltage transients. The rapid switching inherent to PWM can lead to high-frequency voltage spikes.
An RC snubber circuit is used to suppress these high-frequency oscillations. It is typically placed across the switching device (like a transistor) in the controller. The snubber reduces the rate of voltage rise (dv/dt) and helps protect the switch or transistor from voltage stress and potential damage.
A Metal Oxide Varistor (MOV) is used to handle larger, slower voltage transients or surges that can occur due to various factors such as power supply fluctuations or external disturbances. The MOV acts as a voltage-dependent resistor that starts conducting when the voltage across it exceeds a certain threshold, diverting the excessive current away from sensitive components.
In a motor control circuit, the MOV is typically connected across the power supply rails (parallel to the load, but after the snubber), providing a path for transient currents to flow through it, rather than through the more sensitive parts of the circuit. This placement allows it to protect the entire circuit from voltage surges.
In conclusion, the combined use of an RC snubber and an MOV provides a comprehensive protection strategy against different types of voltage anomalies that can occur in a PWM-driven DC motor system.
RC SNUBBER DETAILS
- Capacitor Rated Voltage: 630v
- Capacitance: 0.1uF
- 1 Metallized film resistor (3W, NOT wirewound, which creates its own induction!)
- 1 Varistor 470V 210pF
- Width = 13.4mm
- Height = 13.8mm
- Length = 30.7mm
