The Shelly RC Snubber is a small but extremely effective accessory designed to protect relays when switching inductive devices. It prevents dangerous voltage spikes that can shorten the life of the relay or cause it to operate unreliable.
For use with Shelly 1/1PM and Shelly 2.5, which restart when inductive loads such as fans, motors, roller shutters or those that cause voltage spikes during switching on. The RC snubber should be connected between the output and the neutral of the circuit.
Switching inductive loads (motors, contactor coils) with a smart relay is more challenging due to the voltage spikes (back-EMF) that occur during opening, which can damage the relay contacts, cause them to weld or function irregularly. Therefore, an RC snubber is used to help dampen voltage spikes and reduce electromagnetic interference, thereby extending the life of the contacts and increasing switching reliability. The RC snubber is connected in parallel to the inductive load (ideally as close as possible to it) and absorbs the energy of the voltage spikes.
Problems when switching inductive loads
* Sparking/arcing: When opening, a high voltage (back EMF) is generated, which causes sparking on the relay contacts.
* Contact welding: Sparking can cause the relay contacts to weld together and the relay to remain "stuck".
* EMI/EMC interference: Voltage spikes create electromagnetic interference that can destabilize sensitive electronics (e.g. module restarts, faulty switching).
Contact protection and interference suppression
For protection, you can use Shelly RC Snubber – an RC element (resistor + capacitor in series), which is connected in parallel to the load, or directly to the relay contacts according to the connection (typically between the output and N). The RC element absorbs the peak energy and dampens oscillations, thereby protecting the contacts and reducing interference. With Shelly RC Snubber, it is a series connection of 100 Ω + 0.1 µF.
Benefits for your installation:
- Protection against relay damage
- More stable operation of devices
- Easy installation
- Low cost and high efficiency
- Longer service life of your modules
Možno ak by existovala aj menšia varianta pre nižšie zaťaženie.