Product designers, technicians and engineers are all taught that snubbers act as arc suppressors in electromechanical relays. While true for low-power applications … nothing could be further from the truth for high-power applications (2A or more)! Snubbers provide literally NO value as an arc suppressor in high-power applications.This may be shown two ways: 1) by contact destruction operated under load and 2) using a O-scope to measure arc energy. (Please see Lab Note 103, found here for a detailed analysis.)
The following show the contacts of identical make/model of relays:
Pictures from left to right (side view, and contact face views for all contact sets):
1. Pristine contacts from a relay fresh out of the box.
2. The nearly destroyed contacts from a relay operated under power for nearly 100,000 cycles.
3. Contacts showing nearly identical destruction to the previous, from a relay operated under power for 100,000 cycles with an RC snubber attached across the contacts.
4. The barely worn contacts from a rely operated for 100,000 cycles under power with a NOsparc MMX arc suppressor attached across the contacts.
(More details and information in Lab Note #103 found here. Photographs are the property of Arc Suppression Technologies. Copyright 2011.)
The following are related screen captures from an oscilloscope measuring the arc energy of identical make/model of relays. The screen captures show the break arc for each of the three listed conditions, using the following measures:
- Y-axis: Current shown by blue line (sinusoidal wave), 2V/div = 5A/div; Voltage shown by red line,10V/div
- X-axis: Time, 1ms/div
- Trigger: Externally triggered on the falling edge of the DC coil relay control voltage
Pictures from left to right (O-scope screen captures of identical make/model relays):
1. Relay operating without arc suppression; the break arc lasts about 7ms as shown, until the current approaches the zero-crossing.
2. Relay operating with an RC snubber across the relay contacts; the break arc lasts about 7ms as shown, until the current approaches the zero-crossing.
3. Relay operating with a NOsparc arc suppressor across the relay contacts; the break arc is arrested as it forms, and is suppressed approximately 7ms until the current approaches the zerocrossing. (We refer to this initially arrested arc as an “arclet”.)
(More details and information in Lab Note #103 found here. Photographs are the property of Arc Suppression Technologies. Copyright 2014.