This power supply protection circuit using a relay was found in a 1967 documentation. The components are from the time, but current equivalents can be used depending on the power source current.
This low-frequency relay oscillator was obtained from an article in Electronics Now magazine in...
This circuit trips when the voltage set in the pot is exceeded. The tone depends on C3 and...
This circuit is from an old American publication from 1975 but can be easily implemented with any...