Relay switching is a fundamental element of electrical control systems. Dating back to at least 1833, early electromagnetic relays were developed for telegraphy systems. Prior to the invention of vacuum tubes, and later semiconductors, relays were used as amplifiers. That is, when converting low power signals into higher power signals, or when remote load switching was beneficial or necessary, relays were the state-of-the-art option. Telegraph stations were linked by miles of copper wire. Electrical resistance in those conductors limited the distance the signal could be communicated. Relays allowed the signal to be amplified or “repeated” along the way. This is because wherever a relay was connected, another power source could be injected, boosting the signal enough to send it further down the line.
Electromagnetic relay switching may no longer be state-of-the-art technology, however, it is still widely used in industrial control, and where true galvanic isolated switching is desired or required. Solid-state relays, the second of the two primary categories of relay switch, have some advantages over electromagnetic relays. SSR’s can be more compact, more power efficient, cycled faster, and they have no moving parts.
The purpose of this article, is to show a simple method to increase the power efficiency, and functionality, of standard DC actuated electromagnetic relay switches.”