Types of SSRs

Understanding

A relay is a device controls one electrical circuit when a control is sent to it from another electrical circuit. In this way, a low-voltage signal can be used to control power for a much larger circuit. Many relays are mechanical devices and work by making two metal contacts touch one another, usually by the use of an electromagnet: when the electromagnet is energized, it pulls on a metal lever causing contacts to touch and electricity to flow; when power is cut from the electromagnet, a spring separates the contacts and the electricity stops flowing.

An 'SSR' is a solid-state version of the mechanical switch but essentially does the same thing using electronics instead of magnetism, metal levers and springs. As such, an SSR, or 'solid state relay' is much quieter and can operate much more quickly than a mechanical device.

An SSR can control either AC or DC electricity, but the control signal itself that turns it on or off is almost always low-voltage DC. This allows small computer chips to be able to do the task, such as the PIC16F688 or other chip. Typically, these chips utilize 5vdc signaling, which is usually enough to trigger an SSR to turn on or off when the signal current stops.