SSR

 

   I'm replacing my custom wired relays with SSRs (solid state relays).

  Traditional relays are electro-mechanical in nature. A coil is energized causing contacts to open or close. The equivalent of  such a coil is referred to as a 'solenoid.'

   All such devices make noise and are susceptible to mechanical wear and corrosion and welding of contacts.

   The SSR is composed of  semiconductor devices, typically, mosfets (metal oxide semiconductor field effect transistors).

   In my design, opto-couplers turn the mosfets on or off. A low power signal is isolated from the mosfet circiutry using these devices. The design and construction is more complex than the relays, but is more reliable, quieter, and can handle more power per dollar cost.

The design I'm using is here:

The first is the linear actuator motor control. The second includes the actuator power supply on/off switch.