(A text chat in long ago from my email records - 2007)
Jim: i have a Small problem,it's about relays.me: would u pls give me an information about relays,pls give different types of relays and their differences.
delabs: for what do you want to use the relay for.
Jim: Two door alarm settable for close or open door
delabs: there is a control signal and an output for relay, if you are using just a buzzer for alarm, no relay needed if you want to operate a big hooter or 230V lamp a relay is needed- or even a motor or solenoid to move some thing Even a Solid State Relay can be used.
Bigger loads like large motors may need drives and containers. Some even have speed control. Big doors are more difficult to open and close. safety features needed.
The picture above shows also reed relays that are used for small signals - analog and telecom. In Solid State switching also we have small signal and power switches, using mosfet or triac.
Soldermans Basic Electronics: Relays and Contactors
Jim: let me check dis addr nd i'll get back 2 u just now.
Jim: ok but if i have a problem i'll get back 2 u,bye