relay special applications

I understand how to use a relay to turn something on or off.  The question I have is how do the relays work in the special applications section on this site.  It puzzles me when two or more are wired together, like in the (-) pulse to constant 12v output example.  Any information would be appreciated.  Thanks. 

Also I would like to hear some other possible applications.  I'm looking for ideas with my alarm.

Hey ShaunD912,

If you understand that a relay needs a positive and a negative to energize the coil on pins 85 and 86,  then you're halfway there. 

LESSON ONE - Momentary to constant

To turn a momentary to a constant  we just have to make sure that there is constant pos and neg on the coil of  RELAY 2.  Look at diagram below.  

RELAY 1 sends a positive pulse to pin 85 of  RELAY 2  thereby energizing it. 

RELAY 2 takes the pos signal from pin 30 outputs from 87 and feeds it to itself on pin 85. 

RELAY 2 is now  "Latched" until it loses the ground on pin 86 or it loses pos on pin 85 or 30. 

LESSON TWO - Extend the duration of a shorter signal

To convert a short momentary signal to a longer one, you can sometimes add capacitors and resistors to hold the coil energized for a certain time as in the case below where the capacitor receives a momentary positive current and charging it like a battery but it charges and discharges rather quickly.  Then while it is charged it has enough energy to hold the coil and when it has discharged it releases the coil.  This is handy to extend the domelight duration or other uses.

Hope this has helped you some.  Obviously we can't explain everything we can do with a relay in a forum but if you have special projects then let us know and we'll add to your knowledgebase.  We love a challenge!