Relays

[AidenC]

Hi,

Ive just started as a service engineer and seem to be picking it up quite quick, though the one thing that id niggling me is how do relays work? I cant seem to get my head round how to wire them up (double pole relays) or what triggers them or how to connect them to the outputs etc, if anyone could explain this or maybe show diagrams etc it would be much appreciated.

Nedia

[Guest Cerberus NI]

A relay is basically a remote switch,in that it has a small electromagnet inside which,when voltage is supplied to it,will change the "switch" from one state to another - open to closed (or vice versa).

Double pole means that you have two sets of contacts,which are made up of your common (usually your input that you need to switch), a normally closed and a normally open.The closed and open change when the relay coil is energized.

[Service Engineer]

A Basic SPDT Relay:

Applying voltage to the coil changes the relay state from it's current normally closed position to the then normally open position.

A DPDT relay:

The relay below is simply 2 of the above. When power is applied whatever is supplied to the common terminals is transfered to what were the N/O terminals.

[AidenC]

Thanks for that

I think my main problem is getting used to seeing the different ways they are wired in, cos when i open up panels and see the relays, with wires coming from output/ zones/ signalling etc it all gets confusing for me, but i suppose that will come with experience.

for the help

[bri]

Basically think of it as a light switch, on or off = single pole (living room), on off or on again = double pole (landing light)........then later we get technical

[newbec]

Basically think of it as a light switch, on or off = single pole (living room), on off or on again = double pole (landing light)........then later we get technical

Still not recovered from holiday yet Bri?

Double throw (as the yanks like to call it) or "change over" relays act like a 2 way or landing light switch, double pole is like 2 one way switches activating at the same time.

Look first at where the wires from the A1 & A2 terminals are coming from, if they`re coming from panel outputs then the panel is triggering the relay.

If they`re coming from elsewhere & then you can assume at first instance that something else is activating the relay & the relays function is to provide an input.

There are many complicated ways in which to implement relays into circuits but they are only acting as switches with 2 states, either on or off. Once you get your head around the basic concepts it should all fall into place.

[Guest]

http://en.wikipedia.org/wiki/Relay

http://electronics.howstuffworks.com/relay.htm

http://www.ibiblio.org/obp/books/socratic/output/relay1.pdf

[hastings]

At least you asked !!!

I've just spent the last two afternoons ripping out a load of incorrectly wired relays, they were also 24v instead of 12v because the installer was afraid to ask how it was done.

If you are not sure, always ask someone !

To be fair, this installer has not been doing it long and this system was a bit different, it has maglocks, fire alarm, bms all connected to the intruder alarm.

[AidenC]

You's have been a great help

[Service Engineer]

I've built 30+ zone cell call & attack systems for most of the police stations in the west midlands, almost entirelly out of relays, LED's, diodes, and switches.

Relays are a most usefull tool.