redwall pirs, relays +ve etc etc

[homecctv]

im into cctv in a big way, and now want to expand with sensors and relays etc.

never used a relay before but I understand its simply a switch.

bought my first relay, a 12v activated one, wired a table lamp to the relay, applied a 12v voltage and it worked, turned off the 12v supply and light went off - understood and was simple to learn about

now using relays with alarms etc.

1. I understand a redwall pir cant be used with my above relay to turn my table lamp on - but why?

2. have I got to wire the pir to my cctv drv, then use a out put to trigger a relay to activate my 240 table lamp?

3. will my dvr be outputting 12v to trigger the relay?

4. what is dry contacts? +ve -ve ? volt free?

5. I have texecom alarm, gjd lighting system, and loads of redwalls.

I just want to be able to understand what relays to use and the anserws to question 4?

all my items have different outputs and inputs, all using different triggers and its so confusing as I never studies electronincs.

can some one help me and understand all these triggers and relays etc?

I no im asking a lot but im a quick leaner, I have ptz domes etc etc and I installed them no bother what so ever, so im not a total novice, I just want to be able to understand so I can link cctv to redalls, to my texecom panel and to my gjd system - its these dam relays and triggers that's confusing me!!

 

[homecctv]

ah do you have to be a installer to get in the cctv forum?

 

[Marvo]

Yes, for security reasons I'm afraid you need to be a professional alarm installer to get access to the alarms forum.

I know nothing about alarms but in answer to one of your queries a volt-free contact is just a plain relay contact where you get out exactly what you put in.

 

[tazz]

most outputs from DVRs etc, can only switch small loads at 5v or 12v usually at 500mA max. So we need a 5v or 12v relay to isolate this supply and switch higher loads and possibly different voltages eg 230v mains. Basically a relay is a electromagnetic switch, using a coil, controlling a set of volt free contact switches, volt free meaning we can connected any voltage we wish to the com terminal and switch it on via normally open contact. So now we can switch any voltage or current the relay is rated for. The coil to the relay will only take around 50mA to operate...but the switch contacts will switch say 16A at 230v hope this helps with the diagram below.

 

[homecctv]

cheers starting to understand, infact I already have a relay and it works using a 12v source, so now feel now confident to try it on my dvr.

so ill stick a redwall to the dvr inputs then on the out put ill wire in a relay and see what happens.