Transformer/Driver for 12v DC PIR motion sensors

[mikeuns]

Hi, I'm a newbie on this site and am working on a 12v garden lighting project. I will have 12v led lights along a path with a PIR sensor at each end of the path. Either of the PIR sensors will trigger the lights via a 12v relay. The PIR sensors will not be on the light circuit but on their own circuit. The question I have is what 12v DC transformer/driver spec should I buy to power just the pir's and the relay? The pir's will be approximately 30m apart and will have a very low load themselves (I can't find detailed specs for them unfortunately). I am planning to install 2.5mm2 conductor cable to help with the possible voltage drop over this distance. I hope this is clear, many thanks for any suggestions!

 

[newfutile]

I can't see pir and relay taking much power I would imagine a 1 amp 12 volt supply would be plenty, might be an idea to have a diode reverse wired across the relay coil,as back emf can break things and give you a little shock

 

[mikeuns]

I can't see pir and relay taking much power I would imagine a 1 amp 12 volt supply would be plenty, might be an idea to have a diode reverse wired across the relay coil,as back emf can break things and give you a little shock

Thanks for the suggestion re. the diode - I'll look into this. I was concerned about the 30m or so distance between the pir's - with the cable I'm planning is this not an issue?

 

[newfutile]

Maybe not as volt drop is determined by ohms law, if very little current is drawn and the resistance is small there will be little volt drop,many transformers rated at 12 volts actually put out. Little bit more.

 

[mikeuns]

Maybe not as volt drop is determined by ohms law, if very little current is drawn and the resistance is small there will be little volt drop,many transformers rated at 12 volts actually put out. Little bit more.

Great stuff, many thanks for responding.