I need to know if the standard PIR you get on a halogen 240V external light can be put onto a 12V light? I know you can buy the external PIRs on their own (rated at 1000W for example) but I just want to connect one side to a 12v battery and the other side to some 12v lighting.
Also, say a lamp is 10W 12V, then this draws 0.833A. If a battery was
3000mAH, would this last for 3.6 hours? Am I correct?Thanks for any help.
Mat G Birmingham, UK
You would need to disconnect the relay contact from the live rail.
I modified one to operate a hall light as well as being bypassable :-
"gentlegreen" wrote in message news:gDv7g.65935$ snipped-for-privacy@text.news.blueyonder.co.uk...
I wouldn't be surprised if the low voltage supply for the electronics was derived using a resistor ... You would need to do some more mods to the PCB.
. >
Maybe better using a 12V intruder alarm PIR and connecting to the lighting using a relay (the intruder alarm PIR will *not* be able to switch high currents directly)
Owain
If you have mains available, then you can wire the output of the PIR to a relay with a 230v coil For example
It depends on the battery, the theoretical max would probably be this, however towards the end of the charge, the light would be a lot dimmer, and if the PIR was powered from it, this may start behaving erratically!
Sparks...
snipped-for-privacy@lycos.co.uk wrote on 07/05/2006 :
What you need is a PIR fitted with voltage free contacts, however all the common ones run from 240v and send out the 240v on the switch wire. If it were me wanting to do this, then I would simply remove the 240v feed to the relay and replace it with a terminal to take the 12v feed. Another way to do it would be to have the switched 240v operate a 240v relay or small contactor, you would then have the voltage free contacts you need.
You should be warned that DC switching is very different to AC switching, in that contacts need to be derated for switching DC.
Without working it out, your figures appear to be correct. You should though be warned that a batteries capacity depends not only on its rating, but upon how quickly it is discharged. Your fairly rapid discharge will make the capacity a little less than the 3.6 hours - probably nearer to 3 hours.
They also have no delay before switch-off, unlike PIRs designed for lighting use.
Mains PIRs need 230Vac but have high current (4A non inductive load) contacts.
12V PIRs (alarm system type) need only 12V but have contacts rated in mA. So you'd need a 12V Alarm PIR + a 12V relay with contacts of around 1A+.
I want to fit a PIR in my new stairwell to switch the lights on. I suspect I will use a bog standard B&Q security light minus the light - I'm guessing specially-designed "occupancy sensors" are expensive.
.The message from "gentlegreen" contains these words:
The ain't cheap. I have one in the downstairs loo.
Oooh, look, while googling for a price I found this...
I suspect I will modify a cheapo Halogen light and wire it in parallel with the light switches in such a way that I can painlessly remove it in the unlikely event I ever sell ...
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