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

wrote in message
ups.com...
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?

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 :-

http://uk.geocities.com/gentlegreengiant/PIR.GIF

"gentlegreen" wrote in
message . uk...

wrote in message
ups.com...
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?

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 :-

http://uk.geocities.com/gentlegreengiant/PIR.GIF



just reread the OP.

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.

..

wrote in message
ups.com...
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.

Sort of!

If you have mains available, then you can wire the output of the PIR to a
relay with a 230v coil
For example
http://cpc.farnell.com/jsp/endecaSea...tk=gensea rch
(http://tinyurl.com/z7mte)

and the base
http://cpc.farnell.com/jsp/endecaSea...tk=gensea rch
(http://tinyurl.com/k7bc8)

Alternatively, you can get PIR's for use with CCTV and alarm systems that
work on 12v, however, these usually have a normally closed (light on)
connector, and then only usually activate for a few seconds.

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?


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...

wrote on 07/05/2006 :
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.

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.


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?


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.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Sun, 07 May 2006 15:57:37 -0700, djmg2 wrote:

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?

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+.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html