12volt to 6 volt adapter for PIR unit (anti horse thief)

[petermanndorset]

HELP? We were robbed recently of everything (£1700) from our Stable tack room deep in the Dorset countryside in the UK. Some one has given me a PIR unit, which runs from 6 volts. I want to use it from a 12 car battery and using a relay supply power to any anti thief device I fancy…i.e. a car spotlight. I know nothing about electronics but can use a soldering iron. My question is How to I reduce the 12 volts down to 6 volts so that the PIR unit does not blow up? I know a resistor should be used but have no idea how to work out which one to get.The PIR unit does not have any written data with it. Sorry to sound so dumb but I have to start somewhere. Peter

 

[crust]

Depending on the current draw, you could use a 7806 regulator. Then use your relay to switch a 12V lamp. Is there no AC power in the area? If there is, you can buy the whole integrated unit with dual floodlights and the pir sensor for about $50US, so maybe 30 to 40 in your currency.

 

[Roff]

I'm attaching a schematic that might work for you. I picked an LM317 for the regulator because Maplin doesn't seem to have the LM7806, but I don't know what your resources are. If you select a different relay, it needs to handle 10 amps of contact current and the coil should draw less than 100ma at 12v. The 12 AWG refers to the minimum wire size you need for the wire that interconnects the battery, the relay contacts, and the spotlight. The size of the rest of the wires is not critical.

 

[petermanndorset]

'm attaching a schematic that might work for you. I picked an LM317 for the regulator because Maplin doesn't seem to have the LM7806, but I don't know what your resources are. If you select a different relay, it needs to handle 10 amps of contact current and the coil should draw less than 100ma at 12v. The 12 AWG refers to the minimum wire size you need for the wire that interconnects the battery, the relay contacts, and the spotlight. The size of the rest of the wires is not critica

Many thanks
peter :wink:

 

[Roff]

Peter, go back and look at the schematic I posted. There was an error and an omission, both of which I have corrected.

 

[1Steveo]

Pettermann,
I would use the PIR to trigger a camera.