12V PIR Sensor issue

Thread Starter


Joined Feb 6, 2016
Hello everyone :)

I am trying to build a simple 12V PIR switched light circuit to drive a pair of small 9W triple LED lights.

What I have a small SLA 12V 1.2Ah battery to which I am connecting my PIR.

For info here is a link to the PIR sensor I am using. It is cheap and cheerful but should still do the job?
I know, its a big link :eek:


The trouble is although it is working its not working correctly and wanted some input from shall we say more learned people.

The battery isn't fully charged but is charged enough showing a voltage of 12.15V. I have wired the + & - wires to the positive and negative posts on the battery as you would expect and am left with a single yellow output wire from the PIR. I'm sure the yellow wire is intended for connection to the negative wire on the led lights and as such have wired it that way with the red wire from the led lights going straight to the positive post on the battery.

Now the fun starts....
The sensor has a built in 15 second timer when activated but it seems to be half working and working in reverse. I'll explain.

With the wiring configured as above with the sensor unswitched I am getting a voltage of 12.04V across the light supply. If I wave my hand in the field of the sensor this reading drops to 8.82V. After 15 seconds the sensor unswitches and the reading goes back up to 12.04V.

So it seems to be working in reverse. Also, I would expect if working correctly the unswitched voltage should read Zero because as it stands, when all connected. The Light is brighter unswitched and gets dimmer when the PIR is activated????

Should this be working correctly as a stand alone device or does it require some kind of mini relay perhaps?

Many thanks, Chris


Joined Apr 5, 2008

Can you show us a schematic on how you connected the PIR to the rest of the circuit?

Reading the info on the given page, the PIR can only put out 5 mA.


Thread Starter


Joined Feb 6, 2016
Hello Bertus,

Many thanks for the reply. Sorry but I wouldn't know where to begin producing a schematic for the simple circuit so please accept my apologies.

If it has an output current of 5mA then I'm guessing this wont have sufficient output current to power the lights that I want if to control? Could this be the case and would I need to use some type of miniature relay switched by the sensor to power the lights at their required voltage and current?

Should also point out that I am very much a newb to anything smaller than house wiring!