Where to buy a 12 volt AC Motion Sensor (PIR) or can I buy the components?

Thread Starter

DocK

Joined Apr 7, 2022
26
Hi, I am a All Circuits newbie and a DYI person with a modicum of electrical skills. I am having trouble finding a 12v AC motion sensor (PIR). PIRs are either 120v AC or 12v DC. Couple of questions:

* Any suggestions on where to buy a 12v AC PIR?
* If I start with 120v AC, I could use 120v to power a PIR and then use a tranformer to step down the PIR output to 12v. Any pitfalls?

Thank you,

Michael
 

MaxHeadRoom

Joined Jul 18, 2013
25,212
You normally would obtain the 12v from a wall wart or suitable power supply and interface the PIR with whatever sensing circuit you in tend using.
There are not enough details to give a definitive answer .
 

Thread Starter

DocK

Joined Apr 7, 2022
26
Thanks for replies. The end usage is landscape lighting using 12v AC. The load on the circuit is <50 watts.

I am using a 120v AC to 12v AC transformer to get power into the circuit. I could use a rectifier to turn 12v AC to DC to power a 12v DC PIR but then would need to use an inverter to turn DC to AC.

I was hoping to find a 12v AC PIR. Second choice would be to use 120v AC to power the PIR and then use a lighting transformer to step down the PIR's output to AC.
 

Ya’akov

Joined Jan 27, 2019
5,663
Thanks for replies. The end usage is landscape lighting using 12v AC. The load on the circuit is <50 watts.

I am using a 120v AC to 12v AC transformer to get power into the circuit. I could use a rectifier to turn 12v AC to DC to power a 12v DC PIR but then would need to use an inverter to turn DC to AC.

I was hoping to find a 12v AC PIR. Second choice would be to use 120v AC to power the PIR and then use a lighting transformer to step down the PIR's output to AC.
You would use a relay to switch the 12VAC supply from the PIR sensor. You would not supply them directly.
 

MaxHeadRoom

Joined Jul 18, 2013
25,212
So I assume you are using the PIR to switch in AC irrigation solenoids?
If so just use a DC triggered AC device such as a relay or Triac. SSR. etc.
 

Thread Starter

DocK

Joined Apr 7, 2022
26
You would use a relay to switch the 12VAC supply from the PIR sensor. You would not supply them directly.
Thank you for the reply. I am not familiar with relays. Where would the relay sit in the circuit after the PIR? How would it know to supply 12v AC?
 

Ya’akov

Joined Jan 27, 2019
5,663
Thank you for the reply. I am not familiar with relays. Where would the relay sit in the circuit after the PIR? How would it know to supply 12v AC?
A relay is an electromagnetically operated switch. When power is applied to its coil an internal contact is pulled against another closing the circuit like any switch. You would simply connect the 12VAC supply to the relay's switch and the 12VDC output of the PIR sensor to its coil.

When the sensor is activated the coil is energized causing the switch to close completing the 12VAC lighting circuit. Relays are cheap, easy to use, and readily available.
 

MaxHeadRoom

Joined Jul 18, 2013
25,212
You need some kind of IC to interface the PIR with the Relay.
Give a part No. of the PIR.
Does the PIR have any supporting circuitry?
 

Thread Starter

DocK

Joined Apr 7, 2022
26
A relay is an electromagnetically operated switch. When power is applied to its coil an internal contact is pulled against another closing the circuit like any switch. You would simply connect the 12VAC supply to the relay's switch and the 12VDC output of the PIR sensor to its coil.

When the sensor is activated the coil is energized causing the switch to close completing the 12VAC lighting circuit. Relays are cheap, easy to use, and readily available.
Thank you Yaakov. I will look into it. Much appreciated.
 

MaxHeadRoom

Joined Jul 18, 2013
25,212
Alternatively, wherever your AC supply is, you could wire a duplex socket or use a spare one for a small 12vdc Wall-Wart supply which are numerous.
 
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