PIR sensor voltage - Scantronic 9751

[gingerprince69]

Hi

So I have the above system in new to me house, and have been trying to trace false alarm triggers. Voltmeter over the feed of the PIRs shows only 8 volts.

Have traced wiring back to junction box. Breaking the connections apart I get 13.6 volts from the controller feed. As soon as I wire any one of the PIRs in voltage drops to 10.5, and further when I add more PIRs. I understand that these can be sensitive to low voltage. Current draw is measured at 8-9ma.

What would cause this voltage drop? Current draw as above seems fine, and there's minimal resistance on the loop (about 1.5ohms)

Could it be my backup battery in the controller? Date on battery is 2013. Even on mains would I see a voltage drop when connecting things, or something else?

I have engineer code, manuals, and am comfortable programming it - it was factory reset when I bought the house so had to configure zones, wireless sensors etc.

Thanks

 

[sparkymarka]

Is it a junction box or a zone expander ....and how far from the panel is it ?

 

[gingerprince69]

Not a zone expander, just a small box of screws to tap off. There's +12v, GND and 2 zone connections from the controller to the box, then the 12v feeds to the PIRs taken from here - and the switch loop in series.

It'll be up to about 10m to the junction box, depending on how the wiring has been routed.

 

[sparkymarka]

Have you tried it with the battery disconnected ? How many pirs run off this junction box ? What make and model of the pirs ? Also what type of cable ? It’s not run in steel ( fake alarm cable )

 

[gingerprince69]

Will try with battery removed when I get home later. It's in multicore (8 core I think) cable, no steel. It's powering 4 PIRs, but get a drop even with just one connected.

PIRs are rx40-qz.

Cheers

 

[sparkymarka]

Ok ....use rx40s all the time and never had an issue with any ...and it drops every time you add even one device .?

 

[gingerprince69]

So I found the issue. There was no voltage drop seen at the aux connector on the controller, only at the junction box and the PIRs. Turns out to be a fault in the multicore between the controller and the junction box - high resistance on a couple of cores, including red.

Have now repurposed a different colour for +12v which seems to have done the trick until I get under the lino floor tiles to replace the multicore.

Have also put the zone that was false alarming into soak test mode so as not to annoy the neighbours until I'm sure it was they cause of the false alarms

Thanks for your assistance.