Security Lights with Motion Detectors

[Brianc]

I decided to replace some of my halogen security lights with LED types. Because I couldn't find any with an external switch input (4 core cable) I modified a couple by changing the standard 3 core cable with 4 core, the fourth core being connected directly to the LED PSU i.e. the output of the motion detector electronics.
But first, an unmodified was installed about 1 year ago and is working fine. The first of the modified units was installed about 12 weeks ago. This is installed by the kitchen door and is used almost every day, both manually and automatically. The motion detector system has no packed up and the light will only work when manually switched via the fourth core I added. I haven't installed the second modified light yet.
I cannot see how this mod could damage the detector electronics - can anyone explain how? Or is it that I was again(!!) unlucky to be supplied with a defective unit? Either way, the guarantee is now void  .
Cheers
Brian

[AlanBeckett]

I have to say that in my experience over the years that's not unusual, although I'm talking about conventional Halogen ones not LED. I generally chuck the PIR away and use the Lamp on its own in the Garage or wherever as a new PIR is almost as much as a cheap Lamp with one. I've tried more expensive Models but it doesn't seem to make any difference.

Alan

[Brianc]

Do you mean that the PIR system can be damaged by driving its load by an external source, Alan? I would have thought that it's more like paralleling two switches, one mechanical and the other electronic! I suppose I could always see if the other unit is damaged in the same way if I replace the faulty unit with it.
Cheers
Brian

[AlanBeckett]

No Brian, the PIR just seems to expire. The ones I've had have a Relay in them - you can hear it click when the Light comes on - and I've never had a problem feeding other Lights or Relays from them.

Alan

[Refugee]

It might need a cap across the control wire to prevent it picking up spikes from things like lightning.

[Brianc]

I did wonder about that, Ref. After all, the control wire runs parallel to the permanent live for quite a way and could pick stuff up via that route! Perhaps a Y cap to earth would stop it happening. First, I will replace the faulty unit and see what happens.