Discuss Best solution for LED security lamp flashing in the Electrical Forum area at ElectriciansForums.net

timhoward

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I had a faintly funny situation today.
At the end of another job, the happy customer said "By the way my outside lamp comes on, and then flashes several times before finally turning off. What's up with it?"
I took one look at it and said "To be honest, I have the exactly the same outside lamp, and mine does exactly the same! I haven't got around to doing anything about it yet. I'll ask some wise people tonight what is best to do!"

So - I'm assuming it's induced current causing this.
Should I fit some sort of snubbing device?
Thanks for any ideas.
 

Avo Mk8

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So - I'm assuming it's induced current causing this.
Should I fit some sort of snubbing device?
Thanks for any ideas.
I understood this is a detector 'setup' procedure in the electronics of the lamp to establish 'black/dark' level and 'white/light' level, which I thought might be part of detecting dusk.
I had one that did this, and it didn't seem to be a fault. You could hear a relay clicking inside as it flashed.
So my take on this, is that it's supposed to do it!
 
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timhoward

timhoward

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I understood this is a detector 'setup' procedure in the electronics of the lamp to establish 'black/dark' level and 'white/light' level, which I thought might be part of detecting dusk.
I had one that did this, and it didn't seem to be a fault. You could hear a relay clicking inside as it flashed.
So my take on this, is that it's supposed to do it!
That's an interesting thought!
I inherited this light with my house so have never read the instructions.
I thought this didn't happen on the old halogen bulbs and started happening when when I changed to LED GU10 bulbs.


It has a normal Lux and Time setting, so I didn't imagine it was doing anything sophisticated.
 

Avo Mk8

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I may be attributing more sophistication to the lights design than it deserves, but because it was so repeatable with my (two) lights, I grew to assume it was an intended feature! Moving from filament to led bulbs didn't make any difference to mine.
But I confess just having been Googling about this, I'm finding no hard evidence of my theory, though plenty of rubbish!
I'll creep back to the workshop!
 

pc1966

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It might just be the LED driver is broken. We have had quite a few (as in 40% or so) of the Ansell 50W floodlights fail in that sort of manner, but usually after a few flashing and going off cycles it stays off.

But the light fooling the photocell for the PIR inhibitor is another possible reason.
 
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timhoward

timhoward

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It might just be the LED driver is broken. We have had quite a few (as in 40% or so) of the Ansell 50W floodlights fail in that sort of manner, but usually after a few flashing and going off cycles it stays off.

But the light fooling the photocell for the PIR inhibitor is another possible reason.
Well in this case the 'LED driver' would be part of the bulb.
It might be worth digging out some filament bulbs to confirm my memory that this is an LED only problem.
Then try some other LED bulbs.
I did confirm that this happens in broad daylight at my customers house, so probably not a light / photocell issue. The manual does say that reflections can cause flashing though.

It might be simplest and best for my sanity to just try another light fitting that costs more than 20p.
 

Pretty Mouth

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That's an interesting thought!
I inherited this light with my house so have never read the instructions.
I thought this didn't happen on the old halogen bulbs and started happening when when I changed to LED GU10 bulbs.


It has a normal Lux and Time setting, so I didn't imagine it was doing anything sophisticated.
I've seen a light that looked just like this with exactly the same fault
 
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I had a faintly funny situation today.
At the end of another job, the happy customer said "By the way my outside lamp comes on, and then flashes several times before finally turning off. What's up with it?"
I took one look at it and said "To be honest, I have the exactly the same outside lamp, and mine does exactly the same! I haven't got around to doing anything about it yet. I'll ask some wise people tonight what is best to do!"

So - I'm assuming it's induced current causing this.
Should I fit some sort of snubbing device?
Thanks for any ideas.
My LED porch light has been on the same sensor for 5 years with no issues. Changed the fitting recently and it now has ES LED lamps in and when I turn the switch on in the morning so the light is on when I get home there is a quick flash. Must be the lamps.
 

marconi

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Are you describing the common flashing when PIR sensor-timer controlled lamps are first powered on? Or - some episode of flashing when they (viz the PIR S-T and Lamp combo) are both powered off by an upstream switch? Or - the PIR S-T turns off the lamp but its electronics remains powered on ie after a movement detection ?

And during the flashing can you hear a relay clicking contacts on and off?

If it is one of the second or third cases then it is probable the PIR S-T and lamp are acting as a relaxation oscillator.

A high level description of a relaxation oscillator is here:

Relaxation Oscillator - http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/relaxo.html

In olden times a common relaxation oscillator circuit used a neon, resistor and capacitor and dc voltage supply. It uses the Pearson-Anson effect and is nicely described here:

Pearson–Anson effect - Wikipedia - https://en.wikipedia.org/wiki/Pearson%E2%80%93Anson_effect

One needs to know that some relay's contacts have rc snubbers across the contacts which can pass small currents when the contacts are open. Similarly, triac/thyristor semiconductor switches can leak current anode to cathode when turned off. What can also happen to triacs and thyristors is that they can turn on when off if the rate of chnage of voltage across their cathode and anode is high because it causes internal to component capacitive currents to flow to their gate thereby turning them on. This is often prevented/suppressed by putting a series RC snubber across anode and cathode between cathode and gate.

See page 3 para 1.3 of:

https://www.renesas.com/us/en/document/oth/thyristors-triacs-precautions-use

And to make it even more 'interesting' triacs/thyristor have minimum hold on current flows between anode and cathode which may be achieved during some periods of high potential of the mains cycle but not when the potential is lower. Of course LEDs are low current devices with forward threshold conduction voltages so you can see how this can play out when switched by an in series triac/thyristor.

See also:

TRIAC based on/off circuit showing flash problem with LED lamp - Page 1 - https://www.eevblog.com/forum/projects/triac-based-onoff-circuit-showing-flash-problem-with-led-lamp/#:~:text=%22%20LED%20lamp%20with%20a%20TRIAC,or%20flash%20every%20few%20seconds.%22

Finally, mains LED lamps often use a series capacitor (with bleed resistor in parallel) to drop the mains from 230V to say 50V before it is rectified and current controlled to power the LEDs. A typical LED lamp is akin to this simple circuit and note the places where electricity is stored when power is first turned off - and combine this with what I said earlier:

Mains Powered White LED Lamp Circuit Diagram - https://www.learningelectronics.net/circuits/mains-powered-white-led-lamp.html

Food for thought :cool: Enjoy. You can work up your own theory on what is the cause for cases 2 or 3.
 
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Lucien Nunes

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A possible cause is through poor design and insufficient deadband to guard against feedback when light from the lamp strikes its own photocell. When it gets just dark enough to switch on, the additional light from the lamp pushes it back over the threshold and switches it off again, and vice versa. It's easy to prove whether this is the effect in play by blocking most of the light from the lamp, so that you can still see whether it's on or off but it doesn't spill into the sensitive area of the photocell as much.
 
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timhoward

timhoward

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Are you describing the common flashing when PIR sensor-timer controlled lamps are first powered on?
No
Or - the PIR S-T turns off the lamp but its electronics remains powered on ie after a movement detection ?
Yes, Movement activation. Lamps light (relay click). 30 second timer. Lamps extinguish. 2 or 3 seconds pause. Then about 6 rapid flashes, with a relay click each time. Slight pause, then 2 more flashes a bit slower.
A possible cause is through poor design and insufficient deadband to guard against feedback when light from the lamp strikes its own photocell. When it gets just dark enough to switch on, the additional light from the lamp pushes it back over the threshold and switches it off again, and vice versa. It's easy to prove whether this is the effect in play by blocking most of the light from the lamp, so that you can still see whether it's on or off but it doesn't spill into the sensitive area of the photocell as much.
Thanks. I tried this. covering the lamps doesn't actually change the behaviour at all.
(My customer's unit was actually doing this in broad daylight as no one had ever adjusted the Lux control.)

I can also report that changing to filament bulbs causes the errant behaviour to stop.
My original post was asking if there's anything I can add to limit the effects of what I presume is induced voltage.
Though I'm considering that it might be simpler to try some different units.
 

marconi

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When I looked up the LAP lamp fitting you mentioned earlier is states is uses two LED GU10 lamps (not supplied with it). Among reviewers of this lamp no-one mentions the flashing you described which seems to indicate some particular to your installation or rare fault.

Has it always flashed as you described ever since the first time you fitted LED GU10 lamps? I am wondering if there is a component ageing effect at play. Harping back to my last post, if there is as I suspect a series capacitor mains voltage dropper, these capacitors can reduce in capacitance as they age which would increase their reactance and thus worsen the voltage regulation to the downstream PIR-timer electronics and relay. Thus when the relay turns off there is a higher jump in dc voltage which is 'interpreted' by the electronics as a first energisation event with the typical first switch-on flashing cycle.

Do I take it that there is no post activation flashing if you now use filament lamp GU10s?
 

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