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so what's going on here?????
rob gratze
12 Posts
Question
so ive installed 6 non fire rated LED downlight with dimmable bulbs the covers haven't been fitted yet as didn't turn up with the down lights. all was great when I left Thursday then the customer sends me this video other rooms with same down lights on same circuits fine just these ones having a disco. any thoughts gratefully received 
9 Replies
You may have a loose connection somewhere. Are they DMX controlled or just dimmable? I suggest the dimmer(s) are faulty as a first guess. Try taking them out of the circuit.
mapj1
3555 Posts
Ahh, dimmers and switch mode power supplies - not all a 'dimmable' LED drivers work with all dimmers even the ones that say LED compatible.

Have the dimmers been approved for use on  that make sort of light, or triid out in advance ? At the very least are the dimmers set to be trailing edge cut, rather than leading edge cut as you would for a filament lamp.

edit. The Vtech dimmers (and some others) can be configured for either type of dimming with flicking on and off to get into the programming mode  - has someone been playing with the settings?
Mike.
rob gratze
12 Posts
The bulbs are dim marble but there is just a normal switch at present and when they first went in they worked fine. And if they were all flashing together I’d go loose wire but they are all over the place
geov
26 Posts
What make/model of fittings?
OlympusMons
226 Posts
I am also thinking loose wire. LEDs have low running current but higher starting current. Possibly the impedance of a loose wire doesn't allow enough current to "ignite" all the LEDs on switch on, but enough to ignite one, the demand drops, another ignites, but when a few are on there is not enough current to run them all so one drops out, allowing another to ignite.
It possibly worked fine when you were there since the loose connection was shiny and new, it is now a bit oxidised/stressed.
Or possibly they need the missing trims to work properly

Edit; Does your client know that a video of their bedroom is now on the Web for all to view?
ebee
1166 Posts
It`s one of those effects that if you tried to design it to work like that then it wouldn`t quite look as you wanted.
But as you never intended it in this case then yes it works a treat, Murphy`s Law a.k.a Sod`s Law.

Yes I`m thinking of poor connection too. Poor switch or grit in switch not impossible?
mapj1
3555 Posts
OK, without the dimmer, it is less clear. However I'm reminded of the odd effects when the earth fails on car rear lights,
(rusty old Fords with more body filler than steel were prone to this...) and wondering if there is a continuity neutral problem.

Switch mode LED driver modules are often a "negative-resitance" load - that is to give constant light  over a wide voltage range, the electronics is arranged to draw more current at lower voltages to compensate, and with that type, if somehow you put 2 in series the system is unstable.
Unless perfectly balanced with equal voltage and current,, the one with less voltage will try to draw more current, so lowering its equivalent resistance, so lowering the fraction of the total voltage across it repeating the spiral,  until it goes out altogether and restarts.
Could it be that ?

But I cannot see how you would end up with 2 in series across the mains without a wiring fault of some kind, and I struggle to see how that could occur after you left. Unless it was just balanced by luck.
Mike.
 
ebee
1166 Posts
I have seen wall lights wired in series by an "electrician" . They called me cos funny things were happening when they tried changing lamps
Denis McMahon
340 Posts
Are these lamps 240 V rated (GU10) wired straight off the mains, or are they low voltage (GU5.3) with a transformer somewhere? This could be significant.

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