led bulbs flashing

[elmsoft]

Recently I fitted some LED downlighters with 4w dimmable bulbs. Despite being advertised as lasting for zillions of hours, several have failed quite soon. The nature of the failure is distinctive: the bulbs light intermittently "flashing " in something like a 2 seconds off I second on pattern.
Anyone come across this sort of fault?

 

[stem]

Yes, I had a similar occurence with my 'professionally' installed new bathroom, so, I replaced the failed lights with identical units purchased 'on line' and after a few hours, the same thing happened again. Turned out it was a light / power supply mismatch. The lights were designed for wiring in parallel, but the power supply (constant current) was designed for wiring in series.

I should add that the lights got very hot and one smelled of burning. They had to be discarded.

More new lamps and the correct power supply resolved the issue, and the lights have been working now since April.

 

[elmsoft]

Turned out it was a light / power supply mismatch. The lights were designed for wiring in parallel, but the power supply (constant current) was designed for wiring in series.

Don't understand this. They were run off a transformer? Mine are mains- GU10 I think is the code - and I commoned up four to a junction box and connected all the neutrals to the incoming neutral and all the lives to the switched live of the the dimmer.
Surely all lights have to be parallel?

 

[stem]

OK. If they don't use an LED driver (or Power supply) then you can ignore my previous post. To answer your question though.

LED's are diodes, they let current flow in one direction only but offer very little resistance to current flow, so this has to be limited somehow. A resistor can be used in the supply lead to several LED's wired in parallel. Here a 'constant voltage' power supply is used. Alternatively the LED's are wired in series to increase the resistance and a 'constant current' power supply is used.

Sometimes a light fitting may have lots of LED's built in to it that are wired in series internally, but then the light fitting as an item is wired in parallel with other light fittings.

Having said that, Some complete light fittings containing LED's are wired in series with a driver. I have a set of 3 "plug and play" multi LED garden lights that are.

However if in your case they are mains GU10's none of this matters and I can't help you I'm afraid. Maybe someone else will be along soon that can.

Is it a 'normal' dimmer the sort used with a tungsten lamp? If so, I believe with LED's they will not work at less than approx 10% of their rating.

Interesting that the symptoms you have are the same though.

 

[Chri5]

OP can you give us the figure work from the dimmer unit?

Just wondering if you have a dimmer that doesn't marry to the LEDs. Example being 4 lamps at 7w each gives a load of 28w. If the dimmer suggests a load requirement of 50w-200w then it wouldn't work well.

Another method to check the switch would be to replace the dimmer with a simple 1 pole standard light switch. If the fault stops,Mathis proves the dimmer is the issue.

 

[elmsoft]

interesting thoughts on the dimmer- I hadn't thought to consider load requirements for the dimmer.
I did take two "flashing" bulbs ( I think a purist might call them "occluding" )and put them in a a non dimmer circuit ( my kitchen has halogen GU10s) and they behaved the same way, but don't know if that is because their use in the original fitting has damaged them?
But that is the equivalent of swapping out the dimmer of course
LEDs are very new to me and I am more intrigued than annoyed by the issue!
Thanks to both of you for your input.

 

[phatboy]

I tried a couple of eBay specials a few months ago, and they developed this issue quite quickly.

Solution was to bin them, and buy some better bulbs!

 

[elmsoft]

I tried a couple of eBay specials a few months ago, and they developed this issue quite quickly.

Solution was to bin them, and buy some better bulbs!

There is always that!