240v LED - susceptibility to overvoltage?

Hyppy_ · Oct 18, 2022

I'm trying to replace 4 inset downlights with surface mounted ones: Phoebe LED, Atlanta Universal Downlight 6.5W/3000K, chosen as they'll fill/cover the now hard-to-find 100mm diameter cut-outs the previous lamps used.

I wired one in, attaching the cables to the junction box the transformer the older light had been connected to and all seemed good. I moved to the next, wired that in, tried that and it flickered before going off. I switched off and on again at the wall just to double-check, and the first previously working light did the same: a quick flicker then dead.

Nothing tripped and the circuit is good with the other two old downlights that operate from the same wall switch still functioning.

I took a look inside one of the dead units and I think at least one of the LEDs is burned out. This got me thinking: While being given a sales pitch from a solar company we were shown how our voltage was high, fluctuating around the 250v mark. Assuming that is the case, would such a relatively small overvoltage cause an LED to fail near-immediately?

Thanks in advance for any thoughts you might have, and for any solutions you could offer up. I'm reluctant to try the other units for fear of killing them too.

littlespark · Oct 18, 2022

You don’t have a 240v LED…. It will be 12v or whatever….
However, LEDs require a power supply with a DC output, whereas your old transformer may put out AC

Can you photograph the old transformer, with any details it shows.

Hyppy_ · Oct 18, 2022

They certainly claim to be 240v LEDs but I'm happy to be told that I'm misunderstanding things! It's these which were recommended by the leccy wholesalers: Atlanta Universal Downlight • Dimmable • 6.5W • 3000K - https://www.cromptonlamps.com/Catalogue/Phoebe-LED/Downlights/Atlanta/Atlanta-Universal-Downlight-Dimmable-65W-3000K-12172

The instructions for these certainly talk of being connected to the mains: https://www.cromptonlamps.com/files...01009b01/Atlanta_installtion_instructions.pdf

Anyway, this is what was removed, one of these at connected to a junction box at each cut-out.

Avo Mk8 · Oct 18, 2022

What you have is indeed a fitting that runs directly from 240V, and it has a built in driver on board.
So I don't understand what is happening with yours. I would have expected the driver to cope with a modest over-voltage on the mains. Could it be that something has come adrift in the wiring? eg if power is being fed from the far end of your string of lights, and there's a loose connection nearer your new lights, they could be misbehaving while the others are still on?

I see the 'suspect' LED, but not clear what it means!

Do you have a multimeter, to check that there is mains at the terminal block of the fitting.

Alternatively could you take one of the 'faulty' new fittings down and wire it to a flex with a plug (fitted with a 3A fuse) on the other end, and plug it in to check if it still works? I would encourage you to make absolutely sure that it's not a wiring fault before deciding the lamps are defective

littlespark · Oct 18, 2022

Ok. I see. I misunderstood.

The led power supply is built into the new fitting, and will indeed use 230v

250v is within the allowed tolerance of supply voltage. (Max is 256) so they should work

Hyppy_ · Oct 18, 2022

Avo Mk8 said:
Could it be that something has come adrift in the wiring?
[…]
Do you have a multimeter, to check that there is mains at the terminal block of the fitting.

Multimeter has gone awol, but while I track that down, tested with an old school testing screwdriver and there's something there, but good call: I'll go back to basics and check all's in order there as well as wire up the light(s) as suggested and check those too.

Hyppy_ · Oct 29, 2022

Just to close this off, the multimeter wasn't showing out the ordinary with voltages and all wiring was good. Just duff lights perhaps and not wanting to risk £10 a pop (literally), I found regular GU-10 spots with bases big enough to cover the 100mm cutouts and used them instead. A lesson learned on non-replaceable LED lights …