All Low Voltage Lights Blown Could it be Transformers?


Postby Pete davis » Mon Dec 19, 2016 9:20 am

Hi, advice needed, I have 10 dimmable low voltage lights in the kitchen ceiling all with their own transformers, they have been working fine for 2years although sometimes they seemed to dim then go back to full brightness on their own.
The other morning I turned the lights on, they flickered & the whole lot went off, I have changed the dimmable switch for a standard on/off gang switch but with no change.
If the transformers have gone it means pulling up most the upstairs flooring or pulling down the kitchen ceiling (both painful!)
Any idea's where to start looking for a fix?
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Postby ericmark » Tue Dec 20, 2016 11:04 am

To start with low voltage AC is 50 to 1000 volts, so I am assuming your using extra low voltage?

The ELV lamps we used as the element was thicker than with 230 volt lamps, and as time went by the simple transformer was replaced with an "electronic transformer" which is not really a transformer, but a switched mode power supply.

The electronic transformer has the advantage of regulating the voltage so lamps last even longer, with quartz lamps the voltage being too low will cause the bulbs to blacken and the element fail, the quartz bulb must be kept hot, so you should not use quartz lamps with dimmer switches. (Although many do)

The other advantage is they are cheaper, smaller and lighter, and this means with MR16 lamps often they will fit through the hole the lamp fits in. So removing a lamp you may be able to renew the electronic transformer.

The problem with the electronic transformer is most (not all) have a minimum output as well as maximum which can stop you using LED replacements, they can also produce RF interference so often there is a max cable length. And to use with dimmers they have to be a special type and match the dimming switch. After all the whole idea of the electronic transformer is to ensure a steady voltage whatever the input voltage does.

So if your lamps have one transformer for a few lamps then one lamp blowing can cause the electronic transformer to auto shut down on under current protection.

If you have individual transformers then I would try and see if one will come out of the lamp hole, and I would replace with a GU10 lamp fitting and move from ELV to LV (12 to 230 volt) so you can fit any type of lamp and no worries about type of transformer, and once you have swapped one then you will know if switch and supply is OK.

The MR16 lamp needs to reflect it's light off something white to work well, often this is not the case, so many more lights than really required are fitted, this in turn results in a lot more power being used. So 10 x 50W = 2A just for one room, since ceiling roses are rated at 6A in the main the supply to lighting is 6A, with so much power to one room to keep within the 6A limit it may have an independent supply.

It may come from a separate MCB in the board, or from a fused connection unit (FCU) and fused down but fed from the ring final. There have been many lighting systems where 10A or 16A MCB's have been fitted to get around the massive load from poorly installed MR16 lamps.

The LED lamps are not really MR16 as MR stands for multifaceted reflector and 16 refers 16/8 of an inch across. With the LED often no reflector and the lamp does not cover the full 50 mm so even worse than the quartz lamp at getting the light into the room. A diffuser below the lamps will really increase the useful light, however it may not look as you want, so small surface mount LED lamps are often better than the MR16 compatible lamps at lighting the room.

I have a bathroom with pods where the MR16 lamp is directed at the white wall, and is reflected off the wall, that works well, but pointed down at a dark floor they are useless. I say this now as if you do need to lift floor boards or drop ceiling you may wish to fit other lamps.

I find kitchen is worst room, you want to keep cool, so quartz lamps sending out inferred heat on your head is last thing you want, I have gone for an induction hob to reduce the heat into the kitchen, no point in then using quartz lighting.
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