One by One Downlights go out

[tommywalsh]

Hiya all,

In my kitchen I have 10 downlights, over a period of about a year, one by one has been going out.

Obviously when the 1st one went, my first thought was the bulb had blown, but replacing the bulb didn't change anything, it still didn't work.

One by one they've been going in a similar way, now I've only got 3 lights left at the top end of the kitchen.

This morning I got onto the kitchen table and took out one of the lights and the transformer that wasn't working, there was some carbon black misting over the braded cable running from the transformer to the bulb - apart from that I can't see anything wrong.

Can anyone offer some advice, do I need to replace all the transformers? is this slight blackening of the cables evidence of something?

Thanks guys and gals

 

[sparkiemike]

Depending on the fitting type it could be the lamps (light bulbs).

If the fitting is fire rated and looks like a tin can when removed from the ceiling you need to make sure you have fitted light bulbs or lamps that have an aluminium reflector.

The aluminium reflector allows light and heat to be dissipated forward, reducing fixture/ceiling discolouration and preventing the fitting from over heating.

It will probably mean the 12V MR16 tails and lampholder will need to be replaced.

 

[ericmark]

There are a number problems with the 12v 50mm spot lights.
1) The holders will not stand the heat if some cooling is not available this has been right back to 1970's when I first met the quartz halogen lamp. Worked OK in projectors with a cooling fan running but not so good where cooling was limited.
2) Unlike the GU10/GZ10 where the "Dichroic Reflector" can only be used in the GZ10 so you can't fit wrong lamps. The MR16 will allow both types and it is easy to fit a lamp with a "Dichroic Reflector" in a fitting designed for non "Dichroic Reflector". The "Dichroic Reflector" allows heat to pass through it but reflects the light so as not to overheat the item being lit. Clearly not wanted with ceiling mounted lamps as behind the lamp would get too hot.
3) Although good inverters will auto close down when overloaded this is not true of all. And when the bulb blows ionisation can cause a short circuit which can in turn take out the inverter.
4) The inverter (often called the transformer) was originally designed to reduce the heat in VCR's and has since been used in many applications but it still does produce heat so unless mounted where the heat can be dissipated it will overheat.

The 12V (Extra low voltage) lamp is better than the 230V (Low voltage) lamp as far as light output and lamp life are concerned as the temperature is very well controlled with the inverter and the element is thicker. However the problems with wrong bulbs being fitted, pins burning and damaging holder, and inverters blowing means unless used in bathrooms or other places where SELV is a requirement or where one can touch the supply rails then the GU10 type are in the main cheaper to install and run. Where the voltage fluctuates then the 12V versions can handle this better. But the low voltage type (230v) will also allow you to use cold cathode lamps which as yet will not work with extra low voltage so with consideration of the gradual withdraw of tungsten lamps it may be prudent to move to GU10 type.

 

[ban-all-sheds]

Unlike the GU10/GZ10 where the "Dichroic Reflector" can only be used in the GZ10 so you can't fit wrong lamps. The MR16 will allow both types and it is easy to fit a lamp with a "Dichroic Reflector" in a fitting designed for non "Dichroic Reflector".

Nearly all GU10/GZ10 based lamps have MR16 envelopes. You can get MR11s but they are rare.

 

[aptsys]

...inverters... ...inverter...
...inverter (often called the transformer)...

They aren't inverters. They are switch mode power supplies.

"An inverter is an electrical device that converts direct current (DC) to alternating current (AC); the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits."

 

[sparkticus]

...inverters... ...inverter...
...inverter (often called the transformer)...

They aren't inverters. They are switch mode power supplies.

"An inverter is an electrical device that converts direct current (DC) to alternating current (AC); the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits."

Some switch mode PSUs do the following:

- rectify incoming AC to DC.
- smooth the DC
- regulate the DC down
- convert the DC to AC at a reduced voltage
- rectify the AC to DC output.

So there are inverter sub-systems within some switch mode PSUs. Some output AC by omitting the final rectification stage.

 

[aptsys]

It's not an inverter, it's a switch mode power supply. The input to the device is not DC.

 

[sparkticus]

It's not an inverter, it's a switch mode power supply. The input to the device is not DC.

I did not say it was an inverter. I said there is an inverter sub-system within some switch mode power supplies.

 

[aptsys]

Well I can't think of a SMPSU topology that doesn't work from creating a pulsed DC waveform, but I wouldn't call that AC or any part of it an inverter.

 

[sparkticus]

The PSU in my Sony TV is a SMPS. It does not pulse or chop the rectified DC. It inverts it into a sinusoidal waveform at about 20KZ and then applies that to a transformer.