DIY Doctor

Problem With Kitchen Spot Lights After Blackout

Postby Mike @ keepers » Sun Oct 06, 2013 9:26 am

Hi, please help!!
Recently we lost power to the house due to a broken power line. The lights all over the house dimmed before final black out. Once power was restored, everything was ok apart from 6 spot lights in the kitchen. I have managed to trace all of them back to a single multi output transformer. Power is getting to the transformer and I can read 12v using a circuit meter from all of the light fittings. Do I need to replace the transformer and if so what does anyone recommend? Thanks
Mike @ keepers
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Simply Build It

Postby ericmark » Tue Oct 08, 2013 4:02 pm

First a little about the quartz halogen bulb. The idea is the quartz is so hot the tungsten will not be deposited on the bulb but instead back onto the element in time the thickness of the element will vary so much that it will burn out and fail but not as quickly as with the ordinary tungsten bulb. To work therefore the brightness of the bulb has to be carefully controlled using an inverter to ensure even when the mains power fluctuates the bulb voltage remains consent which is why you should never use a dimmer with quartz bulbs (although people do) as it will reduce bulb life.

The so called transformer is not really that simple but it is a switch mode power supply and the voltage is maintained by altering the mark/space ratio this means there is both a minimum and maximum output so when all bulbs blow it will (or should) auto close down so putting a meter on the output with no load will likely show no volts. This is also why one can't use LED lamps to replace the tungsten.

So only real way to test the inverter/transformer is to fit a new bulb but also the MR16 fitting does have problems with the pins and connections so really try it in all the holders in case the holder you select is faulty.

The problem is today the GU10, GZ10, L2 holder is becoming more the norm as at 230 volt you can fit LED and Cold Cathode far easier than with the MR16 and with LED and Cold Cathode the very well controlled voltage is not required anyway. So this may be the time to change.

The GZ10 will fit all bulbs and is designed for bulbs with special reflectors (dichroic) that allow the heat to pass but not the light. These bulbs need free air behind them so the GU10 holder will not allow these special bulbs to be used so you can't fit a dichroic bulb the L2 holder is designed for new builds and only allow LED lamps to be fitted. The MR16 has no variables and I have seen many problems where wrong type have been fitted.

The wattage and angle of light is another problem. They are after all spot lights and for general lighting they need aiming at a white surface and light is reflected off the white surface. But in practice often they are not aimed at a white surface so can look like a planetarium. Also the move to LED means in the main more fittings. A 50W tungsten bulb around 900 lumens and a single LED bulb of that size is expensive (around £40) but a 2W LED bulb at around 160lm work out at around £9 for three and more lamps spread the light out better so in real terms likely give a better light than the single 50W tungsten so using more lamps often works out cheaper.

I have just swapped from CFL to LED and in theory that means I reduced from 3500 lm for whole room to 2100 lm however the room is brighter. I used candle bulbs but also use GU10 spots in the bedroom as reading lamps and the 2W LED is ample.
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