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PostPosted: Wed Apr 04, 2018 5:42 pm 
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Dear UHM

Since replacing a dead MR16'S 12v bulb in the bathroom yesterday the lights are now displaying a more Christmas light configuration - flashing.
There are three light fittings on this circuit, with only two lights in operation. The 3rd light fitting without bulb is now boxed in. Each light is serviced by its own transformer as explained by @ericmark in a response to @mawallace in a previous post.
The symptoms - there is a significant delay (3 seconds) from when the switch is turned on to when the 1st lights starts a dull flash, followed by a second slightly brighter. At this point the 2nd bulb joins in and two more flashes and both are at full working level. The bulbs are standard MR16 halogens.
I suspect it is one or both of the transformers. How do I check if it is and which one or both?

Much obliged.


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PostPosted: Wed Apr 04, 2018 6:10 pm 
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Check the wattage of the lights you fitted. The transformer is only rated to a certain power and will trip (as you describe) if they are overloaded.

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PostPosted: Wed Apr 04, 2018 7:02 pm 
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As kellys_eye has said, you may have installed 50w halogen lamps, but the transformers are only rated for 35w lamps, so they will flash / pulse.

You have two choices.
Change the lamps for lower rated ones (less than what the transformers are rated for)
Change the transformers to high rated ones.

Easiest thing to do is to take a lamp out and take the transformer out (Electricity off) and see what is written on the transformer, and you may was well look at the lamp too since you would have just taken it out.

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PostPosted: Wed Apr 04, 2018 10:51 pm 
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Checked the bulb and it looks to be a 50w - markings very feint. This is within theTransformer rating, but, when removed, stopped the other light from pulsing. Strange.


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PostPosted: Sat Apr 14, 2018 1:33 am 
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Is the transformer on a simple switch or an electronic switch? It would seem the unit is injecting some interference into the supply line, should not happen with simple switch, but with a dimmer or other electronic switch you may get some problems with one unit upsetting another.


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PostPosted: Sun Apr 15, 2018 9:37 am 
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On a simple on/off switch. No flashing with 35w bulbs and I'm thinking that one of the transformers may be showing early signs of developing a fault.


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PostPosted: Sun Apr 15, 2018 1:32 pm 
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The switched mode power supply (Electronic Transformer) has capacitors which have a limited life, toroidal transformer do not have any electronic components in them and last for decades, the SMPS was used because it was slightly cheaper and it also controlled the voltage to very precise limits, and the quartz lamp needs careful voltage control. However the SMPS will not work with LED's so I would replace it with a toroidal transformer then you have the options as to which bulbs to fit.

The link shows one suitable for one lamp you can get larger ones so many lamps fed from one toroidal transformer I have a 200 VA unit with 4 x 3W LED MR16 equivalent lamps now, it did power 4 x 50W Quartz lamps. It will do either with no problem.

The SMPS or (Electronic transformer) can have a problem with some makes of bulb as the filament is a coil, some time the coil in the lamp just happens to match the capacitor in the SMPS and do odd things as a result, often there are instructions not to use over 1/2 meter of cable between the SMPS and lamp because they can turn into mini transmitters. This is not a problem with toroidal transformers.


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