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I have 2 x 35w halogen bulbs running from a 12v 105w transformer.

When I switch them on (standard on/off switch not dimmer switch), they blink on, go off then come back on and stay on.

If I switch them off and on again they come on immediately and stay on.

If I leave them off for a few seconds they go through the blinking on process when I switch them on.

Before replacing an Aurora transformer with a Varilight transformer they behaved perfectly normally.

What's the problem?

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Does the transformer have an overload shut-off, with an automatic reset?

The resistivity of tungsten increases markedly with temperature. A cold tungsten-halogen bulb will draw much more current then a hot one (and they do get very hot!). So the first switch-on with a cold bulb will:

  1. Draw a very high current, which:
  2. Overloads the transformer, causing it to cut off momentarily, while;
  3. Heating the filament enough that;
  4. The second, immediate switch-on does not overload the transformer.

Just a guess, but if your transformer has this feature, it could be the explanation...

EDIT:

This just in: this site, http://www.varilight.co.uk/lighting/transformers.html, states that their transformer has overload protection with auto reset...

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It sounds like your transformer is defective. If you hadn't listed the bulb wattage and transformer capacity, I'd say it is under-sized since this is a common issue when the transformer isn't sized right, but in your case, it sounds like there is enough capacity.

Now if your bulbs were 50W, I'd say you are cutting it close. You might opt to take an amperage reading to see what the bulbs actually drawing. If it indeed only 70W, then you should replace the transformer.

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