Halogen lighting in kitchen units - how much energy do transformers waste?

buglawton

We plan to have some new kitchen units with small 20v halogen lamps. I understand these are always connected via transformers. Typically, how does the switching work, when you turn them off does the mains to the transformer get disconnected?

Also, while in use, what % of energy is the transformer wasting?

ailuro2

Depends on how they're wired up - talk to the electrician who is doing your work for you.

27col

It is normal for the transformer to be wired, so as to be switched off when the light is not required. But it would be as well to make sure. It is many decades since I did the theory of transformers, but I do remember that they are pretty efficient. Somewhere up in the 90% range.

buglawton

I found out from the kitchen supplier that the default fitting is a wired spur - this is why 99% of peoples transformers are left on permanently, quietly consuming around 10 watts each across the land, with 1 transformer for every 3 halogen bulbs. I decided to go for LED lights and the appropriate, regulated lower power transformer. White high power LEDs have improved hugely but are set to improve even more, so having the right voltage and transformer means can swap out 'bulbs' for better results later. LEDs make good sense inside a kitchen cabinet, you are not then driving 40W of heat into your kitchen cabinet together with quite a bit of UV.

Andreg

buglawton wrote: »

We plan to have some new kitchen units with small 20v halogen lamps. I understand these are always connected via transformers. Typically, how does the switching work, when you turn them off does the mains to the transformer get disconnected?

Also, while in use, what % of energy is the transformer wasting?

The switch is normally on the mains side of the transformer. (It's the same switch type that is used for mains lighting.) So the transformer will not waste energy while the lights are turned off.

Our energy monitor shows that our low voltage kitchen lighting, with 4x20W halogen dichroics, consumes 83W. Assuming the 20W bulbs actually use that much, the transformer is wasting 3 watts.

I assume if we replace the halogen bulbs with LEDs, that the current through the transformer will reduce, and it will waste less energy. Haven't tested that one yet...

buglawton

Apparently typical transformers for halogen lamps are unregulated and supply the correct voltage when loaded. If you connect LEDs the low power means that the voltage can run too high and burn out the LEDs. Power supply needs to be regulated.

Andreg

buglawton wrote: »

Apparently typical transformers for halogen lamps are unregulated and supply the correct voltage when loaded. If you connect LEDs the low power means that the voltage can run too high and burn out the LEDs. Power supply needs to be regulated.

Basic transformer output voltage is dependent on the input voltage multiplied by the ratio of the number of windings on the output side to the number of windings on the input side. I checked ours and the voltage is 12V whether or not loaded with bulbs. Would advise anyone else to check though in case their power supply is different.

dwarvenassassin

Andreg wrote: »

Basic transformer output voltage is dependent on the input voltage multiplied by the ratio of the number of windings on the output side to the number of windings on the input side. I checked ours and the voltage is 12V whether or not loaded with bulbs. Would advise anyone else to check though in case their power supply is different.

Transformers these days do not use windings and it is all done electronically.

Transformers burning 83W of power with 4x12V bulbs will probably still burn a similar amount with 3 bulbs as they do the transform/output regardless of loading. Do not confuse low-voltage with low-energy.