LV transformer selection

[happyhero]

Can anyone advise please, I am putting 12v LV halogen fittings and the lamps will be 50w. The transformers come in 0 to 50W rating and 0-70w rating that are of any interest in this case, so the question is which would you pick to go with a 50watt lamp?

My mate who is also a spark is saying the 0-70w ones but I was always told to try and load the transformer to max or nearly max.

Any help appreciated.

 

[Space cat]

I was always told to try and load the transformer to max or nearly max.

I can only think of one reason why anybody would say that. With a 'real' transformer you get voltage drop in the windings when you draw current from it. If it's a good one it will be designed to give the rated voltage at full current and so you will get a higher voltage if you draw less current. As an example, I recently measured the open circuit voltage of a 24V transformer and got 28V. This is normal.

In your case you will be loading a 70 watt transformer with 50 watts so the overvoltage will be much less. Furthermore, I suspect that you are not looking at 'real' transformers at all. Most of the things sold as transformers are actually switch mode power supplies and their output voltages are regulated. I would definitely go for the bigger one.