I've got a 12V halogen light fitting in the kitchen, but the transformer has just blown (black burn marks on primary winding). The transformer supplied 4 20W bulbs and was marked as 105VA - prsumably to give some margin over the 4x20W = 80W.

The only replacement I can find in the Maplin catalogue which will fit into the casing is a 120VA toroidal transformer, but this has 2 secondary windings of 12V (and hence 60VA) each. Can I wire the two secondaries in parallel to provide a 12V 120VA output?

Thanks

Dave

wire it through a rectified bridge and it will be fine it will have to be dc anyway for your bulb

Pugoetru

The bulbs are 12V AC - and I checked the volts on an identical unit on the other side of the kitchen and it was putting 12V AC onto the metal bars on which the bulb holders mount.

The unit I dismantled had the transformer output connected directly to the bulbs - ie no rectification.

The reason I asked the original question is that I'm concerned that if one secondary winding has a lower resistance, it will try to provide more than half the current and will be overloaded. Does htis sound right or am I talking out of my ar5e again!

Dave

Try Screwfix: they do transformers in there ,and they are good quality.

Alcazar

Dave, You can wire the secondaty windings directly in parallel with no problems at all. Transformer manufacturers usually configure their transformers this way to give maximum flexibility. That way you can have 24V 5A, 12V 10A or 2x 12V 5A, all from one device.

...but make sure that you wire them in phase (the transformer will come with a little diagram), otherwise it will make a very, very bad smell.

FYI, the secondaries are wound by a machine that can count the turns very accurately, so the turns ratio between the secondaries will be precise (i.e. they will be the same). The variation in source impedance of the secondaries will be so small as to be insignificant, so they will load-share without any problems.

As with any transformer (gross generalisation to follow...), the main limitation in maximum power output will be the primary winding and the core construction ('cos these cost money).