transformer wiring 12v 400va

[markopeelo]

Hello, I have just opened a transformer manufactured by universal, which supplied power to a track light fitting, the unit has two sets of 12v secondary outputs, which had both been linked together to supply the track. The track originally had say 6x 50w mr16 halogens. Am I right in thinking that each set of secondary outputs supply 200va and the two together supply the full 400va. Any advice would be greatly appreciated.
Mark

 

[bernardgreen]

It depends on the construction of the transformer.

If there is one secondary winding ( 400 va ) with two sets of terminals then they can be safely connected in parallel. ( they may be individually fused outputs )

If there are two separate secondary windings ( each 200 va ) then if the windings are exactly matched then they can be connected in parallel to obtain a 400 va supply. Manufactures data will ( should ) confirm this but care is still needed.

If the secondary windings are not matched connecting in parallel can lead to heating in the transformer.

Exact matching means more than just having the same off load voltage.

They must have exactly the same number of turns on the two secondaries and the same length ( hence resistance ) of wire in the two windings. If the resistances are not equal then the on load voltages of the two windings will be different for the same load. The load will not be shared equally between the two windings. In this case putting a 400 va load on two parallel connected 200 va windings will overload one winding.

 

[markopeelo]

Hello Bernardgreen and thank you for your reply. There are no details other than the spec on the unit and I can't find a site for the company who supplied it. The transformer looks similar to this one :-

http://img.directindustry.com/image...10-400-va-trafo-tf-k-series-19675-2397331.jpg

Although on one side the supply live and neutral go in and on the other side two sets of cables go out, two from the left edge of the windings and two from the right, to a 4 way terminal block each marked 12v. The 4 core 2.5mm cable connected to them have been then wired to the track light fitting. Each of the two left cables from the secondary winding to one terminal and each of the two rights from the secondary winding to the other terminal.

 

[bernardgreen]

A photo of your transformer would help.

But the best option in the absence of details of the transformer would be to divide the lamps into two separate sets and run each set from one secondary without making any connections between the two sets.