Most of the DIY transofrmers are 50watt...this is great as so are most of the DIY downlights that run off them...SINGLY. If you decide to run two lights off the one transformer, you need to be sure that it is either a 100watt transformer or that you get hold of 25watt lamps (they will fit the 50watt socket with no problem, so sometimes it is tricky to tell).
If you try removing one of the bulbs and the other always comes on reliably, and then you swap them and the one that was missing now comes on reliably while the first one is out then it is definately a transformer that just can't put out the power to fire up both lights. It will work "sometimes" because many tranformers kick in with a power spike and if it is enough to get the lamp started then it will keep glowing, though somewhat dimmer then it should. Sometimes it just sits there for several minutes and suddenly gets the power spike or just a sufficient buildup to start...it is howvere killing your tranformer.
Get a bigger one or go down to using 25watt lamps.
Alex
Alex
May 2006