:cry: Ah...the oldest trick in the book. Create 2 loops, each wired to separate transformers. Then wonder why there are problems crossing a train over between the 2 loops....wall1 Unfortunately, this solution has been pushed from the beginning of time, especially with Lionel.
The best way to solve this problem is to use block or cab control wiring. Principle is the same in DC or AC, 2 or 3 rail. You want to control a locomotive/train with the same transformer, no matter where it goes on the layout. And you want to avoid the situation where the train is receiving power from 2 transformers at the same time.
When trains or locomotives span the insulating pins, rail joiners, or gaps in your current situation, the train is receiving power from both transformers. And the transformers are now directly connected to the outputs of each other, which is why you are seeing sparks. What you are not seeing is the fault current passing through the wheels or pickups of your locomotive that flows between the 2 transformers. This fault current often has
no circuit breaker protection, and can be as large a current as your transformer will put out. Typically, over extended periods of time, the fault current will damage the windings of your transformers, especially post-war transformers that only had circuit breaker protection in the common leg. The sparks also create minute pits on your contact rollers or wheels.
As stated earlier, the cure is to divide both loops into about 4 blocks (electrically isolated sections of track) by insulating the center rail at the block boundaries. Run a feed from the center rail for each block to an Atlas Selector or the center terminal of an SPDT (center off) toggle switch. Run the variable output of each transformer to the inputs of the Atlas selector or to the 2 end terminals of each toggle switch.
Now, you select which transformer powers each block. When you want to cross over from one loop to the other, you just select the transformer you are using for each needed block just before the train enters the block.
Blocks that are not in use should be turned off to avoid powering two locomotives from the same transformer. A minimum of 4 blocks are needed in each loop to allow 2 trains to follow one another without having to stop and wait at each block boundary. Passing sidings should also be separate blocks.
Block or cab control is explained in much better detail in books on model railroad wiring. The cheapest example is
Easy-To-Understand Wiring Basics and Atlas Electrical Controls, but it only features Atlas electrical products. Other good books on wiring are available at
Trains, Model Trains, Model Railroading, Toy Trains, Trains.com.
hope this helps
