The idea is to use low-cost components to drop the starting voltage thereby creating multiple voltages to choose from. Then your relays can pick and choose which one to apply to a particular track block. I show the "diode-dropping" method above using bridge rectifiers. But it's the same idea using a string of resistors or variable resistors (rheostats). There are OGR threads that get into the nitty-gritty about pros/cons of various voltage dropping methods.
So in the example above, I arbitrarily show a starting voltage of 12V AC from the transformer. A $1 bridge rectifier "generates" 2 new voltages...one is about 0.7V lower, the other is about 1.4V lower. But these can be cascaded; so a 2nd bridge rectifier can create 2 more voltages as shown. And so on.
Using your relays, you can select which voltage to apply to your various blocks. You do not need to apply "adjacent" voltages to adjacent blocks. That is, you can apply 12V AC to one block and, say, 9.9V to the adjacent block (skipping the intermediate voltages).
The point about shorting is this. When an engine or passenger car straddles two blocks with different voltages, this only "shorts" the bridge rectifier which is a "harmless" event as opposed to shorting two transformers that each provide power. That is, a bridge rectifier is a passive component that in itself does not provide energy. Of course a transformer is an active component that does provide energy (and lots of it!).
The momentary straddling/shorting of two transformer powered blocks by an engine should be a momentary event. The electrical analysis of what exactly happens gets technically involved depending on various factors; in my opinion this is one of those tolerated but frowned-upon situations...a YMMV scenario. As discussed in earlier posts, there could be a situation where a stopped consist might position a passenger car straddling/shorting two adjacent blocks. This would present a long-term short which should be avoided with alacrity. But if using the diode-dropping method, a long-term short by a passenger car straddling adjacent blocks is a no-harm, no-foul event; the passenger lights would receive the higher of the two voltages.
If this is something you'd like to try, or would just like to explore further in the spirit of OGR being a discussion forum, provide us a little more about what exactly you're trying to do. I'm particularly interested in how you see delay relays fitting in (or not) to the mix.
