DCC and the return loop, I have a question

[Anonymous]

I didn't want to hijack the other thread dealing with return loops, as it looks like a DC question. But any way, it seems to me if you have 1 return loop, you probably would want another to get the train going back the other way at the other end. The layout I'm am thinking up would anyway. Logic tells me that if one controller can switch polarity on one loop, it should re-reverse polarity for the other. Is this right, or am I mistaken?

[rrinker]

Yes, you can hook one autoreverse to more than one reversing section, but then you cannot have two trains, one in each reversing section, at the same time - they would 'fight' one another and just short out.

IN DC, since you can;t change the polarity under a moving train, you normally reverse the polarity of the main line while the train occupies the reverse loop section. With DCC, since the 'polarity' (really 'phase' since it's a square wave AC signal) doesn't matter, the reverse loop controller reverses the phase of the loop trackage WHILE the train is on it.

--Randy

[Texas Zepher]

QUOTE: Originally posted by phatpony
Logic tells me that if one controller can switch polarity on one loop, it should re-reverse polarity for the other. Is this right, or am I mistaken?

The desired polarity on a loop is dependent on which way the train is entering. So if the train is always going to enter the loop on the same "leg", then yes as rrinker said if you have only one train. If the train can enter the loop in either direction it is irrelevant what the power in the "other" loop is.

One often overlooked solution for a one train on a two loop system (which I use for loop-to-loop Christmas Tree displays), is to put the loops on constant power and put the reversing loop control on the main. With DCC it doesn't mater which way the train enters the loop.

[rrinker]

Still really only works for 1 train though, in which case you could just power the loops through the autoreverser. For display purposes, you can also use a block occupancy detector that will both throw the turnout and switch track polarity at the same time, for completely hands-free operation. Or uses the autoreverse and a spring switch.

--Randy

[Anonymous]

Since you are talking about DCC you have totally different issues than you do in DC. The only thing that matters in DCC in a reverse loop situation is eliminating the short that occurs when you enter or leave the reversing section. That's why you can use a single auto reverser for more than one reversing section, as long as only one train is causing a short at a time. If you are talking about a train reversing situation (like the trolley that stops at one end then goes back) you can't do it by changing the polarity of the tracks, you have to do it through DCC, so it will actually be harder than it is with DC. If I understood what rrinker said I have to disagree a little (so I think I didn't understand what he said). You can have trains in more than one reverse loop at the same time, but you can't have two trains crossing the boudaries between the 'normal' section and the reverse section at the same time.