How are short circuits precluded when a train completes the 'balloon' trip to join the track on which it entered?
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Huh?
If the right-side rail is hot' [+] and the left-side 'cold' [-] when entering, the polarity must somehow be switched when re-entering the same track from the opposite direction....to preclude a short ckt. How is this done?
If you are using a straight DC control system, the "balloon track" is wired to a direction switch separate from the rest of the layout. The, while the train is in the "balloon track" the direction switch for the rest of the layout can be switched without affecting the train.
If you are using DCC, there are auto-reversing units to handle the polarity change.
In the case of a 'classic' balloon (one switch and almost a circle of track) you would gap the rails with insulated rail joiners on both rails on both legs of the balloon.
If using DC you then need to connect the now isolated balloon to a reversing switch. If you are new at wiring I suggest using the Atlas HD Twin part number 6928.
Here is a link to an article for DC (scroll down to section 2: reverse-loops-model-trains
If you are using command control, gap the rails in the same way and use a commercially available 'auto-reversing' unit.
Here is a link to an article for command control: Use the link above and scroll down to section 4
I'm guessing the OP is referring to a reversing loop. I may be mistaken, but I believe that in 3-rail it is not an issue since the center rail is hot and the outside rails are both common, no matter the direction of travel.
In 2-rail where each outside rail is different and there is no center rail, I believe it is an issue using reversing loops. I don't have any experience with 2-rail, so someone with more knowledge of 2-rail would have to advise.
Thx, Bob. But it seems that "can" needs to be changed to "must", right? So: [1] You MUST take action while it's in the balloon. [2] Hopefully, switching polarity "for the rest of the layout" will not cause problems...
Simon: Thx for the pointer. It also told me about the part I forgot: The switch frog.
Now I am just jealous. I only wish I had room for a balloon track (a real railroad term for a reversing loop).
If I had that kind of room, I would instead do a four track dog-bone layout, and leave out the switching. As it is, I am stuck with 14x26, barely enough for a four track oval.
phil gresho posted:How are short circuits precluded when a train completes the 'balloon' trip to join the track on which it entered?
You insulate a portion of the balloon track sufficient to hold the train then reverse the section of the layout the train came from. In the "old days" this was done with DPDT switches. Modernly, you can use optical sensors driving a relay or "Frog Juicers/Auto-Reversers". Azatrax (http://www.azatrax.com) has the equipment and the diagrams for this.
Hope this helps.
The above comments are spot on for 2 rail layouts. A balloon track(s) doubling back itself in effect forms a reverse loop. Before DCC came on the 2 rail scene we would isolate a length of track in the balloon loop (longer than the longest train) and control its polarity with a double throw double pole toggle switch. Before the train entered the reverse loop the operator had to set the toggle switch to have the polarity of the reverse loop match that of the track at the entrance to the loop. Before exiting the reverse loop the operator would stop the train and flip the toggle switch so that the loops polarity matched that of the track at the exit to the loop. Easy to wire - but a pain if one wanted hands off continuous running.
On two rail DCC layouts you can replace the reverse loop toggle switch with a digital device that instantaneously matches the phase of the DCC track power between approaching and entry/exit reverse loop tracks. They work great and enable hands off continuous runs through reverse loops. The DCC auto reverse devices also handle DCC (square wave form) phase matching at wye's and turntables.
Let's give that man some photos!!!:
But hey...if you go BPRC you don't have to worry about it 
Attachments
Thx to all of you for the education. Bob D. Those pix help a lot....
I've never heard of reverse curves referred to as balloon tracks.
Dan Padova posted:I've never heard of reverse curves referred to as balloon tracks.
Guessing the term comes from the track shapes resembling the "thought balloons" surrounding dialogue in cartoons.
Simon
see Bob2's comment above. Now you, too, know.
phil gresho posted:see Bob2's comment above. Now you, too, know.
Suggest you read my above post again. Bob2's post DOES NOT explain WHY they were called BALLOON tracks, as in what the terminology was derived from. I think what I speculated above is likely correct. Now you know.
Simon
OK, Simon; let's meet half-way: The 'cartoon balloon' is indeed a useful 2-D projection of an actual balloon, which is 3-D..... And a "balloon track" is, necessarily, a 2-D projection. The "thought balloon" is a sufficient, but not necessary, interpretation/projection.
