I am operating my layout using only DC. I have several basic reverse loops and I would like to find an auto reverse unit that simply changes polarity like the Walthers turntable so I don’t have to wire up DPDT switches and stop the train everytime I use a reverse loop. What seems to be a good auto reversing unit for a DC user? It seems like everytime I find one available it says “For DCC only”.
Thanks,
Brent
I don’t know that they exist! The problem in DC is a bit more challenging than it is in DCC. In DCC you can switch the polarity of the track under the train, and it just keeps going. In DC, that changes the direction, so you also have to change the direction on the power pack. The trick to not stopping the train is to switch the polarity on the mainline, rather than the reversing section. You can do that while the train is in the reversing section, when it hits the main, the polarity will match, and it will keep right on going.
I think Bachmann makes a trolley set that runs along a stretch of track, and reverses direction at each end. It looks like they’ve got some sort of sensor that flips the polarity of the track, so the trolley reverses and goes the other way. This is a DC unit in HO. But, it’s a gimmick, designed for a back-and-forth operation like a store display.
The trouble with a DC reverser is that you have to reverse the main line, not the loop. This isn’t so bad if you’re only running 1 train, but it gets harder to co-ordinate when you’ve got multiple trains running and you have to keep all the blocks lined up.
Also, a DCC reverser has a limited current rating. I think my Tony’s reverser only supports 2.5 amps.
I give that warning because I think you really could use a DCC reverser in DC, with a number of limitations. This is based on my understanding of the circuit, and it may not actually work, but in theory it should.
The reverser would be wired to the main line, not the loop. It has to be this way in DC.
The reverse loop itself would be hard-wired.
You would always have to enter the loop the same way. You could not go “backwards” around the loop.
You would be limiting your main line to the current capacity of the reverser.
Good News! If you have multiple loops off the same main, you only need one reverser to control all of them.
The Theory: A DCC reverser works by sensing a short circuit as the lead wheels of the train cross the insulated gap between the main and the loop. It then flips the polarity of the track under its control. In DCC, that would be the loop, but in this system, it would be the main. If the polarity already matches, then no flipping is done, and th
Not an auto-reverser so much as a wiring trick that simplifies the situation - and eliminates the stop.
First, a little nomenclature:
Reverse switch - found on the power pack or hand controller. Determines whether the locomotive is running forward or in reverse in relation to itself.
Direction switch - found on the control panel, or as a locking relay worked by pushbuttons on the fascia. Determines which way the train is supposed to run in relation to timetable direction (East or West, North or South, Up or Down*)
Reverse loop - a piece of track which causes an entering north (south, east, etc.) bound train to exit running in the opposite direction.
Reverse section - a piece of trackwork which has the same effect on train movement, without the classic balloon shape.
The trick is to wire a SECOND DPDT into the feeders for, “The rest of the layout.” That is the direction switch (which may be a two-coil or latching relay operated from the entrances to the various reversing sections.) The feeders to the reverse loop(s) and section(s) can have no direction switches if they are only run one way, or will have to have separate direction switches which will have to be pre-set for the direction a train is going to enter but don’t have to be thrown while the train is on the reversing section.
In operation, a train operating timetable east will have the direction switch set for timetable east. If switching is being done, the reversing switch is used but the direction switch is left alone. Approaching a reverse loop, the entrance direction switch for that loop will have to be checked (if it is a bi-directional loop. If trains only operate over it in a single direction, it can be hard wired for that direction.)&nbs