I have a small loop of track in my O gauge layout that connects to a larger main line. I would like to be able to run smaller DC locomotives on that loop, but with the ability to run larger AC units as part of the main line. (Not at the same time) I plan on providing two feeders to the small loop with isolation switches at the transformers. I assume I will also need separate ground wires with switches. I have installed fiber pins in all 3 rails at the points the loop joins the main line. Do I need anything else to accomplish this?
To complicate things further, I would like to have switches in the smaller loop, If I operate the switches at a constant voltage, can that voltage be AC?
The first thing I’ll point out is this would probably have better response on the Classic Toy Train section of the forum.
The first thing is if the electrical pickup for the AC is two or three rail. If three rail, the outer two rails are the same side of the transformer, and the middle rail is the other side. On the older track, the outer two rails are shorted together, and most of the older cars do not have insulated wheel sets, which aren’t necessary with the rails distributing the power this way.
The problem comes with the DC, this is usually two rail, meaning the electrical pickup is through the outer rails and the center rail is not used at all. You’d need track that is insulated so that all three rails are electrically isolated from each other, like the old Gargraves track. You’d need two DPDT switches, one to select an AC or DC input, the second to select two or three rail wiring. For the three rail, connect only one of the outer rails and the center rail to the output of the switch.
I think that sounds right, but… Is the DC also center rail powered, or is the DC powered from the two outside rails? I don’t know what you mean by a separate ground wires with the switches? Personally I would use a single isolate switch that selects between one power source and the other. That way both could not accidentally be ON at the same time.
Do you mean turnouts (switch tracks) and turnout motors? Most turnout motors use twin coils and it doesn’t matter if they are powered by AC or DC current. Or are you still talking about electrical switches? Electrical switches don’t care if they have AC or DC current passing through them. To them electricity is electricity.
Bigger question. Instead of using two transformers, why not just power it with the AC transformer
I would NOT run two sets of feeders to the track, one with DC and one with AC. That’s asking for trouble if you make a mistake and forget to open one of the control switches and end up with both connected at the same time. You want ONE set of feeders to each section with a Double pole double throw switch. One side of the switch connects to your DC supply, the other one to your AC transformer, and the center connects to the tracks. Move the switch one way, you’re running on AC, the other way, DC. And never the two shall meet. For best results use a center-off switch so there’s no chance of contact internal to the switch.
This is similar to the occasional threads about running DC and DCC on the same HO-gauge layout. The general consensus is that the tracks should not be connected at all, not even with insulators. The issue is the trains that cross from one zone to the other, thus bridging the gap. It’s very difficult to guarantee that you will never do this with the two different power systems both turned on, so there is always a significant risk to trains and power systems here.
It’s just not a good idea, even though you can do it.
Agreed. There is a lot of such expertise over on the CTT forum. I would run this thread on that forum as well. Between the two, you should get plenty of good advice.
Well except in the DC/DCC situation you can set up a DPDT toggle switch so that the power source is selected before it goes to the the toggles controlling the individual blocks - that is, throw the toggle one way, and the entire layout gets DC. Throw it the other way, the entire layout gets DCC.
I guess where I’m confused is that AC generally means three-rail, either like Lionel trains, or Marklin with the center studs. If that’s the case here, it would be pretty hard to set up the layout so that two-rail DC went to the outside rails, but then be able to throw a switch so that AC went to the center rail and both outside rails. In olden days some O gauge guys did set up their layouts so all three rails were isolated and they could change from two-rail power to three-rail, but I assume they were either using AC motors on all their engines, or had converted the three-rail AC engines to DC using a rectifier and just used DC??