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I know DCS like legacy can control conventional engines via varying the voltage to the track (duh, I know). This is where my lack of knowledge is going to be obvious. I went through the DCS manual, and here is what I got out of it:

1)If you want to run command only, use fixed input on TIU w 22 v into it, then connect the fixed output to the center rail via star wiring (ground obviously goes to outer rail)

2)If you want to run command and conventional (and this I am not too clear on), you power the variable input and the wire from the corresponding variable output goes to the third rail. First question: Do I need to bring voltage to the fixed input? My guess is no, but there is mention at one point of bridging between the variable and fixed input, hence my question. If running in command mode would I need to make sure that the variable output is at 22v?

One rub on this: So as I currently plan to wire it, I am going to wire a conventional transformer to blocks, with a toggle to select between A and B handle (ZW transformer), it may be a while before I have DCS in house for a number of reasons.

If I later want to use a TIU, would I put the output from Handle A into  var input 1 and B into var input 2, and then put var output 1 onto the A side of each block toggle switch and var output 2 into the B side of each toggle switch? If you imagine two loops of track, I could envision running conventional engines on both loops, and I assume var output 1 would control 1 loop and var output 2 would control the other (with the toggle switch selecting for each block var 1 or var 2 and would address either variable output to control the voltage.

If I am right about this, then let's say I wanted to run conventional on 1 loop and command on the other. So loop1 is var 1, you vary the voltage. If I want to run a command engine on loop2, will the command base "see" the engine on there via var2 output channel, and I can just leave var 2 at 22 volts, and control the engine via command?

Hopefully this isn't too convoluted, in a nutshell the layout will be wired for standard block wiring using A/B selector switch and two handles of a transformer, but later on I want to wire DCS to run conventional (using both var channels on the tiu) and also allow conventional operation via either var channel, depending on where the engine is on the layout (no, I don't plan on having conventional and command on the same loop, if running command will be 22v full output, makes no sense to me otherwise).

And oh, yeah, this is just conceptual, when the time comes I fully plan acquire a copy of Barry's book (I think I actually have a copy on one of my machines) before attempting to hook it up or do any other foolish thing

Last edited by bigkid
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You can wire one or all the inputs of the TIU to a single transformer output.  You MUST keep the outputs of the TIU separate.

You can program the variable channels of the TIU in fixed mode, that means they automatically come up with full voltage.  If you decide to run something conventional, just address the variable track with the TR1 or TR2 selection and vary the voltage, it drops into variable mode.

Kind of confusing post.  But conventional operations requires variable track voltage.  That is provided by V1 and V2.  It is also broadcasting a DCS signal unless you turn it off, but the max voltage is what you set running conventional.  So while doable not necessarily practical.  You could even run conventional off F1 and F2 if you had a variable input power supply.  But why?

Lastly the TIU get power from F1 only or Aux input.  So to have control over the TIU you need to have power to it.  Can't just power V1, the TIU would not come on.

So most folks probably have a dedicated loop for conventional engines they like to run.  Or do a quick reconfiguration of having TIU V1 or 2 go out to the loop they want to run conventional.  Really depends on the size of your layout.  G

@GGG posted:
So most folks probably have a dedicated loop for conventional engines they like to run.  Or do a quick reconfiguration of having TIU V1 or 2 go out to the loop they want to run conventional.  Really depends on the size of your layout.  G

Actually, I use Variable #1 on my mainline, it's configured for fixed mode. A vast majority of the time, I simply run in command mode.

However, if I want to run a conventional locomotive, all I have to do is select that track and hit the TZV softkey and I'm in variable mode with no voltage on the track.  Put my locomotive on and start running it using the DCS remote.

This is all good information!  Thank you!  I have been pulling the input and output connections off the TIU and jumping the air gap together with heavy clip leads to run a conventional engine.  I thought of hard wiring a toggle switch to switch between DCS and conventional, but that was too much work.  😄  Setting it up as described would be a lot easier and save having a jumper popping off!  

Mark, I don't rewire anything to run conventional on my mainline.  FWIW, I also added a little relay remote to toggle power to my Legacy Command base so that I can test TMCC/Legacy stuff in conventional mode.  This is useful when I get a repair, I like to test them in command and conventional.  I could just unplug the command base, but it's inside the layout and I have to go under the lift-bridge to reach it.  I do the same testing with DCS stuff, but I can turn off DCS from the remote, so no extra switching needed.

Just thought of one other question, for GRJ or anyone else. So if I am using the variable output to bring power to the track (to run conventional) and it also will be used to bring the command signal to the third rail if running command, I assume that I cannot have more than 1 connection/block from the variable output to the track , correct?

From what I recall of DCS, it doesn't like having more than 1 command signal per section. My layout is pretty small so the blocks are not that large, but if wiring for standard conventional I likely would use 2 drops/block. (my main blocks are probably 8-10 feet long) so if that is a restriction I can live with that.

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