Running DC and DCC concurrently

[steveeusd]

Hello Everyone--

I have a situation that I would like to throw out to the experts. I want to run DC (analog) and DCC (digital) engines concurrently on the same layout.  The layout configuration is a simple oval with two passing siding on the straight aways.  I am using Bachman EZ track, #5 switches, and EZ-command station. 

Here's what I want to do:  I want to isolate both sidings with plastic rail joiners and supply them both with only DC power, which will be controlled by a MRC 1300 power pack.  The rest of the layout would be run on DCC, using Bachmann's EZ-command unit, which by the way operates flawlessly (kudos to Bachmann).  My rationale is I want to have the ability to park a DC locomotive on the siding and cut power to it so the motor does not fry.  As I understand it, if a DC engine operating on DCC remains idle for any length of time on a siding, for instance, I can ruin or fry the engine.  I also understand I must take another step to allow a safe and smooth transistion from DCC to DC and vice versa.   That step includes installing a light or some other device on the wire between the track and the DC power pack.  Further, I think I can use a DPDT switch so I can power the siding with either DC or DCC.  So... to the experts: am I on the right "track" or not?  What would you suggest?  Am I missing anything?

By they way, I realize I could cure this problem by installing decorders on my DC engines.  However, this would be too cost prohibitive. 

Any help is appreciated.

Thanks,

Steve
 

[Jim Banner]

I believe you are headed in the right direction for what you want to do.  The purpose of the light is to limit the current if you accidentally bridge the two systems.  To do this, it must limit the current to a value that your command station can handle.  For the 1.5 amp E-Z Command, you probably should not use a lamp that draws more than 1.0 amp at 12-14 volts.  This will limit you to one or maybe two active switchers in the yard area.  Using a power pack rated at 1 amp is NOT a solution as the 1 amp limit is normally set by a circuit breaker.  In case of a short or bridging, the current can go higher, much higher, until the circuit breaker kicks out.

If you are into electronics, it is relatively simple to install a circuit in your power pack to limit the current electronically.  This sets a maximum current that cannot be exceeded.  The problem with lamps is that they still allow an excess current for a short time, although this is not usually a problem.

[steveeusd]

Jim--

Thanks for your help.  Unfortunately, I am very inexperienced when it comes to electronics, so I could use a little more explanation on the circuit you described in your post, if you would please.  Specifically, what is it?  and where can I get it?  Would Radio Shack have the part? 

[SteamGene]

Let me suggest that you wire the sidings for DCC, but have a switch to turn the DCC power off on those sidings.  Then when you run a DC locomotive onto the siding, you stop it and turn off DCC on that siding.  Yes, you will need to isolate the siding.  Bridging DCC and DC is not a good idea.
Gene

[steveeusd]

Gene--

Thanks for your input.  It makes a lot sense to me.  Now the $64,000 question: what device would you suggest I use to shut off DCC on a siding, while still generating power to the "mainline"?  And how would I go about wiring such a procedure?

Steve   

[Jim Banner]

Unfortunately, it is not a single part that is required for the current limiting circuit.  You would probably be better off turning off the power to the sidings as suggested by Gene.  What you would need is a gap in one rail at the begining of each siding (right next to the turnouts.)  You can remove one rail joiner and install an insulated joiner (available from your local hobby shop) at each gap.  Then, to turn your sidings on and off, you can use toggle switches from Radio Shack.  Simple on/off switches have two terminals.  For each siding, connect two wires to a toggle switch, one to each terminal.  Then connect the wires to a rail with a gap in it,  one wire on the turnout side of the gap, the other wire to the siding side of the gap.  Don't solder them too close to the gap or you might melt the insulated joiner, allowing the gap to close back up.  You will need as many sidings and as many toggle switches as you have dc locomotives on the layout.

[steveeusd]

Jim--

You obviously know what you're talking about.  Let me throw my idea at you, which is probably not too different from your suggestion.  My thought is to place plastic joiners on both rails on either side of the siding as close to the diverging track of each switch.  Using bachmann's terminal track, connect  Bachmann's green wire from the terminal track to an on/off switch you described.  Then, I would connect another wire from the on/off switch to the DCC command unit.  In theory, this seems tenable.  What do you think?

Steve 

[Nigel]

Jim--

You obviously know what you're talking about.  Let me throw my idea at you, which is probably not too different from your suggestion.  My thought is to place plastic joiners on both rails on either side of the siding as close to the diverging track of each switch.  Using bachmann's terminal track, connect  Bachmann's green wire from the terminal track to an on/off switch you described.  Then, I would connect another wire from the on/off switch to the DCC command unit.  In theory, this seems tenable.  What do you think?

Steve 

Steve;

What you describe would work.

Please do NOT do your original plan of using both DC and DCC - you would have smoked the DCC system, and probably the DC power pack as well - and warrenties do not cover blatant abuse like that.

[Jim Banner]

Gapping both rails and using terminal tracks sounds like a good way to simplifying the wiring.  But if you gap both rails, you will have to use both the wires that come off the terminal track and connect them to a DPST (Double Pole Single Throw) switch, also available at Radio Shack.  Then you would run two more wires to your DCC command unit.  If you find that a short occurs when your locomotive crosses the gaps going onto a siding, just reverse the plug in that sidings terminal track.