Control Panel Wiring - Part I

By Ty’s Model Railroad - 1/06/2011 12:42:00 AM

MRC 280 Tech 4 controller beside a completed model railroad control panel

The last 2 months have been insanely busy for me, so up until last week I haven’t had much time to concentrate on my layout. My goal was to complete my wiring and control panel by the new year and even though it’s now January 6, I’m not that far off from my goal. My first a most important purchase was a power pack. I decided on a MRC Tech 4 280 dual cab controller as well as 4 Atlas snap-relays to power my x-section, track signals, and corresponding control panel indicator lights. 

L brackets attached to the underside of a control panel

My control panel and controller need to be able to fold away under my layout when not in use do to the limited space in front of my layout. I purchased a 1/2” thick hardboard panel to use as the base to which my control panel and controller will bolt to. The rear of the hardboard panel will attach to hinges located under my bench work, allowing the entire unit to swing under the layout when not in use. I used L-brackets bolted to the sides of the control box to fasten the control panel to the base.

Wood control panel base with four Atlas Snap Relays attached

Once the base was cut, I cut a large opening to allow access to the inside of the control box. I also drilled holes at this time for the controller wires and power cables. A scrap piece of aluminum the same colour as the control panel was used as the base for the cab controller, and glued to the base. I used small black metal eyelets around the drilled holes for the main power leads to make them look more appealing. At the same time, I attached my 4 snap-relays to the bottom of the base.

Wood control panel base with wicker cladding and completed control panel temporarily placed on top

Only the first 8 inches of the base will protrude out past the layout while the majority of it will be covered by the control box. To cover the visible hardboard, I attached 3/4” titanium L-molding around the edges, just as I did on the control box itself. I used PL Ultimate construction adhesive to glue the trim.

Wood control panel base with wicker cladding and drill holes for wire leads

While the trim dried, I used this time to start wiring everything together. The first item on my wiring list was to connect all the leads from the 8 turnout signals to my resistor board. I also started connecting leads to all of the LED lights and volt meters inside the control box while it was still detached from the base. 

Wire leads from trackside signals connected to the resistors on a PC board

Wire leads from trackside signals connected to the resistors on a PC board

The leads from all of the LEDs were then connected to their appropriate leads on the resistor board and all connections were soldered together and insulated with electrical tape. As I made connections, I tested each circuit to make sure everything worked. One advantage of having all the resistors together on the PC board is that it was very easy to test each resistor anytime I had a short circuit. I also decided that the resistor board would be mounted outside of the control box due to space limitations inside. 

Wiring components together inside a model railroad control panel

Wiring components together inside a model railroad control panel

I then mounted the control panel to the base panel with 4 bolts through the four L-brackets on the control box. I mounted the resistor board to the bottom of the base using brass bolts. I used brass nuts and foam blocks to support and cushion the PC board. I also made a schematic of my resistor board, making it much easier when testing.

A diagram of a custom built PC board for LED resistance management

A PC board with resistors and bridge rectifiers fastened to the back of a model railroad control panel

The cab controller also needed to be attached to the hardboard base. However, it did not have any brackets or holes to mount it. With a little research and testing, I discovered that the MRC cab controller is quite hollow and the printed circuit is located right below the top panel, leaving the bottom entirely open. 

Wiring components together inside a model railroad control panel

I started by drilling two very small holes through the bottom of the controller to inspect and make sure I wouldn’t hit any important electrical components. I then drilled larger holes to accommodate a large threaded screw. I drilled two holes through the hardboard base, passing the larger screws through and into the pilot holes in the controller. This worked great and securely attached to cab controller to the base. I ran the power cord through a hole in the hardboard so it would not be visible from above.

Wiring Atlas snap relays and other components together inside a model railroad control panel

I spent about four entire days wiring everything together. This included making all the connections, soldering, and insulating. Once each circuit was made, I needed to individually test them. Everything worked well with the resistor board for all the LED lights on the system, with only a few shorts that were located and fixed relatively quickly. I spent a lot of time setting up all of the snap-relays as well, making sure that the correct indicator LEDs and switched were lit when the switch control was flipped. 

Power leads attached to Atlas selectors with terminal connectors on a model railroad control panel

One of the most frustrating shorts I had to deal with had really nothing to do with my wiring at all! It had to do with the actual Atlas controller, selectors, and switches on the top of my control box. It turned out that the screws supplied to attach each lead to each Atlas device protrudes further then the base, which in turn contacted the aluminum cladded surface of my control box, thus causing a large system-wide short. I resolved this by making a small copper washer for each screw. 

Wiring components together inside a model railroad control panel with long power leads hanging out

Testing everything as I went along took a lot of extra time, but was worth it in the end. Problems could be fixed immediately and were easily identified, opposed to having to sift through everything if it was completed. Another problem I encountered was with my switch overload indicator lights. This led back to an issue on my resistor board. I didn’t take into account that when one AC lead was powered that the second AC lead would also be powered. This was because both leads shared a common connection on one of the bridge rectifier posts. This was easily resolved by putting diodes (see below) into each converging AC lead, preventing current from traveling down the other lead when either was energized.

Diodes installed in two power leads for switch machine overload indicator LED lights

I temporarily fastened all of the turnout signals to a cardboard holder so I could easily view them when testing, as seen below. They all worked great and matched the corresponding positions perfectly. A switch on the control panel turns the center amber lights either on or off. I then attached an accessory 12V rectifier to the bottom of the base with brackets. This 12V DC power source powers all of the future accessories and LED lights. 

A 12 volt AC inverter attached to the bottom of a model railroad control panel with metal brackets

Complete wiring below and inside a model railroad control panel

I used small brackets to fasten all the cables to the bottom of the base. There was such a large amount of wiring that it was sometimes difficult to keep everything organized. All the control panel wires that connect to the layout run off the back of the control panel base. They will then connect to their appropriate screw on the layout's terminal strips under my table. 

Now that the control panel and all the wiring is complete, I plan to have it attached to my layout by the end of this week. Once I complete this, I will post part two.

Wiring Atlas snap relays and other components together inside a model railroad control panel

Wiring components together inside a model railroad control panel


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