SWAMP CREEK & WESTERN
RAILROAD ASSOCIATION

211 Railroad Ave. Edmonds, WA 98020

LAYOUT ELECTRICAL MANUAL

Established December 5, 2000

Revised by page

VI. DIGITAL COMMAND CONTROL

VI. DIGITAL COMMAND CONTROL:

As DCC is being discussed for the layout the following minimum standards are posted.

Minimum standards for track power

Power Supply: 16 vac 6 amp transformer

These were gathered from the NCE manual.

It must be noted that our layout, while up to the standards required for our conventional throttles, falls below the standards for DCC. Though it would be tempting to ignore these facts we cannot.

The problem is DCC is designed to deliver six amps of power. This is protected by automatic short detection circuits that could be ineffective if lower standards (smaller wires) are used. Such a short, if not detected and turned off, could result in a fire. We cannot risk that. Before DCC could be employed on the layout the wiring would have to be upgraded.

DCC Interface:

Preliminary/subject to change.

The existing wiring could be interfaced with DCC by installing new #12 DCC power busses in three districts. Each district would be powered by a 5 amp power station and each district would be further divided into four sub-districts to aid in fault protection/isolation with Digitrax PM-4s. The interface, or change over from our existing conventional block system to DCC, would be achieved locally through double-pole double-throw center-off toggle switches, one for each selector (approx. 40). Such isolation points would also be of benefit in fault locating.

A strict procedure or special cut-over circuitry would employed to assure both systems could not be used simultaneously as that seems to be a concern.

The buss wiring for the existing system would remain the same through the existing busses where it is connected to the selector switches via terminal blocks. The wiring from that point to the tracks in most cases would have to be upgraded from the current #22 feeders and jumpers to #16 feeder and #22 drops. Power routing would need to be minimized as much as possible, in some cases simply by shifting isolation points (gaps), and in others by adding new selector switches.

As DCC is extremely sensitive to shorts all turnout frog wiring would need to be modified. As they are currently configured a momentary short is likely. The fix, using two relays instead of one, is fairly simple and should be done without regard to DCC.

There is concern regarding the possibility of shorts through contact between the points and opposite rail more likely in the case of longer wheel based locomotives or those with oversized flanges. Ideally, the points are electrically isolated from one another and hard wired to the respective outer rails. Shinohara turnouts points however are connected together with metal bars and the frogs are actually feed current through bronze tabs attached to the points which make contract with the rail they are thrown. In most cases these tabs have been removed from our turnouts (as they were erroneously thought to be the cause of those momentary shorts) and the frog power is supplied more reliably through auxiliary relay contacts on the switch machines. Modifying the turnouts involves removing the point bars and replacing them with printed circuit board bars that are electrically isolated. Obviously, messing around with each turnout not only will take a lot of time but potentially cause a maintenance nightmare. Perhaps the best answer is to leave the turnouts alone and modify them individually only when they demonstrate the need.

DCC POWER DISTRIBUTION:

The layout is divided into three power districts with a 5 amp power booster for each.

These are further subdivided into sub-districts with Digitrax PM-4s that offer short circuit protection and automatic return loop and turntable circuitry.

1. POWER DISTRICT ONE - EAST
   1. WAITSBURG REVERSE LOOP TAIL (reverse)
   2. WAITSBURG LEAD and STAGING
   3. ORCHARD YARD
   4. ORCHARD - TURNTABLE (reverse)
   
   
2. POWER DISTRICT TWO - CENTRAL
   1. MAINLINE - EAST
   2. MINING LINE
   3. LOGGING LINE
   4. MAINLINE - WEST
   
   
3. POWER DISTRICT THREE - WEST
   1. WILLOW GROVE - TURNTABLE (reverse)
   2. WILLOW GROVE YARD
   3. HOLDEN LEAD and STAGING
   4. HOLDEN REVERSE LOOP TAIL (reverse)
   
   

SWAMP CREEK & WESTERN
RAILROAD ASSOCIATION

211 Railroad Ave. Edmonds, WA 98020