SWAMP CREEK & WESTERN
RAILROAD ASSOCIATION

211 Railroad Ave. Edmonds, WA 98020

LAYOUT ELECTRICAL MANUAL

Established December 5, 2000

Revised by page

IX. - RETURN LOOP POWER

IX. - RETURN LOOP POWER:

Triple-track return loops are connected to both ends of the layout and are located hidden under the center peninsula, one over top of the other. Waitsburg Loop is on the east end and is above Holden Loop on the west end. The loops are entered through same name Junctions which are also tied together by a hidden by-pass track called The Gorge which runs across the south wall.

The wiring of these might seem complex however it is really not that complicated. We will break it down into simple components: starting in this sections with the loops, noting they are both wired the same, followed by an explanation of the by-pass and then the train detection system.

A.   Return Loops - General Operation:

To allow continuous motion the loops have been set up for one way operation via a bridge rectifier in the tail section so in all cases you must enter the loops and travel around them in a counter-clockwise direction.

The bridge rectifier only allows your train to move in that direction. It's circuitry doesn't care what direction your throttle is set, it turns the (+ or -) input around to power the trains in the proper direction.

Only the tail section, between the staging exit turnouts and the exit throat, are rectified. Once you begin to exit the loop at some point within travel on this section you must reverse your throttle and align the turnout for exit.

Remember the rule: westbound is up, eastbound is down.

B.   Track Control:

There are three tracks in each loop. The inside track is considered the mainline and should normally be kept free of parked trains, though, for versatility's sake, we have installed isolation toggles on these tracks too. The outside tracks are considered yard tracks for staging purposes. The power is connected to the individual tracks via off/on toggles so trains can be isolated and stopped. There are two staging sections in each track, approximately ten feet long.

All tracks in each loop is first controlled by a mainline cab power selector rotary switch. This feeds directly to the approach track and indirectly via the isolation toggles to each loop track. These feeds are color coded.

The loop tracks between the exit turnouts (staging tracks) and the throat are double insulated and thus isolated from the rest of the layout. Do not attempt to connect the common rail (BLUE/-) in these sections to the common buss (WHITE) or a short circuit will result. They must be connected to the bridge rectifier (BLACK/-) which is located behind the local control panels.

The individual staging tracks are single insulated towards the outside and powered by the isolation toggles.

Note that the negative rails are connected to independent feeder wires (-) WHITE common return. Do not connect these to the DC buss locally. We want to keep them isolated for future (DCC) considerations. They are connected to the DC buss at the control panels.

C.   Bridge Rectifier:

Bridge rectifiers are a simple circuit that use diodes to control the direction of power. Diodes only allow power to flow in one direction. Their symbol is an arrow. Curiously enough the power flows against the arrow. No matter. Picture a four sided diamond with a diode on each leg.

We'll apply one side of our input (track power) to the top of the diamond and the other side to the bottom. Now, both diodes on the left side of our diamond are aligned to allow power to flow to the left so that the left output point between the two diodes will always be a positive voltage no matter if we reverse the input. It will get the positive from either the top or the bottom, it doesn't care which. And the other diode will stop the opposite polarity from flowing and causing a short.

The same is true for the right side where the diodes are reversed so that output point will always be negative.

Thus any power applied to the inputs, regardless of the polarity, will cause a positive output. AC voltage can also be so rectified and turned into a DC voltage.

Instead of using power diodes we are using an integrated circuit: a power bridge rectifier which functions the same as having four diodes arranged as described here.

D.   Track Power Feed Buss Wire:

Because of the distance between the control panels and the loop tracks a ten wire 12 ga. feed buss is employed for each loop with the following designations:

Note: Do not confuse the upper (Waitsburg) loop wiring with that of the lower (Holden) loop as they use the same color code and note their polarities are reversed.

E.   Connectorized Control Panels:

Due to the complexity of the wiring in Waitsburg and Holden control panels the wiring is connectorize. This allows for construction and maintenance to be performed on the workbench.

Two 25 pair 24 ga. telephone cables are employed, for the switch machine, auxiliary LED indicators, and for track occupancy LED indicators. These snap and screw together for a positive connection, and are appropriately labeled.

There are three bundles of 12-18 gauge track power wires. They are the mainline cab power inputs, the return loop power (rectified and isolated A-F), and the switch machine controls. These are labeled and connected with spade clips to labeled terminal strips.

SWAMP CREEK & WESTERN
RAILROAD ASSOCIATION

211 Railroad Ave. Edmonds, WA 98020