Monday, 28 October 2013

Electrical Bus

While the writer favors soldered connections it can be quite difficult when building a DCC power bus because of the need to expose the copper wire. This has lead to re-examining 'Suitcase Connectors' or Insulation Displacement Connectors (IDC's) which allow connection of track feeder to main bus (power supply) wires without having to strip or solder.  

To connect these connectors simply place the crimp over the wires and close the cutter with a pair of pliers. The metal tab pierces the insulation and connects the wires together ensuring a reliable mechanical connection of both wires.

Suitcase Connectors (IDC #567 Brown) for bus sizes #10-12 (max insulation OD .190 inch) and feeder sizes #14-18 (max. insulation OD of 0.145''). Package of 25. These are available from Micro Mart as there is no distribution in Australia.

Track power is supplied from the main bus that rings the completed layout with a NCE EB1 circuit breaker located in the modules electrical panel providing power for the track-work. The panel is located in drawers fitted in each module as outlined in the Modules Article.

The modules power bus is constructed with multi core 1.0 mm square bus and 0.5 mm square for track feeders. 

         Colour code for modules:
                                                        Red / Black  - Track Bus & Feeders
                                                        Blue - Common feeder for point frogs.

Track Connections
Each length of rail has a brass tab 45 mm x 2.5 soldered to the underside of the web. After the rail is spiked into position a tab fitted through a hole drill in the road base, soldered to the rail and the feeder soldered to the exposed tab at the underside of the road base.

The tabs are manufactured from scrap brass etches. Tin both ends then bend one end at 4 mm at 90 degrees - this creates a connection with a small profile and is very strong. It is recommended that a paste flux such as  Laco Regular Soldering Flux be used.

Track connection

It is CRITICIAL that before commencing assembly that it is confirmed the crimp makes contact with the copper wire of the bus and feeder. 

Even though the wire used meet specification there was a no connection on one of the first crimps. After investigation it was concluded that it was bad crimp but it dose open the possibility of poor connections being created during the crimping process. To be sure each cutter was removed and the larger cutter was given a few light taps to close it just a little. The wire was purchased from the local electronics shop and is a Chinese wire so for the rest of the project wire from a reputable supplier will be sourced. 

The first few crimps should be inspected carefully to confirm that the cutter and wire are operating correctly by exposing the edge of the copper on the wire. An alternative is to connect each feeder to the track as the last operation and buzz it before soldering to the tab. Overall this process offers a excellent way to speed up bus connection on any layout but materials should be checked for correct performance before commencing large scale assembly.

Bus Construction
Fixed end with cup hooks
The module bus is constructed from two lengths of 1.0 mm square insulated wire cut to fit between the former's. Fit a 6 mm ring crimp at both ends and do not strip wire insulation to insulate the wire from the rings. 

One end is fitted to a cup hook and the other has a tension spring is fitted between the hook and the ring crimp. The overall length of the wire is set to apply tension to the assembly and keeps the bus under tension making installing pillow blocks easier while keeping the bus tidy.

Cable Fixing Feeders

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