How to Connect a Layout

Notes:

  • Current is always running in both directions - every load has a return path. This loop causes EMI which is dependent on (amoung others) the included area of the loop. Therefore this area must be minimized.
    Route all DCC wires as twisted pairs, even those from the track back to the feedback module. Do the connection of 'DCC+' near to the feedback module, not at the track rails. This avoids unwanted coupling of one current loop to another one.
  • Connect booster outputs and inputs with same sense. See also the hints on the booster page.
  • Connect booster outputs on one side. This gives a return path for the balancing current when a car is crossing supply boundaries. Otherwise this current will influence the s88 feedback bus.
  • The wiring of data line again should be done with twisted pairs. For s88 the usage of network cables is recommended.
  • Wire gauge:
    There are two cases to consider:
    A) The voltage drop along the wire should not influence the cars.
    B) In the case of short circuit there must be enough current flow so that the booster turns off. The voltage drop at the short circuit current must be less than the booster voltage at rated output load. In this calculation the resistors in the cars besides the resistance of the lead and the rail must be taken into consideration.

    I think, a drop of 0,5V at a current of 1A is okay for H0. Recommended wire gauge to connect the rails: 0.8mm² (=AWG20).
    German silver (the material of the rails) has a high resistance, more over the rail links are a weak point. Connect the rails at least every 1.5m.

        Calculating the Resistance of a Wire  
      Material:
      Cross section: [mm²]
      Length: [m]
      Resulting resistance: [Ω]
      Voltage drop:
      Supposed current: [A]
      ΔU (one wire): [V]
      2 * ΔU (both wires): [V]

Example 1: Small Layout

    This examples shows the schematic for a small layout using two booster and OpenDCC, OpenDecoder and feedback modules from Blücher Elektronik. The feedback bus is wired with CAT5 cables. Note: the DCC output from OpenDCC is toggling between 0 and 15V (when measured against s88-GND), so be shure to have at least one optocoupler in the loop from command station over booster to the feedback system. Otherwise you will shorten the output!



    Click on image to get a larger view.

Example 2: Model Club Layout