Common rail question(s) : LUSENET : Wiring for DCC : One Thread

I belong to a club that is rather large in size (120'X 60') that has been legacy wired using common rail with toggle switches feeeding portions of track via panels.

We have come up with a way to wire the layout for DCC without the tearing out of anything. Each panel in each town has 2 throttles (RED-East, BLUE- West) with their own transistorized power pack (club-made). On each of the outputs of the throttles we have put in a 11 pin relay (4pdt) running @ 24v. When an installed switch powering up the relays is thrown, the N/O contact to which the DCC is connected is shunted to the common leg of the contact to where the track output is. (The analog DC is the N/C side of the contact). So far we have not seen much in the way of problems in the yard test area we have setup other than occasional shorts caused by running turnouts or analog locos humming on tracks not turned off.

What can I expect for problems once the system is expanded throughout the layout. We plan on going slow so as not to upset the masses if problems do occur. I would like comments, both pro and con on the problems or situations that we might encounter. Thanks in advance, John Berry

-- John Berry (, November 02, 2004


There can be serious problems when locos cross power district boundaries if they are powered from two different sources of power and in this case different types of equipment (DC throttle Vs DCC booster). Good dispatching should never allow this to happen, but Murphy will prevail. Just like running into an improperly set turn- out...stuff happens. The problems multiply if you will be using more than one DCC booster.

Pro - 1) This can be done will careful diligence on the part of EVERY operator and dispatcher. 2) The ability to operate DC and DCC locos on the same layout will ease the need and pocketbook drain to quickly convert everything to DCC.

Con- 3) You risk fatal damage to DCC boosters and DC throttles when/if locos cross power boundaries between improperly set switches or relays. This also applies to all steel wheeled cars. Both track sections must be set to the same throttle to prevent one power supply from jamming power up the exit end of the other as steel wheels cross the rail gaps. 4) You risk damage to analog DC loco motors if left on tracks powered by DCC. 5) You will need to keep using the manual toggle switch method of operating trains through reversing track sections. Auto-reversing units that work so well with DCC simply will not work with variable voltage DC. 6) Once operators get familiar with DCC they will never want to go back to DC throttles. You are wasting time by coddling both schemes.

Suggestions- A. Every DC throttle and DCC booster MUST have its own power supply, not connected to any of the other throttles. The only common connection point should be where the output (DC throttle or DCC booster) connects to the common rail. B. Use a small amp rated DCC booster, 3-5 amps is more than sufficient. Make sure it trips off if short circuited with a diode. (read C.) C. Protect each DC throttle with 2, 4-5 amp power diodes. One in series to prevent back-flow. The second in parallel to prevent voltage reversal. Place these diodes in the DC throttle circuit after the voltage adjustment circuitry, but before any polarity reversing switch. D. You can use one DCC booster to simultaneously power several track sections when selected (with each operator having his own DCC cab). E. Avoid using multiple DCC systems and/or multiple boosters as separate 'throttles'. The risk of loco decoder destruction is real. F. Ensure that the DCC booster will cut out on a short circuit anywhere on the layout section that it is powering. Become familiar with the E-Stop shutdown mechanism of your DCC brand choice. Providing a manual switch (or relay with multiple shutdown switches) to disconnect DCC power would be a good idea.

Good Luck, DonV

-- Don Vollrath (, November 03, 2004.

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