Still use DCC w/current block system? : LUSENET : Wiring for DCC : One Thread

The club to which I belong currently uses a traditional block wiring system. We are investigating DCC and would like to know if a DCC system will work inconjuction with this block system. We would like to have a one year transition time where both DCC and the conventional systems are used. Is this possible, or do we have to switch over entirely to DCC in the begining? I'm really not sure how DCC would work in an environment such as this.

-- Drew Donaldson (, October 02, 1999


You can connect up a dcc booster as a substitute for one of your track block selectable dc power packs. Just keep flipping the switches so that the dcc track power follows the dcc equiped loco(s) around the layout.

Drawbacks.. DCC equiped locos run, but don't respond well to straight dc. So don't plan on operating dc/dcc mixed loco consists on the old dc power packs. There are some strange potential electrical failure modes when/if steel wheels & locos cross dc/dcc rail gaps between power districts. Back feeding the dcc signal into a dc throttle could cause significant problems. This may be trickey to control and positively prevent in a club environment.

-- Don Vollrath (, October 04, 1999.

Granted there are a few precausions that should be taken if DC and DCC mixed operations are going to be used but it can be done.

First and formost, it should be assured that no unloaded voltage from a DC cab, or anythere source for that matter does not exceed the max safe decoder input voltage, that is 24 volts Nscale, and 27 volts larger scale decoders.

Note the unloaded voltage, as a decoder presents a very small load. Check this with the DC cab turned all the way up, and no load on the output. This is priority1 here.

Now it is true, when a metallic wheel/s cross the gaps between DC and DCC, there is going to be a form of a short. That is DC is polarized, and DCC is bi-polar, so part of the time, no matter which way the polarity of the DC cab is set, the DCC current will be oposite. This is not a cause for Puff or Smoke, either or both the DC cab and the DCC system should handle this. But can cause some erratic operations. This can easily be over come by using 1156 automotive taillamps in series with the DC cab. Basic 1156 lamp is a 14 volt 35watt lamp. The lamps will limit the DC current, and allow the DCC power to over ride the DC as the train enters the block. And if the decoders support analog conversion, will even allow a very smooth transition of operations from and to DC and DCC.

I also do not recommend common return [rail] be used here at all. As this will make a metallic bridged connection between the DC power and the DCC power. Here most of all, the common should be before all electronics. To avoid possible series operations between the two power sources. Note above the max safe voltage of decoders, and if the unloaded voltage is below this, but the DC and DCC go into series operations, the DC voltage will add with the DCC voltage, and now we have Puff with Smoke, and even possible fire at the decoder level. Keep the common return off the layout, and put it at the system level, or power supply level, any where it is before all electronics, and series operations is an impossiblity.

Follow the above guides, and DC and DCC, even AC can and do live happly togehter, no Puff, no Smoke, just good operations, especially with decoders that properly support analog conversion.

But also note, with most layouts setup for legacy DC operations, it is not very long before all block selectors are set to DCC only, and DC is just used for testing. --

Remember Always Have Fun and Enjoy!, Don Crano Akron, Oh NMRA #096211 Visit Model Railroading with DCC at:

-- Don Crano (, October 04, 1999.

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