Power Conversion

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Summary: Power conversion allows a multifunction decoder to operate on a non-DCC lkayout.

Power Source Conversion (CV12)

Known as Alternate Power Source in the NMRA DCC Standard. CV12 is Optional.

Multifunction decoders can operate on non-DCC or layouts using other forms of command control. The most commonly supported power conversion type is Analog Conversion where a DCC-equipped locomotive can operate on a traditional analog layout.

Many users set their decoders to NMRA Digital Only. This prevents the locomotive from running on a Direct Current layout. The purpose for setting it to only operate on NMRA DCC is to prevent runaways. If the decoder loses the digital signal for a defined period of time (30 mS), it will switch to the Alternate Power Source as defined in CV 12. Distorted DCC signals on the track can cause this, often related to poor wiring practices.

Analog Operation

Main article: Analog Conversion

List of Alternate Power Modes

The NMRA DCC standard recognizes the following alternate modes (although none of them are mandatory).

This is not a fixed list, as the NMRA will consider requests from manufacturers to add additional power conversion modes.

Power Source Conversion
CV12 Value System Supported
1 Analog Power Conversion
2 Radio
4 Hornby Zero1
8 Trix
16 CTC16/Railcommand
32 FMZ
These values come into effect when CV 1 is set to Zero.

Using a Primary Address (CV 1) of "0" enables this feature, overriding the Alternate Power Source (Bit 2) value in CV29. A combination of a Primary Address = 0 plus CV12 = '1' results in an immediate runaway when DCC power is connected to the rails.

See DCC History for more on various command or carrier control systems.

See Also