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Installing decoder in a Brass locomotive

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  • Member since
    May 2008
  • 68 posts
Installing decoder in a Brass locomotive
Posted by Moonie on Saturday, August 23, 2008 3:58 PM

Recently, at a local auction, my dad and i acquired several brass locomotives at dirt-cheap prices (mostly Overland, but some Pacific Pike), including several CN GP40-2W's and M420W's, a CN GP9RM, and a beautifully painted CN C44-9WL (it's worth near $1000, and it sold for $45). Unfortunately, it seems that a talented modeler passed away, and the family had no idea what his collection was worth. We did, and made off like bandits, as there was only one other serious bidder. 

Anyway, it leaves us with a decent number of brass locomotives that will eventually be equipped with DCC decoders. A local hobby shop has a service that they will install the decoder for you, and i was discussing this with one of their employees. He said that the brass shell has to be isolated from the rest of the locomotive for dcc operation. It brought me to wonder: is this actually true, and if so, how is this done? Also, what other modifications must be done to a brass diesel for dcc operations?






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Posted by modelmaker51 on Saturday, August 23, 2008 4:15 PM
The only thing that needs to be isolated are the motor brushes or the motor itself.


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Posted by tomikawaTT on Saturday, August 23, 2008 11:33 PM

The shell is no problem.  Neither is the motor frame unless one brush has been irreversibly grounded to it.  The only things that absolutely, positively must be isolated are the motor brushes.

One brush is already isolated.  Isolating the other might require breaking a solder joint or slipping a bit of insulating tubing (stripped from a wire) over the bare side of the wishbone spring on an open-frame motor.

For safety's sake, there should be a layer of insulation between the decoder and anything metal that could be connected to a rail.  A strip of vinyl electrical tape is all that it takes.

Chuck (modleing Central Japan in September, 1964)

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Posted by betamax on Sunday, August 24, 2008 6:34 AM
Your hobby shop's advice was right and wrong.

Typically, the frame, and everything attached to it, is 'hot'. The motor is connected directly to the frame, making wiring easier.

The tender is also hot, and functions as the return for the motor current. It is the opposite polarity of the locomotive chassis. It is isolated from the locomotive, and a wire from the motor connects to it to complete the circuit.

See for details on a simple DCC conversion.

A diesel will be similar, except it will need to complete the circuit without a tender.

PS: Check the motor current draw and that the mechanism doesn't bind.
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Posted by richg1998 on Sunday, August 24, 2008 8:18 AM

Do not attempt this without a VOM. A meter will be needed at som e point to measure motor current, and electrical continuity.


If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

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Posted by gandydancer19 on Sunday, August 24, 2008 6:49 PM

You should also measure the stall current of the loco motor before taking anything apart. This will let you know what amp rating the decoder needs to be, or if the motor needs to be replaced. Just put the current meter (Multimeter) in series with one wire of the DC test power pack and the track the loco is being tested on.


The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.

(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) at home, and N scale at the Club.

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