DCCon old brass engines

[ARTHILL]

I am back after 25 years. What are the real problems in getting DCC decoders in my old brass or is it best to just stay with DC for their sake?

Art Hill

[Anonymous]

Art,
I too recently came back to HO after about 20 years. Although still contemplating my first brass loco conversion, I have done some research and it all depends upon the individual model. Primary considerations are that both motor brushes be isolated from the frame and that the motor "stall" current is less than the decoder's maximum current rating. The very old open frame motors typically had one motor brush grounded to the frame. They also tended to have a higher current draw. You can't just measure the typical current of the model as the decoder is going to use "pulsed" power to control the speed and it hits the stall current ever so briefly with each pulse. Generally, the later brass engines fitted with can motors are fine in regard to max current - assuming that they are running correctly. Beyond that, there are some refinements for steam type models such as adding additional electrical pickup to augment the typical brass loco's one pole from the engine and the other from the tender pickup. That limited electrical pickup can sometimes cause some issues with reversing sections and operation in general but it isn't essential to change it unless you have problems because of it on your layout. One other caveat is that some of the more recent brass - I'm not sure how recent - come with coreless can motors that require higher frequency pulses from the decoder to avoid overheating and burning out the motor. In that case, you would need to choose a decoder that can output those higher frequencies.
Charles

[Anonymous]

Art,

Charles has covered the issues pretty well. 25 years ago most brass used open frame motors (not all - can motors started coming in, in the very late 70's) and I think you will find that in practice you would need to re-motor your OFMs; replacing them with cans will usually be easier than figuring out how to isolate the motor from the engine frame.

Another issue I'll mention is that DCC is extremely sensitive to short circuits because of the high currents involved. So a momentary short which can be common with brass locos, might not faze a DC throttle but will ALWAYS shut down a DCC system.

Finally, if you're into steam (like most brass owners in my own experience) you'll usually be putting the decoder in the tender with a lot of wiring between the tender and loco, and often needing to drill holes in your beautiful brass models.