DCC conversion for smoke units

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I have converted aristocraft mikado and pacific locomotives and a Bachman shay to DCC. I want to install a rectifier to deliver DC to the circuit board to run the smoke units. What type of filtering elements do I need to remove the DC ripple? The best filter circuits seem to use parallel capacitors with a choke between the + leads of the capacitors. There is no indication of what value capacitors and chokes to use -- this is my dilemma (or is a simple single 1000uf capacitor adequate)? Is there a better way to run the smoke unit than what I am trying to use (using Digitrax DG580L decoders)?

-- George Adams (geomar@paonline.com), July 08, 2003


Response to DCC conversion for G scale


What you are trying to do may be very simple.

If the circuit board you want to power was previously connected to the track, you can probably continue to hook it up the same way. You will get smoke all the time this way. You can also hook your smoke unit on the output of your decoder.

DCC doesn't have ripple like typical rectified DC. But there are spikes. Most circuits that need rectification and filtering in model trains already have this built in. I regularly power the sound systems in LGB locomotives directly from the output of a decoder. See my Sumpter Valley http://www.wiringfordcc.com/lgb_mallet.htm

Some of my locos have filters, but that was to prevent false triggering of the whistle in Sierra sound systems. This was per Soundtraxx's recommendation. Hence, the filter you see in this write-up. http://www.wiringfordcc.com/g_generic_sound.htm

However, they made some improvement and suggested that I may not need it anymore. So I left it out. See my consolidation: http://www.wiringfordcc.com/g_bach_xframe.htm

If the circuit you are worried about is only for the smoke unit, it is probably not very sophisticated or sensitive. You should be able to get by without additional filtering. If you want to do it anyway, you can use a 1000uF cap if you want. Since DCC does not have the ripple of regular rectified AC, you can use a much smaller cap.

Circuits running smoke units often contain voltage regulators. Still, whether you run your circuit directly from the rail or the output of a decoder, make sure you do not exceed in the input voltage rating of the circuit. This may be spec'd for your locomotive. Or you can call the manufacturer and ask them what the max voltage they want their loco to see. This should not be a big deal for most people running 18-19V of DCC.

In my Bachmann Shay, I installed two decoders. I use the second decoder to provide the sound and create throttle sensitive smoke! Be sure to program the VMax so that at full throttle, you don't exceed the voltage rating of the smoke unit. You can also set VMin to get the smoke going in the first place.

I am suggesting that you add a second decoder, but it sounds like you are half-way there. If this idea appeals to you, you can see it on my web page. http://www.wiringfordcc.com/bgshay.htm

Note: Make sure you have a good running Shay. Some of Bachmann's Shays, at least the early ones, had problems with gears breaking inside the trucks. Make sure you have a winner, first.

-- Allan Gartner (bigboy@WiringForDCC.com), July 08, 2003.

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