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Reply to "Decoders, Smoke, and Couplers"

Now for the actual installations! I'll start with a general purpose installation that should work to provide fully functional smoke and couplers for just about any locomotive. I'll eventually show a couple of my specific installations as well, to show various other ways to do things, but that may be later, as I have a vacation coming up...

Basic Installation for Smoke and Couplers

For this example, I'll assume a Loksound L decoder is already installed and operating in the locomotive. It's a good idea to get the basic motor, sound, and lighting set up before proceeding to the smoke and couplers. For the purposes of this example, I'll use decoder function outputs Aux3 through Aux7. Adjust accordingly for your specific installation, of course.

Parts List

Here is a suggested parts list for the installation. For the discrete components, any equivalent part will work fine, these are just suggestions.


Rectifier and Regulator

The regulator can be assembled with both the bridge rectifier and capacitor soldered to the inputs of the regulator. The + and - leads of the rectifier get soldered to the positive and negative regulator inputs, leaving the A/C inputs of the rectifier for the track pickups. The capacitor can also be soldered across the regulator inputs. Note the polarity of the capacitor as well. The inputs to the rectifier then just get wired to the track pickups, in parallel with the decoder.


Here is a way to combine the rectifier, cap, and regulator into a pretty tidy assembly:

IMG_7397 [2)IMG_7398 [2)

Be sure shrink wrap or otherwise insulate the A/C leads of the rectifier after you wire them to the track pickups.

At this point, power up the engine on the dcc booster. Hook a voltmeter across the regulator outputs and adjust the potentiometer on the regulator until you get the desired voltage (5V, typically). Now you have a DC power source ready to drive heavy loads.

Smoke Unit

For the smoke unit heater, wire power and ground from the regulator output to the power and ground inputs of the power switch. Wire the outputs of the power switch to the heater element on the smoke unit. Polarity does not matter. Wire the heater control from Aux5 to the 'SW' pin on the power switch. Configure this decoder output as described in (3) in the previous post.


The decoder can drive the smoke unit fan directly, but it still makes sense to power it from the regulator. Test the fan beforehand if you're not sure which polarity results in the correct direction. Wire a power lead from the positive output of the regulator to the fan positive. Wire the fan ground to Aux3 on the decoder. Configure this decoder output as described in (4) or (5a).

Optionally wire Aux3 and Aux4 together on the decoder in the case of a steam engine installation. Configure the Aux4 decoder output as described in (5b).


For the electrocouplers, start by installing the diodes on the power switches. These act as freewheel diodes and protect the switch when used with inductive loads. Note the polarity of the diodes - the band goes toward the positive output of the power switch.

IMG_7399 [2)

Now wire power and ground from the regulator output to the power and ground inputs on each of two power switches. Wire the controls from Aux6 and Aux7 to the 'SW' pins on the power switches. Configure the decoder outputs as described in (2) in the previous post.


At this point, it's a good idea to test the output of the power switches. If they are wired wrong, or if the decoder is configured wrong, the couplers could overheat and be damaged. Put a voltmeter, test lamp, or some other indicator across the power switch outputs, and make sure that they only activate for about half a second when you press the button on the remote.

After confirming things are operating as intended, wire the outputs of the power switches to the couplers. Polarity does not matter.


Here is the complete wiring diagram:


Now go run it, see if the smoke works the way you like, and tweak accordingly.


Images (7)
  • IMG_7397 (2)
  • IMG_7398 (2)
  • install1
  • install2
  • IMG_7399 (2)
  • install3
  • install4
Last edited by thor73
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