QSI Titan smoke



The QSI Titan has some new features to accomodate smoke units. Below is some information to make the setup easier for you and also to explain some of the specific things that affect operation.

"Normal" smoke on off control:

If you connect a "normal" smoke unit that runs from track voltage, you connect it to J1 pins 8 and  6. If your smoke unit is polarity sensitive (most are not) the positive pin is pin 6.

By default, this output is in a lighting group controlled by DCC function 12.

You want to be sure you set the desired voltage if the smoke unit cannot take full track voltage. J1 pin 6 is NOT +18 volts, but rectified track voltage. You can set the desired "brightness" to limit voltage.

"Direct Drive" Smoke:

The remainder of this page is devoted to "Direct Drive" smoke. I call it this because the decoder is driving the smoke and fan directly, like MTH has always done, and Zimo and other European decoders have support for.

You need a smoke unit that has independent and direct access to the heating element and fan, for ezxample:

  • a current model USAT smoke unit
  • an MTH unit
  • a modified Aristo unit of the latest version. (Be sure to read the section on "selecting a smoke unit")

You drive the heater and fan independently and directly from the decoder.

At this time, there are no "dedicated" smoke unit CV's or feature codes. (This is a possible future firmware update, no hardware change needed)


How it works, overview: (steam locos)

The fan is driven by a LED output, default is J2 pin 10, and using J3 pin 11 for the 5 volt supply.

The output is pulsed in time with the chuff by tying the physical output to the "firebox flicker" feature.

(as in the prototype, the exhaust (chuff) causes an increase in airflow in the firebox, and that makes it "brighten" in synchronization)

So the fan motor will pulse synchronized with the chuff, and will move more with a stronger chuff. Very cool and prototypical

The smoke heater element is driven from J1 pin 8, a high capacity output, (track voltage supply is J1 pin 6 but can be any voltage referenced to ground) This output is also used for a rear cab light by default.

F12 turns smoke on and off as previously mentioned, both the fan and the heater.

I'm currently investigating a feature to make this work for diesels.

Smoke unit fan theory:


The fan is driven by a pulsed 5 volts from J2 pin 10, (5 volt supply is J3 pin 11) reference diagram above

For Aristo, USAT and MTH, the fan should normally be driven by 5 volts.

The typical output is J2A-10 (The A means the screw terminal as opposed to the pin) although this is really like the rest of the outputs, it goes to ground. This is also known as LED9 on the pinout drawings.

The positive voltage comes from J3-11 (+5 volts)

For steam locos, a slightly modified firebox flicker is used to drive the fan. Normally the firebox lights will brighten each "chuff" in addition to some random flicker.


Connect the smoke unit fan:

Connect the positive wire on the fan to J3-11

Connect the negative wire on the fan to J2A-10

If you hook it up backwards, then the fan will blow smoke the wrong way.

Steam locomotives:

Fan programming:

Ensure firebox flicker is enabled  (default)

The feature id for firebox flicker is 122, CV 55.122.x, = 1 for on, = 0 for off. Should be enabled by default in steam loco.

We use the firebox flicker to modulate the fan speed, because the firebox lights go brighter when the exhaust "chuffs". (Very realistic, in an actual loco, when the steam is exhausted from a cylinder, it increases the firebox draw, making the coal "hotter" and thus the firebox flicker greater)

Map Feature:firebox flicker to LED9 output (default)

115.122.0 = 9 (so far I have found this to be default.) Of course you can map any led to the output.

You can use any output for the fan, since it's only about 500 ma.

Tune the fan parameters (this will tune the fan to react to the chuffs)

CVs 55.122.x have to do with firebox flicker, settings of min intensity, etc... this is where you will tune the fan

55.122.11 = 0 set the minimum intensity to off (seems to be default) You can play with this and raise it up a little bit, like 5 to have a little "idle" smoke. Again, this sets minimum fan speed, and will vary by fan.

55.122.12 = 255 set max intensity to full on (to give the maximum fan speed)

55.122.13 = 0 set mid intensity to 0 (setting low kills the ambient flicker effect, so you only get the chuffs, I have played with this a little, if you set minimum intensity up, set this one higher)

55.122.17 = 1 ramp up time, this makes it ramp up fast - separates the chuffs, so I set it short to get the fan to react more quickly.

55.122.18 = 18 to 25 - ramp down time (this is the length of the smoke pulse, the longer, more smoke, but the chuffs will run into each other sooner)

I have found all the above to be workable with defaults except for 55.122.18, so set that one. If the fan does not seem to spin up, then set the other CVs

Connect the smoke heater and set CVs

The smoke unit heater is connected  from  J1 pin 6 to J1 pin 8.  (LED12) This output is under variable control.

This output is tied to the rear cab light.

You NEED to set this to lower the voltage, and you must measure the voltage when it is on. Note: although in QSI diagram above, pin J1A-6 says 18 volts, but it is indeed not regulated or set there, it's rectified and filtered track voltage.

The CV for setting the rear cab light intensity is: CV 55.118.12  a value of 255 giving you full rectified track voltage, and lower is, well, lower.  ;-)

Repeat: measure this with a load, not open circuit and use a meter (I used a 24 volt bulb across the output instead of the heater so there was no danger of overheating)

My suggestion is to set for 8 volts and see how it goes. There's more discussion below.

Darrell Lamm has some more on his site, but I need to validate the CV 55.118.0 works as he claims...

CV 55.118.0 - initial state. Darrell says to set this to 1 to make sure it is on, but then states it enables the modulation to "dim" the heater. I'm not sure that is true. If the initial state is 0, then it is off, not running full blast.

55.118.1 - program to be on in all situations,

55.118.12 - this is where you set max voltage

55.138.2 - mapping to which function key, want to map the heater to the appropriate f key


Still to be figured out:

One thing that still needs to be addressed is a way to have different heater settings for different speeds

and of course need to find a way to work this with diesels, i.e. tie a different feature to the fan...




Selecting and/or modifying the smoke unit:

The USAT unit already has separate connections for fan and heater, as does the MTH.

The Aristo unit needs to be modified, see this page:

Modifying Aristo Smoke Units

Notes on tuning the smoke unit heating element:

From my testing, and research, I would never run any smoke unit heater over 12 volts for any length of time. I think that will cause them to fail very quickly. I have tested the new Aristo, USAT w/fan, and MTH (from a G scale Hudson)

Running at 10 volts reduces the heat, but still long term seems to be too hot.

After some research, these units have a working voltage of 6 to 7 volts for constant use, and run higher for short periods, so for now I'm trying 8 volts.

My suggestion is to test and see how hot it gets. Feel around the boiler. If you are using a metal unit and have a metal boiler, I think you can run 10 volts most of the time. Even 8 volts gets the units hot to the touch.

Remember you do not have auto shutoff, so turn the unit off with F12 when sitting idle. You might want to wire a switch in series with the heater to ensure you don't run it when you don't want to, since the default is that it is on when power is applied.

For reference, MTH has minimum, medium, and maximum settings. You CAN burn up an MTH unit by driving it too hard. The Zimo people have modulated the (effective) voltage level when doing direct drive.

I'm tested with a small HO DCC system and full voltage was 11.55 volts.


CV 55.118.12 values:
220 = 10v
198 = 9v
176 = 8v
154 = 7v
132 = 6v
110 = 5v

on my outdoor track, which is runing 23.6 volts true DCC, the rectified voltage was 22 volts.

CV 55.118.12 values:
143 = 12v
131 = 11v
119 = 10v

107 = 9v
  94 = 8v
  82 = 7v
  70 = 6v


NOTE: You must be able to read the pulsed output correctly. If you put a cheap meter on the decoder output, it will most likely read full track voltage, not the RMS value (average). Even with the smoke heater connected you will not get a correct reading.

So, either get a true rms reading meter (over $100 FLuke or HP), or put a small full wave bridge and filter cap on the input to the cheapo meter.

NOTE: If you just try this out and don't measure the voltage, you can overheat the smoke element, and make the unit really hot, and melt plastic nearby, so PLEASE be careful.


Preliminary video.... USA Trains stock smoke unit, unplugged from it's driver board, heater on constant 12 volts, and fan driven directly from the QSI.


Misc Tips:

Aristo reservoir will take 3.5-4.00  cc from empty

USAT reservoir seems to be 2 cc, but when you fill it that much, not as much smoke, 1cc better, but more frequent fills. got about 10 minutes of good smoke at about 9 volts heater voltage

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