Aristo-Craft Smoke Units


There are quite a few types of smoke units used over the years, from simple "tube boiler" types (similar to Seuth), to fan driven, to microprocessor controlled.

Read below carefully, the "rules" are different for each type, but overall NEVER RUN A SMOKE UNIT DRY, and DO NOT USE CRAPPY SMOKE FLUID.

ART29311 - "Prime Mover" (PSMU) - used in most new diesels and steam locos

This is the latest and most sophisticated smoke unit from Aristo.

The Patent

This is more historical/hysterical than helpful ha ha. Aristo made a big deal about patents on it's products. This smoke unit was touted as patented, and the first locos to have this, the SD45, had "patent pending" on the cover. Later units shows the PMSU housing having the embossed patent number, US D469,132S, on it.

Since the first SD45s were suppose to include this new smoke unit, I would expect they were labeled with "patent pending" as was done with the 3 axle motor blocks. This smoke unit patent was filed on Feb.9, 2001 and as such Aristo's China factory had to have been making the new SD45s prior to June 2001. Remember, too, it takes about 30 days via slow boat from China to get products to NJ. The value of all this is that the very first PMSUs may have had changes to it compared to RJ's version having the patent number embossed on it.

"New Prime Mover Smoke Unit"

This unit was first seen in the SD45, which came out about 2001 I believe. It is in most of the newer locomotives, and also has been put in older locos, like the FA, which have been updated.


This is the "top of the line" Aristo smoke units.

The unit has a heating element with a fiberglas wick to vaporize the smoke fluid (a type of oil) and a fan to help create more smoke.

These units have a poor track record out of the box, but many people do not know this since not everyone uses the smoke. For those who do, I estimate it's about 50% that work correctly. More on this later.


The smoke unit is housed in a box that serves as a fluid reservoir and housing for the fan and electronics. The picture below shows the fluid chamber on the right, and the fan/electronics housing on the left. Notice the "wall" between the 2 chambers. Hard to see, but there are 2 small notches in this wall where the wall meets the housing sides. I believe these are for protection against overfilling. The "wall" does not come to the top of the box, so this is where the air flows, from the round opening through the fan, across the top of the wall and into the fluid chamber where the heating element is, and out the top.

This is a large (for Aristo) fluid chamber, about 4 ml.

The circuit board goes face down into this housing, and is covered with a lid. Here is the top of the lid, with the latest version, i.e. the patent number: (notice the large "funnel" opening to make sure the fluid gets into the unit)

The earliest units apparently were manufactured before the patent was approved:







Below is the underside of the lid. Notice the raised "ring" which goes into the hole in the circuit board, more insurance that the fluid gets into the fluid chamber, not all over the board:

So, one to the  guts of the unit. Here is the top view, you can see the hole on the right where the smoke comes out. You can also see the heating element through the hole. It is a wire-wound resistor with a Fiberglas wick around it. The wick absorbs fluid by capillary action, and the heating element vaporizes the smoke fluid. The brown color on the wick is normal, you just don't want to see crud accumulated. As long as you can see the wick "weaving" you are ok:

Notice the "NOV 00" on the upper right corner of the board, the date the board layout  was designed, thus making sense that the first ones arrived in 2001. (This is not a unit date code, circuit board designers put the date they "lay out" the board on the art work.) 

You can see the white power plug on the left hand end.

Let's look a the the underside of the board. Note that this is upside down from the normal orientation, i.e. the wick and fan are pointing down when installed:

You can see the unit. On the left hand side is the heating element with the wick wrapped around it. Notice the metal cap on the end, and the irregular crimping? More later.

The 4 black items (you can see only three here) are diodes to allow the unit to work in any polarity of input voltage, or even AC.

In the middle you can see some small surface mount components, and 2 integrated circuits. You can also see the fan motor, fan blade, and the cylindrical electrolytic capacitors.

Notice there is no barrier on the board between where the smoke is generated, and the rest of the electronics, importantly the electrolytic capacitors.

Here's a side view of the wick:

Notice the metal band clamping the wick to the heating element?

How it works 

For the number of units people ACTUALLY used, many do not operate properly out of the box. Many people report that these shut themselves off after only 5 minutes or less. Also, you have to disconnect power to restart them, they do not automatically reset. There are some reported cases that running these units on PWM (Pulse Width Modulation) power (like Aristo's PWC system) allows them to reset.

Aristo has never specified how long they should run, and also has recently specified less fluid (drops) in one loco over another, even though the two locos have identical units. It seems that most working units will give 20-30 minutes on a full reservoir.

The way the units work is (apparently):

The unit will operate on track voltage or even AC. The 4 diodes around the heating element rectify AC and/or "set" the DC polarity to power the circuitry.

The unit will operate up to 18 volts or more, I have not tested to see what the upper limit is. Running them on my DCC layout, which is 23 volts "AC" is no problem. There is an on-board microprocessor. The microprocessor has "double duty" in that it regulates the input voltage to run the fan and heating element (and itself!). The microprocessor also has the "program" in it to control the heating element power.

Since the microprocessor needs a minimum voltage to operate (5 volts), the unit does not start working until somewhere between 6 and 8 volts. Operation between 5 and 8 volts may cause erratic operation as the microprocessor may reset over and over. Operation below 5 volts will keep it off.

The microprocessor monitors the voltage on the heating element (resistor) and determines when to shut off, sensing a condition that is interpreted as out of fluid.  This is the "burnout" protection.

If the "out of fluid" condition is detected, the unit shuts off and stays off until power is interrupted and restored. (Microprocessor reset)

Analysis of problems and solutions:

Note: when filling, you cannot "equate" drops with a specific amount of fluid. Different fluids and different spouts will give you different number of drops per milliliter. MEASURE the fluid with a syringe. To fill this up to where it does not spill out the overflow slots, use  4 milliliters. You can use 4.5 milliliters if it is bone dry, and you do not tilt the unit, but you are right at the "overflow" point. (This is where you see the two notches in the wall between the fluid chamber and the electronics in the above pictures)

The first problem is erratic operation, does not run long enough. More on this later. 

Another big problem is that since Aristo smoke fluid is a solvent (good thing), it splashes around or condenses in the unit (bad thing). Due to the design, it gets on the circuit board. Get fluid on the board, and the electrolytic capacitors pop right off the board, the rubber plugs that seal the ends of the caps absorb the fluid and expand. It does not help that Aristo did not space the caps away from the board to anticipate this.

When this happens, often the circuit board is damaged, and also there is often some residue on the capacitor leads.  

The fix for this is normally to remove the capacitor completely, trim back some of the expanded rubber, and re-solder. The re-soldering can be tricky, i.e. to bridge the damaged copper traces, and to get good solder joint quality on the leads. I have seen some factory repairs poorly done.

The big problem, and harder to understand and fix is the heating unit. It is a wire-wound resistor. From all the ones I have measured the nominal resistance is 5 ohms. Many are exactly 5 ohms. The basic construction is the winding of a nichrome wire in a loose spiral on an insulating core. 

Then, 2 caps with leads in them are CRIMPED on the ends. CRIMPED, not soldered or welded. If you research this component, the manufacturers STRESS that any force exerted on the caps by bending the leads CANNOT be transmitted to the caps. You must hold the lead next to the cap and then bend the lead to AVOID stressing this CRIMPED connection.

Why all the CAPS?

Because, you can easily see that there is no way the lead was held before being bent, there is just no room where a pair of needle nose pliers could have been. The manufacturer of this component warns that this will cause problems. 

My guess is therein lies the basic problem: A microprocessor that can only sense the voltage across a resistor to know when to shut down, and the resistor has an erratic resistance, thus the system fails to operate properly.

Another observation I have made from reading all the posts about fluid on the circuit boards and swelling radial electrolytic caps is that there are probably 2 possibilities: filling the smoke reservoir without a syringe, spilling it about, and smoke fluid vapor condensing inside the unit itself.

I have taken a brand new unit, held it in a vise, run it, removed the lid and circuit board and found fluid condensed in the fan chamber. By not having any barrier between the smoke chamber and the rest of the electronics, the fluid can condense on one end of the board, and wick over to the other end. 

One user reports: the fan starts to rotate at 7.0 - 7.5V. Also just pouring fluid in soaks everything, the P.C.B. and inside of the locomotive. There is no seal between the smoke unit itself and the top [roof] plate. The power to the smoke unit is taken directly from the track.A full wave bridge circuit located on the P.C.B. allows for AC or DC voltage to be applied. The voltage across the heating element measures approximately 6.0V with a track voltage of 8.0V and above applied. The total current measured 0.54A at 7V [Voltage at the point the fan started to rotate.] As the track voltage was increased the current dropped to approx. 0.3A at 16V DC. As can be expected the current dropped as the resistance changed. The heating element measured 5.0 ohms when cold. The voltage across the fan measured 1.6V with an input of 7.0V. This increased to 2.2V from 8 - 16 volts.

So far, I have found defective repairs to "expanded capacitors" several times. 


Modifying for "Direct Smoke":

Note: for running in "direct smoke drive" where you need direct and independent connections to the motor and fan, as when controlling the fan and heater with a QSI, Zimo, ESU, etc.

To modify the unit, follow the instructions below:

First, unsolder the connector. This will also give you room to let the wires out without cutting the case. You can see 1 of the 3 solder blobs at the top center of the picture below.

Now on the bottom of the board (which faces up in the unit), cut one trace by the large hole as shown. A carbide disk works well.. make sure the copper is gone.

Now wires in the 4 spots as shown. The plus for the fan is the white wire in this case, you can use red instead. the 2 wires for the smoke unit don't  matter, i.e. there is no plus or minus.

On the top of the board, cut THREE traces.

  1. On the upper right, near the black diode with a blue band, just the upper 2 spots. I used a carbide blade in a dremel.
  2. On the lower left near the big black capacitor, you need to cut the trace that comes from the round land (which is where you soldered a wire on the other side. Again I used the dremel
  3. At the tip of the x-acto blade, there is a trace going "up" from that round land, I used an x-acto blade here because it was a cramped space. Be sure to get the copper trace cut through.

Seal the opening where the wires exit so all the fan pressure goes out the smoke exit, you can use some duct tape or maybe a blob of silicon seal.

IMPORTANT: test with an ohmmeter, neither of the smoke wires should have ANY continuity to either of the fan wires, and vice versa. This is important!

FA-1 - ART29305, FB-1

There were 2 versions of smoke units used:

New style:

FA-1 units have the ART-29311 "prime mover" smoke unit, never changed on the FB-1, so refer to that unit above. We will proceed with the early version in this section.

Original style:

This is a 2 part unit:

  • heater and fluid reservoir
  • fan and hose to move air

Internal fan and ducting:

At the end of the loco is a motor with a fan that supplies air to the smoke unit.



The fan pressurized the tube, and pumps air into the smoke unit, the housing is molded into the loco shell to the left:

100 3355

 The "unit" itself, is just a chamber, with a heater and wick... air enters from the bottom (if you are running it right) and exits the top:




The 2 wires on the side bring power to the heater.

Watch out!

There is a 2 position switch that controls the fan, one pumps air into the smoke unit (normal) the other causes a vacuum that pulls air through the smoke unit and exhausts it out the rear fan housing on top of the rear of the loco. (this mode is nuts) F is normal.


The RS-3 has a setup similar to the FA, in that there is a separate, removable  heater and reservoir unit, and a fan and duct system to deliver air.

 I do not know if there is any circuitry is in it. The RS-3 pressurizes the fan chamber like the old style FA-1, but there is no goofy reversing switch.

Heating unit and reservoir: ART-29309

In a design similar to the FA locos, the heater and reservoir are one unit that plugs into the top of the loco. The stack is off to the top right, and the air intake is the slot below.

20221005 150541

 Below is a picture showing the inside of the smoke heater and reservoir. Typical Aristo fiberglas wick and heater resistor.

20221005 151811

 Below is a picture of the fan and the ducting box, and the "receiver" for the smoke unit as cut away from the loco. You see the 2 clips that provide power to the heater.

 20221005 151836

I have not explored the capacity of the reservoir. Try 1 cc of fluid for now.





 Again, the U25-B uses a design similar to the FA and the RS-3


Heater and reservoir - ART29308

Here is a picture of the fan and hose assembly



Old style Rogers:

This loco has a smokestack that has the heater in it, and it has a miniature headphone plug in the end

One from R.J. DeBerg. This is the old style, pre 2008, 7 to 10 drops, no fan.



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