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Smoke Tips

Large Scale Smoke Tips

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Large scale smoke units operate by vaporizing a special oil. The oil is especially formulated to evaporate at a fairly low temperature while forming fairly large and visible droplets. The oil is also formulated to evaporate completely leaving no residue behind. Another important characteristic is that the oil has very low viscosity so that it runs along surfaces well. This last characteristic is what controls the rate of smoke production.

Unfortunately, these fluids only come in white "smoke." It sure would be nice to blow out black stuff, but so far there is no oil that will show black. We'll have to settle for white.

All the available smoke units heat a small quantity of fluid to evaporation. The fluid feed rate is controlled by the design of the generator.

One common characteristic of all smoke units is that their lifetime is very strongly influenced by their temperature which is controlled by the evaporation of the fluid. If this source of cooling is removed, for example by running out of fluid, the heater temperature will increase rapidly and the heater will quickly fail.

There are a variety of different implementations of smoke systems and fluids. Their characteristics and differences are the subjects of this page.

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The LGB or Seuthe Smoke Unit

lgb smoke unit diagramThe LGB smoke unit is a cylindrical unit that sits inside the smokestack. It has a central heater element which is surrounded by smoke fluid. Capillary action draws the smoke fluid up along the heater element where it is evaporated with some considerable force. This causes the vapor to be ejected at high speed. Sometimes the unit will spit and sputter and even blow smoke rings.

It would appear that the LGB smoke unit is manufactured by Seuthe for LGB and others. The Lionel Atlantic uses a Seuthe element. If you can find them, Seuthe units cost somewhat less than LGB units. The LGB units come in 3 different operating voltages, 5 volts, 18 volts and 24 volts. Seuthe units are available at other voltages as well.

The 5 volt units will likely have less of a tendency to burn up simply because their input voltage is usually well controlled to produce an optimum power level of 1.5 watts. For example, the smoke unit in the Lehmann Porter cannot be turned off. It is a 5 volt unit and mine has many hundreds of operating hours with a dry smoke unit and it still works. The higher voltage units are intended to run directly from track power which has a wide voltage range. To get enough smoke at lower track voltages, the unit has to run at much higher power at high track voltages. The dissipation can run to 2.5 watts at the maximum rated voltage and if run dry at high voltage, they are at risk of failing.

The best setup for reliability is to use 5 volt units with a 5 volt regulator from regular track power. With battery power or DCC, where the available voltage is pretty constant, then high voltage units should be used with a resistor in series to limit the dissipation of the unit to about 1.5 watts. At 1.5 watts, the units smoke fairly well and are very reliable. If you want more smoke, then you can run the dissipation up a little and get more smoke at the risk of reduced smoke unit lifetime.

If too much smoke fluid is poured into the unit, the fluid will convectively cool the heater to the point that it'll never get hot enough to smoke. The most common symptom of too much fluid, besides no smoke, is spitting of large droplets of fluid. In this case, you can wait a day or so until the fluid evaporates, or you can run the unit until it spits out enough to start working properly again or you can turn the loco over and pour out the excess.

As the smoke fluid level decreases due to consumption of fluid, more and more of the hot element is exposed and what fluid does get drawn up the heater is heated explosively. The unit tends to generate smoke most violently just before it runs out of fluid. A good load of fluid is about 15 drops +/- 5 drops.

The LGB unit is quite compact so that it is easy to retrofit their replacement units into other locos. For regular track powered locos, I use 5 volt units for replacement because with the addition of a 5 volt regulator and Aristo PWC, smoke production is excellent, even at very low speeds. This combination works much better than the typical LGB constant smoke system, see PWC Tips for more details on voltage regulators. For DCC locos, I use the 24 volt element, sometimes with a 39 ohm 1/2 watt resistor in series with it. This causes the 24 volt unit to run at 16 to 18 volts. It still makes enough smoke and at the lower voltage it smokes longer and is less likely to burn up if run dry. The downside of the LGB unit is that it somewhat expensive, $20 or more depending on where you buy it.

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The Bachmann Smoke Unit

photo of bachmann smoke unitThe Bachmann smoke unit is designed to sit below the smoke stack. A heater element is supported in a small tub. One of my Shay's had the same arrangement as a Big Hauler, the heater is supported on end in the center of the tub. A metal tube is heated by a wire coil wound around the outside of the tube. Fluid is drawn up the inside of the tube from the tub and heated. The vapor is ejected straight upward from the open upper end of the tube. This ejection of the smoke allows most of the smoke to go up the stack even though the unit itself sits down in the smokebox. When making good smoke, parts of the heater often run red hot (above 900 degrees C) which is why these units often don't last very long.

bachmann smoke unit diagramThe other Shay had an arrangement more like this. The heater was horizontal with the four support wires immersed in the smoke fluid. Fluid was drawn up the wires and evaporated directly from the heater coil. I don't think that this was the desired arrangement as this unit burnt up in a very short time.

The Bachmann unit can generate A LOT of smoke, but it also consumes fluid really fast, two or three minutes on a load is typical. Its not a good idea to put more than 5 to 10 drops into the smoke unit. Since the unit sits inside the boiler, any overflow will spill inside the engine. On a Shay, it'll drain out of the boiler and into the front truck. The light smoke oil will then dissolve or dilute the grease in the front truck. If you put enough fluid in to partially immerse the heater element, the fluid will evaporate from the outside of the heater as well. This vapor is not directed up the stack and instead fills the boiler with smoke.

The top of the smoker tube is often partially pinched, probably to increase the velocity of the ejected smoke. However, on SOME units, the restriction seems to be a little excessive, the tube is either completely or almost completely pinched off. The smoke output of a unit that smokes poorly for this reason can be increased by clipping off the very tip of the pinched tube to increase the area of the exit port a little. The unit will consume fluid at a higher rate so be sure to keep track of fluid level and don't let it run dry or you'll be replacing the smoker soon.

On older Bachmann Big Hauler smoke units the wires are wound around lugs on the plastic cup and are pressed against the heat sink castings. These connections can get flaky even of the heater isn't actually burned up. On the Shay, the wires from the smoke unit are wrapped around lugs on the heatsinks themselves so that this problem is avoided.

The best fix for burnt up a Bachmann smoke unit is to either do without smoke or change the Bachmann unit out for an LGB unit. See Bachmann Shay Tips for instructions on changing the smoke unit in a Bachmann Shay. The procedure for a 10 Wheeler is similar.

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The AristoCraft Smoke Unit

Aristo smoke unit diagramThe Aristo smoke unit is a little different than the others. It doesn't run as hot as the others and doesn't eject smoke as well by itself, so Aristo provides a method to pump air through it. The Aristo smoke unit typically doesn't generate the same density of smoke as either the LGB or Bachmann units, but it will smoke much longer, perhaps three to four times, on one load of fluid.

In the diesels and the Pacific, there is a fan that forces air through the smoke unit. On the 0-4-0 and the Rogers, there is a piston type air pump in a cylinder that puffs air through the unit so that you get steadily timed puffs out the stack, although there is only one puff per driver turn instead of the "correct" 4 puffs per driver turn. The C-16 doesn't have any air pump at all. It operates similarly to the LGB unit.

The oil in the Aristo unit is conducted to the heater by a wick and the capacity of the smoke unit is large so that you have to put in quite a bit of smoke fluid or it won't smoke well or at all. 25 drops is the recommended load and it may last for half an hour. Since the wick controls how much fluid gets to the heater, these units can even hold more fluid without getting slowed down like the other units. However, the wick must be positioned so that the smoke fluid can find it. A unit that doesn't make much smoke or smokes only for a short time probably needs the wick moved. Open the unit and arrange the wick so that it sits in the lowest part of the smoke unit floor so that it can soak up any fluid that is in there.

On the diesels, smoke fluid is dripped directly down the exhaust stack. On the 0-4-0, Rogers and C-16, fluid is dripped down the smokestack. However on the Pacific, the smoke fluid is injected into a covered box that is located directly under the smokebox. On the prototype, this box would normally hold train control equipment.

Aristo units are also more easily replaced than the others. In all cases that I am aware of, the smoke unit can simply be pulled out and a new one plugged in. The smoke stack assembly on the Pacific must be partially pulled out to unlock it's smoke unit.

The Aristo diesel units are all molded in black plastic for manufacturing logistics reasons. If you want to paint them, they take paint well and don't get hot enough on the top to damage the paint. I've done the ones on my Warbonnet FA's, Floquil Bright Silver matches the Aristo paint almost perfectly. Floquil Santa Fe Blue matches the blue/yellow paint scheme well. If you do paint them, paint the stack too, then clean off some of the paint around the top of the stack with a lacquer thinner coated cotton swab to simulate the soot stains that are part and parcel of Alco diesels.

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Smoke Unit Power Consumption

The various smoke units are designed to operate on a wide range of voltage ranging from 5 to 24 volts. Running a smoke unit at 20% or so below its rated voltage will materially improve the unit's life expectancy, especially when run dry, but will also result in significant reductions in smoke output.

Some units, such as the LGB 5 volt units, seem to be able to tolerate dry operation well. Others, like Bachmann units, do not tolerate dry running at all. I believe that this is mostly due to the amount of nonlinear resistance that the unit has. As most metals heat, their resistivity increases. With the proper selection of wire for the smoke unit heater, its resistance can substantially increase as it gets hotter, thereby limiting the power delivered to the heater and limiting its temperature increase.

Encased heaters which are not exposed to the oxygen in the air will tend to resist oxidation of the heater wire which will eventually consume the heater. The only encased smoke units that I know of are the LGB units which appear to be manufactured by Seuthe. If you can find Seuthe elements, they will probably cost you a little less than the LGB versions.

The elements have several electrical characteristics which indicate their performance. The cold resistance indicates how much current the unit will draw at turn on. The current will rapidly decrease as the element heats. The smoking current is the normal power consumption of the unit while it is being cooled by evaporation of the smoke fluid. When the unit runs dry and looses its cooling, the heater temperature increases and the current goes down a little more. The larger the decrease in current between smoking and dry, the more the unit will be tolerant of running dry. Note that only the LGB (Seuthe) smoke units show any significant decrease in current.

Note that the cold current is important if you run your smoke unit from the function output of a DCC decoder or other command receiver. Whatever function output that you use MUST be rated for a load greater than the cold current or you run the risk of burning up the function output.

All the units were tested with a DC power supply connected directly to the smoke element itself so that internal voltage drops within a loco's wiring are not taken into account. Also, the voltages used for testing were somewhat arbitrarily selected. Bachmann units were generally tested at lower voltages just to prevent them from burning up during the test.

Smoke Unit DC Current Test Results

Smoke Unit Test Voltage Cold Smoking Current Dry Current Notes
volts Resistance
amp amp
LGB 5 volt 5 6.9 0.724 0.3 0.27 moderate smoke
LGB 24 volt 24 91 0.264 0.10 0.09 heavy smoke
LGB 24 volt 20 91 0.220 0.088 0.087 moderate smoke
Seuthe #7 16 44 0.363 0.141 0.129 heavy smoke
Aristo Rogers 16 27 0.59 0.26 0.25 light smoke
Aristo Rogers 20 27 0.74 0.30 0.27 moderate smoke
Aristo FA 20 14.2 1.4 0.34 0.36 moderate smoke
Aristo RS-3
(old version)
20 8.7 2.3 0.45 0.45 moderate smoke
Aristo RS-3
(new version)
5 4.8 1.04 0.49 0.49 light smoke
Bachmann Shay 16 72.5 0.22 0.23 0.23 heavy smoke
Big Hauler
12 88 0.136 0.13 0.13 moderate smoke
Big Hauler
16 88 0.182 0.18 0.17 heavy smoke
Aristo Long Steel Caboose 20 23 0.87 0.26 0.26 light smoke

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Smoke Fluid

Smoke fluid is a light oil that can also be used for cleaning track. Its so light that its almost a solvent. See Track Cleaning Tips for more information on using smoke fluid on your track. I've used five types so I have a little information on the relative performance of these types.

LGB smoke fluid works very well and has considerably less odor than San-Val Magic Smoke so its considerably better than Magic Smoke for use indoors. The Magic Smoke bottle is easier to pour from, I tend to spill less Magic Smoke that LGB fluid.

San-Val Magic Smoke seems to generate more smoke than LGB fluid, but is has a much stronger odor. The manufacturer claims that it has a pine scent. They must have a really odd idea of the smell of a pine forest as I think that it smells more like the inside of an oil refinery.

Bachmann fluid seems to be a little heavier than either Magic Smoke or LGB fluid and smokes at least as well as LGB fluid in an LGB smoke unit. It has no perceptible odor.

Department 56 "Magic Smoke" should not be confused with the San-Val Magic Smoke described above. This is clearly different stuff. Department 56 manufactures collectable ceramic buildings often found in gift stores. Some of their products have smoke generators and they market their own smoke fluid. I find that Department 56 fluid tends to generate denser smoke than the other fluids and lasts at least as long, in some tests twice as long. Its also cheaper at about $2.50/6 oz. This stuff has a distinct odor that is strong but less intense than the other Magic Smoke. I also find that after I use it for awhile indoors, by eyes sting. I am going to continue with this stuff outdoors only.

Lamp Oil Some people claim that they use ordinary lamp oil for smoke fluid as it is considerably cheaper than the fluids marketed as smoke fluids. I bought a 22 oz bottle at Cost Plus Imports for $2.99. This stuff is Lamplighter Farms Candle & Lamp oil and claims to be 99% pure paraffin. It also claims to be smokeless and odorless. Maybe so if you burn it, but just evaporating it makes lots of smoke that smells strongly of candle wax. The smoke also dissipates MUCH more slowly than the other fluids so I wouldn't want to use this stuff indoors. The label also claims that the fluid is combustible and harmful or fatal if swallowed. I suppose it is reasonable for lamp oil to be combustible. It smokes for about the same length of time as the other fluids and generates a dense smoke stream. I do not know if it leaves any deposits behind that might degrade a smoke unit.

None of the fluids seem to have any impact on painted surfaces so spills are not a big problem, but they should be wiped up.

In an LGB smoke generator, I found that all the fluids worked well with LGB fluid generating the least dense smoke and Department 56 the most dense but there wasn't a really huge difference between all of them. Indoors, I would use the LGB fluid due to its considerably lighter odor. Outdoors, its pretty much a wash. Smoke 'em if you got 'em.

In an Aristo smoke unit, I found that LGB fluid hardly worked at all and Department 56 fluid generated the most smoke of the highest density and ran for the longest time. Since the Department 56 Magic Smoke is the cheapest of the lot (not counting the lamp oil) and I run mostly Aristo stuff outdoors, I'll probably continue with the Department 56.

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All of the fluids mentioned above are refined chemical products. The Department 56 Magic Smoke lists its contents, a chemical called propylene glycol. I found a couple of web sites at Propylene Glycol Fun Facts and ToxFAQsTM for Ethylene Glycol and Propylene Glycol that indicate that this is not particularly healthy stuff. Propylene glycol is a somewhat viscous fluid and is shown in the data to be highly flammable, even explosive. I put a drop of this stuff on the sidewalk and tried to ignite it, no dice. Since propylene glycol dissolves in many other fluids, I suspect that Department 56 Magic Smoke is diluted with something to noninflammable levels.

Because we now know something bad about propylene glycol, it begs the question about the characteristics of the other fluids. These might be just as bad or worse. We can't tell because we don't know what is in them.

Bachmann smoke fluid is viscous and smells and works something like Department 56 Magic Smoke so it might be of similar composition.

San-Val's Magic smoke is much less viscous and has a distinctly different odor that propylene glycol. I have no idea what is in it or how bad it is.

LGB's fluid is very light and is clearly different. It has nearly no odor. I have no idea what this stuff is either.

The candle oil is paraffin which in itself is not particularly toxic. Solid paraffin is used to seal jars of home canned fruits and vegetables. As a vapor, I do not know what impact it has after being inhaled.

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Fluid Flammability

Toxic or otherwise, another important safety consideration is the flammability of the smoke fluid. This stuff will be in contact with a very hot heater element and if flammable, it could melt down a plastic engine or start a fire. Some smoke units can run red hot. This is greater than 900°C (1650°F) and is easily enough to ignite a flammable liquid or vapor.

Since flaming smoke units have not been a serious problem, I would expect that the most common smoke fluids are flame safe. However, I felt that some kind of test is in order. I elected to use a very simple test method with the three fluids that I had on hand. I have a couple of more types at the GIRR Mountain Division, when I get there next, I'll test them too.

The results of the first three fluids was good, they basically don't burn. I tested San-Val Magic Smoke, Dept 56 Magic Smoke and Paraffin Lamp Oil. The paper burned up to the edge of the wet area and then burned around the wet area while burning very slowly into the wet area. After the paper had burned around the wet spot, the flame went out leaving most of the wet area unburned. I assume that the wet area didn't burn because of the cooling due to evaporation of the fluid. When I tried to reignite the remaining area with the gas match, I could get it to completely burn, but only by holding the gas match on the area and only after completely evaporating the remaining fluid.

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© 1997-2002 George Schreyer
Created Dec 8, 1997
Last Updated July 5, 2002