Hello again. I have a Lionel Union Pacific Berkshire Jr. (6-28696) for which I would like to replace the smoke unit resistor, wick and padding in the smoke unit. The original resistor is 30 ohms and generates anemic amounts of smoke . What strength wire-wound resistor would produce better smoke output without being too hot and where might I purchase such a resistor?
27Ω is the “standard” value for TMCC(where the resistor in a standard on-regulator set-up is usually fed something in the range of 9-14V). Lionel service should have them.
For conventional operation, you’re probably be happy with 20Ω. I don’t know of a ready source for these pre-made, but a trick I learned from a few different folks was to buy ceramic resistors with 3-5W ratings and “crack” the ceramic casing around them. Out will pop a near perfect wire would resistor.
You MIGHT be safe to go as low as 16Ω, which is the standard value for MTH resistors and is available from MTH service. I’d watch for excess current consumption and signs of too much heat with this, though.
Thanks for the info. Would you happen to know if there might be a mathematical formula for comparing the temperatures of different resistors of the type we are speaking under the same voltage?
I think there are too many variables involved to calculate temperature-it’s going to be dependent on airflow over the resistor, how much contact there is with the wick material, how saturated the wick material is with smoke fluid, the boiling point/vapor pressure characteristics of the smoke fluid in use, and probably a few other factors I’m not thinking of.
What you can do is first calculate current through the resistor using ohm’s law, V=IR. If you know the resistance(R) and assume that the RMS voltage to the track is the voltage through the resistor(reasonable if the smoke unit is directly across the track power, not reasonable if there are intermediate controls) you can find current through the resistor.
Once you know current, you can find power(in watts) using the equation P=VI
All else being equal, the higher the wattage, the higher the temperature of the resistor in a given situation.
There have been a few smoke unit designs that monitor resistor temperature. The old TAS Turbosmoke units had a thermal diode near the resistor, and would kick the fan into constant full speed plus cut power if the temperature went too high(such as running out of fluid). I think 3rd Rail still uses a smoke unit heavily based on the old TAS design. I have a bunch of these in use, and have never seen a thermal shut-down. Recent Lionel units use a similar set-up, although with the temperature monitored by the RCMC or LCP3 board, and I have no idea what it actually does with the information. The big constant, though, seems to be exceeding some sort of “too hot” threshold.
I’ll add too that in command environments, mechanical puffer smoke units can get hammered HARD because there’s no active airflow when stationary. I sometimes intentionally use an older R2LC(radio board) in those locomotives because the C06 version basically just trickles enough power to keep the resistor warm when stopped. The same problem also rears its head in Lionel’s early attempts at puffing fan driven units-the infamous “semi smart smoke unit”, as well as the “smoke logic PCB” used in some early Legacy locos-don’t run the fan stationary, and these can cook the wick. I’ve redone a couple of mine with Gunrunnerjohn’s SuperChuffer for that reason, although I’ve left the only Semi-Smart unit I still have in stock configuration be since I hope to soon replace the whole unit with a Legacy dual chamber backed by an RCMC.
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I’m a resistor for smoke units. I’ve always resisted putting one in my engines!
I hear what your’e saying, Patrick, but I’m a “rather have it and not need it than need it and not have it” kind of guy.
Thanks again, Ben. My primary goal is to try to make a choice that will result in having a “reasonable” amount of smoke and having to only take things apart once.
It’s a joke, the biggest reason I don’t try one is maintenance.
Old model railroad joke:
Modeler number one, speaking from the other side of a scenic backdrop: “Does your engine a smoke unit?”
Modeler number two: “No.”
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I suspect you’d be happy in the 16-20Ω range.
I’m a bit out of touch on conventional smoke, as I’m 99% command control now. I do have a smoke unit pulled from an early 90s Lionel Mikdao on my bench(replaced with fan driven), and I’ll be putting TMCC in a 785 Hudson in the near future, so can check those.
As I mentioned, in the first few iterations of TMCC, Lionel favored a 27Ω resistor, and as I said typical voltage actually delivered was ~9-14V RMS. Lionel also got a reputation for poor smoke in this era-some can be fixed by improving airlfow and the like, but with a 20Ω resistor they will belch thick clouds of white smoke. I’ve put 20Ω resistors in a few, and ended up dialing them back to 23Ω or using a diode pair to cut the voltage down a bit.
MTH has always had the smoke “reputation”, and they’ve basically used the same formula from the beginning: two 16Ω resistors and “pinch” the wick between them. Protosound 1 locomotives had some logic on the smoke unit that would change the wiring from parallel to series depending on track voltage. Protosound 2 and later just left them in parallel all the time, and I think feeds about 5V.
Lionel has brought their smoke output up a bunch. Their first attempt used a 6Ω resistor with a “smart” regulator that would feed 3-4V depending on setting, conditions, etc(and also give more consistent smoke in conventional). Unfortunately it was not properly rated, and pretty quickly a service bulletin went out saying to change the 6Ω to 8Ω. The regulators still die with some regularity-in fact a couple of weeks ago I was working on a Legacy 0-8-0, was about ready to button up the repair(which involved the speed encoder on the motor) and the smoke stopped working. There was no magic smoke, burnt electronics or shorts involved-the regulator was just working one minute and gone the next. Fortunately I was able to source a replacement, and added an extra heatsink to keep the triac cool…
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If you go the MTH way, this might help you. Based on two 16 ohm resistors in parallel (result 8 ohms), assuming 12 VAC, current would be 1.5 amps split between the two resistors (.75 amps each), power is 12x.75= 9 watts. I think I remember this correctly, but maybe the law has changed. I think the datasheet says they are 25mm long, close to an inch, I believe. Note these are fusible resisters, they will “open” if they get overloaded, so a couple spares might be in order. Resistors are cheap, shipping and now tariffs??? are not. Good luck.
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This reply was based on the statement
“MTH has always had the smoke “reputation”, and they’ve basically used the same formula from the beginning: two 16Ω resistors and “pinch” the wick between them”
Thanks guys for all of your helpful information.