I am repairing a smoking caboose. It did not like tmcc voltages. I have a 27 ohm smoke resistor and I'm trying to figure out how many watts it takes for smoke without melting the plastic smoke unit.
At present I have 4 diodes in series with the resistor. It smokes fine but the plastic does get fairly hot so I am trying to figure the minimum power required for smoke. Thanks; Don
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With one diode in series, you should get 1/2 the voltage that you got connected directly to 18V track power. That is normally sufficient. The side can get warm, just not really hot. Some insulating material between the plastic and the smoke unit helps as well.
With 1 diode it starts to smoke in a few seconds. With 4 diodes it takes about 15 seconds to start and has plenty smoke. with 4 diodes I estimated that the 27 ohm resistor was dissipating about 4.5 watts.
I am wondering what wattage is needed for the 27 ohm resistor to start smoking but not get to hot.
The plastic must be fairly good in that the original resistor burned in half and did not damage the plastic smoke unit. Don
I normally modify the K-Line caboose with a single diode for TMCC use.
Does the K line have a plastic smoke unit? Don
It does in the ones I've modified.
So far I have 2 diodes and a 10 ohm resistor in series with the 27 ohm. It takes about a minute to smoke. This amounts to about 3 watts in the 27 ohm resistor.
Bill said the 27 ohm may be to much heat for the plastic smoke unit. I'm sure without and diode or resistor it would be. Don
Make sure you keep the 10 ohm resistor away from the plastic, it'll get pretty warm as well. 
After about 5 min of operation the resistor was not hot but it is floating in air away from all plastic just in case. It is a 5 watt resistor should be dissipating about 1 1/2 watts.
I probably could do with out the diodes but it does smoke after a while. I'm paranoid about letting smoking locos/cars running out of smoke fluid. Don
Actually, without the diode, you'd have twice the power going to the smoke unit, it's having a larger effect than the resistor. I suspect you'd get LOTS of smoke without the diode.
Yes; I do get lots of smoke with out the diode. I'm probably being more conservative than I have to but I do not want to melt the plastic smoke unit.
It takes a while but it does smoke and the plastic smoke unit does not get real hot. ( I ran it without the cab so I could feel the smoke unit in operation. ) Don
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