Changing resistors & Lionel smoke unit life

you must be talking Lionel...my mth ps2 ps3 diesels belch plenty of smoke on medium and way to much on max settings, can barely breath with 9 locos smoking..part of the fun.

I don't have a clue why Lionel used the 27 ohm smoke resistor for command locomotives, I understand it for conventional running as they apply full track voltage. For TMCC, you get a half-wave rectification of the track power minus a diode drop from the triac on the smoke unit.  If you boost (hold down the Alt1/9 key), you get the full track voltage.  Don't do that too long!

 

I don't know of any issues that have come up from the mod, I've done it a bunch of times.  I did some tests and measured the temperature rise of the smoke triac on the R2LC with the 20 ohm resistor to insure that the change wouldn't adversely affect the life of the electronics.  In all cases, the smoke triac had no more than about 25C temperature rise over ambient, which is well within it's ratings.  The current goes from around 1/3A to somewhat less than 1/2A, also well within the triac ratings.

 

The resistor change brings the wattage dissipated across the smoke resistor from around 3 watts to around 4 watts.  This is in line with what newer Legacy locomotives dissipate in their similarly sized smoke units, so I don't see any major issues with heat.  I can't imagine this would affect the smoke unit motor, I suspect other factors will kill it long before the slight increase in heat.

 

Some folks have gone with as low as 16 ohm resistors in the smoke unit, but I think that's a bit much.  That brings the wattage over 5 watts and also raises the current to over 1/2A through the triac.  With that resistor value, I had a 50C temperature rise in the smoke triac, and things were getting a bit toasty around it.

 

I did experimentally add a heatsink to the smoke triac with the 16 ohm resistor, and that helped with the heat dissipation, but it still ran over 40C temperature rise.  You could probably get away with that, but I choose to be a bit more conservative.

 

I've changed a few Lionel steameras from the 27 ohm to a coated 22 or 25 ohm resistor and either puts out a good amount of smoke, whether it is a fan unit or a pumping style. The 27 ohm one just does not cut it. I also replace the wicking and always cut off that stupid resistor sleeve that should have never been used. It just gets "caked" onto the resistor after some use.

When I do the upgrade, I do indeed change the wick, and of course omit the sleeve on the new resistor.  Finally, I drill out the intake hole to allow more airflow.  I settled on the 20 ohm after doing some tests on the TMCC electronics and trying to determine what would not unduly stress the smoke triac.  It's also a tradeoff to maximize the smoke output while minimizing charring of the wick.

 

It's important to insure the new wick does not block the airflow from the chamber, over the resistor and out the stack.  The resistor should be in solid contact with the wick material, but not totally covered, which will greatly reduce the smoke output.

 

I remember that K-Line engine that you changed the resistor. It smoked great for about two minuets.

1. where do we get 20 ohm resistors?

2. are they ok for both fan units and puffing units?

3. are they the answer for the early Vision Gensets where typically only one of the three stacks smoke well?

Most electronic suppliers have them available. Radio Shack may have them as well.

 

Ted, where did you get the ones you use?

1. I get mine from Digikey and knock the ceramic coating off them.  They're 2 watt wirewound resistors.

 

2. They work fine in puffers, I've put them in a few of them.

 

3. No, the Vision Line Genset has three smoke units, and they are driven by a smoke regulator.  You need to use the stock 8 ohm resistor in those.  You can replace the wick, take a look at enlarging the intake hole, etc. to improve the smoke.  FWIW, my NS one has three smoke units that work pretty well after replacing the wick.

 

Note that the scare talk about having flames with just a change from 27 ohms to 20 ohms is just that, scare talk.   You'd need a lot more than changing the power dissipation of the smoke resistor from the stock 3 watts to 4 watts with the 20 ohm resistor to have that happen.  The newer regulated smoke units, as well as the MTH smoke units, dissipate in excess of 5 watts in the smoke unit, and so far they don't catch fire.

I with john on this. I have done tons of these with no issiue . I even screwed up one time and put a 8ohm one in a old unit . I noticed after I ran the engine it smoked more them Anything I have ever seen and it didn't blow up or shoot flames out. But I like the mth resistors in my old Lionel units . My NYC Nigeria and f3s smoke as good as my legacy stuff.

I've seen one come close to flames, but it wasn't because of a resistor change.  A legacy steamer with a 6 ohm resistor had a smoke regulator failure.  The failure put 18 volts of track power right across a 6 ohm resistor.  It started smoking "real good" as it entered a long tunnel.  By the time it came out, the resultant smoke screen was something to behold!  If it hadn't killed the smoke resistor after a few more seconds, we might have had flames. 

 

That one needed a smoke unit PCB and the smoke regulator.  The smoke output now is much more pedestrian, nothing like the impressive but brief display.   It still smells a bit like burned fiberglass...