My Lionel 18003 Lackawanna northern was rehabbed by others and now I am trying my hand at tweaking the smoke unit. What is the yellow disc in the center of the picture?
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Looks like a 2.5amp resettable fuse, aka PTC. If you have a smart phone or tablet, the Digi Key app is great for identifying electronic stuff. You can even use you camera in the app.
Yes. A PTC. Cheap internal insurance.
John
Thank you for the quick response, Norm. Being electrically challenged, can you tell me what it does? One of its wires is hooked to the smoke unit. It does not appear in Lionel's diagram of the 18003 engine.
@POTRZBE posted:Thank you for the quick response, Norm. Being electrically challenged, can you tell me what it does? One of its wires is hooked to the smoke unit. It does not appear in Lionel's diagram of the 18003 engine.
If heat is generated by high current flow the resistance of the PTC increases to inhibit it (unlike a fuse that burns in the center and opens the circuit stopping the flow ). It normally resets itself unlike a fuse that needs to be replaced.
John
Interesting usage, other than a direct short in the smoke unit, the PTC would seem not to be of much use in this application. I wonder what drove them to install it?
Old timers used to call these ‘chemical fuses’. They behave like a self-resetting breaker. Not sure why it’s on a smoke unit. Maybe to keep the plastic unit from melting from too much power?
As originally issued from Lionel, there was a regular cartridge fuse in line with the smoke generator. That practice was quickly discontinued. Lionel only installed them in a couple of 4-8-4's in the 80's. Ineffective I would guess.
FWIW, if I disconnect the wire from the PTC to the smoke unit, the headlamp goes out.
That supplies power to both the smoke unit and headlight. The original fuse was P/N 8100-90.
The smoke unit has been vexing for years. Does it have a wick? There does not appear to be anything wrong with it, yet I get no smoke.
No, those smoke units do not have a replaceable wick. If you get no smoke when 12 volts is applied directly, the unit will have to be replaced. You can eliminate the fuse, not really needed.
Thanks to all who responded. Chuck, do you sell that part? I got couplers from you long ago.
When I used to run smoke, my wife would flick the basement lights on and off to catch my attention if she could start to smell it upstairs. The engineer behind this PTC placement was pretty smart! The headlight going out could be an early warning system.
Potrzbe, Yes. Please drop an email offline.
E mail sent.
Jim Barrett wrote an excellent article on upgrading these units and why they fail.
Jon 
Hello Jon. Got a run number for the Jim Barret article? I have many old copies of OGR here.
I would be interested too on repairing these type of smoke units.
