If it ain't one thing.......

[wobblinwheel]

On my little N scale layout, I have about ten little "street lamps" lighting various places. These are powered by a separate DC power pack which came from an old LifeLike train set. The power pack is one of those cheap, single-knob deals which is center-off, left reverse, right forward. This way I can dim the bulbs (14 v) to extend their lifespan. Well last night, for no reason, the bulbs suddenly brightened, started smoking (due to plastic "shades"). The little shades actually MELTED! Then, all lights stopped working, and the breaker tripped in the power pack. Now there's a dead short in the lighting circuit (parallel), but according to my meter, the power pack is working correctly, with a maximum of 14 volts wide open. Anybody venture a guess what happened?? The bulbs I've been able to get the shades off of don't "look" burned out. (not discolored). I can't easily access the wiring, so I haven't checked the individual bulbs. Yet. Do you suppose the power pack sent a SURGE to the bulbs?? And then went back to normal?? If I gotta replace all these LAMPS.........SHEEEESH!

[richg]

On my little N scale layout, I have about ten little "street lamps" lighting various places. These are powered by a separate DC power pack which came from an old LifeLike train set. The power pack is one of those cheap, single-knob deals which is center-off, left reverse, right forward. This way I can dim the bulbs (14 v) to extend their lifespan. Well last night, for no reason, the bulbs suddenly brightened, started smoking (due to plastic "shades"). The little shades actually MELTED! Then, all lights stopped working, and the breaker tripped in the power pack. Now there's a dead short in the lighting circuit (parallel), but according to my meter, the power pack is working correctly, with a maximum of 14 volts wide open. Anybody venture a guess what happened?? The bulbs I've been able to get the shades off of don't "look" burned out. (not discolored). I can't easily access the wiring, so I haven't checked the individual bulbs. Yet. Do you suppose the power pack sent a SURGE to the bulbs?? And then went back to normal?? If I gotta replace all these LAMPS.........SHEEEESH!

A burnt bulb will not always be discolored.
Sounds like a lot of current flowed and possibly both wire's cross each other somewhere and the insulation melted causing what you say is a short.

Possibly the power to your house surged for a moment.
I have to assume the lights operated just fine at 14 volts but you did not leave the power up that high normally.

Rich

[wobblinwheel]

Yeah, the bulbs would work fine at full voltage, but I never ran them that high. The plastic "shades" didn't melt either at full voltage. I'll have to remove a covering under the table to check the bulbs and wiring. Just wish I knew what happened so it doesn't happen again!

[Doneldon]

WOBBLIN-

I'd start by connecting a different power source to see if your lighting circuit is intact, and a different load, like different lights or a switch machine, to your power pack to see if it works. You can use a wall wart from some other electronic device as the test power source. Make sure it puts out at least 3/4 amp. A phone charger, tool charger or any old wall wart will work. Then get back to us with your results. Otherwise we'll all be just guessing as to the nature of your problem.
                                                                                                                                            -- D

[wobblinwheel]

Original power pack lights a 14V bulb, and varies intensity as normal. The lighting circuit indicates a direct short. No lights burning.

[utdave]

Have you got your self a volt /ohm/amp meter.    life saver  in trouble shooting    Dave

[wobblinwheel]

Have you got your self a volt /ohm/amp meter.    life saver  in trouble shooting    Dave

Yep. Sure do. Voltage checks zero to fourteen on power pack. Ohms read nearly zero across lighting circuit. Indicating a dead short. If all the bulbs were blown, seems it would show no continuity.?

[Joe Satnik]

Dear All,

Sounds like 2.5V Christmas Tree bulbs, which short out when the filaments break (open). 

Scroll down to "Blown Bulbs and Shunts":

http://www.doityourselfchristmas.com/wiki/index.php?title=Shorten_Mini_Lights

Hope this helps.

Sincerely,

Joe Satnik

[wobblinwheel]

Dear All,

Sounds like 2.5V Christmas Tree bulbs, which short out when the filaments break (open). 

Scroll down to "Blown Bulbs and Shunts":

http://www.doityourselfchristmas.com/wiki/index.php?title=Shorten_Mini_Lights

Hope this helps.

Sincerely,

Joe Satnik

Nope. Not Christmas tree bulbs. N scale "streetlamps". 14V bulbs wired in parallel, as I said earlier.

[richg]

Dear All,

Sounds like 2.5V Christmas Tree bulbs, which short out when the filaments break (open). 

Scroll down to "Blown Bulbs and Shunts":

http://www.doityourselfchristmas.com/wiki/index.php?title=Shorten_Mini_Lights

Hope this helps.

Sincerely,

Joe Satnik

Nope. Not Christmas tree bulbs. N scale "streetlamps". 14V bulbs wired in parallel, as I said earlier.

Yeah, I saw that in your first message. That is why I mentioned that the insulation melted on a pair of wires and they are causing the short, Somewhere.
Maybe right up where the two wires connect to the light bulb. I would suspect rather small diameter wire for an N Scale light fixture.Sounds like a tough issue.
No idea what the wiring is like under the layout if that is how you routed the wires.
Sounds like you need to disconnect, one lamp at a time.

Rich

[James in FL]

Sounds like you need to disconnect, one lamp at a time.

I'm thinking the same...

[GG1onFordsDTandI]

Sounds like you need to disconnect, one lamp at a time.
Rich

At least.... Adding fuses to each(overkill) or fused "Christmas tree" style stacked/ grouped parallel is the way to go for safety in parallel if you ask me (forget google, fuses are your friends, I run about 40 on my dune buggy). The coin-op vending/games industry also uses this method regularly to cut down on issues like this, keeping them more confined. Wire sizes on feeds, and exactly where the short occurred could have caused the "over bright" burn out too. Are you sure your track power feed is not involved in the short too? Over heated wire should be trashed. Best to start fresh with new wire and fuses, and a good wire plan well suited to your power requirements. I think I would junk the old power pack too. It could have an intermediate winding short starting (off & on),cause?, insulation ware from its own vibration. Both my old Lionel (mpc?) dc packs are full of spikes and noise, I only experiment with them now days. Many modern wall warts or an old computer power supply produce cleaner, safer power and you can make it adjustable many ways. This is at your home, best not to take any chances with old crap you have lost confidence or even suspect. Start back at square one.(and get a fire extinguisher rated for electrical fires)
Non shunted, burnt bulbs show no continuity 98% of the time, but the loose element end can sometimes move around, touch and reconnect. A bulb showing high continuity should be considered good until proven bad. Checked at the disconnected bulb base or leads, not in the socket, not through your wiring. Check sockets alone for shorts now too. Bulbs that "look" bad may also be fine and last years, gotta check um with a meter to know for sure(almost know for sure anyhow). Fuses almost the same thing. Ive seen 120v glass fuses that tested bad glow like a bulb from arcing between burnt/broken element ends for hours once enough power was pulled. Working until to little power to jump the gap was available ("half-blown" is what we called them), or till the ends fully burn away like on a carbon arc lamp.( a carbon arc lamp pulls atoms off the element tips. "Burning" there, is really electric particles flowing and taking a bit of carbon with it as it travels trough the air, and then "letting carbon go" to jump to the grounding surface of the other electrode.   Literally like using arc welding rod as a light source. except mostly a all carbon rod
.