SignalTraffic Forums

by **uccsa1** on Wed Jul 31, 2013 6:41 pm

Am I the only one that has noticed that when a light bulb blows on my LTG the fuse blows? I checked all the wires, seals, and the sockets and still, when ever a light bulb blows, the fuse blows. I buy the exact fuses they require. :scratch:

by **jab8356** on Wed Jul 31, 2013 7:17 pm

Consider yourself lucky. I've had bulbs blow and blow a TRIAC, which means when you put a new bulb in, it never shuts off and you have to have the board repaired.

by **Canuck_in_TX** on Wed Jul 31, 2013 7:32 pm

Have only had one of my LTG sequencers go bad on me but was fixed quickly by Lights To Go.

Sounds like the fuse did it's job preventing damage to the board. I am wondering how much wattage was the bulb?

by **pyth** on Wed Jul 31, 2013 7:43 pm

The only time I ever blow fuses on boards is when an output is connected to the common, makes a short circuit. :Phil:

by **Macsignals** on Wed Jul 31, 2013 7:49 pm

I've had a triac blow out on one of mine as well, in fact that's why my backyard setup only had ped signals in one direction (a NYC Eagle EF solved that problem). When the bulb burns out it can draw enough to blow the fuse or burn up a triac, that's partly why they spec fast-acting fuses. A Slow-blow fuse wouldn't blow as quickly and would probably let the triac burn out before it blew.

by **uccsa1** on Thu Aug 01, 2013 9:40 am

Good to know, it is not just me. I would rather buy a new fuse than a new controller any day! :grin:

by **TacomaJoe** on Thu Aug 01, 2013 1:57 pm

I don't get this one. I can't see how going from a loaded (good lamp) condition to an open (blown lamp) would take out a fuse unless the filament in the lamp was to short something out. I guess it's possible for a filament to break and somehow get a shorter piece of itself between the two leads. It the lamp is not shorting when it blows, wouldn't the same thing happen when you unscrew a lamp?

by **vaughnsimon** on Thu Aug 01, 2013 2:24 pm

TacomaJoe wrote:... I guess it's possible for a filament to break and somehow get a shorter piece of itself between the two leads....

I have seen many lamps emit a momentary bright flash of light as they burn out, so something unexpected is happening inside the bulb. Is it possible that a bit of the filament could vaporize as it "blows" and strike a momentary low resistance arc across the electrodes inside the bulb? This would naturally cause a high current pulse. It might not be sufficient to blow a triac in a normal traffic signal switchpack, but those tiny triacs in the LTG are another matter entirely.

Arcs certainly can happen inside a fuse when it blows, making the fuse fail to break a high-current fault. Arc-breaking is an important part of fuse and circuit breaker design.

by **Crunge98** on Thu Aug 01, 2013 8:02 pm

This doesn't sound right? Maybe you got a bad board to begin with?

by **Macsignals** on Thu Aug 01, 2013 9:34 pm

vaughnsimon wrote:
TacomaJoe wrote:... I guess it's possible for a filament to break and somehow get a shorter piece of itself between the two leads....

I have seen many lamps emit a momentary bright flash of light as they burn out, so something unexpected is happening inside the bulb. Is it possible that a bit of the filament could vaporize as it "blows" and strike a momentary low resistance arc across the electrodes inside the bulb? This would naturally cause a high current pulse. It might not be sufficient to blow a triac in a normal traffic signal switchpack, but those tiny triacs in the LTG are another matter entirely.

Having taken bad bulbs and shaken then to get the broken filament to reattach itself further down the stem and watched the results, I will back this theory 100%. The shorter piece of filament is a much lower resistance, probably closer to a dead short than to the original light bulb.

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