Question about using automotive lights for short protection

[joecool1212]

I have put the finishing touches on my mid size HO layout plan and am up to the power district part.  I saw a video on using 1156 and 1157 tail light bulbs for short protection.  I tried to view the video again and cant find it.  Has any one used this method and what are your thoughts?  Joe A. 

[cliffsrr]

I have tried putting 1157 bulbs in one lead of the power line and find that the circuit breaker in my DCC unit shut off before the bulb will light. When I was using regular DC the bulbs worked fine.

cliffsrr

[cacole]

 The purpose of the bulbs is to absorb the excess amperage going to the track when a train derails or something shorts out the track.

I have also used halogen floodlight bulbs for this.  Any bulb rated to operate on 12 to 18 Volts is suitable.  Just wire the bulb into one of the wires between your power pack or DCC booster and the track.

When there is no short circuit or overload, the bulb will remain off and merely pass current to the track.  When a short or overload occurs, the bulb will pass more current, causing the filament to heat up and glow, thereby absorbing some of the excess current. 

These bulbs are no real substitute for a fast-acting circuit protection breaker, though -- they just add extra protection against a heavy overload.  I have encountered situations where the overload was not enough to make the bulb light up or to cause the DCC booster's circuit breaker to trip.  In such a case, the only clue that there was a problem was when a freight car's plastic truck melted from the current passing through the wheelset.

[jrbernier]

The auto tail lights will not act like a fuse or circuit breaker. They will limit the current(about 2.2 amps for an 1156 lamp) that flows through the lamp. If you have a direct short, I would expect the fast acting internal breaker in your DCC command station to trip first. The lamp takes some time to 'heat up' and many times the command station will trip before it can heat up and limit the current flow. I had eight of them on my layout and the did provide an easy way to see where the problem was(just look for the bright light!). I now use fast action Digitrax PM42 breakers that are set to trip before the command station/booster can trip. As far as installation - just wire them in series with one of the leads to the track. If you are not going to invest in the electronic circuit breakers, I would suggest using them for 'power districts' for now. if the load is near the 2.2 amp value(and the lamp is starting to glow, it will limit the current and prevent the command station from tripping. It is the 'no-load' situation that goes to a 'direct short' very fast that the lamp cannot handle. Jim

[maxman]

joecool1212

I tried to view the video again and cant find it.  Has any one used this method and what are your thoughts? 

I tried it and didn't like it.  I think I remember seeing the video on Joe Fugate's website, but I think he has changed the format of his site around.  If it is still there, I can't find it.

There is some discussion of these things at http://www.wiringfordcc.com/track.htm#a6.  You'll have to scroll down a bit, but you'll see a reference to the 1156 bulbs.

 

Edit: wait a minute...thanks to Google I think I found what you were looking at: http://model-trains-video.com/e107_plugins/forum/forum_viewtopic.php?25

(and I still don't like it)

Regards

[rrinker]

 Here is an alternate method that costs about 50 cents per block more than just the bulb but limits the current to .4 amps after a second or two at the 2.5 amp limit.

http://www.rr-cirkits.com/Notebook/short.html

 

                                           --Randy

 

[Vail and Southwestern RR]

Where the bulbs are useful is in the case where you have a 5A booster (for example) feeding multiple districts.  The bulbs limit the current within any one district to about 2A, and yet the booster can continue to operate, and the other districts will continue to be powered.  In the case of a 2A "ish" command station, it is entirely possible, probably likely, that the command station is going to trip first.  Other bulbs might have a slightly different resistance curve, and be more suitable.  I think Joe posted here some bulb combinations to give different current limits a year or more ago.  It might have been on his forum, too.  Or maybe both.