Auto tail light short protection

I actually no longer recommend auto tail light bulbs for short protection.

1. Once current draw in an 1156 bulb protected block exceeds about 60% of 2.1 amps (~1.25 amps), the filament starts to glow, sucking voltage away from the locos and making throttle speed response more sluggish. This is especially noticeable on grades.

2. Sound locos are becoming more popular and they draw a bit more current. A multiunit consist of sound units draws notably more current than non-sound units. This makes the bulbs less useful because the effect listed in #1 becomes even more pronounced.

3. Incandescent tail light bulbs are on the way out, being replaced by LED equivalents. LED bulbs do not exhibit the same short protecting behavior of incadescents. I’m expecting we’re just a few years away from incandescent bulbs disappearing from the market completely as LED equivalents make further inroads.

I now recommend true electronic circuit breaker protection for your DCC layout. My article in the April 2015 MRH entitled DCC bus wiring 101 discusses more modern short protection options:  mrhmag.com/magazine/mrh-2015-04-apr/dcc-bus-wiring-101

Wouldn’t 1156 or 1157 lamps

in series or parallel be kinda’ expensive???

Probably be cheaper to buy a PSX from Tony's Trains.

Nick

@joe Thanks for the update, I

@joe Thanks for the update, I understand your points, but it looks to me like the PSX (for example) is designed to protect an entire district and isn't going to tell you where the short is. What's the cheapest electronic solution that you could deploy individually at the per-block level that would replicate the fault isolation behavior of using one bulb on each feeder wire pair?

On your layout where you used the bulbs years ago, did you ever have to replace a bulb that burned out? They're 1000 hour bulbs, but how long do they last when they are seeing current below the 'glow' threshold?

@nick

You can have 70 bulbs for the cost of one of those PSX boards and protect 70 different blocks with the 70 bulbs. With the board you have to protect the whole district as a unit, and so you have much less refined fault detection.

Hey, why spend one dollar

Hey, why spend one dollar when you can spend fifty to do the same thing?

As for solder & fragility...

For Joe's reasons, I will likely give up on bulbs someday.  But on my layout, they still do fine.

I found the old bulbs often were hard to solder... thus the bulb you show would be nice.  Get some LARGE heat shrink, and cover the base with it... protecting the assembly. 

Also, where you can, get colored bulbs... they help indicate Which block is indicating fault.  Amber / white / are common...  possibly blue - (I've seen some, but don't remember where!)

Having a few won't hurt... deciding to use 'em after they're no longer made... that's another story.  Antique bulb hunting can be a bizarre pursuit  (remember flash bulbs?)

There is nothing wrong with using bulbs

for short protection.  I totally agree with Mark P's comment.  Soldering to a bulb is no issue if you shine up the brass surface and maybe use a little rosin paste.  It just takes more heat to make the solder flow.  This list will give you a choice of amperage ratings

miniature light bulb specs see website below

http://www.jwspeaker.com/bulbs/#product=bulb-1076

577 tubular bulb = 1.41 amp
  
1152 bulb = 1.34 amp

1141 bulb = 1.44 amp
single contact

1142 bulb = 1.44 amp
dual contact

1156 bulb = 2.10 amp
single contact

1157 bulb = 2.68 amp
both filiments wired together

.

@peter-f

heat shrink! Great idea. I'd hoped someone would fill in the rest of the solution for using the wire-lead bulbs.

Bulbs and Sockets

To resolve the mounting problem we purchased sockets with screw or solder tabs. To disconnect a block all you had to do was pull a bulb. Some of the modules used festoon bulbs and sockets which were available in blocks of two to ten sockets (similar to fuse sockets). I think NCE still sells a board for six or eight festoon bulbs for block protection. But as layout currents have increased due to sound and lighting, we found that we were dropping to much voltage through the filaments, so we switched to breakers.

breakers

I'd be happy to consider alternatives that aren't $35 each. 

The bulb technique has two features that nothing else I'm aware of duplicates:

You protect blocks individually (not bus sub-districts), so that a short in one block only stops trains in that one block. 

When a short occurs, the block that has the short (not the sub-district) is specifically identified

If there was a cheap breaker that worked for DCC (in the range of a dollar each), I'd go for it, but the DCC vendors repeatedly warn against this, saying DCC is not DC and it's not AC, and you can't use off-the-shelf electronics, you have to buy our special $35 boards because we designed a complicated system that you can't fix or modify on your own so we'd own you. 

About the Heat-shrink... 2 tricks to add

IF you're still using metal base bulbs, the rear contacts are your solder points... but ANY tugging on them or your attached wire can easily rip the internal wire loose.   So, add a 'strain relief' by looping that wire under the heat-shrink.

If you use the no-base bulb, add a wire tie under the heat shrink to (later) fasten this securely.  Just to make a loop for hanging. 

The metal base bulbs can also be secured under a plastic cable clip of sufficient size (wish I knew the name-- I'' try to describe it)   - a   ' b '  shaped open loop, where the plastic starts at the top of the  b,  extends down and through the loop - travel 270 degrees into the corner of the loop, and then has another leg extending vertically up, returning to the top.  A screw would hold closed the two legs.

Before you (or anyone) goes wild installing these as a 'solution, read Bruce Petrarca's article:

  http://mrhpub.com/2014-11-nov/land/#20    especially the pros / cons on pg 22.

My 1156 based unit is working well

A package of 1156 bulbs on Ebay was a couple of bucks. I built it on a scrap of plywood, drilled some holes, used cable ties to hold the bulbs, and soldered right on to the bulbs. The control panel gives three selections per district: normal DCC, off, and programming track (or DC throttle). I added LED indicators across the bulbs, with a reverse polarity protection diode as well. When a short occurs (running into a turnout in the wrong position) the LED lights, I turn off the power to the district, throw the turnout, and power back on. This saves the contacts on my Tortoise from hot-switching. It's also nice to use the main line as a programming track when adjusting momentum and speed curves; no five-finger crane needed. And this went to my NMRA Electrical AP cert. I do not do sound, but my brother does and all of his locos run fine when we operate. 

In the circuit, the panel switches are SPDT/center off. The resistor is 2.2K. The diode is a 4001. The LED is a 5mm red. As you can see, I just point-to-point wired it on the board. The DCC district feeders connect to the terminal strips. The panel is mounted at the bottom of the fascia, the board sits on a shelf under the layout. The CAT-5 wire could have been any length. I use a pair per conductor; the resistance is negligible for this length.

bulb for PowerCab

it took me a while to realize that the PowerCab power supply did not supply enough current to use an 1156 bulb (> 2A).   

i found the 211-2 T3 bulb that draws ~1A works well with the PowerCab.  soldered wires to the ends.

Electronic circuit breaker vs bulb

Having just read Joe's "DCC Bus Wiring 101" from MRH 2015-04, he brings valid points against using the bulb, and that was back in 2015 even.

And I noticed eastwind's post on the previous page which got me wondering what would it cost to make an electronic circuit breaker, for example this one:  http://www.princeton.edu/~martin/DCC/breaker.html, which also includes the micro-controller code (a simple state machine).

Surprisingly, parts come up to $17 with a PCB (one of those cheap prototype boards that cost almost nothing). The parts list is from DigiKey (https://www.digikey.ca/short/j1ptb9)  so if one was shopping around, might get better prices, especially if building dozens of these. A custom PCB should be also made to streamline the process.

I was hoping it would be cheaper, but this design incorporates 4 N-Channel FET transistors, and a big shocker to me is the cost of 2N2222, which has to be one of those ubiquitous transistors that should cost next to nothing, yet DigiKey wants $2.50 for one.

Cheapest commercial circuit breaker that I can see is $30 (DCC Specialties OG-CB), although maybe there is something cheaper I'm not aware of.

I am sure that all vendors have a healthy profit margin and are also charging premiums to recover their R&D.

Bottom line is, we should find/design our own circuit, pool together the resources and produce 1,000 for under $10, in all kinds of combinations, from uni- to octo- units.

one or both paths

a bulb is in only one path, which protects a short between the rail.

it seems common that an electronic circuit breakers protects both paths.   A short between either rail and something other than the other rail (??) trips the breaker.

perhaps only half the above circuit is really needed.    but it still won't beat the price of a bulb and holder

btw, 2n2222s can be had for < 10 cents

@Trainzluvr : Cheaper now.. not later

Agreed, those parts are weirdly priced.... but   In conversation with the sales staff, you may get their support (and unlisted discount).  Tell them what you want to build... buy the pricey parts and tell them you need these over-prices 2222s.  You may find they'll support your 'development' work by throwing in a handful. Or pricing the few at the larger volume price.    They have more flexibility than they'll advertise, and if you catch their interest, you can benefit from that.

As for why spend So much for parts from the DCC developers...  well, I know I'm Not the only  person who's had a defective decoder replaced No Questions Asked.... 

Yes, by building in quantity, the price drops... and the expectations rise... what's the price of both?