short circuit protection using auto bulb vs. Power-Cab shutdown

[gregc]

i have a small layout with an NCE PowerCab which works great.   But it's time consuming to locate a short when the PowerCab takes several seconds to reboot (?) after detecting a short.

I tried putting a 3021 dome light bulb in between the PowerCab and track both to indicate the short and limit the current to avoid the PowerCab reboot.   A short causes the bulb to light up brightly and the PowerCab doesn't reboot.   Seems like relatively in expensive ($7.50) automative short circuit protection.

Can anyone think of a reason this would damage the PowerCab?  

 

[maxman]

I don't like any of the bulb options.  In my opinion they are just an old fashioned method of accomplishing something that one of the new circuit breakers does better.

Plus, I don't think they "protect" anything.  You still have current flowing that is potentially damaging, not to the Powercab, but to things on the railroad.

In addition, there is still current going through the bulb even though there may not be enough to light the filament.  So as you add more locos, there is more current required, and the more current required starts to light the filament.  So some of the current needed to operate the locos gets robbed by the lighted filament.

Just my opinion.

[RR_Mel]

I’ve done the same thing for over 30 years using a #1157 bulb, it works.  I don’t leave it inline unless I have or anticipate a problem   I have a pair of SPST toggle switches paralleling the bulb filaments to remove them from the circuit for normal operations.  It’s also a good “tool” when I’m working on a problem locomotive to prevent burning something up.  The break filament side draws 2¼ amps and the tail light side draws ¾ amps at 12 volts.  I can use either filament or both using the two toggle switches.

 

I also us a #1157 single filament bulb behind one leg of DPDT toggle in series with two of my sidings for charging voltage to power my battery operated lights in my passenger trains.  A pair of DPDT toggle switches, one in each siding, switches the track power between normal operating and charge.  I use LEDs on my control panel to indicate when the charge current is on.  The charge polarity is wired to forward as protection for dumbness in case I forget to uncouple and remove the locomotives before switching to charge.

 

I’ve never had any problems.  The only time I’ve had to use the bulb to trouble shoot a short was when a part had fallen off of a locomotive and became lodged between the rails near the frog in a turnout (in a tunnel).

 

Mel

[rrinker]

 My problemw ith light bulbs is, they aren't cutting anything off. Whatever current flows through the light bulbs, flows through your 'short'. For 5 amp and up systems, the commonly used bulbs allow about 2 -2 1/2 amps to flow. That's 30+ watts, which can still generate significant heat. For the PowerCab you need lower current bulbs, or the PowerCab will just trip and there will be no benefit - NCE has the CB6 which has 6 1 amp bulbs in it which would work for this.

                     --Randy

[skagitrailbird]

I'm with Maxman. The DCC Specialties OG-CB is perfect for the PowerCab. Costs only $25 at either Tony's Train Exchange or Litchfield Station, both very reputable dealers.

[gregc]

I should have tried this before I posted something.  

maxman

In addition, there is still current going through the bulb even though there may not be enough to light the filament.  So as you add more locos, there is more current required, and the more current required starts to light the filament.  So some of the current needed to operate the locos gets robbed by the lighted filament.

When I did, and tried operating a locomotive, the bulb started glowing every time the locomotive started drawing current which caused the voltage across the bulb to increase, the voltage across the track to drop, until the locomotive slowed and the cycle repeated.

maxman

Plus, I don't think they "protect" anything.  You still have current flowing that is potentially damaging, not to the Powercab, but to things on the railroad.

when designing a circuit that may short, I'm usually concerned with protecting devices up stream of the short that the current passes through.   This is normally the power supply but can also be switching devices, not the mechanism causing the short.   If it isn't simply a metal short across the rails, it can either handle the current or is already damaged.  

One way to provide protection is to simply limit the current by having a simple feedback mechanism the reduces the voltage.   This is how many high quality (HP) power supplies provide protection and how I had hoped the bulbs would work.

I'll add a switch to place the bulb in the track circuit when troubleshooting a short

thanks for all the info

[maxman]

gregc

I'll add a switch to place the bulb in the track circuit when troubleshooting a short

Although someone else mentioned doing this, I don't think I understand how putting the bulb in the circuit helps troubleshoot anything.  If there is no short, the bulb does not get put into the circuit.  And if there is a short, I think that would be recognized before putting the bulb in the circuit.

From what I've seen of shorts that occur during operation, they are mostly caused by some unwanted interface between the train and the rails.  So that immediately gives a starting point.  I don't think I see any advantage to search for such shorts with current still flowing, other than looking for something that has become extremely hot to the touch.

Maybe there is something I'm missing.

[gregc]

maxman

Although someone else mentioned doing this, I don't think I understand how putting the bulb in the circuit helps troubleshoot anything.

I had a problem where a wheel shorted between the frog points and stock rails (I understand about DCC compatible turnouts).  PowerCab would shut down and take several seconds to apply power to the track when I tried to find the problem, which made it difficult to find the problem.   I probably used a voltmeter to find the problem.

I think it's another tool that can be helpful and one I don't have to hold to indicate when the problem occurs.   (I'll find out).

On one perplexing project at work, someone suggested removing the fuse and look for the component that smokes.  It's not always easy.

[rrinker]

maxman

 

gregc

I'll add a switch to place the bulb in the track circuit when troubleshooting a short

 

 

Although someone else mentioned doing this, I don't think I understand how putting the bulb in the circuit helps troubleshoot anything.  If there is no short, the bulb does not get put into the circuit.  And if there is a short, I think that would be recognized before putting the bulb in the circuit.

From what I've seen of shorts that occur during operation, they are mostly caused by some unwanted interface between the train and the rails.  So that immediately gives a starting point.  I don't think I see any advantage to search for such shorts with current still flowing, other than looking for something that has become extremely hot to the touch.

Maybe there is something I'm missing.

 

Well, on a larger layout, with a 5 amp system, or maybe even multiple booster, you can break the layout down into even more sections with a light bulb on each. This can serve two putposes - it will tell you exactly which section a train has shorted in, which sure, is very simply when you're the only one running and only one train is running, but not so much with a dozen operators having 8 trains on the move simultaneously, and second, since the current allowed by the light bulb is less than the booster output, only the shorted train stops and gets a lit up light bulb, other trains in different sections keep right on going.

 Dick Bronson at RR-CirKits published a slightly more complex alternative to the simple light bulb, using a PTC resistor to controla  dual filament bulb. It starts out allowing the 2.1 amps of the one filament to keep flowing, but then switches to the .4 amps of the smaller filament. Still not as good as just completely cutting the power, but .4 amps keeps the current low enough to not melt plastic trucks or weld rail. This is still super cheap - the PTC resistors are less than 50 cents each, so the bulb is still the more expensive part. Not really suitable for a lower power system like a PowerCab, it will take too long to heat up the resistor and get it to flip, plus the larger filament in the bulb is 2.1 amps, which means the PowerCab would trip first anyway.

                            --Randy

[richhotrain]

maxman

I don't like any of the bulb options.  In my opinion they are just an old fashioned method of accomplishing something that one of the new circuit breakers does better.

Plus, I don't think they "protect" anything.  You still have current flowing that is potentially damaging, not to the Powercab, but to things on the railroad.

I'm with maxman on this one. Use a circuit breaker.  But, what I wonder is if it is a "small layout", why is it so hard to spot the short in the first place? With limited activity going on at any one time, wouldn' t the cause of the short be immediately obvious?

Rich

[fisker76]

"I'm with Maxman. The DCC Specialties OG-CB is perfect for the PowerCab. Costs only $25 at either Tony's Train Exchange or Litchfield Station, both very reputable dealers."

 

Roger Johnson

The OG-AR is not compatible with the NCE Power Cab as it is designed for systems with more than 3 amps. The PSX Power Shield breakers are designed for use with low current systems like the Power Cab. The PSX can be programmed for use with systems starting at approximately 1.5 amps all the way to 18amps. 

Erik Fiske, Tony's Train Exchange

 

 

[DigitalGriffin]

maxman

I don't like any of the bulb options.  In my opinion they are just an old fashioned method of accomplishing something that one of the new circuit breakers does better. Plus, I don't think they "protect" anything.  You still have current flowing that is potentially damaging, not to the Powercab, but to things on the railroad.

 

Except the light bulb it significantly cheaper and does limit the current.  It's the current that does the damage usually.  Not the fact it's moving through a part, but there's too much.

It's an acceptable answer and works well when bridging DC-DCC sections

[BroadwayLion]

LION has tried the LIGHT TRICK... and is pleased with it. Him will incorporate it on the layout of him, but him will need about four lights in parallel for the amount of current him consumes on the layout of him.

LION has a 10.2 volt x 12 AMP regulated power supply with current to the tracks at all times, but him has not DCC. Problem is in the tracks. LION has embedded resistors to slow the trains down at the stations (and a gap to stop the train). If a train derails between the resistors it will draw enough current to burn the resistors, but no where near enough to trip the power supply's internal protections. Power supplay says : "Ah, you want 5 amps, ok, I got that for you." and simply does not suht down for such a short.

LIGHTS coming on, on the other hand, tell me that there is a problem and to go look for it.

As a matter of fact, a smaller fuse would do the same thing, but it might not wake up the sleeping LION to the fact that their is an issue out there. LIONS frequently run trains without even watching the layout, him is at the work bench with some other project.

ROAR