Circuit breakers to protect tracks?

[mmagliaro]

What about a 12 volt or so grain of wheat lamp in series on one leg of the feed within each loco . You could paint it black . Would that frig up the DCC , I don't think so . This might protect each loco and be more sensitive that a power supply output CB , though that is also needed .

It would depend on the motor, but it would probably not work well.  A GOW lamp has too much resistance, and during normal operation, would limit the current going to the motor by too much.  For example, in a quick bench test using a standard Atlas motor, at full speed, it draws about 80 ma.  With a GOW lamp in series, the circuit only draws 62 ma, so the motor is being effectively starved of current.  And as a matter of fact, it was obvious that the motor wasn't getting up to full speed.  Further, under load, a standard loco motor can draw more like 200 ma (that's not an uncommon draw for a Kato Mikado, for example).  So the GOW lamp is going to severely limit the power and top speed of the motor.

The way to see this is to think about how much current a GOW lamp typically draws on its own - only about 60 ma.  So if you put that in series with anything, it's going to limit the current to something in that neighborhood.

The reason people used to use 1156 automobile marker lamps for this is that those lamps have a much lower resistance and draw about 2A in a normal circuit.  So they only limit the current to 2A, which is plenty for a model train motor.  It's also true that the resistance of the lamp goes up as it lights and heats up.  So at, say, 0.5A in  typical model train motor, the 1156 won't even begin to light and as such, its resistance will be much closer to zero and it won't affect the motor.  The bulb is supposed to kind of act like a "smart resistor" whose resistance goes up when more current passes through it, causing it to limit the current.

I like the idea of having an individual bulb inside each loco, because the range of allowable current is limited and it might be easier to find a bulb that will simultaneously limit the current below a "melt safe" point and also allow the full motor current to pass under normal conditions.  But when you think about it, there is probably no such device.   Allowing a full motor current of 250 mA (a reasonable number unless you are using a coreless motor), means that you would have to choose a lamp that would limit the current to 250 mA.  But 1/4 amp x 12 volts (worst case during a short) is still 3 watts, and that is a LOT of heat.  A 3 watt resistor (or a 3 watt light bulb) inside a plastic loco is still going to melt things.

The nut of the problem, which has been beaten to death before, is that the power supply to the track can cause serious damage to the inside of a loco if it is channeled through the wrong place during a partial short circuit (some thing wiring or a pickup strip).  If 2A of current flows, all through one fragile wire, the overload device will not trip, a "protection lamp" will only limit the current to 2A, and you will still have melting and damage.

We are trying to find some "intelligent" device that will somehow know that "2A is okay when all the engines are running and the current is being shared across multiple devices, but it's NOT okay if all of it is flowing through a single pickup strip".

The OP's original problem, where a derailment caused loco damage, is not specific to a DCC system.  If you have a partial short through a wheelset on a DC system because it derails at a switch frog, for example, and 1 or 2 amps of current flows through the wrong place, no overload device will save you - not a bulb, not a breaker, not a high-speed "crowbar" circuit, nada.

[C855B]

Don't forget that shorts that melt trucks or wheelset insulators are frequently within the truck itself. Any protection inside the loco is only going to guard against shorts between the trucks.

Case in point - I had a recent truck meltdown on a too-light TOFC flat splitting a frog. The insulated wheel bridged the rails and heated-up rather spectacularly, melting the insulator, heating sufficiently to ruin the truck. Best defense I can think of is to set electronic protection districts at the lowest current point to allow MU consists and no more.

[Bob]

I had this in another thread - the photo shows what happened to one of my ScaleTrains ES44s - burned/melted wires leading from the truck to the decoder, and the decoder was shot as well (just got it repaired).  The until derailed at an improperly lined switch on the lower level, shorting out this section.  But, I was on the other side of the layout happily running a train on the upper level, and did not know about the short until the train I was running entered the lower-level block and came to a halt.  So, this poor locomotive was jsut sitting there getting zapped for goodness knows how long.  I think the NCE unit has something that protects the cab, but a short does not lead to power cut-off to the tracks.  Thus, should I put a light bulb or circuit breaker in line, one for the lower deck and one for the upper, as these are my two electrical blocks?

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[peteski]

That is exactly what I've been tryign to say - the locos internal electric conductors (wires, pickup strips, etc.) are not robust enough to survive high current flow caused by some operator's error. But unfortunately that unsafe-for-a-single-loco current is needed to properly operate the layout.  And, as it has been mentioned,  even if we had breakers installed in each loco, it would not protect the electrical paths contained within the truck itself (or between the trucks of a passenger car.  Running a switch (or in DC crossing a block boundary when block polarity is reversed) will still cause meltdown of the truck or plastic car floor.  The best preventative is simply not to run into that sort of a situation.  Don't text or check email on your smart phone while operating your train. 

[peteski]

I had this in another thread - the photo shows what happened to one of my ScaleTrains ES44s - burned/melted wires leading from the truck to the decoder, and the decoder was shot as well (just got it repaired).  The until derailed at an improperly lined switch on the lower level, shorting out this section.  But, I was on the other side of the layout happily running a train on the upper level, and did not know about the short until the train I was running entered the lower-level block and came to a halt.  So, this poor locomotive was jsut sitting there getting zapped for goodness knows how long.  I think the NCE unit has something that protects the cab, but a short does not lead to power cut-off to the tracks.  Thus, should I put a light bulb or circuit breaker in line, one for the lower deck and one for the upper, as these are my two electrical blocks?

So like I said, the internal loco's wiring is not robust enough to handle a current supplied by the booster or a throttle.  That is a common situation in many N scale models. But that problem is easily fixable (as I suspect that decoder and other parts of the circuitry) are still ok.  But there is no easy way to prevent this from happening again (other than being careful when running your trains)>

[mmagliaro]

In short, Bob, no, there's nothing you could have done.   The overcurrent trip in the booster DOES cut off power to the tracks, but that overload did not trip, because the short you are showing did not draw enough current to trip it.  It only drew enough current to melt those wires.
Adding breakers or an inline bulb would not help.   Those devices would still allow at least a couple of amps to flow without tripping anything, and those thin wires you showed would still have melted.

What we have here is essentially something that home wiring systems are forbidden to have by the electrical code.
Namely, if you put 15A wire in your walls, but you connect it to a 20A breaker in your panel, you could overload that wiring with 18A and burn your house down and the breaker would never trip.

Inside our locos, we have insulated wheelsets, pickup strips, and fine wires that can probably only tolerate 1/2 amp at best, but they are connected to a power source that is protected by a 2A or 5A (or more) breaker.

[C855B]

... I have managed to burn out 3 locomotives - two derailed going through an incorrectly lined turnout (my bad) and by the time I noticed, they were toast.  I have an NCE system and I think a 2 amp power system. ...

I was alerted by a lurker (hi, Scott!) that the circuit breaker in the NCE needs a 5 amp power supply, where a 2 amp supply will not be sufficient to trip the short circuit protection.

It may seem counter-intuitive, but the system is basically OK passing 2 amps as normal running power, but needs more - even for just a millisecond or two - to detect a short. Upgrade your power supply and you'll stop smoking your locos.

[Bob]

Wow!  Not as easy as I thought - completely counter-intuitive to go to 5A (am pretty sure my power source is 2A), but your explanation makes complete sense.  As several of you have noted, if I stop doing stupid stuff like mis-aligning turnouts, I won't have this problem!

[peteski]

  As several of you have noted, if I stop doing stupid stuff like mis-aligning turnouts, I won't have this problem!

Yup - that is the best solution, guaranteed to work. 

[Ron McF]

Deleted (covered in my later post)

[Ron McF]

I have an NCE system and I think a 2 amp power system.

According to NCE's information sheet comparing its EB1 Circuit Breaker and the NCE CP6, https://ncedcc.zendesk.com/hc/en-us/articles/202382035-EB1-vs-CP6-, if you are using a Powercab Starter Set without a booster or Command Station then for short circuit protection "you are limited to the CP6 ONLY."  Remember that their CP6 is just a bank of light globes that trip when the current reaches 1 amp. They don't cut off the current - just limit it to 1 amp.

The NCE EB1 circuit breaker is configurable, but the lowest setting is 2.5 amps, which makes it unsuitable for the 2 amp Powercab rating.

[nkalanaga]

Ron:  That's one of the reasons I have the lights on my accessory supply.  The main bus can handle 25 amps, but the "local" wiring certainly can't.  A short in one of the layout scenery lights would probably melt, and possibly vaporize, the wires.  By limiting the current to each terminal strip to one amp, that risk is reduced, and hopefully eliminated.  And if the main bus shorts, the supply's breaker will blow.  If the short is IN the supply, it also has a fuse on input side.

[Maletrain]

The PSX Power Shield breakers have adjustable setpoints that can be set down as low as 1.27 amps.  So, that does provide a method for some additional protection for a 2 amp NCE Power Cab.  Besides limiting the current to about 1 amp, it shuts it off instead of letting it continue to flow like the light bulbs do at about the same current.  Nowhere as cheap, though.