How can that happen...

How can you get a diesel with the front truck sitting across a gap from the rear truck such that you have a short through the decoder wiring?  It’s not quite as easy as you might think.  If you run a loco into a turnout set against it, as soon as the first wheel crosses the gap you have a short and the booster trips.  If your wiring is in good shape (and if it’s not fix that first).

The situation where I’ve seen the short through decoder situation was a result of running up to the end of a siding toward a turnout lined for the siding, stopping, and the turnout got thrown against the loco to let a train get by on the main.  This was on a layout that had previously been wired for DC cab control and power routing turnouts.  There were gaps a few inches past the turnout, but it meant it was possible to stop a loco so that it looked like it was in the clear, but have the front truck completely sitting on a rail powered from the frog and the rear truck on the other side of the gap.  So, as soon as the turnout is thrown against the engine sitting across the gap - short.

With DCC friendly turnouts it’s much less likely to happen.  DCC friendly turnouts with unpowered frogs, it won’t happen at all.  Or you can use a frog juicer to power the frog, and it won’t happen.

No doubt turning decoder traces into toaster wires can and does happen, but it’s not quite as likely as it might first seem, and it’s easy to arrange things so it can’t happen (at least not by having a turnout thrown against you).

purpose of booster protection circuit

is a separate low power district created by simply using a circuit breaker?

i believe many modelers are under the mistaken belief that because a booster has short circuit protection that circuitry will protect equipment on the layout.   Circuitry in a booster is there to protect the booster.   Separate circuit breakers are needed to protect equipment on the layout.

a power district may need to be divided if the current limit needed to support the number of locos expected to run within that district is high enough to damage a loco when a short occurs.

while shorts are more likely around turnouts, how do you prevent multiple locos from simultaneously crossing turnouts and exceeding the current limit supplying the turnouts.

Is the layout wiring ok?

Thinking about the original scenario I can't help think that this is a result of poor layout wiring (too light cable, poor quality connections) as I have never seen this happen on my layout or our club layout. 

I use circuit breakers on my layout which will cut the circuit at overload before circuit board traces fail or decoder wires overheat.  Wiring and circuit breakers are tested with the coin across the track test to check correct operation - if the breaker doesn't cut right away investigate and fix right away.  

There are of course opportunities for things to go wrong - particularly cross wiring where a piece of track may get feed via 2 different circuit breakers.  A methodical approach works best with good documentation and consistent wire colour use.

Another approach for this scenario is the use of the individual reversers for turnout frogs such as the Tam Valley frog juicers.

Power supply

Greg’s note about using a beefy enough power supply bears repeating.  If you wire up a 10 amp booster to a power supply that’s not AT LEAST as powerful as recommended, you may well end up with a dead short causing enough voltage drop within the power supply itself to keep the booster from tripping it’s protection circuit.  Spend the money to get a nice big transformer with some headroom.

In this discussion... Accept the premise

Hi,

In this discussion, I would ask that anyone commenting, please accept the premise of the article itself (direct quote):

Decoders can be damaged by short circuits,
by a stall over reverse loop gaps and/or across frog gaps. Printed circuit
loco motherboards and decoder wiring traces can become a weak
spot for short circuits.
Also common now are motherboard replacement decoders, as well as
the enhanced motherboards from vendors like TCS with their Keep
Alive technology on board.
Most manufacturers state their boards are protected from short
circuits, but the interconnect traces which carry the rail power can be
small. They’re large enough to power the locomotive, but may be damaged
by a short circuit, even by a brief one. This damage can happen
all at once or be spread over several intermittent incidents.

No one left any article comments challenging base station/booster setting, or the unlikelihood of this happening under "proper" configurations, and I really don't care about that either. I accepted the premise of the article based on general comments I had heard from other sources, as well as the article itself. What I am asking: is it a worthy scheme to protect against individual loco shorts in certain track configurations, as described, perhaps by using a fast acting, lower current breakers/power interrupters/tiny power districts?

GregC: Your comment about ganging all such protected turnouts together also occurred to me early this morning. If you have a district where there was only one loco set operating at a time, it might work, but not in the general case -- agreed, and thanks for pointing that out.

Now with that said, one could conceive of a low cost, fast acting, auto reset breaker that might protect designated small track segments in the event of poor train handling. I am actively wondering about the effectiveness and operation of such a device. It is this possibility I am exploring.

Again, relevant comments in this context, particularly by those who have actually read the article, are most welcomed.

Have fun! 
Best regards,
Geoff Bunza

Fast acting auto-reset breakers

Geoff, have you looked at the frog juicers?  They are pretty much exactly what you’re asking about, specifically for frogs.  If you’re talking for a more general short piece of track, there are a number of options for electronic breakers that are relatively low cost, with auto reset capability.

That’s what I was thinking ... frog juicers

That’s what I was thinking, frog juicers more or less address the main problem at turnouts: powered frogs that you can run with the turnout thrown against you and you don’t get a short.

Another trick is to put an incandescent 1156 tail light bulb in the feeder to every turnout frog. That way the bulb consumes 2.1 amps of the short if you do run the turnout when it’s thrown against you, dropping the short current from 5 amps to 2.9 amps.

So to do what Geoff suggests would be easiest, I think, if you focus on the frog area only since that's where the shorts happen and it's already isolated most likely with gaps on both sides of the frog.

In effect, you create a low amp frog feeder bus and run it around the layout and run feeders to the frogs to that. Assuming you might have up to two locos at a time (coincidence) on a frog and assuming the worst sound loco draws 0.6 amps you're looking at a 1.5 amp booster "district" as the low power frog feeder bus. You could also run that to the frog juicers everywhere.

Or if you run each frog feeder through an 1156 incandescent tail light bulb, that will consume all of the 1.5 amps if there's ever a short at the frog.

Less than Juice

Hi All,

When I first thought about going down this rabbit hole, I was more focused on a low-cost, fast acting, damage preventative -- a mechanism to remove the short. A frog juicer, or a DCC breaker might do the job, but I was looking for a "smaller" fix, potentially for wider application for other potential shorting conditions. Also, I keyed off of the original article, which portrayed the situation without a juicer to reverse polarity. Remember the engineer was accidentally driving his loco into a set of points set against his line of travel. A juicer would not necessarily reverse the switch throw without additional help.

Nonetheless, this short discussion leads me to think that a lower limit, fast acting, current switch might have some value. I have a bit more to consider. I appreciate the comments. A piece, or some form, of the original idea may have some merit. Hmmm...

Have fun! 
Best regards,
Geoff Bunza

Polyswitches?

People vs. switches

It’s not easy to protect people from all the dumb things they do to cause trouble around switches.  A dead frog or a frog juicer will protect you from the short and eliminate the possibility of frying things in the loco.  If you want to throw the turnout too there are things that will do that, like the hare: https://www.dccspecialties.com/products/hare-ng.htm.

But every train has 2 ends and a middle.  There are no engines on the back end for something like the hare to notice if you’re about to back through a turnout set against you.  And let’s not forget the classic throwing the turnout under a train maneuver.  With a sufficient investment in wheelset resistors, block detectors, and automation software you could probably prevent all of them from occurring.  But there is a point of diminishing returns for time/money invested.

For me, I think the sweet spot on the time/money to benefit curve is preventing the short, and let the derailments happen.  And my approach to that is a dead frog with a feeder wire so if it turns out to be a problem I can had a frog juicer easily later.  On my previous two layouts dead frogs were not an issue once I got point jumpers in, but adding a frog feeder leave unconnected under the benchwork when laying track is cheap and easy future proofing.

Second the prof idea

I was thinking the same thing.  I am 3 weeks behind on MRH forums due to business travel and family.

I use frog juicer but Geoff raises valid points.   Something like  a fusible link on the decoder board.  I have them on both battery banks on my sailboat.  They are located close to the battery terminals and are the fail safe mechanism if the circuit breaker don't limit the current.

A battery fire while on the open water makes for a very bad day.