How DCC operator can make a mess and fix it

[Onizukachan]

Wow. Thanks for sharing the pictures of the carnage Carl. I was there, and something was tripping the breakers but no one could find it, till Carl noticed his had crept.

[peteski]

Wow. Thanks for sharing the pictures of the carnage Carl. I was there, and something was tripping the breakers but no one could find it, till Carl noticed his had crept.

Hmmm . . . I thought the whole reason for the carnage was that the breaker *DID NOT* trip. 

[boisecity]

Hmmm . . . I thought the whole reason for the carnage was that the breaker *DID NOT* trip. 

The same thing happened to a friend of mine and we always wondered how it happened and why the breaker didn't trip.  Peteski's earlier post explains the how.  Could the breaker not tripping be a result of a reduced current due to dirty track and wheels?

John F

[cgw]

How far away from the command station or booster was it?  On long runs the buss wire acts as a resistor and the command stations/boosters do not trip from a short.    Do a quarter test.   Put a quarter on the track where this occurred and see if the unit shuts down.  If the system shuts down then it is working.   If it does not you should modify the  buss wiring  to a heavy gauge or add additional power districts/boosters.     On some DCC systems the short is detected and the unit cuts off power.   After a brief period of time it check again to see if there is a short by turning on the power.  If it still detects, the unit will shut down again and the process  will repeat over and over till the short is removed.   That will eventually cause the  truck to heat up and melt.   

[boisecity]

It is a medium layout, four sided about 10 x 12 feet.  A coin test at all parts of the layout tripped the circuit breaker, a PM42.  So it's still a bit of a mystery unless, as you say, it is the repeated on/off that caused it.

John F

[Maletrain]

I think this is mainly a DCC issue, for 2 reasons.  First, DCC allows locos to creep at almost imperceptible speeds because of the BEMF capabilities provided to give full-voltage jogs to the motors.  And, throttles can be set to start creeping at the first speed step.  So, an accidental bit of a nudge to the throttle knob can start the creep, say when putting the throttle on the layout or into an apron pocket.  Second, DCC always has full track voltage, so a short on DCC with an engine creeping is going to draw much higher current than a short on DC where creeping occurs at a low voltage on the track, itself.

So, it seems to me that the layouts need to be designed to deal with this issue.  Keeping tracks and wheels clean is a good, but not usually fully attained goal.  I would not count on achieving it to protect my locos.  To me, the best solution is mechanical switches that kill power to tracks where locos will be parked for extended periods.  Roundhouse stalls, yard pockets, and other such locations where locos will be "left" without continuous attention seem like they warrant that type of protection. 

Another part of the protection could be a practice of electronically disconnecting the throttle from the locomotive whenever it is left unattended.  "Dispatching" the loco from a Digitrax throttle is a good idea, but not all systems have a "dispatch" type function.  With my NCE system, I try to "recall" a non-existent loco number when I set a throttle down or put it in a pocket.  But, as with all such practices, they are often forgotten by visitors, and even layout owners, when there is a distraction. 

[carlso]

CGW wins the test. He has identified exactly what happens.

First off, we have two main line busses. Each main is divided into 6 power districts and we have three PM42 each with 4 boards, so we have a protector for each power district. We have done the quarter test but nothing shuts down. Onisukachan stated "something was tripping the breakers". Partially true but the PM42 was off showing the red indicator for a short. As CGW stated they stay off, for a period, and then turn back on. They will continue this off/on game until something gives and, in this case, it was the loco truck or the short causing problem is removed. The layout has caused this several times. There is a problem somewhere which we will be tackling today. By the way the gurus have attempted to adjust the PM42's to stay off for a longer period with no success. I am not a fan of the Digitrax stuff so there may be better power protection out there.

Thanks for the comments and help,
Carl


PS:

I just read Maletrain's reply and he, IMHO, is exactly correct in every respect. The mechanical switches for 3 sidings will go in today. For the throttles in a pouch, I think that may be the cause in my case. The two throttle knobs rest on the material and it does not take a lot of effort to move the knob. I think that somehow I tweaked that loco's throttle to "1" and it slowly crept to the switch.

[mmagliaro]

Carl,
I'm really curious about this part...

"By the way the gurus have attempted to adjust the PM42's to stay off for a longer period with no success."

Looking at that PM42 board, one fairly simple brute force mod you could make would be to use the lines to the RED "trip" LEDs to trigger an external  latching relay that would just flat-out shut off that power district until you manually reset it.  I'm not a fan of auto-resetting overload protection, exactly because of things like this.  I'd rather have to push a button.

The "latch" circuit would require a small amount of electronics, like a transistor and a couple of other parts, plus the relay.   If you've got electronics "gurus" at your disposal, it would be easy to build on a little board and wire it into that PM42.

The cut-off switches you are proposing are fine, but are still plagued by human error.  If somebody forgets to throw the switch when they park an engine, or the switch gets bumped, you still have the problem.  Overload protection isn't supposed to rely on humans taking certain actions.  It's supposed to protect your equipment no matter what happens.

[narrowminded]

I had asked this earlier but thought I might ask again as it wasn't answered.  Wouldn't this specific issue, not the shorts in general but the specific instance where the loco unwittingly creeps onto a switch, be covered by the use of a frog juicer on the switches?  I ask because to me it would make another case for the expense of using them.  The layout I'm running on uses them on all turnouts and I would like to confirm that my thinking is correct, that a short of this type wouldn't happen with frog juicers.  It appears to me that this is correct. 

[rodsup9000]

I had asked this earlier but thought I might ask again as it wasn't answered.  Wouldn't this specific issue, not the shorts in general but the specific instance where the loco unwittingly creeps onto a switch, be covered by the use of a frog juicer on the switches?  I ask because to me it would make another case for the expense of using them.  The layout I'm running on uses them on all turnouts and I would like to confirm that my thinking is correct, that a short of this type wouldn't happen with frog juicers.  It appears to me that this is correct.

 Mark,

 They will keep from melting the trucks, but you will still have a problem of the loco derailing on the opposing thrown turnout and doing damage and possibly still melting a truck.



  I've been using 1156's (not 1157's that are a duel filament bulb) and now 3156's for over ten years and I've still manage to melt one truck. It just takes awhile longer to melt as the bulb is taking most of the energy. But I have a big bright light telling me that something is shorting and I can shut down that booster down till the short is found..


 I really like Max's idea and might explore a way to do this.

[carlso]

I am going to reply to each of the above posters and BTW, I do appreciate comments and suggestion.

 Max:

I totally agree with what you have posted, I am however installing simple toggle switches that are recessed into a 3/4" pvc cap and that unit will be set flush into the facia, so no accidental turning switch off or on by bumping it. After being bit I will not take any chances. Actually, my stupidity or being caught up in the open house excitement I failed to dispatch that loco from my throttle. Had I done that there would not be an issue.

I agree with your idea of not relying on an auto reset gadget as the PM42. What happened is, yes the 42 detected a short and went into red mode as it should. The problem is it does not wait long enough to reset and comes back on and them immediately off and it will continue to do so until somebody wakes up and finds the problem and removes it from the rails, if it does it long enough it will melt plastic. Ask me how I know. Here is the real killer about this entire mess and that is that nobody knew the power districts by a number so therefore nobody knew where the problem was, that was being pointed out by the 42. Sort of screwy, right! !

Mark:

To attempt to answer your concerns I don't even know how to begin. I for one, and most likely no other member, even knows what a frog juicer is. I think narrowminded hit it on the head.

To address our wiring problem, today two guys went around and identified each power district and marked them, to be identified on the layout somehow. The PM42's (3 of them ) had a total of 12 districts available and actually only 10 have been utilized. Our club purchased some NCE thingys that are bulbs and tested them out today and they will be installed. I try to stay out of the discussion on the electrical wiring and such. If I had wired originally it would be much different.

Now, my loco problem was caused by me. As stated earlier, I did not dispatch that loco after parking it. I should have ! ! ! Duh ! Also, I carry the 402 throttle in a home made cloth pouch hung around my neck and I am positive that I inadvertently moved the throttle knob for that engine. I, like most of us, like to see the units creep vvveeerrryyyy slowly at a speed step of "1". I am sure that is what caused the unit to move to become a real problem that was not easily found with our set up ? ? ? Had I dispatched the thing it would have never picked up the "1" command ! !

Things will be fixed and soon,
Carl

[peteski]

The question  I have is whether dispatching a loco which is still receiving speed >0 commands will stop it, or will it continue running at the last speed step setting received?

I know in NCE when another (existing or non-existing) address is selected on the throttle, that will leave the previously controled loco moving at the speed step it was on. WIll not stop it.

[boisecity]

On the Digitrax Super Chief system, and I assume most other Digitrax systems, there is an Option Switch - OpSw 15 which can be set to force a loco to speed 0 at the time of purging.  Purging is set initially at 200 seconds, when unattended locos will be purged to make room for other addresses to be selected.

So theoretically a creeping (unattended) loco will be stopped after 200 seconds.  Would this be enough to prevent any melting?

I had this switch set on my layout so that locos would stop if an operator went home with their throttle without zeroing the loco.

[Onizukachan]

Nce cp6’s Carl?

[carlso]

Richard - yes I think they are cp6's.

Perte - Your guess is as good as mine. I was told on the TRW that that would stop it from receiving commands until the address is called up again. One of our members also said that is what he does at home. I will try this, perhaps I can build in some peace of mind.

boisecity - Thanks for that tip. I shall get out our wonderful D-trax manual and try to figure that out. I don't think any of us are aware of that opSW 15 setting.

Thanks all for the input.

Carl