# Short-circuit induced DCC Runaways!



## Tom Lapointe (Jan 2, 2008)

*Curious *to know if anyone else using the NCE PowerHouse Pro 10-Amp system has experienced this phenomenon







; about a week or so ago, I was getting set up for an afternoon's operation. I had 3 Bachmann locos on the track - my 3-truck Shay, 2-6-6-2T Mallet, and "Centennial" Mogul (minus it's Phoenix-sound equipped tender, which I hadn't brought out of the house yet - *fortunately, as it turned out*). The Shay (with an Accucraft short D&RGW caboose coupled behind) & Mogul were sitting on the 2 lead tracks to my A-frame turntable; the turntable was aligned to the track the Mogul was on, the loco facing towards (but not on) the table. The Mallet was sitting on the mainline; it & the Shay were both facing away from the turntable. The NCE DCC system was powered on, getting the sound systems going. I was placing some Accucraft & Bachmann "Spectrum" 1:20.3 cars on the main by hand as I carried them from the house, making up a freight behind the Mallet. While putting an Accucraft flat on the rails, I caused a *momentary short *across the frog of a turnout; without warning, *all 3 locos lurched to full throttle in the same direction! *







(The Mogul was facing in the opposite direction of the Shay & Mallet). I grabbed the Mallet to keep it from jacknifing it's train all over the place, but the Mogul & 3-truck Shay (both out of easy reach







) *raced towards the turntable! *







(Which has a *2-foot drop to the ground opposite the lead tracks! *







). I had a piece of 2X4 pressure-treat positioned at that spot just under the "grass" carpeting I laid over the yard last year (but hadn't gotten around to screwing it down yet!). The Mogul ran across the table, it's sharp-pointed pilot managed to shove the block aside, it went over the edge & hit the ground.







The 3-truck Shay (by far my most powerful loco), running in reverse, actually shoved the Accucraft caboose *up the turntable's A-frame bracing wires *







, stripping off some of the brake rigging from the rear truck, before coming to a stop with it's drivers spinning madly in reverse. Somehow, while restraining the Mallet, I managed to reach down to the tote box I keep the DCC system & power supply in, yanking out the dual banana plug that connects the track power feed to the booster output, & preventing any *further carnage. *









I actually got "lucky"







a bit in terms of the rolling stock damage; the Mogul actually hit in a tuft of thick grass which cushioned it's fall, it's only damage was a broken cab step casting (easily replaceable)







. The Accucraft caboose brake rigging damage was repairable with gap-filling ACC, the glue joints only visible if you look underneath. The Shay, Mallet, other rolling stock, & relatively delicate turntable were all undamaged; I rerailed everything, power-cycled the NCE DCC system befor I reconnected the track, & operation proceeded *normally *for the rest of the afternoon.

What has me concerned a bit is that *I've seen this occur once before *







- we had a large party in progress in the yard, several trains were on the railroad (but stopped at the time), *when everything suddenly took off full throttle without warning! *







(Fortunately at that time, I was able to shut down power *quickly, *before any collisions occurred). I'm concerned *I might not be so lucky next time *







- (and we have another large party around the railroad planned for this afternoon!







) Anyone else had experiences like this







*Tom*


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## Greg Elmassian (Jan 3, 2008)

probably a combination of analog mode enabled and some stray DC on the rails... 

never had it happen on my NCE system, usually from old style decoders. 

what decoders are in the other locos (I know what's in your shay) 

by the way, keeping a throttle handy and punching the red button 3 times is a good plan. 

Regards, Greg


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## Tom Lapointe (Jan 2, 2008)

That's an interesting thought about having the analog mode enabled, Greg! (I do enable analog operation, at least on the decoders I've programmed myself). The Bachmann 3-Truck Shay has the factory Tsuanmi / "Quasinimi"







sound decoder installed & other than the chuff rate (which I "maxed out" the CV on to make it more believable for a Shay's fast exhaust rate), is at *factory default settings *otherwise. (That's even why it's *"#3" *on the "Watuppa Railway" roster - vinyl lettering was a *lot cheaper *than buying a programming track booster just for *ONE *loco!







). The other 2 locos *each have different decoders - *the Mogul has a *Digitrax DG-583S *(which is the decoder type I've used in most of my locos), while the relatively-new Mallet has a *QSI Sound decoder *installed (my first venture into QSI, it was attractive specifically because it *was "plug-&-play" *(although I wish Bachmann had pre-installed a speaker! - It was a pain having to disassemble the loco substantially just to install a 3" speaker under the boiler). I know I won't have time to reprogram all the decoders before our party tomorrow; just have to keep an eye on things. Fortunately, it has *not *been a frequent occurrence (think it's occurred only 2 ~ 3 times over at least a year) - but that's also why it can *sneak up *on me!







Thanks for the suggestion!







*Tom*


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## George Schreyer (Jan 16, 2009)

It is unlikely that a short caused the issue, but if the DCC data gets corrupted for some reason and the decoders can't determine that the signal on the track is DCC, they will just rectify the signal to DC and then think that they should go full blast if analog conversion is enabled. 

This is actually a somewhat common occurrence in DCC systems. 

If you don't actually use analog conversion, turn it off. Set CV29 to 2 instead of the default of 6 (or whatever other value you need)


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## Cougar Rock Rail (Jan 2, 2008)

Wow! That's bizarre, but George's explanation makes sense. What I don't understand is why the NCE central station didn't sense the short and shut the whole thing down? 

Keith


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## Greg Elmassian (Jan 3, 2008)

Too brief, or not 20 amps at the booster. 

Good point though, always good to do periodic short tests to make sure you deliver enough current to trip the NCE booster. If I remember right, George tested it and it trips around 20 amps. 

If your power supply won't supply enough current, or too much resistance, it will happily pump out 10 amps all day, right though your short. 

Regards, Greg


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## Tom Lapointe (Jan 2, 2008)

*Greg & George, thanks for both your suggestions. *







Sounds like disabling the analog mode on most of my locos is the way to go.







(George, your suggestion that the decoders may interpret the garbled DCC signal from a short-induced transient as DC makes a *lot of sense). *I *rarely *operate on conventional DC these days; although at our party this afternoon, a friend who was one of the earliest garden railroaders in this area invited me over to operate on *his *railroad (which is *entirely analog DC operation *) next weekend.







His being a much older railroad, he has a fair amount of *R1 curves *







, so most of my 1:20.3 rolling stock will probably be staying home; I'll most likely bring one of my Phoenix-sound-equipped 2-truck Shays, Climax, or Heisler over, as I know they will all *happily run on R1. *







(I might even try bringing over the big Bachmann Mallet, as I was *amazed *







to find that it was a flexible as a snake around the R1 curves of my old indoor layout - until I tried to run it through a tunnel portal on an R1 curve & found the cab swing wouldn't quite clear the portal!







).

By the way, operation this afternoon for the guests was about as flawless as I could ask for - only "incident"







was a *very low-speed rear-end collision *between the 3-truck Shay & a freight hauled by the Mallet when I forgot to throw a turnout from the passing siding back to the main







- speed was so slow that the 3-truck Shay just *shoved the Mallet's entire train a few feet further down the track *







- didn't even derail anything!







(I *gotta *come up with some means of determining turnout position from a distance, such as prototypical switch-stand mounted "flags" or working switch lanterns). Otherwise, didn't even have a *single derailment all afternoon. *







Ran a couple of RC-controlled live-steamers as well (with the NCE system powered down - *both *locos - Accucraft Mich-Cal Shay #2 & "Ruby" #11 2-4-2 with 4-wheel tender have uninsulated drivers). Even the Ruby was better-behaved on the grades than usual (I'm finally getting the hang of keeping the speed on it well-regulated downgrade via RC).







*Tom*


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## TonyWalsham (Jan 2, 2008)

Tom. 
If you are taking a DCC equipped loco to run on an analog DC track make sure the track controller is linear DC and not PWM. 
PWM can play havoc with DCC decoders.


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## George Schreyer (Jan 16, 2009)

SOME forms of PWC will freak out SOME decoders. Large scale Digitrax decoders will run quite happily on the PWC made by the trackside RX but freak when driven from an old 5490 operating as a trackside RX. 

- gws


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## Tom Lapointe (Jan 2, 2008)

*Valid point on PWM, *Tony & George, & fully understandable.







Shouldn't be a problem at my friend's layout; he was one of the *very first *garden railroaders in my area, most of his rolling stock is LGB. Unless he's since replaced it (which I highly doubt), his power supply was the old reliable *MRC 6200 - *about as *analog *a pack as you could get, using standard block control.







At *most, *it *might* have the capability for the old 1/2-wave DC method of "pulse power", but I don't ever recall having ever seen it used in any manner other than *straight DC power.* For the most part, he runs *smaller LGB locos, *although I know he *does have an LGB 2-6-6-2 Mallet *(not sure if it's the *Sumpter Valley *tender version, or the *Unitah *tank version). In fact, does anyone know if the LGB US-prototype Mallets were *factory-equipped with MTS decoders*







(I'm not "up" enough on late LGB products to know for certain whether some of the higher-end locos came with MTS from factory, or was it an *option*







). Reason I ask is, if they *are MTS-equipped, *he might be able to run them on DCC here at my layout (this is assuming that MTS decoders are compatible with the NCE system). Thanks again for the suggestions.







*Tom*


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## Cougar Rock Rail (Jan 2, 2008)

Tom, you will have to check under the loco on the motor block of the Sumpter Valley to see if it has a decoder built in--some did, some didn't I believe. You will see a silver (if my memory serves me right) sticker that says digital/MTS on it. If it has one of the onboard decoders it will work on any DCC system. You will just have to find out what the address is (or give it a new one) and away you go. 

Keith


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