I've had my new Digitrax DCC installed for only a few days and I must admit, regardless of the somewhat, sometimes confusing, instructions and procedures (ie: learning the initial in's and out's as with anything new), I'm enjoying this.
However, there is one thing that really puzzles me. For all the hoopala I've read and heard about the issues of running DC equipment on DCC, like the "singing" or chattering from DC locomotives, or issues regarding lights, I have (so far) experienced absolutely none of these issues. Even my oldest and cheapest DC locos run quieter and more smoothly on DCC than they did with regular DC. And the lights stay on full all the time which is nice. And the passenger cars with the DC lighting modules work just fine on DCC too. And I can run DC locos on the same track at the same time as DCC locos and control both independently at the same time as if they were all DCC.
About the only excuse I can think of is that much of information about the problematic issues of running older DC equipment on DCC is, with current DCC equiment of today, is a myth. Maybe the older DCC systems are somewhat different or don't have the compatibilities that more recent DCC systems have?
I'm having none of the issues I thought I'd have, which is one of the reasons for not making the change sooner. If I knew I could pull out my old Model Power Shark Noses and run them concurantly on DCC with DCC locos, and that they would run smoother and quieter than on DC I would have done this a long time ago.
You can indeed run DC engines on DCC...what you can't do is leaving them on the track when they're not running.And this isn't possible with every DCC system.
ArtoMaybe the older DCC systems are somewhat different or don't have the compatibilities that more recent DCC systems have?
A lot of those issues had to do with open frame and other somewhat dated motor technology. This tended to be rattle cans.
Keep in mind you're on Digitrax. NCE, for instance, doesn't bother with DC support. With sub-$20 decoders available, that's not missed much by many of us.
In large part, this is due to the fact that you still can only run a single DC loco on DCC systems that support DC running AFAIK.
Mike Lehman
Urbana, IL
If you leave a DC loco just sitting there not moving, you will eventually fry the motor - older, hefty stuff will probably take longer to damage, because all that mass of metal makes a good heat sink. But as long as you don;t leave things just parked with power, it's not dangerous to the loco. I wouldn;t run like this permanently - eventually you'll want to put decoders in all your locos so you can actually control them independently.
One thing to watch out for are things with lights. If they use incandescent light bulbs, they could get too hot and melt the plastic, or just burn out. Those made for DC operation don;t expect that you run constantly at full throttle, and so the voltage used for the light bulbs is such that they come on at a reasonable speed yet can still handle bried periods of full throttle - which in DC is usually only 12V. The DCC track voltage for HO is usually closer to 15V, so the bulbs are getting over their rated voltage, plus it never goes down - it doesn't vary like DC power. A 12-14V bulb in direct contact with the shell of a loco or car and running for hours at a time WILL melt the plastic, sooner or later. Heck I've seen that long before DCC even when the loco wasn't run at full throttle all the time. Something to keep in mind before you see a big hole melt in the roof of one of your favorite passenger cars.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
mlehman Arto Maybe the older DCC systems are somewhat different or don't have the compatibilities that more recent DCC systems have? In large part, this is due to the fact that you still can only run a single DC loco on DCC systems that support DC running AFAIK.
Arto Maybe the older DCC systems are somewhat different or don't have the compatibilities that more recent DCC systems have?
Just to clarify, do you mean "just ONE DC loco" or is there some kind of limitation to using more than ONE DC loco unit (as in a consist)?
Because quite frankly, for the time being, that's all I need to do. I was under the impression that locos like my fleet of older Model Power shark noses would be shelved or have to be upgraded to DCC if I wanted to use them on DCC. I don't want to invest the time or money in those as there are much better/nicer models of those available now (which are an even more expensive investment and not a priority at the moment).
The other issue regarding leaving a DC loco on the track, how long is a long time? 30 seconds? 30 minutes? hours? I have no intention of just leaving the DC locos just sitting somewhere on a siding. I only have one siding at the moment and that is an isolated block with a toggle switch so I can turn off power to it. Anything that is a "favorite" (lighted passenger car or loco) will be upgraded to DCC first.
All I'm saying is that with Digitrax supporting DC locos, it makes the transition easier with less pressure to change everything over to DCC so I can continue using it. I didn't know it would work so well. Some of this stuff I'll probably never convert to DCC so it's good to know that I don't have to and won't destroy anything as long as I'm careful.
Very good now that we have more details.
When a DC only loco sits still, the motor armature oscillates at the DCC frequency. The point at which the motor brushes contact the armature gets quite hot. Arcing will be occurring at that point because the brush and commutator contact is interrupted at the DCC frequency. Any break in contact will always result in a spark.
I used a infra red temperature scanner some years ago and saw the temperature rises as the motor was stopped but still connected to the DCC signal. I did open frame and can motors. The scanner can sense though the can motor shell.
Your mileage may vary as some would say here.
Like Randy said, some DCC systems as high as 15 volts and standard 12 volt light bulbs will get quite hot. Under DC control, a 12 volt bulb will never get to see 12 volts.
I did that some years ago with an old MRC2k. I could bring a DC helper steamer up behind a DCC freight set and help it up a grade. The helper was an HO 0-8-0 Camel based on MDC old time 2-8-0 with open frame motor. Great fun.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Arto mlehman Arto Maybe the older DCC systems are somewhat different or don't have the compatibilities that more recent DCC systems have? In large part, this is due to the fact that you still can only run a single DC loco on DCC systems that support DC running AFAIK. Just to clarify, do you mean "just ONE DC loco" or is there some kind of limitation to using more than ONE DC loco unit (as in a consist)? Because quite frankly, for the time being, that's all I need to do. I was under the impression that locos like my fleet of older Model Power shark noses would be shelved or have to be upgraded to DCC if I wanted to use them on DCC. I don't want to invest the time or money in those as there are much better/nicer models of those available now (which are an even more expensive investment and not a priority at the moment). The other issue regarding leaving a DC loco on the track, how long is a long time? 30 seconds? 30 minutes? hours? I have no intention of just leaving the DC locos just sitting somewhere on a siding. I only have one siding at the moment and that is an isolated block with a toggle switch so I can turn off power to it. Anything that is a "favorite" (lighted passenger car or loco) will be upgraded to DCC first. All I'm saying is that with Digitrax supporting DC locos, it makes the transition easier with less pressure to change everything over to DCC so I can continue using it. I didn't know it would work so well. Some of this stuff I'll probably never convert to DCC so it's good to know that I don't have to and won't destroy anything as long as I'm careful.
Yes, that is the 'limit' - you can only run one DC loco at a time. It's not a limit imposed by DCC, or Digitrax, it's the exact same thing as if you had only 1 DC power pack hooked to the layout. You can only run 1 DC loco at a time.
How long is too long? It really depends on the loco, more specifically, the motor. A larger heavier old motor can take it longer than a modern lightweight can motor. One specific caution, some high end brass from the 70's on and a few modern locos, like the new Kato F40PH, have coreless can motors. They can NOT be operated on DCC without a decoder - the motor will overheat in seconds. You would know if you had any of these motors - the locos with them would be your most superior running locos, and it's generally a selling feature so it's unlikely that having a coreless motor would go un-noted on the box or by the seller if you picked one up second hand. These motors need as close to pure DC power as possible - very old DCC decoders can even damage them, but any current decoder would be fine. Early on, decoders used low frequency PWM motor drive, which could make motors buzz. This too caused heating in the coreless motors and could damage them. All modern decoders have a high frequency drive, "silent running" or "supersonic" or some other marketing term, but it all means the same thing. These decoders are safe to use with coreless motors.
Having the siding with a toggle to isolate it is a good thing. As long as you shut off any DC loco when not actively using it, you will be fine.
I was so impressed by the DCC/system and locos - I dumped all my DC ones. However, I did not have a big investment in them so it was easy to do. In fact I made money selling off my old DC locos. Ebay is great for reaching collectors - I know that some newbies are always looking to get some DC locos for their first layout so its a win-win. I did it myself.
Anyhoo, DCC is the way to go, I love those CV's to change stuff you dont like.
Chris.
Loco Guy - is a state of mind - not an affinity to locomotives.
Sit back and enjoy your track...
Being out of the hobby for 16 years, I am gobstruck (waited 60 years to use that term) by this discussion. All the descriptions of DCC are of a high (relative to DC) current with pulses, yet to run a DC and DCC loco concurrently, the DCC must be operating at a lower and varying current, no?
Henry
COB Potomac & Northern
Shenandoah Valley
rrinker Arto Just to clarify, do you mean "just ONE DC loco" or is there some kind of limitation to using more than ONE DC loco unit (as in a consist)? Randy Yes, that is the 'limit' - you can only run one DC loco at a time. It's not a limit imposed by DCC, or Digitrax, it's the exact same thing as if you had only 1 DC power pack hooked to the layout. You can only run 1 DC loco at a time. --Randy
Arto
Randy
So if I put two or three DC locos together on one track ~ you're saying I can't do this? And if that's the case, why not? (I haven't tried this yet, just one at a time, and they all ran better on DCC than they did on DC)
BigDaddy Being out of the hobby for 16 years, I am gobstruck (waited 60 years to use that term) by this discussion. All the descriptions of DCC are of a high (relative to DC) current with pulses, yet to run a DC and DCC loco concurrently, the DCC must be operating at a lower and varying current, no?
No, the current will always vary with the load regardless of DC or DCC.
From what I understand (just a little at this point) it has something to do with "zero bit stretching" and using the short (two digit) address of "zero" on the throttle which is not a valid DCC address for DCC locomotives. The throttle's speed & direction commands are used to directly modify the DCC track signal waveform and timing. It basically fools the DC motor into thinking it's seeing DC. As mentioned by others further up the thread apparently not all DCC manufacturers support this technique.
No, if you put 2 DC locos on the track and run them, they will all move together, just like they did under DC. You can't get independent control without adding a decoder.
Let's leave the 'current' part out, just because the booster is capable of 5 amps doesn't mean it 'pushes' 5 amps on the tracks. That's not how electricty works.
The DCC sisgnal is a square wave, centered around a common point. It is, when NOT running a DC loco, symmetrical - it is positive the exact same amount of time it is negative. Thus the measured DC component is 0 volts. Think about it: +5, -5, +5, -5, +5, -5. Add those all together. Sum is 0. So a DC loco will not move.
The DCC specifications are such that a pulse under a certain duration is the 1 bit for a binary signal, and anything longer than a certain amount is the 0 bit. Typically the 0's are all the same size, just longer duration than the 1's. On systems that allow you to run a DC loco, when you select the DC loco and increase the throttle, either the top half or the bottom half of the 0 portion of the waveform is made longer. If it's the top half, you have a net positive DC voltage, if the lower half, a net negative DC voltage. Such as: +5, -5, +5, +5, -5, +5, -5: add those together, you get +5. Now the DC motor 'sees' a DC voltage across the motor and can turn.
The peak values for the DCC waveform remain unchanged. Only the duration changes. A DCC decoder on the same track continues to see the same DCC signal, the extra long 0 bits do nothing other than slow down the total overall number of packets that can be sent in a given time, which is why if you are trying to run a lot of DCC locos, running that one DC loco can slow down the response of all the DCC locos. But if you're talking 5-10 DCC locos plus the DC loco - no one will notice.
Ken G Price My N-Scale Layout
Digitrax Super Empire Builder Radio System. South Valley Texas Railroad. SVTRR
N-Scale out west. 1996-1998 or so! UP, SP, Missouri Pacific, C&NW.
Below is what the waveform looks like. A volt meter on the motor contacts would see varying DC, depending on speed selected for DC loco, and constant AC voltage.
http://members.shaw.ca/sask.rail/dcc/DCC-waveforms/DCC_waveforms.html
Since I just got myself an oscilloscope to play around with, I had to note those pictures show some really horrible undershoot on the square waves. I haven't dug out my Zephyr to give it a go and see what the waveforms look like on my scope yet. One more thing i didn;t get around to doing over a whole 2 weeks off, because my knee is acting up and I can barely walk, so not going to run downstairs and climb around the piled boxes to dig out my DCC stuff.
If a DC engine runs OK on DC (and better on DCC using the "zero" ID), they'll run even better if you add a decoder. It can really make an improvement. I had an old Athearn F7 that ran pretty well but slowed way down up the (slight) grade and speeded way up on the downgrades. With a decoder with Back EMF, that was eliminated, and it ran the same speed up and downhill...plus started and stopped much more smoothly, thanks to the momentum settings. So I'd suggest, before spending $200 or whatever for a new engine, spend $25 for a good decoder and see how the old engine runs first.
Randy is right about the ability to "run" more than one DC loco, but not independently "control" more than one DC loco. This mode is back to "running the track," our old description of DC vs. "running the trains" on DCC.
One DCC feature that will not work with DC engines is autoreversers. They will enter the loop, get to the other end and ping-pong back, because the autoreverser flips the polarity of the loop. As often as not, this won't happen fast enough and the engine will sit at the gap and generate a short.
I've got a Lenz system, which does support running a DC engine. I've tried it and I didn't like it one bit.
It takes an iron man to play with a toy iron horse.
IF your layout is already wired for DC, i.e. blocked with switches where needed to distribute power to control myultiple DC locos using more than one powerpack/throttle, there is another solution. The MRC Tech 6 is a DC powerpack that has the ability to also address and control a DCC loco. AFAIK, the Tech 6 controls just one DCC loco at a time, but you could install multiple Tech 6 in each of your DC cabs and do more than one DCC loco at a time that way, so long as you're willing to send them power by using the block power toggles to assign the cab to the loco.
If you haven't built a DC system yet, you're probably better off just heading toward DCC if that's your goal. But this does offer a solution to the OP's initial misperception that Digitrax allows mutiple DC locos to run, because the Tech 6 offers a way to do just that if combined with typical DC block/cab wiring.
MisterBeasley Randy is right about the ability to "run" more than one DC loco, but not independently "control" more than one DC loco. This mode is back to "running the track," our old description of DC vs. "running the trains" on DCC. One DCC feature that will not work with DC engines is autoreversers. They will enter the loop, get to the other end and ping-pong back, because the autoreverser flips the polarity of the loop. As often as not, this won't happen fast enough and the engine will sit at the gap and generate a short. I've got a Lenz system, which does support running a DC engine. I've tried it and I didn't like it one bit.
If you look at the text accompanying the scope waveforms Rich posted, it may explain why running a DC loco on Digitrax actually works pretty well. It hints that Digitrax may throw in some extra 0 bits when running DC. instead of stretching the 0 out to the NMRA allowed limit. One long stretched 0 will make for a much more harsh 'buzz' in the DC motor than multiple shorter 0 bits. Sort of a variation on the high frequency motor drive from the decoder. Long low frequency vs shorter higher frequency. Net DC voltage is the same.