# I'm confused???



## dozer (Jan 2, 2010)

I keep reading about people saying most dcc systems allow at least one dc engine to be used on the layout. Well, if this is true how does it work? I mean, in a dc layout the voltage to the track is supplied using the throttle, in dcc the track always has nominal voltage, but the dcc system comunicates to the decoder in the engine. So, in theory, if you put a dc engine on the track, and turn on the power supply, then engine should just take off around the track at an uncontrollable full throttle, correct?


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## bradimous1 (Mar 3, 2010)

just got a mental picture of this... hilarious in this empty head of mine.

I have to say that your theory seems spot on to me.


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## dozer (Jan 2, 2010)

Wow really? Everybody keeps telling others that you can run dc engines on dcc tracks, but NO ONE has any explanation for this? Makes me think then that those who say it can be done don't actually do it therefore have no proof.


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## Reckers (Oct 11, 2009)

I don't know Jack about DCC, but I love the image of the engine racing hysterically around the track! How about adding some background: Jethro Tull's "Locomotive Breath"? "Old Charlie's stole the handle, and the train it won't stop going, no way to slow down!"


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## tjcruiser (Jan 10, 2010)

dozer said:


> Makes me think then that those who say it can be done don't actually do it therefore have no proof.



Hee hee! It's a big myth ... a cleverly orchestrated ruse! Bigfoot, Loch Ness Monster, and DC running on DCC! They're all in cahoots!

Seriously, I don't have a clue ... your logic does seem quite reasonable to me. I'll "stay tuned" to see what the experts decree!

TJ


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## IlliniViking (Dec 13, 2009)

I'm can't explain how it works, but I run a DC loco on DCC. I know you can only run one DC loco, as it uses address 00. Also, when I put the DC loco on the track it hums the whole time the track is on, whether I have it selected or not. It also runs slower than my DCC loco, but I guess that could be the loco itself.


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## bradimous1 (Mar 3, 2010)

sounds to me like it probably isn't very good for the engine... but that is just my instincts telling me that, not any factual basis


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## IlliniViking (Dec 13, 2009)

bradimous1 said:


> sounds to me like it probably isn't very good for the engine... but that is just my instincts telling me that, not any factual basis


Yeah it's recommended not to leave the DC loco on the tracks when you are not using it.


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## tjcruiser (Jan 10, 2010)

Gents,

I did a little reading, and it all comes down to something called "zero stretching" which is essentially breaking the conventional constant-voltage DC power into a stepwise series of square-wave power pulses.

In DCC, power sent to the rail is a generally-symmetric square wave, i.e., short positive pulses followed by short equal-and-opposite negative pulses. The TIME of these pulses is used to send control signals to the trains, much like the funny bar-code things that we see at the store when we buy anything.

However, with "zero stretching", an intentional "break the rules" trick is played ... the duration of a positive pulse is stretched so that it is longer than it's negative-pulse mate. They don't cancel each other, but rather add a net sum greater than zero (in the positive voltage direction). That makes a conventional DC loco go. To go faster, the DCC system extends the biased offset between the positive and negative pulses to yield an even-longer net sum greater than zero.

But all the while, the traditional DC loco is STILL seeing (and receiving) a rapid series of positive and negative pulses ... hence, the "humming noise". And hence, the rationale that this is ultimately bad for the motor to leave the loco sitting idle on the track for any duration.

TJ's disclaimer ... please don't think that I really know what I'm talking about! I'm just babbling after a read of the info below, at this link ...

http://www.loystoys.com/info/how-dcc-works.html

Hope this helps!

TJ


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## dozer (Jan 2, 2010)

tjcruiser said:


> Gents,
> 
> 
> TJ's disclaimer ... please don't think that I really know what I'm talking about! I'm just babbling after a read of the info below, at this link ...
> ...


 Ok, now that was funny! lol...Thanks for the info though, I appreciate it.


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## tankist (Jun 11, 2009)

dozer said:


> I keep reading about people saying most dcc systems allow at least one dc engine to be used on the layout. Well, if this is true how does it work?


its probably a form of power width modulation. in any case this compatibility is not the healthiest thing for DC locomotive. and this feature is going away slowly. less systems are compatible.


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## therailchannel (May 18, 2010)

The one loco, BTW, could be as many DC engines coupled together as you care to put on the DCC track. It's just that you can only control them as one. 

-Aaron


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## dozer (Jan 2, 2010)

Well, I can now call BS on all this. I tried 3 different DCC systems from several years old to a brand new Advance 2 system, tried several different loco's using different address's and it doesn't work. If and when you can get a loco to move, it's so inconsistant that it's not even worth it.


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## therailchannel (May 18, 2010)

If you use an MRC DCC system, they do not support DC on a DCC system. I am told NCS and Digitrax support it. I have actually seen it work. it didn't work well, though. Your mileage will vary, of course. As you have found, it may not work at all in some cases. 

When I converted to DCC, I sold a lot of my old engines that I thought were not worth keeping (first generation Bachmann Spectrum N scale) and bought decoders for the ones I kept. I now buy an engine and a decoder at the same time. With an industrial switching layout, I don't need as many engines as when I had a huge layout.


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