DCC basics?

[peteski]

Since my Digitrax system will run DC locos (as opposed to NCE) I don't need a DC throttle.

Ah the old zero-streching (address 00) on the Digitrax system. How are your DC loco's motors, especially coreless ones doing?  Running a bit warm and buzzing a lot? 

This is right from Digitrax Bob:
http://www.digitrax.com/tsd/KB674/zero-stretching-operating-a-non-dcc-equipped-locom/

To operate an analog locomotive with Digitrax you will use address 00 to send commands to the locomotive.  The magic that makes this happen is called zero stretching. With Zero Stretching, an analog locomotive going forward receives an unusually long positive voltage, followed by a very short negative voltage. The much larger positive voltage ensures the locomotive moves forward. The brief negative pulse causes a low buzzing that will vary with the speed of the locomotive. This method of control causes locomotive motors to run hotter than normal.  For this reason care should be taken when using this method of control.  The motor is being switched on and off even when the loco is set at 0 speed and is standing still.

It is highly recommended that you remove any analog locomotives being run on DCC from the track when they are not actively running.  DO NOT LEAVE AN ANALOG LOCO SITTING ON A DCC TRACK AT 0 SPEED!!!  This can cause heat damage to your locomotive.

You are really comfortable using that method? 
Joe has mostly DC locos and he originally wanted to just get a control box to let him activate sounds in a sound-decoder-equipped loco he bought. We talked him into buying an easy-to-use and intuitive DCC system, so he can easily reprogram the decoders.  I think in his case it makes perfect sense to retain is trusty DC throttle and not depend on a digital kludge. 

[robert3985]

Peter,

I only run my non-DCC locomotives to test them prior to converting them to sound-DCC...so I am perfectly comfortable running them for a while to see if they need work before installing speaker and decoder.

However, my son runs his analog SP engines...mainly brass and Kato GS-4's at shows with no problems whatsoever...for hours on end.  My programming track can be shut off, so he parks them there while running his DCC equipped engines during the shows.

Now that I'm running Digitrax Duplex, the old programming track isn't used for much programming any longer.

Yes, they do "sing" while stationary before the siding gets turned off.  I kinda like the tune... 

When I first got my DCC system (Digitrax Super Chief Radio) several years ago, only my Athearn Big Boys and Challengers had DCC.  One of the selling points for me was that I could run a DC train with an analog engine or engines (which most of mine were at the time) and still run my DCC engines simultaneously...which kept my DC engines from sitting on the shelf until they got decoders.

As opposed to NCE, which would have required me to use an additional DC throttle, and either remove my DCC electronics or develop a switching protocol to change from DC to DCC, isolating each system from each other...it appeared to me (and still does) that the "kludge" as you call it that Digitrax conveniently includes in their system, makes it a whole lot easier to run DC engines along with the rest of the DCC-ized ones.  NCE offers no convenient feature to allow simultaneous running of DC and DCC equipped motive power, which to me is much worse than a "kludge" that actually works.

Like Joe, my locomotive roster was mostly DC at first.   Unlike Joe, my intent was to eventually run nothing but DCC, and I am still working towards that goal.  However, to park motive power on sidings back in my DC days, I routed power to my sidings by which way the turnouts were thrown using Tortoises under the layout.  I assume that Joe runs only one train at a time per DC throttle, and engines on the layout that aren't running are on tracks that are turned off...so, if he had chosen Digitrax they wouldn't hum and cook their little armatures, just like my son's analog GS-4's don't cook either since he switches off the track they're parked on.

I run NCE on a couple of other layouts, and I do not find it any more "intuitive" or "easy to use" than my Digitrax system.  I'm old, and it took me many years to finally make up my mind to go with DCC.  I found that NCE did not offer me any advantages over Digitrax whatsoever other than perhaps manuals that were easier to understand.  I overcame that slight problem by referring to online sources and questioning my friends who were using Digitrax.  Took my son and I about three evenings to figure it out completely, and now it's second nature...and I am still good friends with my model railroading buddies who chose NCE systems...but then sneak over to my portable layout during shows to run their newly purchased DC engines. ...because with NCE, their DC engines are paperweights.

However, if Joe is happy with his setup, that's just fine with me.  But, being able to run both a DC lashup and all the other DCC engines simultaneously in the same block and on the same tracks is a feature, not a "kludge" that NCE does not have, and Digitrax does.

Cheerio!
Bob Gilmore

[peteski]

I'm glad that your DC models are ok, and that you like those singing locomotives. 

Understanding the electrical principals in theory and practice, I'm a leery of any control system which constantly feeds full track voltage to the model where the total voltage at the motor always ends up with close to 100% duty cycle. So the motor is always under full voltage (with the armature twitching at the frequency of DCC signal), using the out of balance voltage to provide the motor with equivalence of DC voltage to make it run.

That is the opposite of how the the decoder's PWM motor drive system powers the motor. In that instance the voltage is off most of the time, just supplying full voltage pulses to drive the motor.  So unlike in the zero-stretching method, in normal operation the motor controller by the decoder only sees what would be the DC voltage it woudl see from a DC throttle.

While I agree that the zero-stretching was a feature, but it to me is also a clever kludge.  While I have no positive proof, I highly suspect that in the infancy of DCC it was a measure to allow the owner of the DCC system to be able to run DC locos while converting their fleet to DCC.

As I pointed to the Digitrax article, even they don't recommend using address 00 operation for any extended period of time. Most modelers converting from DC to DCC already own a DC throttle of their choice.  Even if the DCC system does not offer the address 00 operation, wiring a DPDT switch to switch between DC and DCC is not that difficult.

But to each his own - you find zero-stretching a viable alternative to DC throttle while I do not (for the above reasons).  Even if I did not understand the principals of its operation, that Digitrax article would make me think twice about using the zero-stretching with my DC models.

[Joetrain59]

Wired in a DPDT the other night. Makes me happy for now.
 Joe D

[robert3985]

Wired in a DPDT the other night. Makes me happy for now.
 Joe D

There ya go Joe!

I'm glad that your DC models are ok, and that you like those singing locomotives. 

Understanding the electrical principals in theory and practice, I'm a leery of any control system which constantly feeds full track voltage to the model where the total voltage at the motor always ends up with close to 100% duty cycle. So the motor is always under full voltage (with the armature twitching at the frequency of DCC signal), using the out of balance voltage to provide the motor with equivalence of DC voltage to make it run.

That is the opposite of how the the decoder's PWM motor drive system powers the motor. In that instance the voltage is off most of the time, just supplying full voltage pulses to drive the motor.  So unlike in the zero-stretching method, in normal operation the motor controller by the decoder only sees what would be the DC voltage it woudl see from a DC throttle.

While I agree that the zero-stretching was a feature, but it to me is also a clever kludge.  While I have no positive proof, I highly suspect that in the infancy of DCC it was a measure to allow the owner of the DCC system to be able to run DC locos while converting their fleet to DCC.

As I pointed to the Digitrax article, even they don't recommend using address 00 operation for any extended period of time. Most modelers converting from DC to DCC already own a DC throttle of their choice.  Even if the DCC system does not offer the address 00 operation, wiring a DPDT switch to switch between DC and DCC is not that difficult.

But to each his own - you find zero-stretching a viable alternative to DC throttle while I do not (for the above reasons).  Even if I did not understand the principals of its operation, that Digitrax article would make me think twice about using the zero-stretching with my DC models.

Peter, I understand your point.  I too was "leery" of it, but in actual use, it has not been problematic for me, my son, or others guests who run on the layout with their DC powered trains.  Even with all the anecdotal, second-hand stories out there about engines "cooking" I have yet to come even close to that with any DC engine on my layout.

Of course, we don't park DC engines on powered track...which seems like a fairly simple rule to keep.

Digitrax is not the only DCC system that allows option "00".  Lenz and Easy DCC both do, as well as two or three others.  Evidently these manufactures also feel that even today, when DCC is well past its "infancy", it's a convenient option to have.  I have to assume that if option "00" were regularly killing engines, it would not be offered by so many DCC manufacturers.

It comes down to this: Your non-viability opinion is based on your own logic-train, and my pro-viability opinion is based on running actual trains..regularly without any problems. 

And Joe doesn't give a damn...haha, and good for him! 

Cheerio!
Bob Gilmore

[peteski]

Digitrax is not the only DCC system that allows option "00".  Lenz and Easy DCC both do, as well as two or three others.  Evidently these manufactures also feel that even today, when DCC is well past its "infancy", it's a convenient option to have.  I have to assume that if option "00" were regularly killing engines, it would not be offered by so many DCC manufacturers.

Actually, I'm quite familiar with the CVP EasyDCC system and they removed the address 00 functionality in one of their firmware updates.  I also poked around the NMRA DCC specs and I didn't find anything which would imply that this mode of operation is part of the DCC standard.  Might be something that the manufacturers themselves decided to implement. Or maybe I just didn't look hard enough. 

[robert3985]

Actually, I'm quite familiar with the CVP EasyDCC system and they removed the address 00 functionality in one of their firmware updates.  I also poked around the NMRA DCC specs and I didn't find anything which would imply that this mode of operation is part of the DCC standard.  Might be something that the manufacturers themselves decided to implement. Or maybe I just didn't look hard enough. 

You are quite correct that option "00" is is not part of the NMRA DCC standard, but has been added by some manufacturers.  In my case, it influenced my decision to go with a system that had it.  Of course, there are plenty of DCC users out here who are not influenced by its absence, or who don't know it's missing until they want to run a non-decoder equipped engine.  It certainly gets plenty of "bad press"...but like I've stated, my experience with it isn't bad.

Cheerio!
Bob Gilmore