Would a dual mode decoder run on address zero?

Model Railroader Electronics and DCC
1

This question is just be cause I am feeling curious, I really can think why I would be important but I’ll ask anyway!

So today many DCC decoders are dual mode, meaning they run on but DC and DCC. Now most DCC systems can become ‘DC’ systems by running with address one. When running with address 0 the layout becomes DC and the DCC equipped locomotives don’t run at all. What I’m wondering is what a dual mode decoder will do when you run address 0. Will it run as a DC loco, or will it ignore the DC signal and sit still doing nothing.

Again just a curiosity, I don’t actually have a DCC system at the moment, though I do run on others systems.

2

Note that only some DCC systems support the address zero feature. My Lenz system does, but many do not.

3

Duly noted!

I am most firmiliar with Digitrax systems for the information of those replying.

4

I have 4 locos with dual mode decoders. 3 Atlas, and 1 Bachmann Spectrum. Since I turned my lay out over to DCC, I’ve never set it back to DC to try these locos on DC, to see how they work.

It’s an easy switch for me, flip a switch, unplug one power system, and plug in another, and I can go from DCC back to DC.

I have run locos (analog) with out decoders on the DCC lay out, and my Digitrax manual says to set the address of an anolog loco at “00”.

If I were to go to DC mode with the lay out, I don’t know what the address of the dual mode decoders would set to, as acording to the instructions, there is nothing I need to do to the locos to run on DC. Their default address for DCC is “03”.

I don’t know if JMRI reads anything, or even works with DC. I have it, but it’s not actively connected to the lay out, I use it as a “stand-alone” for decoder work, sometimes.

I would think that a dual mode loco, placed on a DCC system, would read only the DCC signal, and an address change to “0”, the loco probably wouldn’t work. But I don’t know that for sure.

Not sure if I contributed to an answer to your question, or just rambled on with some thoughts on it all. [%-)]

Mike.

5

No, the decoder will not run on address 0, because as soon as you set it on the rails, it will see the DCC signal and be in DCC mode. At most, you might confuse it and have it take off at full speed, which is one of the reasons I disable DC operation in all my decoders.

There are few if any decoders made today that are not “dual mode” and will work on DC or DCC.

–Randy

6

i don’t believe a DCC sytem “can become a DC system”.

I don’t believe the layout becomes DC when address 0 (or 1) is used.

A DCC system can control a single DC locomotive using address 0 by skewing the DCC signal to have a DC offset.

i doubt any decoder can be programmed with address 0. You would select loco address 0 in the controller to control a single DC loco and can continue to control other DCC equiped locos using their assigned addresses.

or am i confused (not the first time)?

7

Correct on all counts Greg.

8

That’s exactly what it’s doing - stretiching out the positive half oor the negative half of the 0 bits in the DCC signal (since the definition of a 1 bit is a bit time less than some value, and a zero is any bit time over some other value, with a dead space in the middle). Assuming a loco wired per NMRA DC standards, positive on engineer’s side is forward, if the phase of the 0 bit on the right rail is longer than the phase of the 0 bit on the left rail, there is a net positive DC offset to the right rail and the loco moves forward.

You can;t remove the negative somponent completely, or DCC decoders will not work, and DCC decoder equipped locos would only be able to move in one directions. So the DC motor still sees an AC voltage, just one that is more positive in one direction or the other. Hence the buzzing Stopped, there is an equal amount of postive side and negative side, so the armature doesn;t turn, but just vibrated back and forth. No airflow, basically a short through the windings , Depending on the motor, it will burn up in seconds (a coreless motor) to hours (a big heavy massive open frame motor) if left sitting there.

It’s OK for a quick test run (except coreless motos) but not really suitable for long term running. Decoders are cheap, just put a decoder in it. Also, by extending the 0 bits to make the DC offset, it increases the time required to transmit full DCC packets to decoder equipped locos, slowing the response to throttle, direction change, and function control.

–Randy

9

My first DCC system was a MRC2K that had three trottles on a panel and two on a lanyard. Throttle one on the panel was for DCC or a DC loco by design.

On the Bachmann EZ Command you press button ten for a DC loco.

I gave the system away and bought a NCE Power Cab that does not run DC locos.

Running a DC loco on stretch zero is hard on the motor. I did temp measurments with an infrared scanner with the loco in a test stand some years ago. Motor brushes where they contact the armature get hotter when the motor is stopped and DCC still applied.

https://sites.google.com/site/markgurries/home/technical-discussions/dc-loco-on-dcc

Motor and light decoders are about $20.00 each depending on place you get them.

Many just do not want to seem to do any research but make assumptions. The Internet is loaded with info on this subject.

Rich

10

I have never seen this stated. I can’t disagree, but I have yet to see a thread on this forum, or on any other, where this is discussed and/or taken as a given. I do know that entering Add “00” on my Digitrax DT400 throttles with a DB150 backing them will allow me to run DC-only locomotives. I only tried it once. That was plenty. No, really…

I don’t know about “0”, but “00” is what we are asked to enter for an address if we want to run a strictly DC motor using the Digitrax systems. I don’t think our systems support the address “0” or “00” for DCC operations because the default for all decoders that are NMRA compliant is “03”. So, to address your question, a DCC-enabled decoder (set in CV29), should do nothing if you go to Add “0” or even “00” and attempt to get any powered decoders to do something…anything. They will power up, and do everything in neutral that you had them doing the last session (I’m pretty sure), but they should not turn lights off/on, sound the horn, turn the drive mechanism, consist

11

Address one on a digitrax will not operate a DC loco, only 00 will. I have a DCC loco with address 01 and it runs on DCC. I’m not sure fan has his facts straight.

12

A DCC system does not become DC. You can run a DC loco on DCC, as I stated, Digitrax says to set the address to “00”.

But the system does not “change” into DC, and a DCC loco will run, as it should.

Mike.

13

It seams I have caused some confusion by accidently saying address one instead of address zero. I am aware that address zero is the one that runs DC locomotives (at least on a Digitrax system). Apologies for any confusion, the title has been corrected.

14

i thought it was your statement that the system/layout becomes DC and DCC equiped locos no longer work that was inaccurate.

A DCC decoder can work on a DC layout if enabled to operate in DC mode.

15

nope …

the DCC system sends out packet information for DCC first, which the decoder can accept …

it is only after this that it sends out the DC information, which if the DCC was valid, the decoder cannot accept … simple …

16

Wrong. On my Digitrax DCC DB150 with the DT400 throttle, I can run a loco without a decoder on one throttle, and a DCC loco on the other.

The DCC system does not become DC.

Mike.

17

I had no idea you could run a DC locomotive and DCC locomotive at the same time! Are you sure that would work well? The speed the DC locomotive is running at would determine the maximun voltage either could recieve (as DC locos speed is controlled by the amount of colts applied to the track). So if the DC is running slowly the DCC locomotive could only run the same speed as the other DC engine or less. Correct me if I’m wrong, hope I make sense…

18

Tell ya what, when I get back here later this am, i’ll set it up and try it. I have two throttles on the DT400, so I can control 2 seperate locos.

Mike.

19

A DCC system changes the polarity of the track voltage to send packets. The average voltage is normally zero.

It can control a DC locomotive by stetching a positive or negative cycle so that the average voltage is not zero. While a DC locomotive may run, there’s a lot of wasted AC current (the signalling for DCC decoders). Address 0 is used to control this DC value.

20

To operate a DC locomotive on a DCC system, a technique called “Zero Stretching” is used. Usually referred to as Address 0, an address isn’t allowed in DCC. All the DCC locomotives will continue what they are doing, as they just ignore that packet.

Not all systems support Zero Stretching, as it not part of the DCC standard. For those that do, they simply alter a null packet by making one rail high (energized) for a longer period of time than it would normally be. The longer it is held high, the faster the DC motor will turn. Speed is determined not by voltage, but by time.

In a DCC system there are no AC voltages, nor are there positive and negative voltages. Just a sequence of high and low voltages on each rail, where one is energized (high) and the other is not (low). It is a digital system, after all.

While Rail A is high, the current flows through the motor to Rail B (at zero volts), and it turns, providing motion to the locomotive. In this case, Rail A is more positive than Rail B, so current flows from the energized Rail A to B and back to the source. To reverse direction, Rail B is held high, current flows from B to A and the motor turns in reverse. Rail B is now more positive than Rail A, so it will turn in reverse. Repeating this packet this fast enough keeps the motor turning.

When address 0 is in use, it generates a lot of packet traffic which can bog down system response. Even when set to speed step 0. To power a DC locomotive a lot of packets have to be sent at address 0.

Under normal DCC operation, the high frequency of the pulses on the rails cause the effective flux in the motor to cancel, as the direction of current flow changes rapidly. This can result in overheating, and some motors, such as coreless types, can be quickly damaged. The motor is also going to make some noise as the torque vector keeps reversing, causing the amature to vibrate.