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DCC on DC Piggyback System - A Possibility?


xveitch
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Hi All, 

 

Would love to pick your DCC-Brains about something I've recently been thinking about. 

 

The two questions are: 

A. Is there a way to detect, quickly and automatically, whether a DC or a DCC Locomotive is sitting on a section of track. 

B. Is there a way to control DCC Locomotives generally, without using their DCC Address 

 

It's probably best if I frame them in the situation itself. 

 

My model railway club has a large analogue model railway system, including block systems, automated running between stations and various other DC - based technology. Therefore moving to DCC would not be desired. However, as more and more club members move over themselves to DCC, it would be ideal to find a way that DCC locomotives could also run. The easiest solution would be to build a small DCC model railway and run this separately. This would be, however, a resource drain on the club, as well as not contributing to the main model itself. I was thinking whether it would be possible to build a small piggyback circuit onto each DC control unit (including the automated DC controllers), that could detect a DCC locomotive and then convert the DC voltage into a DCC signal. 

 

The operation steps would probably look something like this: 

 

1. A block is selected, connecting the DC controller (and therefore the Piggyback DCC) to this block. 

2. The Piggyback DCC sends a signal to detect the presence of a DCC locomotive 

2a. When no DCC locomotive is detected, the Piggyback is bypassed, connecting the DC Controller to the track directly, as per normal. 

2b. When a DCC locomotive is detected, the Piggyback converts the current DC voltage it receives from DC Controller into a DCC signal to drive the locomotive. 

 

For question B, a work-around would be to program all the DCC Locos as Address 3 (Or any other number), so that the DCC Controller just controls number 3. As there is a block system, it would therefore control only one locomotive at a time. This is by no means ideal, as every locomotive would have to be programmed Address 3. 

 

I see several problems: 

1. DCC is a one-direction control system; there is no built in feedback system from the locomotives. Therefore detection would have to be somehow passive, or through another system (e.g. reed switches or other physical detectors). 

2a. Either the detection would have to be so fast and fluid that as a train moves from one block to another, there is no observable stop and start. 

2b. Or the system would need to track the DCC locomotive, pre-switching every block it moves into for DCC. 

3. Except the example of programming on a programming track with more than one locomotive, where you can program several locomotives together, without specifying their DCC Address (usually something that is avoided), there is no example of controlling a DCC locomotive without before choosing its address rather than a general, open command. 

4. What is the damage of sending a short burst of DCC information (to detect the presence of a DCC Loco) on a DC locomotive? This would undoubtably be very short, however if it occurred at every block intersection, this could add up. 

 

Is there anything that I've missed? And is this even possible? Or is there a better solution that I haven't thought of? 

 

Many thanks, 

 

Xander

 

 

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Why not just ensure that everyone enables DC running in CV29 of any DCC locos that are brought top the Club layout - if you do this then they will just act like any other DC loco that exists on the layout.

 

Or am I missing something? 

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Hi Xander,

 

My understanding of DCC is that power in the track is full on and the throttle is in the decoder within the loco.  Furthermore the track power may be AC rather than DC with the rectifier circuitry in the decoder.  Thus any DC locos on the track would either shoot off at full pelt or respond badly to the AC supply.

 

I am sure that others with much more knowledge than myself can expand further.

 

Cheers

 

Darius

Edited by Darius43
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3 minutes ago, WIMorrison said:

Why not just ensure that everyone enables DC running in CV29 of any DCC locos that are brought top the Club layout - if you do this then they will just act like any other DC loco that exists on the layout.

 

Or am I missing something? 

 

Clearly, that is a possibility. However for club members, the ability of DCC Sound and other features is desirable, more than merely acting as DC locomotives. Otherwise they would generally be happy with driving the current DC locomotives on the layout. 

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3 minutes ago, Darius43 said:

Hi Xander,

 

My understanding of DCC is that power in the track is full on and the throttle is in the decoder within the loco.  Furthermore the track power may be AC rather than DC with the rectifier circuitry in the decoder.  Thus any DC locos on the track would either shoot off at full pelt or respond badly to the AC supply.

 

I am sure that others with much more knowledge than myself can expand further.

 

Cheers

 

Darius

best read this thread before you start saying anything about AC or DC :)

 

 

 

BTW - a DC loco on DCC will simply buzz loudly and get warm and after a period of time you wont have a loco, you will have something for the mantelpiece as a static exhibit :)

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3 minutes ago, Darius43 said:

Hi Xander,

 

My understanding of DCC is that power in the track is full on and the throttle is in the decoder within the loco.  Furthermore the track power may be AC rather than DC with the rectifier circuitry in the decoder.  Thus any DC locos on the track would either shoot off at full pelt or respond badly to the AC supply.

 

I am sure that others with much more knowledge than myself can expand further.

 

Cheers

 

Darius

 

Thanks Darius, 

 

From what I understand, DCC sends an AC pulsed signal at a set amplitude. The pulse width conveys the bit information to control the decoder within the locomotive. It's true what you mentioned about the DC locomotives, however if the pulse was short and quick enough, a DC Locomotive would only move a couple mm at most. If this was still a problem then the block sections would have to be pre-switched. 

 

Xander 

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1 minute ago, WIMorrison said:

best read this thread before you start saying anything about AC or DC :)

 

 

 

BTW - a DC loco on DCC will simply buzz loudly and get warm and after a period of time you wont have a loco, you will have something for the mantelpiece as a static exhibit :)

 

Ahh okay; guess that means the only option would be pre-block switching 

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11 minutes ago, WIMorrison said:

Xander

 

IMHO silence is golden ;)

 

And if you do find an answer to your quandary can I suggest you patent it?you me be reaching for the Philosopher’s Stone and whilst that is a laudable aim itmay be unachievable 

 

Haha will do! I think there is no easy solution here! I'll have a little think over and chuck some of my thoughts up on here. Most likely it will require pre-block switching - I don't see a detection system that is fast enough or harmless enough to use. Also finding a system that avoids modification to either DC or DCC locomotives is tough. If anyone does see a better way, or a chink in my metaphorical armour, I would love to hear it. 

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It is hypothetically possible, but I don't know if it would be practical.

 

A DC loco has the motor connected directly across the track. That means a fairly low resistance path when static, or back EMF when running.

A DCC loco would not normally have a resistive path below a volt or two (due to the rectifiers) and would not give any back EMF when running.

 

For the "sections", I'd make everything DCC and have some fixed DCC decoders that switch in to control the track sections with DC locos on?

 

It's definitely not a simple or straightforward proposition.

 

Edit - 

Or, have small enough sections and only power then after whatever loco bridges the isolation to the section it's coming from? 

 

Then it's either DC on the track, or alternative polarity DCC power; easily detectable.

Either power system could then be switched in to the new section, before the loco gets totally off the previous section...

 

A bit like automated lighting "following" someone along a long corridor; no power except where needed.

 

Edited by RobjUK
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Another issue you must take notice of is..

 

Any electronic track cleaning devices such as Relco can not be used with any DCC equipped locomotive as they will destroy the DCC Chip

 

Eltel 

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This all sounds very complicated. Surely DC is used to avoid some of the complexities of DCC?

Please avoid mixing DC & DCC on the same layout. You can't be there every week & you are likely to come back to a couple of very broken controllers/locos with everyone denying any knowledge of doing anything wrong.

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1 hour ago, WIMorrison said:

Xander

 

IMHO silence is golden ;)

 

And if you do find an answer to your quandary can I suggest you patent it?you me be reaching for the Philosopher’s Stone and whilst that is a laudable aim itmay be unachievable 

 

The best advice may be the same as that given by GB Shaw to a young man who asked for his opinion on his getting married: "Don't"!

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My Club has a DC layout that we converted to be switchable between DC and DCC.  Given the apparent complexity of your layout, this might not be feasible.  Such a switchable system does require a disciplined system to switch between the two modes, especially to protect DC locos from the DCC track voltage.  It does however work for us, and there has been no damage to locos or controllers in the 5+ years it has been running.  To avoid accidental switching, or switching by inexperienced users, the DC/DCC switches are located inside a control panel, away from normal view.

 

For a switchable system to work, you will need to install Double Pole Double Throw (DPDT) switches to do the switching, and will obviously need a DCC controller.   

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As W.I. Morrison said in the first reply on this topic.... what you want is to ensure all visiting dcc locos have dcc running enabled, AND picking up on some other needs... NO RELCO or other HF devices ( like lighting or Codar sound on analogue) or pre-electronic ie non-smoothed output analogue controlleys. ( Track feed interference suppression capacitors are not a problem as you are still using analogue to power the layout - this would NOT be the case if you switched dcc through to the block.)

Full price/quality Sound decoders such as loksound 3  onwards and zinc and digitax and...  will still produce sound on analogue dcc. ... you may have 'pause' at 5 volts as the decoder "wakes up" and applies sounds ( including bells) as the speed determines

Hornby TTS however will remain silent on analogue.

In G-scale ... an early user of dcc ... many users remain analogue but still enjoy the compatible sounds.

 

Edited by Phil S
Correcting auto-corrected spelling
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practically , reliably detecting the presence of a DCC decoder as distinct to the DC loco would be difficult to effect reliably , secondly feeding  a section automatically based on that dubious recognition would be problematic as a mistake would enable DCC power to a DC loco ( and that may not be obvious to the operator ) 

 

Hence , short of throwing a considerable amount of electronics to make the detection reliable , its not really practical 

Added to this is the difficulty in controlling locos with all the same address , Note that there is a " broadcast " DCC address , but gain not all decoders in my experience react correctly  to it 

 

Basically its a non runner 

Edited by Junctionmad
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