Adding a Reverse Loop to the Bus


Eric
 

In Alan's web site the possible length of a bus element is 27-30' from the booster. Does this length also include the reverse loop wiring? For instance if my bus length to the reverse loop is 20' and the reverse loop is 12', have I exceeded the 27' limit? If so I would have to move the booster closer to the loop or add another curcuit breaker.

Also, should a long bus always be terminsted?
RicZ


Vollrath, Don <dvollrath@...>
 

Eric,
You will need an auto-reverser for the reverse loop. Just locate it near the reverse loop itself and connect it up to the existing DCC bus at that end of the layout and to the reverse loop tracks. The 27-30ft length is not an absolute limit, but merely a suggestion for optimum performance. Adding an R/C snubber/terminator to the DCC bus wires at the far end from the booster (near the input to the reverser) will also help prevent signal degradation. Yes, twisting the DCC distribution bus run also helps to minimize problems. Is it absolutely necessary?... No but it you are building the layout, it is a good idea.

DonV

-----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of Eric
Sent: Monday, June 11, 2012 4:46 PM
To: WiringForDCC@...
Subject: [WiringForDCC] Adding a Reverse Loop to the Bus

In Alan's web site the possible length of a bus element is 27-30' from the booster. Does this length also include the reverse loop wiring? For instance if my bus length to the reverse loop is 20' and the reverse loop is 12', have I exceeded the 27' limit? If so I would have to move the booster closer to the loop or add another curcuit breaker.

Also, should a long bus always be terminsted?
RicZ



------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links


Zak, Charles <zakc@...>
 

What is a RC Snubber?


From: Vollrath, Don [mailto:dvollrath@...]
Sent: Monday, June 11, 2012 06:05 PM
To: WiringForDCC@... <WiringForDCC@...>
Subject: RE: [WiringForDCC] Adding a Reverse Loop to the Bus



Eric,
You will need an auto-reverser for the reverse loop. Just locate it near the reverse loop itself and connect it up to the existing DCC bus at that end of the layout and to the reverse loop tracks. The 27-30ft length is not an absolute limit, but merely a suggestion for optimum performance. Adding an R/C snubber/terminator to the DCC bus wires at the far end from the booster (near the input to the reverser) will also help prevent signal degradation. Yes, twisting the DCC distribution bus run also helps to minimize problems. Is it absolutely necessary?... No but it you are building the layout, it is a good idea.

DonV


-----Original Message-----
From: WiringForDCC@...<mailto:WiringForDCC%40yahoogroups.com> [mailto:WiringForDCC@...<mailto:WiringForDCC%40yahoogroups.com>] On Behalf Of Eric
Sent: Monday, June 11, 2012 4:46 PM
To: WiringForDCC@...<mailto:WiringForDCC%40yahoogroups.com>
Subject: [WiringForDCC] Adding a Reverse Loop to the Bus

In Alan's web site the possible length of a bus element is 27-30' from the booster. Does this length also include the reverse loop wiring? For instance if my bus length to the reverse loop is 20' and the reverse loop is 12', have I exceeded the 27' limit? If so I would have to move the booster closer to the loop or add another curcuit breaker.

Also, should a long bus always be terminsted?
RicZ

------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links


Steve Haas
 

Ric Z inquires:

<<In Alan's web site the possible length of a bus element is 27-30' from the
booster. Does this length also include the reverse loop wiring? For
instance if my bus length to the reverse loop is 20' and the reverse loop is
12', have I exceeded the 27' limit? If so I would have to move the booster
closer to the loop or add another curcuit breaker.>>

Alan has done a fantastic job of putting a lot of good
information together in a common location. I agree with 99.9 percent of
what his pages contain.

However, I disagree with him on several topics, one of which
is the maximum length of bus runs.

For example, the NCE Power Pro System Manual has the
following recommendations:

Runs to twenty-five feet: #16
Runs to fifty feet: #14
Runs over fifty feet: #12

Knowing that longer runs will inevitably create incremental
problems, most DCC manufacturers have understated the length of wire run
requiring a specific size wire. There is no need for the rest of us to
hobble ourselves further by placing additional constraints on the length of
a bus of a given size.

One local layout where I support the DCC system has #12 AWG
buses running almost eighty feet. All boosters and DCC circuit breakers are
clustered in one corner of a 28 x 42 foot room (owner's choice). From that
corner, to the opposite corner of the building are two bus runs; one serves
the port area, the other serves a reversing block in the same area. These
blocks are fed with 12 AWG wires approximately 80 feet long with no issues.

We haven't consciously twisted the wire pairs for each
district, but all the track bus wiring headed in one direction from the
command and booster complex are bundled together, with each pair split off
from the bundle as it reaches it's booster sub-district. We have been
adding choke/filters/snubbers at the end of the long track district runs
before they are split into the track feeders for individual blocks.

Bottom line - Alan's recommendations are a bit conservative
and can be pushed. However, the more you push them, the more you should be
prepared to implement the techniques used to avoid some of the problems of
long bus runs, namely twisting the pairs (three turns per foot), and adding
a snubber at the end of the bus.

<<Also, should a long bus always be terminated?>>

Always is a pretty strong term. Many folks exceed the
normal paramters and never have any problems with the operation of their DCC
systems. On the other hand, terminators are cheap and easy to implement,
and while their presence may or may not help the quality of the signal on
any given layout, they'll never harm a system or its performance by their
presence.

If in doubt, add the terminators. The cost of the
components is negligible, they're easy to put together and install, and
they'll never hurt.


Bet regards,


Steve Haas
Snoqualmie, WA








Also, should a long bus always be terminsted?
RicZ



------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links


Eric
 

Thanks, Don and Steve. I am unfamiliar with the term choke/snubber/filter. Can one of you explain?
RicZ

--- In WiringForDCC@..., "Vollrath, Don" <dvollrath@...> wrote:

Eric,
You will need an auto-reverser for the reverse loop. Just locate it near the reverse loop itself and connect it up to the existing DCC bus at that end of the layout and to the reverse loop tracks. The 27-30ft length is not an absolute limit, but merely a suggestion for optimum performance. Adding an R/C snubber/terminator to the DCC bus wires at the far end from the booster (near the input to the reverser) will also help prevent signal degradation. Yes, twisting the DCC distribution bus run also helps to minimize problems. Is it absolutely necessary?... No but it you are building the layout, it is a good idea.

DonV


-----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of Eric
Sent: Monday, June 11, 2012 4:46 PM
To: WiringForDCC@...
Subject: [WiringForDCC] Adding a Reverse Loop to the Bus

In Alan's web site the possible length of a bus element is 27-30' from the booster. Does this length also include the reverse loop wiring? For instance if my bus length to the reverse loop is 20' and the reverse loop is 12', have I exceeded the 27' limit? If so I would have to move the booster closer to the loop or add another curcuit breaker.

Also, should a long bus always be terminsted?
RicZ



------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links


Eric
 

Thanks, Don and Steve. I am unfamiliar with the term choke/snubber/filter. Can one of you explain?
RicZ

--- In WiringForDCC@..., "Vollrath, Don" <dvollrath@...> wrote:

Eric,
You will need an auto-reverser for the reverse loop. Just locate it near the reverse loop itself and connect it up to the existing DCC bus at that end of the layout and to the reverse loop tracks. The 27-30ft length is not an absolute limit, but merely a suggestion for optimum performance. Adding an R/C snubber/terminator to the DCC bus wires at the far end from the booster (near the input to the reverser) will also help prevent signal degradation. Yes, twisting the DCC distribution bus run also helps to minimize problems. Is it absolutely necessary?... No but it you are building the layout, it is a good idea.

DonV


-----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of Eric
Sent: Monday, June 11, 2012 4:46 PM
To: WiringForDCC@...
Subject: [WiringForDCC] Adding a Reverse Loop to the Bus

In Alan's web site the possible length of a bus element is 27-30' from the booster. Does this length also include the reverse loop wiring? For instance if my bus length to the reverse loop is 20' and the reverse loop is 12', have I exceeded the 27' limit? If so I would have to move the booster closer to the loop or add another curcuit breaker.

Also, should a long bus always be terminsted?
RicZ



------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links


Vollrath, Don <dvollrath@...>
 

Some people (me included) use words that almost fit but don't quite belong. The function is to help prevent voltage spikes and signal reflections on the bus wiring caused by abrupt voltage changes of the DCC signaling scheme. The issue has comes up when the switching speed (how fast the transmitter changes the voltage signal) starts to become less than about 1/10 the time it takes that signal transition to sweep down the wire, be reflected and return back to the source. A properly placed Resistor and capacitor wired in series and placed across the far end of the bus absorbs the energy and prevents it from reflecting. The actual propagation speed is controlled by inductance and capacitance of the wiring... ie: distance between the wires. This is why twisting them together works better than other random flow of the wires. Long leads also enter to the formula for reflections. The R-C network should be called a terminator when used in this context, as it terminates or completes the transmission line like characteristics. In other circles an R-C network is called a snubber as it 'snubs' or absorbs voltage transition energy or even a filter as it filters out high frequency components, like 'ringing' reflections. See http://www.wiringfordcc.com/track_2.htm#c2

DonV

-----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of Eric
Sent: Tuesday, June 12, 2012 10:46 AM
To: WiringForDCC@...
Subject: [WiringForDCC] Re: Adding a Reverse Loop to the Bus

Thanks, Don and Steve. I am unfamiliar with the term choke/snubber/filter. Can one of you explain?
RicZ

--- In WiringForDCC@..., "Vollrath, Don" <dvollrath@...> wrote:

Eric,
You will need an auto-reverser for the reverse loop. Just locate it near the reverse loop itself and connect it up to the existing DCC bus at that end of the layout and to the reverse loop tracks. The 27-30ft length is not an absolute limit, but merely a suggestion for optimum performance. Adding an R/C snubber/terminator to the DCC bus wires at the far end from the booster (near the input to the reverser) will also help prevent signal degradation. Yes, twisting the DCC distribution bus run also helps to minimize problems. Is it absolutely necessary?... No but it you are building the layout, it is a good idea.

DonV


-----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of Eric
Sent: Monday, June 11, 2012 4:46 PM
To: WiringForDCC@...
Subject: [WiringForDCC] Adding a Reverse Loop to the Bus

In Alan's web site the possible length of a bus element is 27-30' from the booster. Does this length also include the reverse loop wiring? For instance if my bus length to the reverse loop is 20' and the reverse loop is 12', have I exceeded the 27' limit? If so I would have to move the booster closer to the loop or add another curcuit breaker.

Also, should a long bus always be terminsted?
RicZ



------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links



------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links


D. L. Turnock
 

Thanks for the explanation. I went to the web-site and read through and
have a couple of additional questions.



I'm still working track plans and such but I'd prefer to get things figured
out before I have to re-do it J



One of the comments at the web site was terminating the bus (if required) at
each end. But, this is also after talking about sending the bus two
directions from the booster with the booster in the middle. So, first
question is: If using a terminator, is it required at the end of the bus
run away from the booster or is it also required at the booster?



Second question is: Even if you keep the run down under 30', would a
terminator undermine performance? I mean, it's a resistor and a capacitor
soldered between the end of the bus wires. It's not exactly rocket science
- or expensive - and if it doesn't hurt, other than the effort, what are
you at?



Thanks,



Dave T



*******************************************

D. L. Turnock

The_crusher@...



From: WiringForDCC@... [mailto:WiringForDCC@...] On
Behalf Of Vollrath, Don
Sent: Tuesday, June 12, 2012 11:17 AM
To: WiringForDCC@...
Subject: RE: [WiringForDCC] Re: Adding a Reverse Loop to the Bus





Some people (me included) use words that almost fit but don't quite belong.
The function is to help prevent voltage spikes and signal reflections on the
bus wiring caused by abrupt voltage changes of the DCC signaling scheme. The
issue has comes up when the switching speed (how fast the transmitter
changes the voltage signal) starts to become less than about 1/10 the time
it takes that signal transition to sweep down the wire, be reflected and
return back to the source. A properly placed Resistor and capacitor wired in
series and placed across the far end of the bus absorbs the energy and
prevents it from reflecting. The actual propagation speed is controlled by
inductance and capacitance of the wiring... ie: distance between the wires.
This is why twisting them together works better than other random flow of
the wires. Long leads also enter to the formula for reflections. The R-C
network should be called a terminator when used in this context, as it
terminates or completes the transmission line like characteristics. In other
circles an R-C network is called a snubber as it 'snubs' or absorbs voltage
transition energy or even a filter as it filters out high frequency
components, like 'ringing' reflections. See
http://www.wiringfordcc.com/track_2.htm#c2

DonV

-----Original Message-----
From: WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
[mailto:WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
] On Behalf Of Eric
Sent: Tuesday, June 12, 2012 10:46 AM
To: WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
Subject: [WiringForDCC] Re: Adding a Reverse Loop to the Bus

Thanks, Don and Steve. I am unfamiliar with the term choke/snubber/filter.
Can one of you explain?
RicZ

--- In WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
, "Vollrath, Don" <dvollrath@...> wrote:

Eric,
You will need an auto-reverser for the reverse loop. Just locate it near
the reverse loop itself and connect it up to the existing DCC bus at that
end of the layout and to the reverse loop tracks. The 27-30ft length is not
an absolute limit, but merely a suggestion for optimum performance. Adding
an R/C snubber/terminator to the DCC bus wires at the far end from the
booster (near the input to the reverser) will also help prevent signal
degradation. Yes, twisting the DCC distribution bus run also helps to
minimize problems. Is it absolutely necessary?... No but it you are building
the layout, it is a good idea.

DonV


-----Original Message-----
From: WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
[mailto:WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
] On Behalf Of Eric
Sent: Monday, June 11, 2012 4:46 PM
To: WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
Subject: [WiringForDCC] Adding a Reverse Loop to the Bus

In Alan's web site the possible length of a bus element is 27-30' from the
booster. Does this length also include the reverse loop wiring? For instance
if my bus length to the reverse loop is 20' and the reverse loop is 12',
have I exceeded the 27' limit? If so I would have to move the booster closer
to the loop or add another curcuit breaker.

Also, should a long bus always be terminsted?
RicZ



------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links
------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links


Allan <wire4dcc@...>
 

Don,



Do you think I should admit that I have runs well over 30', no twisted
wires, and no snubbers??? J My railroad was all wired before we decided
all these things are a good idea. I still think they are good ideas to
ensure that people don't have problems.



When you and Mark first mentioned these things, I wasn't having trouble, but
I thought maybe since you both were using NCE, I thought their rise times
might be faster than Digitrax. Now I am a half-NCE user. I have replaced
two of my Digitrax boosters with NCE boosters. I just added the second
booster. I'm waiting to see if I develop problems.



My reason for using NCE is that the Digitrax boosters are overly finicky at
tripping. They are supposed to be 5A boosters, but they start tripping at
about 2A. I called Digitrax, but received a technically unsound reason for
the problem and no offer of a solution. So I thought I'd try NCE and so
far, things seem to be good.



Allan





From: WiringForDCC@... [mailto:WiringForDCC@...] On
Behalf Of Vollrath, Don
Sent: Tuesday, June 12, 2012 11:17 AM
To: WiringForDCC@...
Subject: RE: [WiringForDCC] Re: Adding a Reverse Loop to the Bus





Some people (me included) use words that almost fit but don't quite belong.
The function is to help prevent voltage spikes and signal reflections on the
bus wiring caused by abrupt voltage changes of the DCC signaling scheme. The
issue has comes up when the switching speed (how fast the transmitter
changes the voltage signal) starts to become less than about 1/10 the time
it takes that signal transition to sweep down the wire, be reflected and
return back to the source. A properly placed Resistor and capacitor wired in
series and placed across the far end of the bus absorbs the energy and
prevents it from reflecting. The actual propagation speed is controlled by
inductance and capacitance of the wiring... ie: distance between the wires.
This is why twisting them together works better than other random flow of
the wires. Long leads also enter to the formula for reflections. The R-C
network should be called a terminator when used in this context, as it
terminates or completes the transmission line like characteristics. In other
circles an R-C network is called a snubber as it 'snubs' or absorbs voltage
transition energy or even a filter as it filters out high frequency
components, like 'ringing' reflections. See
http://www.wiringfordcc.com/track_2.htm#c2

DonV

-----Original Message-----
From: WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
[mailto:WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
] On Behalf Of Eric
Sent: Tuesday, June 12, 2012 10:46 AM
To: WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
Subject: [WiringForDCC] Re: Adding a Reverse Loop to the Bus

Thanks, Don and Steve. I am unfamiliar with the term choke/snubber/filter.
Can one of you explain?
RicZ

--- In WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
, "Vollrath, Don" <dvollrath@...> wrote:

Eric,
You will need an auto-reverser for the reverse loop. Just locate it near
the reverse loop itself and connect it up to the existing DCC bus at that
end of the layout and to the reverse loop tracks. The 27-30ft length is not
an absolute limit, but merely a suggestion for optimum performance. Adding
an R/C snubber/terminator to the DCC bus wires at the far end from the
booster (near the input to the reverser) will also help prevent signal
degradation. Yes, twisting the DCC distribution bus run also helps to
minimize problems. Is it absolutely necessary?... No but it you are building
the layout, it is a good idea.

DonV


-----Original Message-----
From: WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
[mailto:WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
] On Behalf Of Eric
Sent: Monday, June 11, 2012 4:46 PM
To: WiringForDCC@... <mailto:WiringForDCC%40yahoogroups.com>
Subject: [WiringForDCC] Adding a Reverse Loop to the Bus

In Alan's web site the possible length of a bus element is 27-30' from the
booster. Does this length also include the reverse loop wiring? For instance
if my bus length to the reverse loop is 20' and the reverse loop is 12',
have I exceeded the 27' limit? If so I would have to move the booster closer
to the loop or add another curcuit breaker.

Also, should a long bus always be terminsted?
RicZ



------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links
------------------------------------

http://www.WiringForDCC.comYahoo! Groups Links


Mark Gurries
 

On 6/12/12 at 3:23 PM, the_crusher@... (D. L. Turnock) wrote:

Thanks for the explanation. I went to the web-site and read through and
have a couple of additional questions.



I'm still working track plans and such but I'd prefer to get things figured
out before I have to re-do it J


One of the comments at the web site was terminating the bus (if required) at
each end.
No DCC manufacture require termination but it is recommended by
some. Placement is at the far ends of the wire longest run
relative to the booster. The booster itself terminates its own end.


But, this is also after talking about sending the bus two
directions from the booster with the booster in the middle. So, first
question is: If using a terminator, is it required at the end of the bus
run away from the booster or is it also required at the booster?
Yes. Think of each bus run away from the booster as it own bus.

Second question is: Even if you keep the run down under 30', would a
terminator undermine performance?
No. In fact just the opposite if you check out the scope photos
of the results.


Best Regards,

Mark Gurries
Electrical Engineer
DCC Website & NMRA DCC Clinics: www.markgurries.com


Steve Haas
 

Dave T asks:

<<So, first question is: If using a terminator, is it required at the end
of the bus run away from the booster or is it also required at the
booster?>>

At the far end of the bus run is more than sufficient.


<<Even if you keep the run down under 30', would a terminator undermine
performance?>>

A terminator will not undermine performance in any way, shape or form.


Best regards,


Steve Haas
Snoqualmie, WA