# Track Power Bus Location Distances - NMRA Recommendations?



## bdelmo (Oct 21, 2010)

Currently, I have a single location for connecting the power/control to my small outdoor layout inverted over and under loop with siding for operation with mobile Lenz DCC system with 5 Amp AC power source. Thus, my tethered throttles (cabs) are also limited to this location. My sound decoders may be impacted by this single power/control connection. I am planning to add a track power bus with multiple locations and a control bus to reach at least two locations for my tethered throttles. I plan on adding a second larger oval loop with power booster station this Summer. 

Are there any NMRA recommendations, which I could not find, for distances between connections for the track power bus, assuming it is needed?


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## George Schreyer (Jan 16, 2009)

If your trains don's slow down when they are furthest away from your one connection point, then don't worry. 

I initially ran a 300' loop, no issues. If you have SS rail, YMMV.


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## bdelmo (Oct 21, 2010)

I have bronze rails on my layout with approximately 100 feet of track. The sound was breaking up for the Tsunami sound board with Lenz decoder, which perhaps is due to problems other than track power distribution. I have no problems with sounds breaking up from QSI sound decoder.


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## Greg Elmassian (Jan 3, 2008)

Tsunami's do that, I was running an HO one on my small loop, and it would cut out and reset all the time. Took it out (anyone want to buy one cheap? Light steam) and put in a Zimo 642, perfect. 

It's the Tsunami. 

Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 11 Mar 2011 08:23 AM 
Tsunami's do that, I was running an HO one on my small loop, and it would cut out and reset all the time.


I don't own any Tsunami sound decoders, but do they not have the option of adding a capacitor to prevent that cut out and reset?
All other sound decoders that I'm familiar provide that and even many non-sound loco decoders. 


Knut


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## Greg Elmassian (Jan 3, 2008)

I think they do... they come with a electrolytic cap attached, but it turns out that seems to be a high pass filter for the speaker. 

I can tell you they are more sensitive to power interruptions, as I mentioned, pulled it out and put Zimo in same loco and much improved. Can't beat an AB test! 

Anyway, back to the original question, it will depend on the connections between your rail sections, joiners, clamps, soldered jumpers, etc. 

How many locos will be run at a time? 

Greg


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## krs (Feb 29, 2008)

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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 11 Mar 2011 09:04 AM 
Anyway, back to the original question.......



Seems to me the original question was at least partially about the sound cutting out, bdelma may have assumed it was caused by the single feed and thus asked the question about it.

Currently, I have a single location for connecting the power/control to my small outdoor layout inverted over and under loop with siding for operation with mobile Lenz DCC system with 5 Amp AC power source. Thus, my tethered throttles (cabs) are also limited to this location. *My sound decoders may be impacted by this single power/control connection.* I am planning to add a track power bus with multiple locations and a control bus to reach at least two locations for my tethered throttles. I plan on adding a second larger oval loop with power booster station this Summer. 

Are there any NMRA recommendations, which I could not find, for distances between connections for the track power bus, assuming it is needed?

Knut 


PS: I give up.
How does one show text in the body of a reply as a quote?

There is no icon that I can find, I tried [q], [Q] and so far and nothing worked, all with the appropriate end, ie [/Q] etc. 



Now I see ...... gave me quotation marks which don't really make the quoted part stand out.
I wanted a box like at the beginning of this post, preferable with the word 'Quote' in the top left corner superimposed on the upper left outline of the box.
The way quotes are normally shown


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## rdamurphy (Jan 3, 2008)

Are you using NCE? You could go to radio throttles... 

Thanks, Robert


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## bdelmo (Oct 21, 2010)

Good addition above to my original posting here. Lenz DCC system is being used with electric powered engines. I also have one live steam.


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## rdamurphy (Jan 3, 2008)

OK, legitimate question here, as a DCC beginner, I really don't know... 

Couldn't you take a multimeter, voltmeter, etc, and measure the voltage at the booster, then various places around the layout to see the voltage drop to evaluate if an additional booster is required? What would be considered an acceptable drop?

Thanks, Robert


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## Greg Elmassian (Jan 3, 2008)

Yes, and without a load on the tracks, the voltage will not vary. 

You need to put a load on the tracks to see the voltage drop. 

I built a unit to put an 8 amp load on the track, then you can identify what and where the voltage losses/drops are. 

Remember Ohms law, V (voltage drop) = I (current) times R (resistance)... 

If you are using a voltmeter, there is basically no current drawn, so in the equation above if I is small, then V is small no matter what the Resistance of the connections, so you will not be able to measure any appreciable voltage drop. 

The more current you are drawing, the easier it is to see where the voltage drops occur. 

Regards, Greg


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## rdamurphy (Jan 3, 2008)

So you'd have to remove the voltage from the track and measure the resistance from the power connection to the far point of the loop of track. Which of course would be off because of the resistance in the wire that was that long... 

Correct? 

Robert


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## Greg Elmassian (Jan 3, 2008)

No, you do it with power on, a load and a voltmeter. 

The entire point is without a significant amount of power flowing you cannot find the problems. 

If you _could _accurately measure very small amounts of resistance, you _could _use an ohmmeter to measure the resistance of each joint and see where the problem is, but you are talking fractions of ohms, you do not possess the equipment to do this, it's *VERY *difficult. 

So the technique is to run a lot of current through the system, and because of Ohms law, the large current will "amplify" the voltage drop across connections, thus making it easy to measure with an inexpensive meter. 

Greg


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## krs (Feb 29, 2008)

Robert,

Why do you even worry about voltage drop or resistance?
With G-scale (code 332) track which you have I believe, the resistance (and thus also the voltage drop) is less than most wire you would use for a power bus. 
The only place where a power bus would help you is if the electrical connection between the rail sections is poor.

Here is a chart showing the resistance of brass G-scale rail vs various standard AWG wire gauges.


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## rdamurphy (Jan 3, 2008)

I'm not worried about it all, not my thread, I'm just curious. 

Thanks, Robert


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## krs (Feb 29, 2008)

Sorry, 

Didn't go back to the beginning of this thread.


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## Greg Elmassian (Jan 3, 2008)

The joiners Knut. And for long runs, SS can use a hand. 

Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 13 Mar 2011 08:16 PM 
The joiners Knut. And for long runs, SS can use a hand. 

Greg


I did mention that in my reply Greg, but in a bit more generic fashion:
"The only place where a power bus would help you is if the electrical connection between the rail sections is poor."

As to SS rail, I don't use it myself but I wonder if anyone has some first hand experience.
The manufacturers of SS track in Europe swear that they use long runs of SS track without any extra feeds with no problem but the resistance of SS rail is relatively high in comparison to brass (see that chart I posted), so one would expect that feeders are needed for longer runs.


Knut


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## Greg Elmassian (Jan 3, 2008)

The connections between the rail sections is ALWAYS worse than the continuity of the rail itself. 

SS just exacerbates the situation. 

Greg


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## bdelmo (Oct 21, 2010)

Perhaps I could steer these replies back to my original question here, recognizing that it likely is not needed for my short 100 feet track length. 

Does NMRA have any DCC recommendations for the track power bus with Code 332 brass rail track?


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## Greg Elmassian (Jan 3, 2008)

No


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## krs (Feb 29, 2008)

Posted By bdelmo on 14 Mar 2011 07:48 AM 

Does NMRA have any DCC recommendations for the track power bus with Code 332 brass rail track? 


Not that I have ever seen.
Since the resistance of code 332 brass rail is about the same as AWG7 copper wire a separate power feed would only make sense if you either don't have a good electrical connection between track sections or you have a dog bone type layout where you can feed the cetre of the dogbone with a relatively short run compare to the distance the track takes.

Power busses are useful for H0 and the smaller gauges.

Knut


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 13 Mar 2011 11:04 PM 
The connections between the rail sections is ALWAYS worse than the continuity of the rail itself. 



You think two proper solder joints and an inch or two of 14 gauge copper wire to make a connection between rail sections has a higher resistance than say a five foot section of code 332 brass rail?
I rather doubt it, but even if I did, when you run a power bus you still end up with two solder joints per feed.

The resistance in either case is so small it doesn't really matter in the end.

Knut


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## Greg Elmassian (Jan 3, 2008)

Joiners... are you not reading my posts? 

Joiners... 

yes if soldered jumpers no problem, one feeder. 

Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 14 Mar 2011 09:24 AM 
Joiners... are you not reading my posts? 


Yes, I read your posts.

I just didn't agree with the statement in your next post especially with the "always" capitalized.

_"The connections between the rail sections is ALWAYS worse than the continuity of the rail itself."_

There it sounded as if you're talking connections in general, not rail joiners specifically. 
Anyway, slight misunderstanding - glad we're back on the same wavelength again.


Knut


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