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Power Fade

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  • Member since
    February 2001
  • From: US
  • 21 posts
Power Fade
Posted by terryb on Sunday, October 12, 2008 5:44 PM

I have a DC layout using Atlas nickel silver track where the mainline is wired with multiple "blocks" of varying lengths. Each block is wired back to an Atlas Controller attached to a MRC 2500 power source. The linear length of the main track is approximately 135 feet. I have some trouble with the power fading the further the engines get from the power source, not necessarily the power contact point within the "block". Of course, with the more engines on the train or the longer the train being pulled, the worse the fade seems to be. With no engines in these "blocks" the power reading on the volt meter is the same as the non-fading "blocks". When taking a reading with the "block" under load, the voltage is down from what it is normally. I have run an additional contact point to these troublesome "blocks" with only a small difference made in the fade.

After searching and reading some of the troubleshooting suggestions, I'm beginning to think an upgrade to my MRC 2500 may be in order as the first step to take. The trouble seems to be worsening over time. A few years ago the trouble was not as pronounced. Would anyone have any additional insight?  

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  • From: Orig: Tyler Texas. Lived in seven countries, now live in Sundown, Louisiana
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Posted by jeffrey-wimberly on Sunday, October 12, 2008 5:50 PM
Seems to me that wire going to those blocks is too light and is causing resistance. Try using larger wire.

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  • Member since
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  • From: Sierra Vista, Arizona
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Posted by cacole on Sunday, October 12, 2008 6:25 PM

I agree with Jeffrey-Wimberly, your wire is too small a gauge to handle the current load that you're trying to draw through it.  Use a heavier guage wire for the track feeds to the areas where you're having a voltage drop or simply run another wire parallel to the existing wire and connect it at both ends, being careful to keep the polarity straight. 

 

  • Member since
    January 2001
  • From: SE Minnesota
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Posted by jrbernier on Sunday, October 12, 2008 6:32 PM

Terry,

  I can think of several reasons for your 'power fade':

  • Size of 'bus' between the block control switch and the block.  I would suggest nothing smaller than #18 gauge wire.
  • How many places in the 'block' does the power feeder touch?  It sounds like you may be depending on the actual rail joiners to transmit the power though the block.  Each section of rail should have a feeder attached to a 'bus' that goes back to the control panel.  I suspect some of those rail joiners are corroded and you have a high resistance joint. 

  Even with standard DC cab control wiring, most model railroads seem to have the cheapest wiring possible!

Jim

Modeling BNSF  and Milwaukee Road in SW Wisconsin

  • Member since
    December 2004
  • From: Bedford, MA, USA
  • 21,483 posts
Posted by MisterBeasley on Sunday, October 12, 2008 8:53 PM

And if all this about bus wires and feeders doesn't have you in a frenzy of excitement, there's always the old standby:  When was the last time you cleaned your track?

I spent part of today running a CMX car around in my subway tunnels, which are kind of unreachable for that sort of work, so track cleaning is on my mind.

On the other hand, if you want my best guess at what is wrong, I'm going to say that you need thicker bus wires and more feeders, just like everyone else.

It takes an iron man to play with a toy iron horse. 

  • Member since
    October 2005
  • From: Ulster Co. NY
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Posted by larak on Monday, October 13, 2008 12:09 AM

Are we correct in assuming that you are taking voltage readings from the track?

If you are observing voltage loss at the power supply then the supply is overloaded or going bad. If voltage at the supply is constant but you observe loss down the line you need larger bus wires and/or more feeders.

Also, how do you connect rail sections?

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  • Member since
    February 2001
  • From: US
  • 21 posts
Posted by terryb on Monday, October 13, 2008 8:29 PM
Thank you everyone for your replies. The general consensus seems to be that larger gauge wire is needed so that's where I'll start. I'll try it on only one of the troublesome blocks first to see what changes occur and go from there.
  • Member since
    February 2005
  • From: Vancouver Island, BC
  • 23,330 posts
Posted by selector on Monday, October 13, 2008 9:30 PM

It isn't quite that simple.  The gauge should be largest the closest to the source.  Thereafter it can be reduced in each of the short feeders that connect to the rails here and there.  A typical setup comprises a "bus" of 14-18 gauge wire that generally follows the axis of either the main track or the layout bench.  Soldered at one end to the bus are short 20-22 gauge feeders, while their other ends are obviously soldered to the rail bases or their webs.  The idea is to ensure a largely unimpeded voltage is carried by a robust, less resistive, wire to the extremes of the layout, and then use the thinner wires for short distances up to the rails where voltage losses will be minimal.

I just wanted to correct what I gathered was a wholesale bent on your part to increase the gauge of all the wiring on your layout.  It isn't necessarily going to be your salvation, and probably not in your best interests.

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