Mythbusters MRR Style - Feeder Wire Overkill?

[jwils1]

Does a higher amp system help to overcome deteriorating track joints, e.g., would a 5 amp system have fewer problems than a 2.5 amp system?

[claymore1977]

Does a higher amp system help to overcome deteriorating track joints, e.g., would a 5 amp system have fewer problems than a 2.5 amp system?

 

I would say that 95% of time it wouldn't make any difference at all for two reasons:

1)  If a layouts electrical system sucks that bad then the locos won't be able to draw power, so having EXTRA power does one nothing.

2)   Its not really amperage capacity that is the 'concern' of the various approaches detailed in this thread, but more of the degridation of voltage from the power source to the locos.

 

  High Amperage draw across poor connections (read High resistance) can make things worse, but we are talking about amperage, voltage, resistance and wire length values that are just not present on a layout.  As has been detailed in this thread, people have run 50+ linear feet of track with a single feeder and never had problems.  That being said, any wiring above and beyond that only increases your layouts reliability and longevity.

But to answer your question directly....no a 5 amp system would not have fewer problems than a 2.5 amp system. 

[doctorwayne]

Texas Zepher

doctorwayne

All track is soldered together at the railjoiners, with gaps cut where required.

Sort of off topic (but serious) question here.  Why do you solder the rail joiners and then cut a gap?  We have people at the club that do this.  They will solder a joint and then cut a gap 1" away.  Why not just leave a gap in the track or use insulated rail joiners in those locations?  They can't explain why they do it other than habit (or not seriously - a soldering fetish).

When I first layed the track, the entire layout was one block.  After operating for a while, it was easy to see where gaps were needed in order to isolate trains while another was running.  Each track in staging is controlled by a separate on/off switch, and its necessary gap, allowing entire trains to be held without disrupting operations elswhere.  Likewise, a gap and an on/off switch were installed at passing sidings and anywhere else that I might want to park a locomotive.  Of course, gaps were necessary for proper operation of the wye, but it was easier to lay the track first, then cut the gaps where appropriate.  Another reason for not merely leaving gaps as you lay the track is that you can get a much smoother flow of the rails through curves.  Once the track is fastened in place and ballasted, there's less chance of something shifting out of line when you do cut the gaps.  Also, the gaps that present themselves as you lay flextrack and install turnouts seldom fall where you really need them to be.  And since I'm no wiring wizard, I try to keep things as simple as possibe.

In this picture, the near siding (with the gondola), plus both main lines have gaps and are controlled by on/off switches, as this is a busy interchange point.

 

Here, a train on the mainline (centre) is held, while the train on the passing siding (right) runs by.  The tender of a third loco can be seen (left): its power also shut off while the move is being made.

 

Finally, this wye wouldn't function without gaps.

 

Wayne

[jbinkley60]

Okay, it sounds like everyone is using flex track so I think I'm the oddball here as I'm using sectional track (Atlas True Track NS code 83 in 9" long sections with regular rail joiners). 

I'm using 5 amp DCC with 130' of track and 3 sets of feeders roughly equally spaced.  It's been running very well for about a year.  I've had some discussion on this with Jeffrey Wimberley but now I'm wondering about the future?

How do you prevent electrical conductivity problems with sectional track?  Please don't say don't use it, unless that's the only answer. 

I might also point out that all my track is loose-laid on top of foam.  No glue.  It just floats.  I did this at first thinking I may want to move things around but I'm happy with the arrangement and won't be moving much.  With the plastic built-in roadbed, everything locks together well and doesn't move, except for possible expansion/contraction.  Painting the foam and adding scenery tends to hold the track in place as well.

Would appreciate any suggestions.

 

 As you read through this thread (and similar ones here) there are some good comments, some urban legends and some things which just don't add up.  For instance a general good comment is that more feeders are better than less feeders but taken to an extreme, there are drawbacks.  An urban legend is a comment that additional feeders will make up for dirty track, paint on rails from weathering or similar wheel to rail contact issues.  The comparison here is on the order of a few ohms of additional resistance from less feeders vs. hundreds to thousands of ohms of additional resistance from wheel to rail contact issues.  Additional feeders will make up for bad joiners but why not fix the joiners ?  And the things which often don't add up or raise eyebrows, pretty much most comments about the AC characteristics of DCC and such (which often includes voltage drop debates on DCC at speeds less than 100% throttle).  So now that I have possibly offended many here, let me give you my simple suggestion.

Focus first on how you will grow your layout once you exceed the capacity of the largest booster.  I have yet to see a DCC manufacturer that can cluster boosters so you must plan for what will happen once the total current draw of your locomotives (and those you may get in the future) exceeds your booster (you can buy a bigger one but do we really want 20A boosters in the future ?).  Because once you reach this condition you will need to find a way to address it.  I suggest breaking layouts into more blocks instead of a single monolithic block that covers the entire layout.  This may include the mainline, depending upon its length the current draw of the total number of locomotives on it compared to the booster output.  The advantages of multiple blocks is that you don't need to do major rewiring when you reach the booster limit, smaller blocks will allow for shorter buses and potentially smaller wiring, blocks  improve troubleshooting when problems occur and having blocks can make adding things like detection systems easier in the future.  Once you have focused on the growth and have a reasonable amount of blocks, then you can focus on the actual phsyical wiring characteristics.

The one thing I continually hear folks say is that they only have a handful of locomotives or they will never get into sound so they won't exceed the booster output.  I don't know about you but my crystal ball isn't polished this well.  Who can tell me that I won't buy sound locomotives.  When I started my current layout 6 years ago I was on DC and had no sound locomotives.  Today I have DCC, multiple boosters and many sound locomotives.  I also can't tell you what the manufacturers have planned for the future that might draw more current but whatever it is, I will likely buy it.  For me the move to DCC was extremely simple.  I swapped DC circuit breakers for electronic ones and then figured out which breakers mapped to which boosters. 

So that's my suggestion.  Now I put on my fire retardant suit to ward off the flames.

   

[jbinkley60]

Does a higher amp system help to overcome deteriorating track joints, e.g., would a 5 amp system have fewer problems than a 2.5 amp system?

In general the answer to both is "No".  Under just the right circumstances it would have the opposite effect but that is an extreme case.

 

[jbinkley60]

There is this - if all you "feeder fiends" are overdoing it, there's no serious downside. If I'm wrong, in five or ten years I'll be crawling around on and under the layout adding feeders everywhere. BIG downside! Still, I'm bull-headed enough to take that risk! I do run 12-gauge busses, so the main distribution network is there if I have to add more taps.

The main downside is that if they didn't plan for growth and have to breakup a large monolithic buss wiring scheme, there could be some rail cutting and rewiring involved on a finished layout.

 

 

[jbinkley60]

When I first built my layout I had a single set of feeders for each block. Most blocks were less that 8'. I used 14ga stranded connected to 18ga stranded with wire nuts. The feeders were soldered to the bottom of a rail joiner like the ones Atlas sells.  None of the wire runs were over 10'. All was well - for about 7yrs.

I then began to notice that at low to medium speeds the locos would slow ever so slightly when operating at certain spots of the layout. Other places it was more noticeable. No amount of track or wheel cleaning would help.

I decided to find out exactly why this was occurring.  I loaded each block one at a time with a .250ma electrical load. Using the voltage drop method, I began to check for losses. Not exactly the wiggle and jiggle method but one that works very well in giving accurate results. I was surprised at what I was seeing on the DMM. Some blocks were losing close to 1v; many were in the .600 to .700mv range. The further from the feeder in each block, the higher the voltage drop. Loose or contaminated joiners caused the losses.

I carefully replaced all of the joiners and added extra feeders in all of the blocks over 3'. I used extra caution to not get any ballast glue on the joiners. A joiner never gets reused. After another eight years a recent test showed my drops all under .080mv. No more slow order areas.

When you initially build a layout, everything will be (or should be) electrically tight. Over time this will change. How much it changes depends on you.

Jim

I am going to climb out on a limb here and guess that this was a DC system.  In DCC the voltage delivered to the decoder inputs is not the same as the voltage delivered to the motor.  In DC the voltage that reaches the wheels is what gets sent to the motor.  That difference can easily make up for small voltage drops that might be incurred from the closest feeder to the locomotive wheels.  The DCC driving current for the motor is actually a constant differential DC component of the signal across the rails (i.e. rail A is 180 degrees out of phase with rail B).  The differential DC component of this signal creates the maximum available DC voltage (minus the voltage drop of the decoder itself) which is going to be higher than the actual voltage delivered to the motor, unless your throttle is at 100% and you don't have a Vmax set on the decoder. 

 

[simon1966]

An urban legend is a comment that additional feeders will make up for dirty track, paint on rails from weathering or similar wheel to rail contact issues.  The comparison here is on the order of a few ohms of additional resistance from less feeders vs. hundreds to thousands of ohms of additional resistance from wheel to rail contact issues.  Additional feeders will make up for bad joiners but why not fix the joiners ? 

Jeff, no flame intended, but I don't think that anyone suggested that more feeders make up for track that has been made dirty from painting, weathering and ballasting.  The conductivity breakdown that can occur here is not the wheel to track (which can and should be cleaned with normal methods), but the conductivity breakdown that can occur in the joiner to track interface.  I have had first hand experience with this where I had installed feeders to a siding but had not yet soldered them to the bus.  Everything worked fine prior to ballasting and weathering the track.  After this was complete and the track cleaned it would not run.  Capillary action, I assume, had caused my joiners to no longer provide a good contact.  Soldering on the feeders to the bus restored power to this section.

[Texas Zepher]

Everything worked fine prior to ballasting and weathering the track.  After this was complete and the track cleaned it would not run.  Capillary action, I assume, had caused my joiners to no longer provide a good contact.  Soldering on the feeders to the bus restored power to this section.

I had to laugh when I read this.  A few months ago I was cleaning track at the club preparing for an open house operating session.  There was one section that came up totally clean.  This was most unusual, but I attributed it to the fact that someone had just been working in that area and they must have cleaned it - right?  Anyway, the first train that came rolling into that area stopped dead.  We wiped the rails again - clean.  Checked the power supply and the feeders - all good.  We finally figured out that the capilary action of the wet-water had sucked up some ballast glue over the top of the rails.  That is why it didn't seem dirty to the cleaning rag.  All the dirt was under a layer of glue....