A different way to use dropper wires?

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b9y
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A different way to use dropper wires?

Postby b9y » Wed Feb 21, 2018 11:53 pm

So all this talk of droppers / bus wires and all that confuses me. Is it not possible to just have the following:

Connection to track from controller via clips / powertrack.
Dropper wires between each section of rail, or at least sections with poor connectivity.

....done?

I mean if you're using the wires to bypass the connection used by the fishplates, why do you need a bus wire?

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Re: A different way to use dropper wires?

Postby D605Eagle » Thu Feb 22, 2018 1:43 am

It would be very time consuming to link out every fishplate. It would work as the track itself is quite a good conductor. The interface between track and fishplate is a source of resistance, so its best to avoid too many of them between your power input and your loco. If you put droppers every so many meters connected to ring main from your controller or bus wire, your loco is effectively been powered from both ends of the track its on. If you take care to make sure your fishplates are tight you shouldn't have too many issues, and only a few droppers will do. I used to have a 16x16ft layout with only two power points on each circuit. I never had any issues with it, and it was steel track too which is not as good a conductor as nickle sliver.

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Re: A different way to use dropper wires?

Postby b9y » Thu Feb 22, 2018 2:00 am

So I don't need a bus wire? Not sure why people use them anyway? So just track connection, dropper wires, done? What do you mean by main ring? Cheers

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Re: A different way to use dropper wires?

Postby b308 » Thu Feb 22, 2018 9:17 am

Bus wires are a "DCC" thing, I've never felt the need to use them on DC layouts. Every rail on a DCC layout is live, unlike a DC layout, therefore a "bus" wire is the easiest way to supply the whole layout. You just lay two wires (or rails) the whole length of the underside of the board and the dropper wires connect them to the rails. Simple.

"or at least sections with poor connectivity."

There's no way of knowing where they are so using dropper wires connected to the bus wire eliminates that issue, as Eagle has said fishplates are notorious for proving bad connections and can get worse over time. Whilst you can correct them with some fettling the use of bus wires eliminate that. Many Garden Railways use them even though they are DC simply for that reason, outdoor weather plays havoc with connectivity so a soldered wire to rail is much more reliable...

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Re: A different way to use dropper wires?

Postby Bufferstop » Thu Feb 22, 2018 1:46 pm

My DC layout is sectioned for operational flexibility in what would be classed as "cab control with common return. So the return is from the "outer" rail via a bus wire. Purely because of the lengths involve between any break points most sections gave only one joiner (fishplate) in their length, so the feed is a wire from each section switch to each section. It could be changed to DCC simply by throwing all of the section switches one way. The switches are currently single pole two way with centre off, the choice being which handheld feeds which section. Given the relatively short lengths involved it would not be worth rewiring if I introduced DCC. (ulikely given the number of loco's involved, all of them being on the small side.)
Fishplates becoming a problem is more common with settrack laid in standard short lengths, sometimes after a year or so being taken apart and put back together (deadly to conductivity), They are a pig to remove to, should you wish to replace them, it's that little spot weld that does it. If comparing lengths of nickel silver rail versus a bus wire, a decent size copper wire wins out almost every time.
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Re: A different way to use dropper wires?

Postby Flashbang » Thu Feb 22, 2018 2:56 pm

Bus wire is conventionally from copper and a correctly sized copper bus wire has a much lower resistance than nickel silver (modern rails are normally NS). Therefore with less resistance and much lower volt drop being incurred it allows for ultra fast fault current flow and this is especially important with DCC that fault currents can return to the base unit quickly and allow the unit to trip. The Bus wires also allow for power to reach all places virtually unhindered.

On DC a High Resistance rail joiner problem can occur, but the power (current) flowing is much lower than with DCC and typically on DC to a maximum of around 1.0Amp. (N and many OO/HO). High resistance metal rail joiners are revealed on DC layouts by locos suddenly and noticeably slowing or stopping in a section of track.

On DCC where high powered units are being used which can provide 4.0Amp or more to the rails any High Resistance connection is going to start getting warm or very hot as power is trying to pass though the resistance. The bus wire removes all this. Something for the DCC user to remember is if the rail volts are a nominal 15v then with a 4.0Amp units (Hornby Elite etc) there can be up to 60 watts of power flowing. 60 watts flowing gets very hot!! Even at 12 volts there is still 48 watts available. These larger than DC currents are designed to be used with DCC and wiring needs to reflect this!

Reliance on plug-in power clips is at best a poor choice and really suited to the train set style of operation where the layout is set up then taken down again, while their larger brother the 'Power Track Section' are better, you're still relying on Plug-in wires and metal rail joiners! The very best connection to rails is by soldering the wires to the rails outer web area or for invisible wiring to the rails underside before track laying.

Fishplates or metal Rail Joiners should ideally only be used to align two adjacent rails. They are rather poor at passing power (and for DCC data too) rail to rail. They can easily become high resistance due to looseness or ingress of airborne dirt and where rails have been painted.

Bus wires have been used in model railway wiring for decades and since models were electrically powered. A Common return wire is a Bus wire. Even a feed from a DC controller to the rails is a Bus wire where it has more than one take off to the rails!
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b9y
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Re: A different way to use dropper wires?

Postby b9y » Thu Feb 22, 2018 7:38 pm

Oooh ok that does make a bit more sense. But I could get the same effect just from wires connecting the rail sections, and not going underneath connecting to a bus right? I just need to improve conductivity without wiring a whole thing. So, wires from controller to track, feeder wires between sections to eliminate crappy fishplates.

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Re: A different way to use dropper wires?

Postby TimberSurf » Thu Feb 22, 2018 7:48 pm

The Americans always "sodder" the rails, it achieves what your talking about. I believe it is common practice to solder jumpers across the fishplates on large scales when used outside, but even they have been known to run bus wires under the track and connect under the rails, it's much more visually pleasing than seeing wires across each join.
The point is it's up to you, we are just expressing the logical/technical best practices for the best aesthetics and trouble free operation, you might have no problems in years, but you may also get problems later that are harder to retrofit buss droppers too.
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Re: A different way to use dropper wires?

Postby flying scotsman123 » Thu Feb 22, 2018 8:03 pm

b9y wrote:Oooh ok that does make a bit more sense. But I could get the same effect just from wires connecting the rail sections, and not going underneath connecting to a bus right? I just need to improve conductivity without wiring a whole thing. So, wires from controller to track, feeder wires between sections to eliminate crappy fishplates.


It'll certainly achieve the same thing but I'm unconvinced that it'll be any easier than having 2 wires from controller going all along the layout with droppers coming off for each section of track. It's twice the amount of soldering onto track for a start, which requires slightly tidier soldering than just a big blob of solder to connect a dropper to a bus wire, which is much more my style.
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Re: A different way to use dropper wires?

Postby Bufferstop » Thu Feb 22, 2018 9:31 pm

It would be useful to know the cross sectional area of code 100 rail, before I get the calipers out does anyone happen to how what it is?
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Re: A different way to use dropper wires?

Postby TimberSurf » Thu Feb 22, 2018 10:02 pm

BufferStop

See here

The usual formulation of nickel Silver is 60% copper, 20% nickel and 20% zinc
So 40% of it is only 25% as conductive as copper (60% + [25% of 40%] 10% = 70% of copper)

Material IACS (International Annealed Copper Standard)
Ranking Metal % Conductivity*
1 Silver (Pure) 105%
2 Copper 100%
3 Gold (Pure) 70%
4 Aluminium 61%
5 Brass 28%
6 Zinc 27%
7 Nickel 22%
8 Iron (Pure) 17%
9 Tin 15%
10 Phosphor Bronze 15%

But the cross section is smaller than you think, so Code 100 rail is equivalent of less than a 7/02, 0.22mm!!!!!!!!

AWG mm2 Amps
26 0.129 2.2
28 0.081 1.4
30 0.0509 0.86


My layout is going to be big, I need at least 1.5mm CSA wires! Trust me, I am an Electrical design engineer and have done the volt calculations!

On a large layout (20-40ft) from one end to the other with worst case scenario, I calced it at 5 volt drop from one end to the other! Not including loads of bad electrical connections through the fishplates!
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Re: A different way to use dropper wires?

Postby Peterm » Fri Feb 23, 2018 12:19 am

Well that's sorted that out then. :) I'll stick with soldering wires to every single piece of track, even catch points. I never have problems with dead spots or loco's slowing in certain places. I also know that if there's a short, my controller will trip out properly.

It's well worth reading Timbersurf's post and taking note of it. My Lenz kit produces 5amps and I've seen posts about loco bogies getting melted due to a short on track that hasn't been wired properly.
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Re: A different way to use dropper wires?

Postby b9y » Fri Feb 23, 2018 2:08 am

flying scotsman123 wrote:
b9y wrote:Oooh ok that does make a bit more sense. But I could get the same effect just from wires connecting the rail sections, and not going underneath connecting to a bus right? I just need to improve conductivity without wiring a whole thing. So, wires from controller to track, feeder wires between sections to eliminate crappy fishplates.


It'll certainly achieve the same thing but I'm unconvinced that it'll be any easier than having 2 wires from controller going all along the layout with droppers coming off for each section of track. It's twice the amount of soldering onto track for a start, which requires slightly tidier soldering than just a big blob of solder to connect a dropper to a bus wire, which is much more my style.


I mean the I'm thinking about it. With a bus wire, I would first have to have enough length of cable to cover the layout. Then I would need to drill down twice on each side of the track multiple times, solder the wires, connect them to the bus. In this instance I'd just be connecting the track up via two wires each side for each section so if anything it seems less effort? I mean I could be wrong, I'm new to all of this, but from it sounds like it's less work. I'm struggling to see the benefit of having a bus wire unless it's just for aesthetics.

b9y
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Re: A different way to use dropper wires?

Postby b9y » Fri Feb 23, 2018 2:16 am

The reason I'd like to do it without a bus is that I want to paint the wires grey and utilise them within the scenery, like those wires you get connecting one third rail to another etc :)

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Re: A different way to use dropper wires?

Postby Richard Lee » Fri Feb 23, 2018 6:43 am

I have two small DC layouts. With both, I decided not to rely upon fish-plates, and have droppers to each rail. Both my layouts have what people who use DCC would call a "bus" - cables underneath the layout from which the droppers are connected to. There are a couple of places where it was inconvenient to do a dropper from underneath, so I did a little, dropper-sized wire from the next rail. If I understand the original poster correctly, that is what he is suggesting for the whole layout. I have also taken wires from frogs of points to sidings that I want to be isolating sidings to power the rail that comes off the frog.

My thoughts are that I am happier doing that trick in sidings and extremities of layouts than the main bit. Although soldered joints should be very reliable for a layout that isn't going to be moved about much, it is always nice to think that power might have an alternative path if a joint deteriorates or gets broken without you knowing. Also, I find the statements about copper wire being a much better conductor than nickel-silver track eminently believable.


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