A different way to use dropper wires?

Post all your model railway electronic problems, solutions and discoverys here.
User avatar
Jim S-W
Posts: 1210
Joined: Fri Dec 04, 2009 5:38 pm

Re: A different way to use dropper wires?

Postby Jim S-W » Fri Feb 23, 2018 7:24 am

I use 2 droppers per rail wired to a bus. The advantage is if a dropper fails it doesn’t affect the supply at all.

Using droppers to wire between rails misses this completely. If your dropper fails at either end everything the other side of the dropper to the power supply is dead. Really it’s a lot more work than just using fishplates but you have the same fundamental disadvantage.

HTH

Jim

User avatar
TimberSurf
Posts: 2107
Joined: Wed Jan 08, 2014 5:47 pm
Location: N.Wales
Contact:

Re: A different way to use dropper wires?

Postby TimberSurf » Fri Feb 23, 2018 7:35 am

I think we need to put this in perspective! First of all, Rule 1 applies!
A bus is not obligatory!
Don't forget, having a bus serves two purposes, one to ensure a low resistance path to all parts of the track and two, to supply ancillary devices around the layout! There is no reason that lots of spurs (pairs of small wire) could not be wired individually to several points around the track and ancillary points! Its just easier to have a 2 wire bus rather than big bundles of wires running from the supply point.

Were it is important, is on a large layout were volt drop gives a huge impact. On a small layout (and that probably means most UK modellors) it is less important. There are also a few other factors that make an impact.
Volt drop = I x R. So if the loco draws 1 amp, and 40ft equates to 3 ohms, then volt drop is 3 volts, but if the loco is more modern and only draws 0.3 Amps then the volt drop is only 1 Volt!
If there is a fishplate every 1 meter, on a 4 meter long track, there is 10 times less chance of a high resistance fishplate joint, than a 40 meter long track.
On a large layout on DCC there will be 4-10 amp boosters, with the possibility of running consists drawing several amps, therefore a large volt drop due to the large loco current, if only a small layout and a small controller is used < 2 Amp (usually only 1.2 Amp), then the maximum volt drop is less (defined by the max output of the controller).

So you see that on a smaller layout, going mad with a bus is not really necessary. It is certainly good practice and I would recommend supplying lets say a 3+ meter long layout with more than 2 droppers (one at each extremity and say the odd branch line and individual sidings (as they should have IRJ's if electrofrog) and perhaps more if the track is not all flexitrack (std track will have more fishplates)

Linking across fishplates will certainly eliminate the risk of bad fishplate joints, but it will not improve the volt drop on a large layout.

My principle (and its a personal choice) is to have feed wires to every 2 meters of track (one of the reasons being that I will have block detection and braking sections every 4 meters) but I would have at least 1 dropper per 4 meters (i.e. 4 x flexitrack lengths) as a minimum, this ensures I only have a maximum of 3 joints per dropper, that might give trouble (easy to diagnose if they do, as a very small section)

I would also advocate on a booster supply (> 2 Amp) to not only use districts but also create sub districts that are protected by electronic fast fuses or the "21W lamp in series" current limiting bulb.
Image
Lumsdonia <--- Hit link to go to my website for full story and wiring advice!

b9y
Posts: 52
Joined: Sat Jan 13, 2018 6:22 pm

Re: A different way to use dropper wires?

Postby b9y » Sat Feb 24, 2018 1:04 am

Oooh ok thank you. Sorry it's all a little confusing for me at times. Ok the whole thing about failing droppers etc makes more sense. Thanks guys :)

heda
Posts: 353
Joined: Fri Oct 09, 2009 9:56 am

Re: A different way to use dropper wires?

Postby heda » Sat Feb 24, 2018 11:21 am

Hi b9y
To put it simply, every rail of the track needs power, without a bus you are relying on connections (fishplates) which are not reliable. if you solder wires across the joins as you suggest, it is better but if one wire gets broken or detached that rail will only have power from one side and the wire will be difficult to replace once the track is ballasted. If you use bus and droppers each piece of track is powered, if one dropper fails that section of track is still powered from both ends.
Hope that helps.
Dave

User avatar
D605Eagle
Posts: 2502
Joined: Mon Mar 22, 2010 12:58 am
Location: Staffordshire
Contact:

Re: A different way to use dropper wires?

Postby D605Eagle » Sun Feb 25, 2018 11:26 am

You say fishplates are not reliable but in my experience if you make sure they are a tight fit they will work reliably for years and years. The only situation I've found where they won't is in damp conditions, ie an outdoor layout.

b308
Posts: 4752
Joined: Sat Apr 15, 2006 5:48 pm
Location: North Worcs

Re: A different way to use dropper wires?

Postby b308 » Sun Feb 25, 2018 11:34 am

Yes i agree, I've only had the odd fishplate "fail" on my many exhibition layouts and it's been easy enough to find and fix... Where a bus wire comes into it's own, though, is on large layouts where voltage drop is an issue, none of my layouts have ever fallen into that category, though!

User avatar
Flashbang
Posts: 3236
Joined: Thu Oct 18, 2007 1:07 pm
Location: SE United Kingdom

Re: A different way to use dropper wires?

Postby Flashbang » Sun Feb 25, 2018 3:42 pm

D605Eagle wrote:You say fishplates are not reliable but in my experience if you make sure they are a tight fit they will work reliably for years and years. The only situation I've found where they won't is in damp conditions, ie an outdoor layout.

They are unreliable! Even the tightest will allow the rails to move inside the fishplate due to temperature changes (expansion and contraction) which in turn introduces microscopic airborne dust partials between rail and inside of joiner. The ultimate result is a poor connection rail to rail resulting in DC locos slowing on a particular section or even stopping. While on DCC the loco will usually stop due to loss of data.

What works for one person is fine and they may work for the rest of the railways life if never disturbed, but its not good practice and whenever possible the best advice is 'dont scrimp', soldering isn't hard to learn and once mastered dropper wires can be pre fitted to rails at a rate of speed where fitting them isn't any issues. :D
Broken? It was working correctly when I left it.

heda
Posts: 353
Joined: Fri Oct 09, 2009 9:56 am

Re: A different way to use dropper wires?

Postby heda » Sun Feb 25, 2018 7:14 pm

Fishplates are a potential weakness, they may or may not cause problems. A bus and droppers will eliminate the chance of power failure to the rails.
Dave

User avatar
D605Eagle
Posts: 2502
Joined: Mon Mar 22, 2010 12:58 am
Location: Staffordshire
Contact:

Re: A different way to use dropper wires?

Postby D605Eagle » Wed Feb 28, 2018 1:30 am

Flashbang wrote:
D605Eagle wrote:You say fishplates are not reliable but in my experience if you make sure they are a tight fit they will work reliably for years and years. The only situation I've found where they won't is in damp conditions, ie an outdoor layout.

They are unreliable! Even the tightest will allow the rails to move inside the fishplate due to temperature changes (expansion and contraction) which in turn introduces microscopic airborne dust partials between rail and inside of joiner. The ultimate result is a poor connection rail to rail resulting in DC locos slowing on a particular section or even stopping. While on DCC the loco will usually stop due to loss of data.

What works for one person is fine and they may work for the rest of the railways life if never disturbed, but its not good practice and whenever possible the best advice is 'dont scrimp', soldering isn't hard to learn and once mastered dropper wires can be pre fitted to rails at a rate of speed where fitting them isn't any issues. :D

No they are not. Tight fishplates do not allow dust in when the track moves, the movement keeps the contact area between the two faces clean and free of oxide. In 45 years of modeling they have proved very reliable.

User avatar
Flashbang
Posts: 3236
Joined: Thu Oct 18, 2007 1:07 pm
Location: SE United Kingdom

Re: A different way to use dropper wires?

Postby Flashbang » Wed Feb 28, 2018 10:49 am

OK ... You run your railway relying on metal slide fit joiners and I'll run mine with soldered wires to the rails and just use metal joiners to align abutting rails. Each to their own! :D
Broken? It was working correctly when I left it.


Return to “Electronics”

Who is online

Users browsing this forum: No registered users and 3 guests