Bus wire size?

[Porkster]

Hello, can anyone give me some guidance as to what size the buss wire and droppers should be. I was thinking in terms of 1mm sq solid for the droppers and 2.5 mm sq stranded for the buss. Also should the buss wire be twisted. Thank you Porkster

[poliss]

Suggestions for bus wire sizes on Brian Lambert's DCC pages.

http://www.brian-lambert.co.uk/DCC.html

[Fishmanoz]

There is more in the forums on DCC bus (not buss), droppers, terminators and twists than you can jump over.  Do a search. Also look for Mark Gurries, he is a good source and links to his content are also to be found here.  Then you might also look for this content on the DCC Concepts web site.

 

Remember, you aren't powering Auckland, just a model railway with wire sizes to ensure low voltage drop across a few metres at maximum 60 watts.

[Porkster]

Thank you very much for your replies. Your advice has been most helpful. I have easy access to scrap cable so will prob run with the 1mm droppers and 2.5mm bus. Cheers 

[morairamike]

 problems maybe encountered using 1mm solid for the droppers. The holes through the base board will have to be exactly lined up to ensure no strain on the soldered connection to the rail. in my case I use 7/.02  droppers and solder to the base (not the sides) of the rail in the centre of the length (if possible). Other problem is that 1mm solid is not easliy laid under the board and any bends will/may be difficult to form.

Just my input.

[Chrissaf]

I agree with MM.....I too use 7/0.2mm for droppers.....much easier to work with as more flexible. Talking of flexibility.....solid conductors can be prone to fatigue induced breakages (fatigue.....movement due to vibration or track flexing). Like MM, I too solder to underside of rail (during laying) not the side of the rail. But unlike MM, I prefer connecting at end of a track length, not the centre, particularly easier if using flexitrack.

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I'm assuming that you were intending to use un-insulated 1mm solid copper wires stripped out of domestic mains cables. Being un-insulated there is more scope for un-intended short circuits to occur.

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PS - for the main under-board BUS wires I use 16/0.2mm. Ideally, these should be formed into a 'twisted pair' to reject induced electrical interference.

[poliss]

Peter used 15amp fuse wire for droppers. He was a professional TV repair man, so he knew a thing or two.

 

[Flashbang]

The problem with using fuse wire as droppers is it's a bare conductor and can very easily make contact with adjacent droppers of opposing polarity.

It is far better to use an insulated conductor as the dropper. 7/0.2mm is ok so long as each section of track has a dropper and the distance between rail and bus wire is kept short. Ideally no longer than 300mm rail to bus wire.  Otherwise use the larger 16/0.2mm equipment wire. 

 

As for bus wire size, this will always be contentious.   I recommend the minimum bus wire to be 32/0.2mm equipment wire or 1.5mm2 solid wire. The reason is that any fault current has to reach the DCC console extreamly quickly.  On a medium sized layout (Medium sized think 'Garage sized') fed with a 4.0Amp DCC system the fault current can reach well in excess of 6Amp or more before the system trips out.  This is around 90 watts (6 X 15 = 90).

At maximum power current of a 4.0 Amp power suppy to track then around  60 watts of power can flow normally. = 15 v at 4.0Amp is the expected output of the Hornby eLink when using the larger 4.0Amp power supply so 60 watts of power is easily obtained. The Elite is 3.0Amp to track as supplied.  (Select is 1.0Amp using the supplied power pack).  A Hornby Booster will provide 4.0Amp to track before shutting down under higher fault current. Try touching a 60 watt bulb when lit - it's very hot. In fact don't do this its too dangerous!  Think of the reports of point blades burning and smoking!  Thus is all due to the larger currents involved with many DCC systems!

 

The best test is the 'coin across the rails' test applied at many places around the layout as practicable with the DCC system turned On..  Everytime the coin is touched across the rails the DDC console MUST trip immediatly. Any delay or failure to trip must be immediatly resolved as it indicates there is a serious defect in the layouts wiring or rail connections 

[poliss]

Did you watch the video Flashbang? I can't see how it would be possible for them to contact adjacent droppers.

[Porkster]

Thank you all, this is very good advice. Ok, so here is my latest latest decision. I have another favourable cable supplier who can supply me with a very flexible multi stranded cable. So I will run with 1.5mm (twisted) for my bus and .5mm for my droppers. Should I have droppers on every rail and turn out? And if so, what happens in a reverse loop, do I power up every rail from the RLM? 

[Flashbang]

For the optimum performance of both power feeding and data transfer having droppers on every piece of track is the best. This is the norm on many DCC exhibition layouts where the best reliability is needed.   But if you wish it is not essential to do so.  You then rely on the metal fishplate passing power and data rail to rail.

On a Reverse Loop make up a sub bus pair of wires which are fed from the RLMs output.  Then connect the droppers from the loops rails to this sub bus.  Just ensure no other rails are allowed to connect to the sub bus - only those of the reverse loop. Perhaps a wise percaution would be to use two totally different coloured wire insulations for the sub bus pair?

 

[Porkster]

Thank you Flashbang, that is great advise which I will follow. Just out if interest, could you join say every second piece of track ( by soldering the fish plates ) and thereby effectively halve the total number of droppers required. 

[poliss]

You shouldn't solder the fishplates. The track should be allowed to contract and expand in different weather conditions. Soldering the fishplates prevents that and can lead to the track warping.

[Rog RJ]

If you did solder the fishplates you would probably find it very difficult without the correct flux.  I think Hornby fishplates are stainless steel.  Peco fishplates are much easier to solder but as others have said, don't solder them, especially in a climate such as the UK has where temperatures can vary greatly.

[Porkster]

Thank you everyone. I have taken it all on board cheers Porkster