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Hello Folks:

I know this is an older thread but I thought I'd add my thoughts, on my previous layout, which had a life of about seven years, I found that eventually I had to bond all the rail joints as the joiners themselves fill up with gunk and don't fully conduct, the gold plated Peco joiners were very good, bet they're not made any more! Spraying with a good switchcleaner periodically, Servisol is good, (not WD40 it's an oil), does help but the older the layout got I had to put more bonds in, a gas soldering iron is good for the work, and the wire can be pretty thin.

As regards track power, Tom is right on the money, the thicker the copper core the less resistance over longer cable runs, there is nothing to prevent you using thinner cable from the track itself to a lineside junction box, but the long lengths should be at least 2.5mm.

Lighting feeds can be pretty thin, especially with LEDs. For point motor feeds I used recycled quad microphone cable, I use the screen as common and I can feed two motors from one run, however I do use a good cap discharge unit off a twenty four volt supply, so there's plenty of "thwack"!It will happily fire two motors on a crossover. Computer cable could be used for points or lighting I would say, although some of the cores are thin, so I really wouldn't recommend it for track power.

I hope this is useful.

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It's extremely useful to know what other members use on their layouts. To those, like me, who understand very little about electrical matters, it can become very confusing when we are told we must use a certain gauge wire for different applications only to read elsewhere that we should be using something altogether different.

I run 2.5mm for bus wires with short lengths of 7/0.2mm for 'droppers'. I've never had a problem to date with double heading DCC sound loco's, so I assume that to be okay. For my point control I use standard 8 core alarm cable which I find convenient for its colour coding.

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Sat as I am by an equipment measuring 1000V to 1000.0000V Accuracy

I can confirm,

if you add two identical transformers by connecting + to - and measuring end to end you are in Series and double the Voltage for the same current.

If you add two identical transformers by connecting + to + and - to - you are in parallel and double the current for the same voltage.

Roddy, The transformers you are using are they boxed and labeled? if they are what make and what is the writing on the bottom I MIGHT be able to decipher what you've got.

As to knowing the current of a particular Loco or Tram, the only way is to measure it. You would need a digital multimeter set to the 2 Amp range in ONE leg of the wires going to the track. ( or better one leg of the wires going to a rolling road, ) then power up the loco to the max and take the reading.

DO NOT connect a multimeter set to amps across the output of a transformer or across both rails there will, if you are lucky, be a little pop as your fuse dies, if you are unlucky there will be a little cloud of smoke as your transformer turns itself into a smoldering wreck.

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I would never rely on track connectors to conduct power the track, indoors or outdoors, but would bond each section to a power bus running round the track via droppers.

For the mains bus I'd by a drum of 2.5mm cable from your local DIY store or the internet. This is WAY over rated for the power used by a model railway. But we are not talking about power levels here, but losses due to the resistance of the cable. ALL cable has resistance the thicker it is less

less it has.

1.5mm wire has a loss of 29mVDC per meter per amp (rough figures for single core cable)

2.5mm wire has a loss of 18mVDC per meter per amp

So if you have a 30ft out and 30ft back track outside that is roughly 20 metres. 1 large 00 Loco can draw close two 2 amps under heavy load.

So using a 1.5mm Bus you would lose 0.029X2X20) 0r 1.16 volts

OR using 2.5 mm Bus you would lose 0.018X2X20) 0r 0.72 volts

Now this doesn't sound a lot but every soldered inline connection to the track WILL reduce the voltage further.

Just relying on track connectors each will introduce a resistance that with time will get worse, don't do it !!!

Try to keep the bus with as few joints as possible everyone can introduce higher resistance and possible faults.

I have seen a layout where every dropper was met with a joint on the bus line itself, not just attaching the dropper to the bus. it caused a huge total resistance and had to be rewired.

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  • 4 years later...
On 8/6/2012 at 3:27 PM, mick said:

It seems the consensus is on using 0.2mm stranded wire of sometimes 7 and sometimes 16 strands as 'droppers' when connecting to a power bus. Ideally I guess it should be the larger 16 strand.

7 strand 0.2mm would be much easier to conceal at the side of the sleepers on an outdoor layout if it was capable of supplying the required power. It's a pity that we can't go directly through the baseboards close to ground level without a lot of additional work.

As far as I can make out with droppers, the idea is that they are so short that it doesn't matter. If you are running a bus and droppers to every piece of track, provided the bus comes reasonably close to the track then all the droppers have to do is supply whatever is on that one piece of track. It won't make any significant difference how far your dropper is from the controller or booster provided the bus is sufficient.
On an indoor layout where the bus is generally under the track and the droppers are less than 12cm (5") long then 7/0.2 isn't going to be a problem. The times you may want to consider 16/0.2 for the droppers is where your droppers have to be a bit longer or where the demand on them might be greater, like say a diesel depot where you might have a few sound locos sitting on one piece of track.
I find 7/0.2 is much easier to solder to the track and I'd rather extend the bus than have long droppers. I know some people use block detection and therefore have much longer droppers so might need 16/0.2 on those.
If I'm wrong on any of that then please correct me.

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On 12/14/2015 at 11:24 AM, TheQ said:

1.5mm wire has a loss of 29mVDC per meter per amp (rough figures for single core cable)
2.5mm wire has a loss of 18mVDC per meter per amp

So if you have a 30ft out and 30ft back track outside that is roughly 20 metres. 1 large 00 Loco can draw close two 2 amps under heavy load.

So using a 1.5mm Bus you would lose 0.029X2X20) 0r 1.16 volts
OR using 2.5 mm Bus you would lose 0.018X2X20) 0r 0.72 volts

Now this doesn't sound a lot but every soldered inline connection to the track WILL reduce the voltage further.

Thank you for the info there. As I've got just under a 20m run around the garden and the way it is with the bridge I'll have to do a U shape which comes to about 15m, so these figures are useful.

Just a small question though, what is an acceptable level of voltage drop at the end of the run?

I'm just wondering at what point the next size up listed at Screwfix (4mm sq, 7strand per core) becomes preferrable?

Thanks,
Barry.

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