DCC Dropper Wires

[JST]

Being new to all this I am gathering all the info I need to proceed. The basic question is at what intervals should I install dropper wires. I will be using Peco code 100 track, about 35 pairs of electrofrog points (plus 2 crossings and a couple of double slips). There will be 2 continuous main lines plus two branch lines giving a total of about 200 yards of track. The tightest curves will be Setrack radius 4. I am guessing at putting dropper wires on every other section of code 100 track. I am going to solder the fishplates on very other join of the Setrack (making a double curve) and putting droppers on every other section. I am aware of the issues and needs of all the electrofrog gear and crossings.

 

Any views? Over the top or not enough?

 

Cheers

 

John

[michaelp]

Droppers on every piece of track is how I'm doing mine.

 

Michael

[Oldddudders]

Droppers on every piece of track is how I'm doing mine.

 

Michael

And that, a wire to every piece of rail, is the recommended method, not only for DCC, but also best practice for ordinary DC too. Relying on rail joiners is fine when everything is new and clean, but time can take its toll. A little extra work now can avoid frustration later.

[RFS]

I would strongly caution against soldering fishplates to the rails.  You need to gaps to allow for expansion and contraction in hot weather, otherwise the track can buckle.  Rather than soldering a fishplate on alternate pieces of rail, and a dropper also on alternate rails, I'd advocate just soldering a dropper on each rail which is what I do. Same number of solder joints in the end. 

[beast66606]

And that, a wire to every piece of rail, is the recommended method, not only for DCC, but also best practice for ordinary DC too. Relying on rail joiners is fine when everything is new and clean, but time can take its toll. A little extra work now can avoid frustration later.

 

2 wires in our case, even tiny lengths, and anything embedded such as yard tracks has a wire every couple of inches, gaps or not. If we use fishplates (normally fiddle yard only) they are seen as a bonus.

[amdaley]

Being new to all this I am gathering all the info I need to proceed. The basic question is at what intervals should I install dropper wires. I will be using Peco code 100 track, about 35 pairs of electrofrog points (plus 2 crossings and a couple of double slips). There will be 2 continuous main lines plus two branch lines giving a total of about 200 yards of track. The tightest curves will be Setrack radius 4. I am guessing at putting dropper wires on every other section of code 100 track. I am going to solder the fishplates on very other join of the Setrack (making a double curve) and putting droppers on every other section. I am aware of the issues and needs of all the electrofrog gear and crossings.

 

Any views? Over the top or not enough?

 

Cheers

 

John

 

If you solder droppers to every piece of track & the toe end of every point you use then you are very unlikely to ever have a problem. Its the correct & recommended way to wire a layout DC or DCC. Do not solder rail joiners as doing this removes the expansion joints needed to allow rail to expand & contract.

I'm not saying you can't get by with bell wire & a prayer but if you're going to do it then its worth doing it correctly first day rather than spending valuable modelling time trying to find & repair faults.

Very important as well is to use the correct thickness of wire for the main bus & dropper wires.

[JST]

Fair enough, every bit of track it is! The reason for soldering the fishplates on the Setrack is that they are only very short pieces so I figured there would still be enough expansion joints... unless you tell me otherwise.

 

Thanks for the advice.

[amdaley]

Fair enough, every bit of track it is! The reason for soldering the fishplates on the Setrack is that they are only very short pieces so I figured there would still be enough expansion joints... unless you tell me otherwise.

 

Thanks for the advice.

 

Are you doing 200 yds of track all in short pieces of setrack ?

If you are then solder several short pieces together & use one set of droppers to each soldered section. One set of droppers to each yard of soldered track.

[The Bigbee Line]

This is very harmonious, all seem to be singing from the same hymn book.  I'm cynically waiting for the 'I've used 2 bits of PO wire for 25 years and never had a bit of trouble........'.

 

Seriously never too many feeds.  Try and have some form of colour coding and test as you go along.  Having a loco to run as its being wired soon highlights any error.  Been there got that badge...

[amdaley]

This is very harmonious, all seem to be singing from the same hymn book.  I'm cynically waiting for the 'I've used 2 bits of PO wire for 25 years and never had a bit of trouble........'.

 

Seriously never too many feeds.  Try and have some form of colour coding and test as you go along.  Having a loco to run as its being wired soon highlights any error.  Been there got that badge...

 

Its Easter time 

[Phil S]

'The test' which the completed layout should pass is the 'Coin Test':   It should also be noted that wiring capacities are related to the proposed current capability of the central unit/ Power district.

 

Unlike an analogue layout, which only carries current, in practice, when an occasional loco is passing through the section, with dcc, and especially once lighting and sound are included in your stock, the 'quiescent' current' demand can become consideerable.  For example - my storage area takes 0.65A, continuously,in coach lighting, from all the rakes of stock waiting there.

 

Unless you have divided your Power District into sub districts, each perhaps with a PSX or similar intelligent circuit breaker, you must ensure that ALL parts of the Power District can....

1/ Receive sufficient voltage when the MAXIMUM current is beng drawn across the District ... a drop of a couple of volts may be acceptable, but that is all ... or sound locos may start dropping out.

2/ The MAXIMUM current for the Power District should be able to reach that part of the layout without 'restriction' through inadequate wiring ... causing voltage loss (and heating in the wiring or components on route)  

3/ The Central unit will cut out, for protection, at a value ABOVE the MAXIMUM CONTINUOUS rating of the Unit .... the resistance of the loop wiring controller > track > controller MUST allow that current to flow, or the protection will never be able to cut-in as it should.

 

THE (minimum) WIRING for the above will therefore vary, with the chosen output of your Central Station: the higher it is, the less resistance the wiring including track, must have.

From V=IR   and given the same starting voltage - as the current rating goes up, the maximim resistance MUST proportionally to a lower value.  eg 2A, 8ohms >> 4Amps, 4 ohms, 8A >> 2ohms.

 

When checking your wiring, you MUST assume the 'worst case scenario' of a short circuit on ANY part of the track ... eg place a coin across the rails .. hence the 'coin test'. This MUST cause your controller to immediately cut out.

 

This may explain why you hear of some users contnuing with their 'analogue'/sectionalised wiring: if they bought a minimal current starter controller - eg 1A, then it is similar to its analigue predecessor, perhaps .... but if a 5A central station was used,it may fail the coin test, and become a fire risk.  (Dividing into Sub Districts each with its own lower protection, eg with a PSX set to 2A, can allow lower-capacity wiring, as the protection limit is reduced to the 2A maximum / perhaps 3-4A trip, of the protecting device.

 

Note I havn't related this to 'droppers' in any way; IT IS THE END REQUIREMENT of passing the coin test which is needed.  How you ensure that depends on your track etc.

[JST]

Are you doing 200 yds of track all in short pieces of setrack ?

If you are then solder several short pieces together & use one set of droppers to each soldered section. One set of droppers to each yard of soldered track.

 

Nope, mainly code 100 yard lengths. The Setrack is just for the tightest curve.