Power district allocation

[Dale]

Hi folks,

 

I am in the process of wiring up my layout at home and would like a little advice on the allocation of power districts.

 

I have a card which effectively splits my DCC bus into 4 sub districts.  I forget the name of it but I am sure you all know the one I am referring to.  A short in one district trips that sub bus but not the other three or the control system.  My question is "to what do I allocate these districts"?

 

Its a cassette fiddleyard to terminus layout (24' x 3') with goods yard and engine shed's (inc turntable) so my thinking is:

 

1. Main running lines and goods arrival/run around line

2. Fiddleyard

3. Cobalt point motors and any other fixed ancillary decoder driven accessory's (the Metalsmith turntable?)

4. Goods/Engine Sheds

 

I would very much like your thoughts on this question before i start tying droppers to buses...

 

D.

[RFS]

I assume you have the PSX 4-way circuit breaker from DCC Specialities.  How you divide up your layout is your choice (and to me it looks good), but you do need to ensure that both rails are isolated with IRJs between the districts.  Having a separate bus for points is a good idea as it allows you to change points when a short has occurred due to your having forgotten to change one!

 

Are your Cobalt motors the digital version? In which case you may not be able to use the built-in frog polarity change for Electrofrog points, as it would mean the frog being powered from the accessory bus.  If a loco shorts on the frog, it will short the accessory bus preventing you from changing the point to resolve. Hence you may need to use the separate SPDT switch on the motor for polarity changing to get round this problem..

[Phil S]

The accessory bus items want to be an independant bus, but they probably don't need to go via this protective circuit (if it is a PS-X, for example) - as they are unlikely to either experience a short circuit from a trian derailing, or running onto a wrongly set point.  They do not require protection from Lighting/sound surge currents.

 

Therefore you may be able to consider yourself as having 4 SUB districts (I say SUB, becasue they are coming from a single Central unit - unless you meant that they have their own power supplies ie 3 are boosters), in addition to the Accessory Bus.

 

I would then divide the layout 'geographically' so that fault-finding was made easier - with the sizes chosen to ''best equalise', or limit, the current consumption in each area.

 

Consider: IF you have a 'short' somewhere in your storage area - mine is about 10-13m in length and all at a lower level - this is a large area to localise a fault in .... unless you are aided by knowing only 1 train was moving at the time, OR you can further sub-divide locally (no need for extra PSXs - just switches)  to localise the problem even more.

 

Some peope opt for 'Main line up'  'Main line down' and 'Slow LIne Up' and 'Slow Line down' as their preferred  arrangement - this may work well for a large club 'Oval' layout in which the 4 lines are really independant, and this could well kep 3 trains running round whils a problem is sorted on the 4th.   My 'geographical' or board- by board method would have them ALL stop at a particular board .... but then my layout  is effectively 'X' shaped with 4 different 'branches' which relate to geography.

[Dale]

The Cobalt's are indeed the digital ones and good point, well made.  Will need to get my head around this... best put the kettle on.

 

D.

[Dale]

I am trying to get my head around the best way of dealing with the points.

 

What sort of shorts are i likely to come across?

 

Certainly something metallic dropped across the tracks - say a pen in the fiddleyard.  The op is scribbling a note down "loco XXX runs badly" and drops the pen, it hits the tracks and shorts.  Alternatively a point is set against a movement and the wheels short the track?

 

With the two feed droppers for the cobalt coming from the points bus and the frog feed going to the track, if the points bus shorts out the track itself retains power to all sections except the frog - would that be right?

 

Using a separate switch for polarity would enable the frog to remain powered right?

 

With the two feed droppers to the point motor coming from a separate bus but with the frog feed coming, as it does from the frog to the 'frog' termination on the point motor, should the points bus short out we loose the ability to drive the points until the short is removed and the bus reset.  During this time we retain full track power except on the frog.  This takes its power feed through the point motor from either of the two droppers depending on polarity?

 

My concern was that if Ihave a point bus trip I am now unable to move a loco off of the point - the frog has no feed.

 

An option is to use a separate polarity switch and i think the cobalt has in built but separate switches?

 

Lets say a and b are the point motor feeds from the point bus, c and d are feeds from the track bus and e is the frog feed.

 

Point bus trips and we loose the points but retain full track power.

 

I may have this all wrong in my head though...

 

Is the points bus even likely to trip like this or is the track bus more likely to short?

 

Confused.com

~ Dale.

[Grovenor]

I am trying to get my head around the best way of dealing with the points.

 

What sort of shorts are i likely to come across?

 

Certainly something metallic dropped across the tracks - say a pen in the fiddleyard.  The op is scribbling a note down "loco XXX runs badly" and drops the pen, it hits the tracks and shorts.  Alternatively a point is set against a movement and the wheels short the track?

Yes, those, especially the latter.

With the two feed droppers for the cobalt coming from the points bus and the frog feed going to the track, if the points bus shorts out the track itself retains power to all sections except the frog - would that be right?

Unlikely, wiring it this way the train will be connecting the track bus to the points bus and most likely both will trip, bad practice and defeats the object of having a separate points bus.

Using a separate switch for polarity would enable the frog to remain powered right?

The separate switch will keep the short on the track from affecting the point motors, the frog won't be powered but you will be able to change the point and thereby remove the short (If the short is caused by a loco on the frog and not by a dropped pen).

 

With the two feed droppers to the point motor coming from a separate bus but with the frog feed coming, as it does from the frog to the 'frog' termination on the point motor, should the points bus short out we loose the ability to drive the points until the short is removed and the bus reset.  During this time we retain full track power except on the frog.  This takes its power feed through the point motor from either of the two droppers depending on polarity?

Yes and no, see above.

My concern was that if I have a point bus trip I am now unable to move a loco off of the point - the frog has no feed.  

An option is to use a separate polarity switch and i think the cobalt has in built but separate switches?

Make sure you use those separate switches for the frog polarity so that the two buses are kept completely separate, then it will do what you want.

 

Lets say a and b are the point motor feeds from the point bus, c and d are feeds from the track bus and e is the frog feed.

 

Point bus trips and we loose the points but retain full track power.

Yes so long as there is no connection between a,b and c,d, the switch has to connect the frog, e to either c or d and not to a or b.

I may have this all wrong in my head though...

 

Is the points bus even likely to trip like this or is the track bus more likely to short?

So long as the frog is not connected to the point bus then that is very unlikely to have any shorts, it is the track which is exposed and is the source of shorts, either from dropped items, derailments or trailing into points when set against, and for the last of these you need the points bus working to clear them.

Regards

Keith

[RFS]

 

What sort of shorts are i likely to come across?

 

 

~ Dale.

 

The great majority of shorts are caused by running a loco through points set against it, or the loco derailing on them.  These are relatively easy to fix. More difficult are those which are not easily explained, which is why it's a good idea to break your layout into sections which is what you are planning to do.  Unexplained shorts can come in a  number of ways: wiring faults can develop, for example. Another issue is making isolating gaps in the rail and not using insulated rail joiners: do this in the winter and then in the heat of the summer they can close up and cause a short.  This happened to me several times on my first layout, but on my current one I always use IRJs so that the rails can't come together.  If your layout is broken into sections, you can at least narrow the problem down to one section, just as you would with a DC layout.