Eventually going DCC - Advice needed

[ianb26]

Hi there,

 

Can someone help me please.

Attached is the track plan of my layout (HO). I am in the build & test process at the moment running on DC but eventually - when all the bugs are ironed out - going DCC.

 

 

I have just discovered that when I open PM 5 & PM 6 or PM 7 & PM 8 - to switch tracks, - that the locos reverse when they reach the other set of tracks. I should point out that the only connections to the track - at present - is at the "+" & "-" at the bottom.

 

Points/turnouts are as follows:

PM 1, PM 2, PM 7 & PM 8 are Peco SL91

PM 3 is Hornby R8073

PM 4 is Hornby R8072

PM 5 & PM 6 are Peco SL92

 

At PM 1 I have Peco Turnout motor PL10

At PM 2 I have Peco Side-mount PL11

At PM 3 I have Hornby Underboard mounted R8014

At PM 4 I have Hornby side mounted motor

At PM 5 - 8 all will be side mounted PL11 as access underneath is limited at those locations.

 

2 things I would like advice on are:

 

1. Where would be the best places to add droppers to the main DCC bus?

 

2. How do I keep the locos in forward running when they use the crossovers at PM 5 - PM 8. When PM 5 & PM 6 or PM 7 & PM 8 are set to change running tracks, all power to tracks at that section of the layout (and I presume the rest of the layout) is lost. At the moment - for testing purposes - I am manually "feeding" the locos through the crossover, then change the turnouts back to straight through running, this is where the locos reverse.

 

If anyone can help and markup for where the droppers should be, either copy the attachment, print and markup and repost or send via Private message, I would be most appreciative.

 

Thanks

[SRman]

Disregarding the above (correct!) advice for just a moment, even on DC, your power feed should be between PM3 and PM4, otherwise if you switch PM4 to the curved route, and PM1 to curved and/or PM3 to straight, you will lose power to those sections. Ideally, you would also need another feed on the far side of PM1 to feed power into the siding.

The return loop needs a double pole double throw (DPDT) switch to do as Dutch_Master advises on DC, which would require you to stop a train in the reversing section, throw the DPDT switch, then reverse the power feed to start the train forwards again, but the auto reverse module would be much better for DCC use and would allow the trains to keep moving.

 

Once on DCC, you would need power feeds (droppers) into all dead-end sidings as well, to keep them alive.

[ianb26]

3) for DC use, you need a simple switch that reverses polarity of the section when a train is traversing it. This can be automated, but given your question I deduct you lack the knowledge (on electrickery) to do so.

 

HTH!

I actually do have knowledge of electricity, I was an electrician for 40+ years, but more concerned with AC than DC. The old brain cells are not what they used to be.

 

Thanks for your reply. I still want to run on DC for a bit longer yet, as I have to fill in the tunnel sections, (the blue section from PM 6 & PM 8 to the left hand side as far as where the blue section finishes and the yellow section from where it dives under blue at PM 6 to about where the curves of the 15^o/30" and 15^o/15" join)and complete other tweaks such as inserting check rails.

 

Where do you suggest droppers be inserted to connect to the DCC bus. In fact I was going to run the DCC bus very soon even though I will still be running DC for a few months yet. Am I right to assume the insulated fish plates would go between PM 2 & PM 7 in a clock-wise direction, and PM 4 & PM 6 in anticlockwise direction.

 

I am going to ask the obvious, where/how do I put the auto reversing switch. On the control panel or in a temporary position on the layout?

 

If I have any more queries on that part of the post, I will put replies to individual posts.

 

Thanks again.

[ianb26]

Disregarding the above (correct!) advice for just a moment, even on DC, your power feed should be between PM3 and PM4, otherwise if you switch PM4 to the curved route, and PM1 to curved and/or PM3 to straight, you will lose power to those sections. Ideally, you would also need another feed on the far side of PM1 to feed power into the siding.

 

The return loop needs a double pole double throw (DPDT) switch to do as Dutch_Master advises on DC, which would require you to stop a train in the reversing section, throw the DPDT switch, then reverse the power feed to start the train forwards again, but the auto reverse module would be much better for DCC use and would allow the trains to keep moving.

 

Once on DCC, you would need power feeds (droppers) into all dead-end sidings as well, to keep them alive.

Thanks for that, your reply came in whilst I was replying to the previous post!!! As mentioned in my reply to Dutch Master, which would be better - on control panel or a temporary switch on the layout itself?

I already have my Digitrax controller, but I don't want to use it just yet if I don't have to.

 

Thanks also for your reply.

 

PS. Where in Melbourne are you. I was thinking, if I'm not being to rude, if you could come and view the layout and make suggestions.    

 

Thanks

[Mallard60022]

I'm not surprised that 1) the power 'disappears' when you switch the crossovers and 2) the trains reverse direction at that point. What you have is in essence an oval encircling a figure-of-8-loop and you've created a giant short circuit by putting these crossovers in place

 

What you need to do is the following:

1) insulate the entire section between PM2 and PM7 and also the section between PM4 and PM6. It needs insulating fish plates on both rails in each location. There MUST BE NO CONNECTION TO THE REST OF THE LAYOUT!

2) each insulated section needs to be fed from an auto-reverser, or a pair of frog-juicers (normally used to power-route the frog of a point) which may be cheaper. Mind that the frog-juicer units only work on DCC, not on DC!

3) for DC use, you need a simple switch that reverses polarity of the section when a train is traversing it. This can be automated, but given your question I deduct you lack the knowledge (on electrickery) to do so.

 

HTH!

Interesting advice that is useful to me too. However, I have read somewhere recently about an Aussie firm's Cobalt Alpha that can be used on DC as well. DCC Concepts. Could this be useful to the O Poster? I'm no good at trickery but maybe their juicers would do the same? 

Phil. 

[34theletterbetweenB&D]

...

I already have my Digitrax controller, but I don't want to use it just yet if I don't have to...

Candidly, you need to start using it right now, during the construction.

 

Here's why. DC is very tolerant of brief short circuits in particular, and DCC is completely intolerant of same. You can build yourself an adequately functioning layout for DC operation which proves to be a nightmare when DCC is used. I have had to fix several layouts long - and successfully - operated on DC; to eliminate the wiring short cuts, poor connections, and inadequate track components which DC tolerates, but which had the DCC system tripping out every other minute.

 

Just don't go there, build and test with DCC and kill this potential problem off at source.

[Phil S]

As 34... suggests, it is better to start off directly with dcc especially since you already have the required controller !  Just one DCC-fitted loco is required to then thoroughly test the layout.

DCC wiring advantages come when they DO NOT COPY the 'sections' chosen by DC/analogue users, but instead follow a grouping more appropriate to easy-diagnostics:

This will vary in style slightly according the the design of the layout. 

 

In general you want 2 dcc busses ...  1 for accessory control - even if your points etc are not dcc powered at this stage - consider it now.  

Depending on your track choices, their decoder(s) might be built-in to the point motor, and add-on to an individual point motor, or a module for typically 4 (but possibly 2,4,6, or 8) .  

 

Whilst SOME are capable of running happily off the DCC bus  (eg Roco Digital Point Motors - for Roco Track obviously, or a decoder incorporating a CDU Capacitor Discharge Unit  (eg Hornby POINT decoder, etc) - because they only take a SMALL current at any time, OTHER TYPES might prefer or NEED a separate 12V or 16Vac 50Hz POWER distribution bus, to avoid a huge drain on the dcc bus whilst the point is changing (eg when using Peco Solenoids, without a CDU).

 

Whilst an analogue layout required 'CAB-sections' to allow more than 1 loco on the layout at a time, the DIGITAL layout CAN make use of  'sub-sections' within each 'Power District', to make isolating a fault easier... if these are fed via automatic devices like the PSX intelligent circuit breaker, then they will each try to reset themselves every few seconds, whilst the fault is located and cleared.

 

AUTO REVERSERS - as already mentioned, these can be automatic in DCC. Most simply detect a short on a rail as the FIRST METAL WHEEL bridges a rail gap. However, LDT ofer a kit or ready-built module of a more advanced type, which PRE_SELECTS the required polarity with a 40mm sensing section at each end  .... and this needs to be allowed for; most easily when track laying.

Don't forget that the reversable section needs to be longer than any train.

 

AND FINALLY, BUT FOREMOST: ADEQUATE WIRING to meet the protection requirements for the DCC Controller: THe LARGER ITS CURRENT CAPABILITY, the larger the wire gauge needs to be, to ensure that SUFFICIENT short-circuit current can flow to trigger a shut down ... 'the coin test' when a coin is placed across the rails....

In this regard, some former-dc layouts, with wiring for maybe 1A per section, will be able to use the same wiring - IFF the new DCC CONTROLLER is of a LOW CURRENT eg 1-2A design, BUT NOT if replaced with a DCC unit capable of outputting 3-5A without either wiring improvements, OR PSXs (or similar) to reduce the current limit beyond it/them.

[ianb26]

Candidly, you need to start using it right now, during the construction.

 

Here's why. DC is very tolerant of brief short circuits in particular, and DCC is completely intolerant of same. You can build yourself an adequately functioning layout for DC operation which proves to be a nightmare when DCC is used. I have had to fix several layouts long - and successfully - operated on DC; to eliminate the wiring short cuts, poor connections, and inadequate track components which DC tolerates, but which had the DCC system tripping out every other minute.

 

Just don't go there, build and test with DCC and kill this potential problem off at source.

Ok, thank you for your advice. I'll make a start on running the DCC bus tomorrow. As I said in my initial post, where would be the best places to place the droppers? I presume I still have to do what Dutch Master suggested of insulating the sections between PM 2 & PM 7, & also PM 4 & PM 6? The problem I have is that being on a fixed fortnightly income, I have to watch the $ & c. The credit card has had a belting since January with purchasing track etc on eBay. I have bought 4 locos as well, 2 of them are Australian locos, and I have a Flying Scotsman loco on watch list which expires on Thursday sitting at $A50. Just hoping it doesn't suddenly rise in price! And it is DCC ready!!! Sorry I got a bit distracted there!

 

FWIW The DCC controller is a Digitrax DCS50.

 

Anything else I should have to worry about?

 

Thanks again.

[smokebox]

Ideally you should have droppers soldered to every piece of track and connected to the bus main. The tracks in the isolated section should also have droppers attached but these should then connect to the auto reversing unit, using a separate bus if necessary. If you have 2 auto reverse units, each should have its own auto reverser bus with connections to the relevant isolated sections.