DC and dcc control on same layout

[terrysoham]

My model railway club are considering whether to convert their recently wired 00 gauge DC layout, Wickham Market, so that it can operate in either DC or dcc mode (but not both at the same time!). They are at the stage where the layout can be operated in DC but have not yet started on the scenery so if they are going to go down the DC with dcc route, they need to do it soon.

 

Has anyone got a dual DC/dcc layout or do you know of one where my Club could gain a knowledge of the pros and cons?

 

My knowledge is limited to dcc wiring and I can see that the principle of the dcc bus could be adapted to DC but that infers a total rewiring of the layout as it is presently uses 7/.2 wire!

 

Your thoughts, ideas and experiences would be most welcome.

 

Thank you.

Regards

[peter220950]

In theory, and at it's simplest, if you disconnect the two wires feeding the DC into the track, turn on any section switches, and substitute a DCC feed it should work.

 

However it's not usually quite that simple or straightforward, particularly if the layout has already been wired up, and particularly if someone has seen fit to wire it with common return and several controllers.

 

The only experience I have is with two of our Club 0 gauge layouts, a small BLT that was retro-fitted with DCC and the main 'roundy round' which was designed for DCC from the start, then retro-fitted for DC on discrete parts.

 

Perhaps the first thing to be established is if the intention is to have either all DC or DCC or a mix of both, It's sometimes useful for a Club layout to be able to run both simultaneously, if the layout is large and there are readilly identifiable sections which can be isolated.

 

The BLT layout (24' x 2') was wired conventionally and just plugs a DCC or DC controller in, wiring is relatively light gauge, (probably also only 7/02). Because there are only a limited number of loco's in use at any time (probably 2) there has not been any indication of problems or erratic running caused by this wiring method in several years. It should be noted, however, that the rating for this wire is only around 1.4A so it should be treated with some caution.

 

The roundy round (40' x 16') was designed with DCC from the start, it has two main running lines, a loco shed, and a separate control bus for signals and control. The shed is still running with the coppper tape that we started with, but the other three buses are heavy duty speaker wire that's more than adequate, to minimise voltage drop.

 

 

 

Point control is also a factor, if the control circuitry is kept separate from everything else it should help to keep things simple, with DCC a short caused by running into a facing point can shut a layout down, if the control bus is separate it can change the points to remove the problem, otherwise it requires the big hand from the sky to sort the mess out.

 

By having a couple of buses for the two main running lines it means we can run one DCC, and one DC as long as the crossovers are left alone!

 

 

So in summary, I would suggest you consider how big the layout is, whether you want to have 100% DC or DCC, or a mix of both, think about how many loco's are going to be in use (and standing on shed), and how points are controlled.

 

In the short term it's worth just trying to plug a DCC station in, and seeing how it runs, if there's any substantial voltage drop, and the sort of current that's being drawn in use. If you want a mix of control on separate parts of the layout consider putting in a DCC bus for just part of it, the remainder can be considered for conversion another day. Droppers can always be put in now, before scenics, but without connecting them to a bus at the moment, to make a retro-fit easier.

 

These things usually evolve to suit the situation, on our main layout we started with copper wire on each bus, with small connectors between boards, and it worked fine, however over time it was seen to be a better plan to run hefty wire buses, so we replaced them piecemeal.

 

On the BLT we literally just plugged a different controller in and it's been going for many years.

 

Hope this helps,

 

Peter

[Ray H]

Our large O gauge layout - approx. 40' x 20' - was wired for tradition (dc) cab control which was extended as the layout "grew". There was a common return all round the layout and only a single feed to each (switched) track section.

 

We did experience some voltage drop at the section ends remote from the controllers and the worst area for this was subsequently provided with a secondary feed direct from the control panel to the remote end of the section concerned.

 

Our initial experiments with DCC involved nothing more than introducing a DPDT switch between controller and control panel with one side of the switch connected to the original DC controller and the other to the NCE PTP panel into which the PowerCab throttle was plugged. We ran the layout like this for many months, sometimes operating up to four (sound fitted) locos on the DCC section, albeit only two normally moving.

 

We decided to develop the DCC area further and introduced an accessory decoder linked to the track bus - there was no accessory bus. As far as we can make out this decoder wasn't too impressed with the limited wiring and failed. It was replaced FoC but with the suggestion that we improved the layout's wiring and power supplies which we're in the middle of doing.

 

Shortly afterwards we had a loco based decoder fail. We don't (definitely) know why this happened but suspect that said loco traversed the single section of the layout - a through siding - that allowed stock to move between the now mainly DCC section and the (DC) bulk of the layout with the loco managing to bridge the DC and DCC sections where they joined - the siding was divided in two electrically with the track power source for each part controlled by the point setting at the respective siding end. We suspect that we failed to switch both points to ensure the two electrical systems remained isolated.

 

The current re-wiring of the DCC section is along conventional (DCC) lines, with dropper wires to each length of rail and a separate accessory bus. We have removed the facility to move trains between the DC and DCC section for the time being to minimise the risk of further decoder failures and have also added individual short circuit protection devices to the DCC buses and upgraded the DCC system to a PowerPro. We have also completely isolated the DCC section of the layout from the layout's common return.

 

In the longer term we aim to introduce droppers/buses to all the DC sections of the layout to improve the operation of that part of the layout and make any future switch to DCC quicker to achieve.

[rockershovel]

The Market Deeping Club have a 00/H0 test track wired so that it can be switched between DC and DCC, they also have a fixed 00 layout which has separate DC and DCC sections. They have a website; send them a question. Deeping isn't stupidly far (45 miles) from Ely either, if you decide it worth a visit.

[Brian]

Hi

I wired my clubs OO layout for DC twin controller (Now three DC controllers) or DCC.  

It is wired common return for the three controllers and basically just needs the DC controllers turning off and disconnecting and the DCC power applied and all section switches turned On.  However I wanted to go one step further...

 

The selection DC/DCC on this layout is automatic, with the DC controllers all being disconnected as soon as power is applied to the DCC input terminals on the control panel, so there is no risk of anyone accidentally turning on a DC controller while DCC is being used.  A 4 Pole relay is operated via a bridge rectifier wired directly across the DCC input terminals and as soon as DCC is connected the relay energises and disconnects the DC controllers track outputs. I decided on an automatic change-over as I wanted to be 100% sure of the disconnection of the DC controllers. Of course the section switches are still turned on manually.

 

Depending on the number of DC controllers in use would determine the number of relays needed if automatic DC disconnection is required. If you're sure no one would connect a DC controller while running DCC then you don't need the relay auto changeover!

[terrysoham]

Thanks for all these replies.   When I have had a chance to digest what you are telling me, no doubt I will be back for clarification.

[34theletterbetweenB&D]

When I went DCC I had a conventionally wired three cab switched section common return layout. I took the controllers off cab positions 2 and 3, and connected the DCC system track outputs to cab 2 connections, and the programme track to cab 3 connections. All done! That enabled any section to be powered DC, DCC, or DCC programme, by appropriate positioning of the section switches. Very handy as one route can be selected for DC test running while the rest of the layout is operated on DCC, and if DCC programme track is required it can be available wherever the loco is standing.

 

A little care not to drive over the section breaks is all it needs, your inner signalman has to do his stuff.

[RAF96]

The essential advice is you must not allow DCC and DC controllers to command the same track bus - ​at the same time.

 

The simple solution is to install a 6-terminal DPDT switch (ON-OFF-ON).

 

The DCC controller feeds one outer pair of terminals and the DC controller the other pair of outer terminals and the selected inner terminals output goes to the rails.

By dint of the switch logic either controller is definitely switched to isolate (Off) before being selected to the other controller, so never the twain shall meet.

 

Once the layout has been fully transmogrified to DCC then you can either lock the switch in the DCC position or simply remove it and bridge the wires.

 

To operate either DCC or DC within the same session takes a bit of consideration as whilst DCC locos will happily cope with DC, the reverse is not true - as leaving a DC loco on a DCC circuit will invoke buzzing, heat and possibly even smoke before its demise due to the DC motor feeling a pseudo 15v AC DCC signal all the time it is stood on track, even when not selected.