DCC reverse loop problems

[Tim Brien]

I hope to maintain my railroad as both DC and DCC but the problem arises in that I have two reverse loops. For DC analogue operation, I use bridge rectifiers and stop the loco in the loop and reverse polarity, then move on. Of cause this will not sit well with DCC wiring. I will need to isolate the the analogue bridge rectifier section of wiring supply to the loop, most likely with a DPDT switch.

I have looked at the schematics of both the Massoth and Lenz modules. The Massoth seems to enable an arc free transition over the loop, but the detector sections, each end of the loop, would cause havoc with analogue wiring. The Massoth in 'open' short circuit detecting mode seems to work like the Lenz module in that the loco senses a potential short circuit at both the entry and exit to the loop section. This always assumes that either the train is shorter than the loop section (which mine is not) or that plastic wheels are used on all rolling stock to prevent the metal wheel bridging the gap section and causing a short circuit at each the end of the loop.

The easiest method would be to isolate the loop when in DCC mode and use only in analogue operation. Who said that DCC was just two wires to the rails!

Any advice, or am I missing something. All my trains have metal wheelsets, but almost none collect power for lighting. I do have a few sound cars. Would I need bridge rectifiers in these to prevent shorting with pickups either side of the loop gapped sections?

 

[Gizzy]

I've just gone DCC, and I had to remove the 3 analogue diode reversal tracks (LGB 10151) that I had and sell these on. This funded the purchase of a 2nd hand LGB 55080 MTS reversing module. I also did some track rationalising and lifted one of the loops that I hardly used.

AFAIK, you can not use both with DC and DCC, for the reasons you have surmised. The only way is to be able to switch between the two as you mentioned, which of course has the added complexity of extra wiring....

 

[Tim Brien]

Why both?

Simple, at present I have three locomotives with decoders with another to hopefully 'decoderise' this weekend. On the analogue side, well simply far too many to count and I am not going DCC on those. I will pick a few examples and add decoders to them for normal use. I still want the option to run my analogue creations now and then. Many have factory LGB sound (analogue and digital) from the 1990's and this does not bode well with DCC signals.

 

[Cliff George]

Hello Tim,

I believe that the latest Massoth Units will work in Analogue mode as well as digital mode. Maybe some from other manufacturers do as well.

Probably will need an extra power feed to the the reverser and also I assume that the rule about all of the train (that picks up power) needing to be in the reversed section would still apply.

 

[Tim Brien]

Cliff,
the Massoth units will work in analogue with a dedicated power supply to the loop section. I do not know if the dedicated supply feeds the loop power or is there to merely power the relays inside the module. The problem is that to use it I would need to dispense with all my rolling stock metal wheels as both my loops, by necessity, are only as long as my longest locomotive. The analogue bridge rectifier method has worked flawlessly (except when a lighted car bridged both sides of one of the gapped loops when polarity reversed). Adding two small bridge rectifiers to each car would solve the short circuit issue on analogue.

The simplest method would be to isolate the analogue side of the loops and not use them in DCC. Apart from the short circuit 'arcing' method of detection in DCC mode, I cannot see another method at present. This method still has the issue of metal wheels and lighted cars bridging the loop gapped rail sections.

 

[don9GLC]

the Massoth units will work in analogue with a dedicated power supply to the loop section. I do not know if the dedicated supply feeds the loop power or is there to merely power the relays inside the module. The problem is that to use it I would need to dispense with all my rolling stock metal wheels as both my loops, by necessity, are only as long as my longest locomotive. The analogue bridge rectifier method has worked flawlessly (except when a lighted car bridged both sides of one of the gapped loops when polarity reversed). Adding two small bridge rectifiers to each car would solve the short circuit issue on analogue.

Hi Tim,
I have no practical experience with the Massoth reverse loop module 8157001, but from the instructions I downloaded the separate DC supply to the module for analog operation is only to power the module, not the track. One fundamental difficulty you are going to have when trying to operate analog and DCC together is that the direction of travel in DCC is related to the loco (e.g. tender first or last) but for analog it is related to the track (east or west, as NMRA describes it). Its a fundamental issue when considering reverse loops and basically means that you cannot use the Massoth module for both analog and DCC with the same wiring.

I suspect that if your reverse loops are 'by necessity' long enough only for the loco they are actually part of a wye arrangement, and the Massoth module is unlikely to be suitable for analog operation, since it reverses the polarity in the main track with the recommended wiring connections, not the loop as your rectifier solution does.

One possible solution is to use a DPDT switch to manually reverse the polarity in the 'reverse loop'. This should work for both analog and DCC but you will have to remember to operate the switch while the train is in the loop especially with DCC. I would recommend that you stop all trains, analog and DCC then operate the switch before moving off. The DCC locos will still travel in the same direction but if you have not operated the switch there will be a short at the rail insulator, both on analog and DCC. You will also have to remember to operate the switch back once the train has completely cleared the loop, to reset it for the next train, otherwise there will be a short at the rail insulator at the beginning of the loop.

You could even use signals with auxiliary contacts to switch a relay (to replace the DPDT switch) to make operation seem more prototypical and 'explain' the stop to operate the switch and reverse the controller in analog. Track contacts could also be used, but you would have to fit a magnet under each loco. To avoid the problems of illuminated stock causing short circuits across the rail insulators you could consider relocating the insulated sections to form a 'loop' long enough for the entire train. The 'electrical' loop does not have to be the same length as the physical loop.

Just to make sure that this solution is feasible please confirm that you will operate only one analog loco at a time controlled by the DCC central station. Its a bit more complicated if you want to switch from all analog to all DCC, but still 'do-able'. If you want to run part analog and part DCC, its even more complicated and fitting decoders to everything might not seem such a bad idea!

To keep this comment reasonably short and readable I have omitted a lot of detail, but if anything is not clear let me know and I will try to prepare some diagrams / extra explanation.

regards, Don

 

[Tim Brien]

Don,
thankyou for the detailed reply. My intent is to run the railroad as all analogue DC or all DCC, depending on my whim. In analogue 'DC' mode I would be running only one loco at a time. I will not be running a DC loco (unchipped) on a DCC circuit. My easiest solution is to isolate the reverse loops in DCC mode as there is no way to increase the loop length, without impacting on the rest of the railroad. One loop is a typical reverse loop, but the semicircular loop part is only a removable trestle bridge section. When removed, the legs of the loop become analogue sidings.

The main reverse loop forms part of the continuous run in that the loop crosses diagonally across the circuit and in the opposing direction so that two switches face each other forming the short circuit.