DCC and diodes, do they play together?

[Tim Brien]

On my analogue track (soon to be digital), I have two sidings which terminate out of sight and have a diode on one rail each to stop an analogue locomotive before it reaches the buffer stop. These sidings terminate approximately five foot off the ground and prevent a loco over running the buffer stop and experiencing the effect of gravity.

My question relates to how the diode in each rail will impact on DCC operation on each siding. Will a decoder equipped locomotive, under digital power, stop automatically under the influence of the diode, or will it career into the buffer stop and fall to the ground?

 

[Gizzy]

I don't believe it will stop the loco.

It will half wave rectify the signal, so you may get half the command signal or worse a corrupted command signal to the loco's on board chip.

I think that the diode could possibly block the command signal to the DCC chip. You could easily experiment with this and confirm it though, as I'd be interested to know for sure!

I think that a better and simpler solution, would be to replace the diode with a push button, which you hold on to release a loco when you reverse out of the sidings. You could have a push button with an indicator light if required, so that you know if DCC power is fed to that section of track....

 

[Gizzy]

Thinking further about this, I used to operate DC (ART Train Engineer and LGB Controllers) with LGB 10151 Reversal Loop sets. These sets incorporate diodes to reverse the DC polarity.

On going to the dark side at the begining of this year, I had to sell on my three lots of LGB 10151 track sets and replace them with a DCC compatible LGB 55070 reverse loop module, as the diode based units will not work on DCC....

 

[Tim Brien]

Gizzy,
thankyou for the info. The particular length of track also doubles as a tram shuttle circuit. The diodes allowed a degree of automation. The end sidings terminated out of sight and thus the diodes afforded a degree of confidence. I will need to compromise my plans. I already have ruled out one reverse loop to analogue ops only and it now looks like the shuttle circuit will need to be sacrificed as well. I need to obtain a reverse loop module to digitally power my other reverse loop or maybe it also may be sacrificed. The pushbutton solution may be an alternative for the end of siding issue.

Looks like analogue DC and DCC do not make compatible bedfellows!

 

[muns]

Diodes on DCC do not mix as they cause the DCC signal to be chopped. The DCC signal is a series of changes in polarity at different time intervals.

A decoder would loose the DCC signal and probably think it was on an analog track if it entered into a section protected by a single diode.

 

[Tim Brien]

Mark,
thankyou. I feel that if I bridge the diode with a momentary switch or pushbutton switch then I could still retain the diode for analogue operation. In digital mode I could activate the switch and thus allow the signal to bypass the diode.

 

[dunnyrail]

Mark,
thankyou. I feel that if I bridge the diode with a momentary switch or pushbutton switch then I could still retain the diode for analogue operation. In digital mode I could activate the switch and thus allow the signal to bypass the diode.

Another alternative, (as you appear to want the layout to operate on DCC and Analogue) would be to wire in a Rotary Switch. Position one would be for analogue with the Diodes for your reverse unit wired into that circuit and connection to the analogue set up. Position two ALL OFF. Position 3 DCC with your push button wired in to give power to the section when you want to recover a locomotive that has stalled in the section. Needless to say you would need to do as a Double Pole set up, but a 3 way rotary would have plenty of conrtacts. You could even wire in bulbs to show that you are in DCC or Analogue Mode. You could of course DCC the Tram and if you are getting Massoth Kit do the Shutle with that. It does have the facility but don't ask me how to set it up!
JOnD
JonD

 

[Tim Brien]

Jon,
thankyou for your suggestion. Yes, it is mandatory that the railway be both digital and analogue.

 

[nicebutdim]

Quite simple if you use a centre off spdt switch. the switch one way is wired across the gap, when the other way wires the diode across the gap for dc and when in the centre leaves the gap open so all trains will stop.

 

[Tim Brien]

Tim,
that is an excellent idea. I had thought of simply using an on/off switch with the track powered by digital through the 'on' position and the diode powered when in the 'off' position. A centre off would give me peace of mind should a loco travel to the end of the line, thus stopping short of the buffer stop and certain disaster.