To DCC or not to DCC there are so many questions

Discussion in 'DCC Control' started by Graeme, Feb 1, 2019.

  1. Graeme

    Graeme Full Member

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    Because I am running the layout on DC (red and black wires) using the future DCC bus that I am wiring, so that I can test curves with my largest loco, it should be OK for me to to just connect my DCC controller to the bus when I finally convert it to DCC is that correct?
    I am using DCC block convention but the whole layout is "hot" when the DC controller is connected.
    My wire colour is the reverse of what is suggested ie black to front when viewed from inside the loop perspective.
     
  2. Toto

    Toto I'm best ignored Staff Member Founder Administrator

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    Mmmmmm, keep you DCC away from this for the moment until some clarifications have been made.

    A sketch of your layout track plan and some details on how you gave wired it would be helpful. I dont like the " hot " comment. That worries me. What gauge wire are you using ?

    The more info you provide the better.

    Cheers

    Toto
     
  3. Gary

    Gary Wants more time for modelling.... Staff Member Administrator

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    Is the DCC block convention only used to isolate issues if they arise ?

    On my latest shunting layout, I have wired the layout for DC using typical block control, using on/off (SP/ST) switches. These are wired through to a DP/DT switch, from there I can switch between either DC or DCC. This is how I wired Casula Sidings...


    If the wiring or layout is getting hot, it could be due to under gauge wire...

    A few years ago, during an exhibition in Elgin, we had problems with Cobalt point motors blowing out (frying themselves) due to under gauge wiring.

    Cheers, Gary.
     
  4. Andy_Sollis

    Andy_Sollis Staff Member Moderator

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    I think he leans “live” when he says hot!
     
  5. Graeme

    Graeme Full Member

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    Basically I fed a DC controller output into the end of my loop, in the loop there is a passing siding with 2 Peco electrofrog points opposing each other.
    All the exit tracks of the points are insulated as per a suggestion further back in this thread.
    I added feeders from my future DCC bus to the tracks between the point exits.
    The bus is connected electrically to the each end of the loop.

    A quick sketch of what I have is attached, apologies for the lack of detail I am not good at those drawing programs.

    I have run a loco across this set up with no arcs and sparks so I call this all good.

    When I convert to DCC can I just use the same wiring?
     

    Attached Files:

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  6. Andy_Sollis

    Andy_Sollis Staff Member Moderator

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    I am assuming you mean Live not hot as it temp? I’m a little bemused as to why your blocking on DCC? The whole idea of DCC is so the whol layout is live and you don’t need block sections as one loco can draw up to the next with no issues. I would have expected a block section for DC so you can isolate yards etc?

    Can you clarify?
     
  7. Andy_Sollis

    Andy_Sollis Staff Member Moderator

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    I don’t see any issue with the wiring diagram you have supplied.

    Without sounding stupid, I take it you are literally unplugging one controller and connecting the other to the same feed wires or as suggested above, look at getting a DPDT (Double Pole Double Throw) switch, preferably with a centre off position (then you know the whole layout is dead/isolated when it’s in the middle)
     
  8. Graeme

    Graeme Full Member

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    The area I am working on consists of a passing siding with 2 opposing sets of points I took some advice from a reply earlier on in this thread (Post #17) and isolated the exits of the points, the rest is a standard loop so far
    When I said "hot wiring" I was talking about running temporary jumpers across between the rails.
    It is a flash back to when I was working in a security environment where we would use jumpers to test a system we used to say we'll hot wire this to see what happens when we activated it.
     
  9. Graeme

    Graeme Full Member

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    One controller only (DC), DCC controller is not even the equation (all locos are DC only with no chips fitted ), I have just started building the DCC bus and am using it to feed the DC being seriously polarity conscious.
    The DCC bus will not be a loop it will be open ended with snubber circuits fitted at the end when DCC becomes the only controller in the future.
     
  10. Andy_Sollis

    Andy_Sollis Staff Member Moderator

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    Snubber circuits?
     
  11. Graeme

    Graeme Full Member

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  12. paul_l

    paul_l Staff Member Administrator

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    It does no harm to fit a snubber, but are only really required for runs over 25m from the booster, unless you are getting interference or weird responses towards the end of the runs.
    As for running DC & DCC, provided the droppers (track feeds) are thick enough then DCC can easily work on a DC layout, you just make all tracks live. Easy way to test if your wiring is up to is to try the coin test - get a coin of the realm big enough to cover both tracks (for O gauge and above use a nail), thenwith the power on place the coins over the track, if the coin gets warm, or the short circuit protection on the system doesn't trip then your wiring isn't up to DCC, and will need to be upgraded.

    Paul
     
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  13. Jim Freight

    Jim Freight Full Member

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    Agreed, I looked into this last year after a heated discussion seen on another forum and so I tried to see the difference on the tracks with an oscilloscope and in some cases the rc-filters reduced overshoots due to shorts and in other places no difference. (technically they are not snubbers, but I do not wish to debate that).

    However just having another loco parked in the same DCC district had the same affect, i.e. reducing potentially hazardous overshoots.

    In the end I left them in place, 1 per district, 1 on each end of a 'long' district but I used higher power rating resistors than recommended sizes because their case temperatures reached over 50C on a cool day which a stray back of the hand would not appreciate. A resistor of a higher power rating runs much cooler for a given current flow.

    In addition I reduced the track voltage slightly at the command station/boosters to further reduce power dissipation at the loco decoders and further reduce any overshoots, mind you the side effect was to reduce the top speed of the locos, most of which I have already limited to an estimate of prototypical top speed.

    However reduction of track voltage from the default also puts more load on the voltage regulation circuits of the command station/boosters, so slightly more heat dissipated there.

    Still not sure rc-filters make much real difference on my layout but I have left them in place with no adverse side effects. :scratchchin:
     
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  14. Andy_Sollis

    Andy_Sollis Staff Member Moderator

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    Not sure if it’s related, but I have two locos that will suddenly just run off on their own? (None of the others have ever done this) one is loco number 2 and the other is loco 54, so there appears to be no connection other than they are Lenz decoders.
     
  15. Jim Freight

    Jim Freight Full Member

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    In my experience this can happen when you have the DC mode enabled and momentary bad track pickup makes the decoder think it is running on DC and says ok, full speed ahead.

    Disabling this mode stops this effect, so does very clean track, wheels and pickups, but that is fine in an ideal world. Jim :hammer:
     
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  16. Andy_Sollis

    Andy_Sollis Staff Member Moderator

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    Oh, that’s a thought. Not considered if DC is activated? (Not that I use it)

    odd thing is, they only do it when stationary?
     
  17. Jim Freight

    Jim Freight Full Member

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    That does sound odd but then again with the track always live contact could still be intermittent, needing only slight vibration of the baseboard to cause 'lift-off'.

    In my case it usually only happened to a slow moving loco, and when it got bored (or realised it was on DCC afterall) it reverted to the speed it was supposed to be running at, then the wagons it was pulling piled up behind it :facepalm:.

    I have just got into the habit of always disabling that feature when fitting a decoder to a loco as I never use it. :)
     
    Last edited: Apr 28, 2020
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  18. Andy_Sollis

    Andy_Sollis Staff Member Moderator

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    Hi Jim,

    I’ve checked this in the last few days. They are decoders with a DC option (oddly all appear to be Lenz 1024’s) but it’s not selected.

    I’ve also not known them do it with the guagemaster controller or the Bachmann controller, so I suspect it’s something of a compatibility issue with the ZTC and these lenz decoders. I do remember an article by ztc asking at one point re “runaways” but wasn’t having an issue at the time, so didn’t progress it. It’s now some 18 years old, so no longer under any kind of warranty. (It certainly doesn’t owe me anything as I won it in a completion from Model Rail Magazine)

    Andy
     
  19. Jim Freight

    Jim Freight Full Member

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    Wow, I'm a newbie on the block with DCC, didn't realise DCC decoders had been around for 18 years!
     
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  20. Andy_Sollis

    Andy_Sollis Staff Member Moderator

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    Probably longer...

    we had the Hornby Zero 1 around 1983/4 which was a much cruder version of what we have today.
    Airfix also had their own system, but I’ve never seen anything of it.

    the system we know today appears to have originated in the late 1980’s by Lenz.

    https://en.wikipedia.org/wiki/Digital_Command_Control
     

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