Can you have too many droppers to your DCC bus?

Discussion in 'DCC Control' started by David Mitchell-Todd, Mar 18, 2021.

  1. David Mitchell-Todd

    David Mitchell-Todd Full Member

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    I am having ongoing issues with running DCC locos on my layout. I know that some are the issues relate to dirty track/bad connection, but some do not. There are some sections were DC locos run fine, but DCC one do not.

    For example there is one 30cm straight section between two points that DCC locos always stall on, but DC ones do not. To prove this I took the decoder out of one loco and it passed across without issue. I have previously been advised that every section of track should have a dropper wire, but now I am not so sure?
     
  2. Jim Freight

    Jim Freight Full Member

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    A very contentious aspect of DCC.

    My own compulsory rule : Never trust a fishplate to provide a long term reliable electrical connection.

    I apply a pair of droppers to any piece of track long enough to hold even a short loco.

    Others will disagree :avatar:

    Jim
     
  3. Walkingthedog

    Walkingthedog Full Member

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    No you can’t have too many. Your description just shouts out poor connection between track and wheels.
     
  4. David Mitchell-Todd

    David Mitchell-Todd Full Member

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    That is what I have done, which results in quite a jumble of wires in some sections with several points.
     
  5. Jim Freight

    Jim Freight Full Member

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    In which case I would check that the problematic piece of track is not distorted, dented or otherwise uneven, DCC is very unforgiving to momentary interruptions, and be sure that all the wheels and pickups of this loco are clean and correctly adjusted.

    DC does not suffer from a decoder being reset (not the reset of cvs, but the speed it was commanded to achieve) by very short interruptions, the motor acts as a flywheel for long enough to move past the point of lost contact. A reset decoder will ramp up speed again according to any delays or acceleration settings during which any further loss of contact effectively means the loco is unable to move.
     
  6. paul_l

    paul_l Staff Member Administrator

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    I'm of the "each piece of rail should have at least one dropper connected" camp

    Paul
     
  7. gormo

    gormo Staff Member Administrator

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    In a nutshell David, even for DC ( Anologue ), don`t rely on rail joiners for electrical integrity. Just use them for rail alignment.
    It`s more work to set up your track with droppers, and when you`re in a rush to get some trains running, it`s tempting to not add droppers, however in the long run if you add droppers, you will not be going back over your rail joins trying to add wire droppers to sort out problems when they occur.
    Plug and play is just not as reliable as solder and forget.
    :tophat:Gormo
     
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  8. David Mitchell-Todd

    David Mitchell-Todd Full Member

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    That is exactly what I have done, apart from the ends of a couple of sidings. When I laid the track I ran a few trains on it before connecting on the droppers, relying just on fishplate connection, and they ran reasonably well. The only obvious issue was the trains not being responsive when they were furthest away from the power connection.

    For reasons not related to this issue, I have decided to relay some sections of track. So I am going to isolate all the sections and get each section running smoothly before I reconnect the next section.
     
  9. Jim Freight

    Jim Freight Full Member

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    Does not sound like your problem.

    Isolating sections is unnecessary except where you have or require :-

    1) a layout split into districts (i.e. areas on a DCC layout which have independent DCC circuit breakers),
    2) auto-reversal DCC equipment for reverse loops or crossings,
    3) frog polarity switching on Electrofrog points,
    4) where in my case to stop potential long circular track loop issues (a belt and braces approach),
    5) where I have micro-switched protection at lift up sections (to stop trains dropping into a chasm!)

    Trains being unresponsive far from the power source indicates that the bus wires are too thin, does it pass the 'coin' test, i.e. if you short the rails with a coin furthest from the power source does the DCC system trip out, if it does not then the power bus wiring either has a poor connection somewhere or is not of sufficient wire cross section for the load and distance covered.

    If you have many static decoders for accessories or anything else connected to the power bus do the test with them active.

    Jim
     
  10. David Mitchell-Todd

    David Mitchell-Todd Full Member

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    The isolating is just a temporary measure. The plan is to get one section running smoothly then move onto the next. Once every section works on its own I will link them all up and see how it goes.

    The unresponsive issue only happened before I connected up the bus and was just relying on the track. I used 16 amp mains cable for the bus wires.
     
    Last edited: Mar 19, 2021
  11. Jim Freight

    Jim Freight Full Member

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    [/QUOTE]

    Misunderstood that, Jim
     
  12. David Mitchell-Todd

    David Mitchell-Todd Full Member

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    Misunderstood that, Jim[/QUOTE]
    No worries, these 'why is this doing this' posts can get very complicated.

    So far I have relayed a section of track with cork underlay, I initially laid direct onto the baseboard (Don't!), and the underlay has made an obvious difference.

    I have also discovered my Bachman Fairburn responds to both address 1 and address 3, so who knows what this effect this was having on my Webb Coal Tank 'test loco', which was set to address 3. I had previously set the Fairburn to address 1 as it is the biggest loco on my layout. This has a LaisDCC decoder in it which I am now going to bin and probably get a Zimo. Though I am tempted by the Rails Connect with 'Brown-out protection for silky-smooth motor operation'. Twice the price of a LaisDCC, but at £19.95 it is not going to break the bank.

    Anyway, further tinkering tomorrow and let us see what transpires?
     
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