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Re: [Z_Scale] Re: Z SCALE

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  • Alan Cox
    ... Short answer: because electricity doesn t work like that - it s all relative. So providing there is only one side cross connected anywhere (which is the
    Message 1 of 10 , Aug 3, 2010
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      > what i dont understand is when both loops are in difference directions then i have the plus side of one pack connected to the neg side of the other pack via the common rail why dont i get a short?

      Short answer: because electricity doesn't work like that - it's all
      relative. So providing there is only one side cross connected anywhere
      (which is the case with a common return and Märklin controllers as they
      each have their own transformer) then if you join them together one one
      side that simply becomes a common voltage between the two. Join both
      together and bad things happen.

      If you join one side together and then connect a voltmeter across the
      other two you'd see a voltage that varied according to how you turned the
      knobs. With one on zero and the other turned you will see the voltage for
      that one (-8 to +8 or thereabouts), turn them both the same way and you
      will see a low voltage or even 0 if they were turned the same amount.
      That is of course the normal case when you run a train between loops -
      there is little voltage difference between the two loops.

      The bad case is if you turn the knobs in opposite directions, you will
      then see up to + or -16v on the voltmeter, which is more than the models
      are designed to take in normal use.

      They are a good deal more robust than you might think however because
      they are designed to survive a variety of situations where the model
      carries more power than you would like - just as they get a certain
      amount of 'will it bounce' considered in the design strength.

      Other scenarios that are usually considered in designing models include

      - derailment where one truck comes off the track and ends up with the
      wheels shorting the other rail. At this point the short is through the
      wires in the locomotive

      - Similarly where a locomotive moves from one section to another which
      already contains a locomotive that is currently not being fed power. At
      that point the second locomotive is potentially being powered through
      the wiring of the first.

      - Running through electrofrog points the wrong way

      - Putting a locomotive using overhead on the track the wrong way around

      But 16v across a model designed for 8 isn't very good for it - especially
      if its more than briefly.

      Alan
    • Tony Dalileo
      thank you how come my meter reads 14v dc on a marklin z power pack with no load on the track when model max is 8v dc can i isolate the other rail by putting a
      Message 2 of 10 , Aug 3, 2010
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        thank you
        how come my meter reads 14v dc on a marklin z power pack with no load on the track when model max is 8v dc


        can i isolate the other rail by putting a cut in the uncut rail on a marklin 8588 isolation track or will that not work


        tony



        --- On Tue, 8/3/10, Alan Cox <alan@...> wrote:

        > From: Alan Cox <alan@...>
        > Subject: Re: [Z_Scale] Re: Z SCALE
        > To: z_scale@yahoogroups.com
        > Date: Tuesday, August 3, 2010, 5:04 PM
        > > what i dont understand is when
        > both loops are in difference directions then i have the plus
        > side of one pack connected to the neg side of the other pack
        > via the common rail why dont i get a short?
        >
        > Short answer: because electricity doesn't work like that -
        > it's all
        > relative. So providing there is only one side cross
        > connected anywhere
        > (which is the case with a common return and Märklin
        > controllers as they
        > each have their own transformer) then if you join them
        > together one one
        > side that simply becomes a common voltage between the two.
        > Join both
        > together and bad things happen.
        >
        > If you join one side together and then connect a voltmeter
        > across the
        > other two you'd see a voltage that varied according to how
        > you turned the
        > knobs. With one on zero and the other turned you will see
        > the voltage for
        > that one (-8 to +8 or thereabouts), turn them both the same
        > way and you
        > will see a low voltage or even 0 if they were turned the
        > same amount.
        > That is of course the normal case when you run a train
        > between loops -
        > there is little voltage difference between the two loops.
        >
        > The bad case is if you turn the knobs in opposite
        > directions, you will
        > then see up to + or -16v on the voltmeter, which is more
        > than the models
        > are designed to take in normal use.
        >
        > They are a good deal more robust than you might think
        > however because
        > they are designed to survive a variety of situations where
        > the model
        > carries more power than you would like - just as they get a
        > certain
        > amount of 'will it bounce' considered in the design
        > strength.
        >
        > Other scenarios that are usually considered in designing
        > models include
        >
        > - derailment where one truck comes off the track and ends
        > up with the
        >   wheels shorting the other rail. At this point the
        > short is through the
        >   wires in the locomotive
        >
        > - Similarly where a locomotive moves from one section to
        > another which
        >   already contains a locomotive that is currently not
        > being fed power. At
        >   that point the second locomotive is potentially
        > being powered through
        >   the wiring of the first.
        >
        > - Running through electrofrog points the wrong way
        >
        > - Putting a locomotive using overhead on the track the
        > wrong way around
        >
        > But 16v across a model designed for 8 isn't very good for
        > it - especially
        > if its more than briefly.
        >
        > Alan
        >
        >
        > ------------------------------------
        >
        > Z-scale:  minimum siZe, MAXIMUM enjoyment!
        > Yahoo! Groups Links
        >
        >
        >     z_scale-fullfeatured@yahoogroups.com
        >
        >
        >
      • Alan Cox
        On Tue, 3 Aug 2010 13:34:11 -0700 (PDT) ... Put a load on it. The newer ones are also quite smart and don t simply output 0-8v smoothed DC but know how to give
        Message 3 of 10 , Aug 3, 2010
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          On Tue, 3 Aug 2010 13:34:11 -0700 (PDT)
          Tony Dalileo <tony_mrr@...> wrote:

          > thank you
          > how come my meter reads 14v dc on a marklin z power pack with no load on the track when model max is 8v dc

          Put a load on it.

          The newer ones are also quite smart and don't simply output 0-8v smoothed
          DC but know how to give better motor control than that.
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