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Re: Power for MTL turnouts

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  • viktor_kovacs
    ... Newer marklin controllers operate from a dc only wall adapter, so the accessory output has dc too. When using diode logic for route selection, dc is
    Message 1 of 8 , Jul 30, 2009
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      --- In z_scale@yahoogroups.com, "Jeff BAZ-man" <sjbazman49@...> wrote:
      > Lindley,
      > You got the summary:
      > AC for the turnouts and MOMENTARY pushbuttons (or MOMENTARY
      > toggle switches, SPDT-CO Single Pole, Double throw, Center Off).
      > Use almost any AC source, even a 12v filament transformer from
      > the old days. Fuse the load side at 1/4 amp, slo-blow if you do.
      > AC wall-warts are harder to find but the surplus stores up here
      > have them.
      > If you put continuous voltage to the solenoids, they can get
      > quite hot.

      Newer marklin controllers operate from a dc only wall adapter,
      so the accessory output has dc too. When using diode logic
      for route selection, dc is required. I use momentary single pole
      triple throw (center off) switches for direct turnout control
      and momentary pushbuttons with diodes for route selection.
      (and double pole triple throw for cab control)

      > Note about LEDs: you can use AC on them, they are just like
      > diodes, conducting only one way. They won't be as brite as DC,
      > about half, as they only turn on half the time. Accessrory
      > terminals are fine for these too. Connect up to 3 white ones
      > in series and use a 100~1000 ohm resistor, depending on how
      > effecient the LED's are.

      Many small leds have a very low reverse breakdown voltage, so
      many wiessman signals have a protection diode in them, so an
      accidentally reversed voltage can't burn them out. Many lights
      don't have this protection, so if you use very small smd-s, then
      almost anything above 5V AC would burn them out. For this, you
      either have to add a protection diode or use dc power. Running
      them closer to the turn on voltage, means less heat is generated
      by the resistors and everything runs cooler.

      I use the following power sources:
      -standard maerklin wall adapter power pack (the same is used
      for minitrix, but with a bigger wall adapter), the output
      is a totally flat dc voltage for the trains and a constant
      dc voltage for accessories; also works from a 9V battery or
      a 12V rechargable cell because they can be plugged into the
      socket of the wall adapter (i use it for my briefcase layout)
      -standard wall adapter with variable voltage output (wallwart),
      with a home made voltage controller, the output is the same
      as in the maerklin case (i used the same chip), but reversing
      is done by a dptt switch and I used a higher precision pot
      -standard atx computer power supply, 300W, 12V/5V with built
      in short circuit detection and soft on/off; it's an old pc
      power unit where I connected the power on (green wire) with
      a ground (black wire) through a switch so it can be turned
      on without a motherboard, the output is very smooth and the
      short circuit protection was designed to protect highly
      sensitive electronics so it's very good and you can turn it
      back on by powercycling the unit through the main dpdt switch;
      one controller is a variable voltage chip as in the maerklin
      controllers and the other one is a pic based pwm controller,
      which is essentially the same as a dcc decoder
      -my backup transformer is a (very heavy) piko fz1, but I only
      use the track output (the accessory output is too high) and
      only turn the dial to 1/4 of the scale; it runs most locos
      nicely because it uses 50Hz variable amplitude pulse power

      ps:
      Using a 12V/5V DC source means the lighting can use 5V and needs
      smaller resistors, you can power most microcontrollers and other
      ttl chips directly and the train controllers can get 12V (dropped
      to 10V max. at the output, depending on the internal voltage loss
      of the controller/driver ic). A maerklin controller for example
      uses a 11V DC wall adapter, puts the input directly on the
      accessory output and the 3 legged speed controller chip loses
      around 1V, so the output is in the range of 0-10V, while reversing
      is built into the speed controller knob. (these controllers can not
      be used with common rail wiring on a layout because they would
      short out if one controller is reversed, so it is better to isolate
      both rails and use cab control, this has the added benefit, that
      one controller can later be replaced with a dcc controller and
      the layout could be used at the same time by analog and digital
      trains. (they can mixed together without the dcc signal damaging
      the motors in the analog locomotives and analog locos could be
      driven by cab control while dcc locos could be controlled in the
      normal way and the only constraint is that you can't place two
      different locos in the same block at the same time)
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