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65104Re: Marklin transformer polarity

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  • zeeglen
    Jul 23, 2010
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      --- In z_scale@yahoogroups.com, "luckykid43" <luckykid43@...> wrote:
      > Actually, I was not clear in my purpose with this question. I thought there might be a problem if I was using more than one Marklin transformer/controller in my layout and the polarity of the transformers themselves ended up different.
      > I hope that helps.

      This is a valid concern. I do not know if Marklin power packs are prone to AC phasing differences, but is known to be critical with some MRC power packs. There are two issues here, DC polarity (locomotive direction) and AC phasing if these power packs output half wave rectified.

      DC polarity is easily understood. Both power packs should be the same make/model and both set to the same direction as the loco crosses an insulated boundary between two blocks powered by the two individual power packs. Speed should be set to approximately the same on both power packs. If the power packs are inadvertently set to opposite DC polarity the loco will stall as it's wheels bridge across the rail gaps and the power packs drive each other into overload shutdown through the locomotive wheels, if properly designed no permanent damage except possibly to the loccomotive. The same can happen with a single power back when block boundaries are set to opposite directions, but less damaging current flows.

      Generally it is not a very good idea to have a locomotive cross a block boundary between power packs unless both power packs are the same make and model and set to the same speed, and definitely to the same DC polarity (direction). Differences in output waveforms (DC, halfwave sine, fullwave sine, pulse-on-DC) can make different models from the same manufacturer incompatible with each other when run in parallel (due to the wheels bridging the rail gaps) even for a short time.

      Even then the pulse phasing between the same models will not necessarily match, if so the AC power cord of one must be reversed. Involves rewiring if the AC plugs are polarized (one wide blade) and cannot be reversed in the wall outlet.

      If the power pack outputs half-wave-rectified sine and AC input is 60 Hz, output voltage pulses are present for 8 milliseconds followed by a gap (no voltage) for another 8 milliseconds, then the cycle repeats. In other words 60 pulses and 60 interleaved gaps per second.

      If using more than one power pack for separate blocks, the phasing must be the same so that as a locomotive straddles insulated blocks and momentarily receives and bridges power from both packs the half wave relative to AC line polarity must be synchronized among all power packs. Otherwise the loco will speed up while straddling blocks as it briefly receives full wave created from two opposite-phased half wave sources, even when the DC polarity (loco direction) is matched. In other words, the two power packs can alternately fill in the gap between each other's pulses instead of both producing the 8 millisecond pulse at the same time.
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