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Re: Voltage on Z

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  • BJKRONEN@xxx.xxx
    John: First, welcome to the list. ... Oh boy. Your first question will no doubt have quite a response. This is not the easiest of questions. Brace
    Message 1 of 7 , Dec 12, 1999
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      John:

      First, welcome to the list.

      > I have a question on Z scale voltages.

      Oh boy. Your first question will no doubt have quite a response. <grin>
      This is not the easiest of questions. Brace yourself for several different
      answers.

      > I have both Marlkin and MT engines. The documentation
      > for both say that you should not exceed 8 volts.

      Aaaaahhh. Read that again. MT says not over 10 volts. Marklin, for 24
      years, said nothing over 8 volts. Marklin recently brought out a new power
      supply and now says no more than 10 volts. But mind you, the new Marklin
      pack is not a "DC" pack, its a processed waveform pack.

      > Also the MT says not to run them on pulse power.

      That is a correct statement of what the label says.

      > I own 2 Marklin power packs (the large white ones
      > that cost alot of money and aren't as good as some
      > MRC power packs that I have for HO). I put a dc volt
      > meter on them (actually I tried 2 different ones)
      > and both power packs put out a maximum of 12.5
      > volts. So what I do is only run them up to 3/4
      > maximum. Am I missing something?

      One thing at a time.

      First, if the power supply in question uses a resistor to vary the output
      voltage, and you measure its output with no load, you will see the full
      rectified output of the transformer. Why? Because if there is no current
      across the variable resistor, you will not have any voltage drop between the
      transformer and your point of measurement. It will always show you a false
      reading, no matter the knob setting. If you really want to see what it puts
      out, put a automotive stop light bulb across the output, so some real current
      flows. Then measure it.

      If the power supply is a solid state unit, measuring its output may or may
      not meaning anything.

      The problem is that almost any meter a hobbiest can afford is an RMS meter.
      That simply means the meter expects to encounter re-occuring and identical
      sine waves and give you a reading on the "heating effect" of that sine wave.
      In other words, what DC voltage would be equal in "power" to the AC waveform
      you are measuring.

      But if the supply puts out a pulse or processed waveform, and all bets are
      off as far as the meter telling you anything meaningful. I have a chart I
      picked up from an engineering magazine that gives you a multiplier if all you
      have is a "affordable" meter and a strange waveform. The multipliers run
      from 0.2 to 3.8 depending on the waveform you think you are connected to.

      > Also why does MT say not to run them on pulse (do they have coreless
      > motors)?

      The fatal enemy of any motor is heat. The purpose of any pulse supply is to
      force more enegy into the motor than it would otherwise accept at a given
      speed. While this results in a more responsive motor, the result is also
      extra heat.

      In the case of MicroTrains, their motor is totally encapsulated inside a
      metal loco weight. There is no place for the heat to go. I guess is, the
      motor runs at a safe temperature margin, but at the top of the range.
      Anything beyound that and Poof !! Neither Marklin or MicroTrains has a
      thermal path for heat to escape the motor.

      So, what should you do.

      Well, if you want to be very conservative, stay with pure DC, and insure you
      buy a pack that does not put out too much voltage (Marklin or MT). Or epoxy
      a "stop" to block the knob of a 12vdc pack so it cannot exceed the rated
      voltage. Or put diode pairs in its output leads to "kill" the extra voltage
      (that's another email).

      If you elect to try pulse, you can use solutions others have found to be
      acceptable over the years. Use some caution in taking "advice" and ask more
      than a few questions. Its YOUR train that will burn up.

      Or you can monitor the temperature of your motor every 30 seconds for an hour
      of operation to see if "this loco" and "that kind of pulse pack" is a good
      combination. Folks on the Nn3 list write about Marlin motors going up in
      smoke in 60 seconds on some exotic pulse-width type pulse packs.

      You see a lot about the 2800 packs. Folks I have a high level of confidence
      in use them. It is NOT a pulse pack, rather it has an interesting processed
      and complex output waveform. But plan to block them at less than full
      rotation. At full output, it puts out a full 12.5vdc RMS on the rails. Far,
      far too much. Measuring it with a "normal" meter is only accurate near the
      high end of the speed control. At the low end, your meter will lie, without
      a doubt.

      I actually own a "true" RMS meter. One that is not bothered by waveforms.
      Thank heavens for oil company surplus equipment auctions, otherwise I'd never
      own one ($3,000usd). Internally, it uses the input voltage to heat a
      thermocouple, then measures the temperature of the thermocouple and reads in
      "volts" of effective DC. If I can get "roundtuit" I'll hook a 2800 up to the
      meter and see where the 8 and 10 points are. You are the second person I've
      promised that to. Guess I'd better get busy.

      So what do I use. I make my own throttles from LM317 integrated circuits.
      Pure 8 VDC. Works for me. Very similiar to this circuit (not my web page):

      <A HREF="http://www2.ebtech.net/~pais/TTR_Throttle.html">TTR Throttle
      Circuit.</A>

      Clean rails, wheels and drivetrains are more important than exotic throttles
      in this scale anyway, or at least I think so.

      > I installed a Digitrax DCC in one of the
      > Marklin engines. When I run it on DCC I set the VMAX
      > to 8 volts (but don't know if I have to).

      Now I'm jealous. And yes, 8 volts is typical. Remember, DCC puts pulse
      power to the motor, not DC. Watch the heat. If you are really into DCC,
      some DCC motor overheating discussions can be found at:

      <A
      HREF="http://elnus.etech.hs-bremen.de/dccproject/measurements.html">Measuremen
      ts</A>

      and the full decoder project described at:

      <A HREF="http://elnus.etech.hs-bremen.de/dcc_decoder.html">dcc decoder </A>

      Glad to have you with us.

      Bill Kronenberger
      Houston
    • gunnar.edebrant@xxxxx.xx
      Greetings, Nothing much to add really after Bill and Jeffreys postings, but here are a few points who might be of interest: First of all: Märklin states that
      Message 2 of 7 , Dec 13, 1999
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        Greetings,

        Nothing much to add really after Bill and Jeffreys postings, but here are a few
        points who might be of interest:

        First of all: M�rklin states that the locos will cope with
        a max output of 10 V. Apparently they've tested this, at
        least it says so in the Swedish catalogue, and found that it
        won't harm your engine. I now too sure about that, but since
        you seldom run your trains on full speed it's probably not
        your main concern.

        Secondly, the only M�rklin power-pack that I have, 67011,
        (don't know the US one though) uses some modified pulsed
        way of supplying the power. From what I can remember it
        starts out using the pulsed output and then, once you turn
        the speed (knob) up, it converts to plain DC-levels.

        What really is the trouble is the wave-form of the pulsed
        output. A pure PWM (Pulse Width Modification, an output
        of max voltage hacked up into smaller parts) generates a
        lot high frequency components in the output. (I could
        probably try to explain this but since it was so long since
        I took the course in Fourier-analysis I'd probably make a
        mess of it.) Anyway, these high frequency components do not
        really like the coils in the engine and create a certain
        amount of excessive heat. The more square shaped the pulsed
        output is, the more high frequency components needed.

        Regarding the heat-dissipation, the steam locos usually have
        metal casings but are much more cramped under the shell. The
        electric/diesel engines has more "air" under the shell but
        their shell is plastic (at least on the M�rklin ones). I
        can't tell which one is the worst combination, I do not have
        the experience needed in this area...

        Myself, I use both M�rklin and CoolCrawler power-packs. Both
        works fine but since my layout isn't completed yet (will it
        ever?) I seldom get the long running hours.

        Well, these are just my 0.05$,



        Cheers GeDe, from a cold and winterlike Gothenburg, Sweden.


        Ps. The CoolCrawler uses a sine-wave pulsed output which
        generates less amount of these dreaded high frequency
        components. For me, it works great, I haven't had any
        problems running my locos on this. I know there is a web-
        site somewhere describing how to build one of these but I
        no longer have that URL in my memory/history list. Anyone
        else knows?

        ----------------------------------------------------
        Guide Datakonsult AB Volvo Penta AB
        gunnar.edebrant@... it5.edebrant@...
        Guide: +46 (0)706 840142 Penta: +46 (0)31 667988
        ----------------------------------------------------
      • BJKRONEN@xxx.xxx
        ... http://www.mcs.net/~teller/www/tractronics/articles/ccartcl/ccartcl.html From a warm, but rainy Houston. Bill Kronenberger
        Message 3 of 7 , Dec 13, 1999
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          Gunnar:

          > I know there is a web-
          > site somewhere describing how to build one of these but I
          > no longer have that URL in my memory/history list. Anyone
          > else knows?

          http://www.mcs.net/~teller/www/tractronics/articles/ccartcl/ccartcl.html

          From a warm, but rainy Houston.

          Bill Kronenberger
        • Ztrack@xxx.xxx
          ... True statement! I was once shown an unfortunate MT F7 that someone tried to run on pulse power. The shell was not warped, it actually was melted through!
          Message 4 of 7 , Dec 13, 1999
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            In a message dated 12/12/99 8:28:38 PM, jmac_han@... writes:

            >The danger, I believe, is not to the motor per se, but to the shell
            >which could possibly warp.


            True statement! I was once shown an unfortunate MT F7 that someone tried to
            run on pulse power. The shell was not warped, it actually was melted through!
            Now that took some heat.

            Rob Kluz
            Ztrack Magazine
          • M. Gottschalch
            Gunner, ... In my opinion the metal body should be the best as it acts as a heat sink to draw the heat off and let a much larger area disipate it. A principle
            Message 5 of 7 , Dec 14, 1999
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              Gunner,

              >Regarding the heat-dissipation, the steam locos usually have
              >metal casings but are much more cramped under the shell. The
              >electric/diesel engines has more "air" under the shell but
              >their shell is plastic (at least on the M�rklin ones). I
              >can't tell which one is the worst combination,

              In my opinion the metal body should be the best as it acts as a heat
              sink to draw the heat off and let a much larger area disipate it. A
              principle used in cooling many high output electronic parts that would
              get too hot by themselves is to add a heatsink, just a large chunck of
              metal with fins in it to increase the heat disipation area.

              I think that the plastic shell even though it has air space adds to the
              heat because it does not even allow air flow to get to the motor. The
              best heat disipation there is through the metal frame. Though the body
              does allow heat out through the plastic, that plastic is not as good a
              conductor of heat as metal is.

              Manfred
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