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Re: Voltage on Z

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  • Jeffrey MacHan
    Hi John, Welcome to the list. George Menzie of MT is a member of the list. Perhaps he has some wisdom to share with us regarding the warning concerning pulse
    Message 1 of 7 , Dec 12, 1999
      Hi John,

      Welcome to the list.

      George Menzie of MT is a member of the list. Perhaps he has some wisdom to
      share with us regarding the warning concerning pulse power with the MT F7...

      ...in the meantime I will hasard a guess.

      Small DC motors tend to warm up considerably when running on pulse power.
      The MT F7 has no air space to help cool the motor and the shell is quite
      thin. The danger, I believe, is not to the motor per se, but to the shell
      which could possibly warp.

      Some modern transistor throttles inject pulses at low voltages to help
      overcome resistance and to get the loco off to a slow speed start. The
      pulse form drops as voltage increases until the loco is ultimately running
      on pure DC at normal speed. The problems would start to show up with a Z
      loco running constantly at a crawl on pulse power. It wouldn't take too
      long to generate a lot of heat and turn the shell to putty.

      The floor is open to other opinions.

      Happy Holidays,
      Jeffrey

      >From: jjabour@...
      >Reply-To: z_scale@onelist.com
      >To: z_scale@onelist.com
      >Subject: [z_scale] Voltage on Z
      >Date: 13 Dec 1999 00:35:05 -0000
      >
      >Hello
      >I have a question on Z scale voltages. I have
      >both Marlkin and MT engines. The documentation
      >for both say that you should not exceed 8 volts.
      >Also the MT says not to run them on pulse power.
      >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? Also why does MT
      >say not to run them on pulse (do they have coreless
      >motors)? 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).
      >Thanks for any help in advance.
      >John Jabour
      >
      >------------------------------------------------------------------------
      >CraZy 'bout Zee!
      >
      ><< text3.html >>
    • 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 2 of 7 , Dec 12, 1999
        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 3 of 7 , Dec 13, 1999
          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 4 of 7 , Dec 13, 1999
            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 5 of 7 , Dec 13, 1999
              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 6 of 7 , Dec 14, 1999
                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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