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Re: Amps

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  • Kari Sarmanne
    Take a look at the following page: http://www.fr-model.de/english/information_scratch_battery.htm You can use a 0.4 W potentiometer with the LM317T regulator.
    Message 1 of 6 , Jul 1, 2004
      Take a look at the following page:

      http://www.fr-model.de/english/information_scratch_battery.htm

      You can use a 0.4 W potentiometer with the LM317T regulator.

      I have built some battery power packs using a 0.4 W potentiometer
      and a transistor ( BD244C ). They work just fine.

      Without a regulator or transistor you must have at
      least a 4 W potentiometer, but I do not recommend it.

      I have built two cigar box layouts, but I have not put
      the 9 V battery in the box. I just have a connection to
      a battery power pack or to 230 V power pack.

      Kari S.

      --- In z_scale@yahoogroups.com, "Paul Hertel" <paulhertel@c...> wrote:
      > Thankz. I was think the amps were pretty small. I know about the
      voltage
      > as I'm
      > working on a cigar box layout to be run with a 9V battery.
      > Last night I had the pleasure of burning up a potentiometer. A 9V
      battery
      > made the insides glow nicely.
      > Then the tell tail smell of burnt electronics!
      > Maybe I'll have to get the voltage regulator from ZTrack. I was
      hoping for
      > a cheaper alternative.
      >
      > Thankz again!
      >
      > Paul
    • Glen Chenier
      ... wrote: ... Last night I had the pleasure of burning up a potentiometer. A 9V ... Sorry for the delayed response, have just been browsing recent messages
      Message 2 of 6 , Jul 5, 2004
        --- In z_scale@yahoogroups.com, "Kari Sarmanne" <kaikari@l...> wrote:
        > I have built some battery power packs using a 0.4 W potentiometer
        > and a transistor ( BD244C ). They work just fine.
        >
        > Without a regulator or transistor you must have at
        > least a 4 W potentiometer, but I do not recommend it.

        > --- In z_scale@yahoogroups.com, "Paul Hertel" <paulhertel@c...>
        wrote:
        ...> > Last night I had the pleasure of burning up a potentiometer.
        A 9V
        > battery
        > > made the insides glow nicely.


        Sorry for the delayed response, have just been browsing recent
        messages and came upon this one.

        A resistor (potentiometer) voltage control is fine for a layout with
        no changes in load - ie flat landscape. If there are grades on your
        layout, the regulated voltage option (transistor) will maintain a
        more constant train speed.

        When using a 4 watt (or more) variable resistance (potentiometer) go
        for at least 50 ohms, better 75-100 ohms. Use only 2 terminals in
        series with the track. Some uses of a potentiometer use all 3
        terminals where the ends of the resistance terminals are placed
        across the power source and the variable voltage is taken from the
        central wiper contact. This is not required for locomotive speed
        control and will waste battery life un-neccessarily if all 3
        terminals are used since battery current is drawn through the
        potentiometer and does no useful work.

        If you have grades on your cigar box layout the regulated voltage
        circuit helps to keep the speed more constant. The transistor
        regulator maintains a constant voltage to the locomotive by
        constantly self-adjusting it's electrical resistance to compensate
        for variations in current demand by the loco (it measures it's own
        output voltage and adjusts itself to keep this voltage at a constant
        level). A fixed resistance (potentiometer) instead without this self-
        monitoring feature will drop more voltage as the loco current demand
        increases to climb a grade, this results in even less current
        available and the loco slows even more. If drastic speed changes are
        the desired effect, then go for the resistor approach. If you wish
        to maintain a more constant speed, use the transistor regulator.

        BTW, the simplest form of regulated voltage adjustment is a series
        string of silicon rectifier diodes, about 10 cents each if bought in
        bulk, like a pack of 25. Unlike a resistance, each diode in it's
        forward conduction polarity drops a constant 0.7 volts regardless of
        the current through it. A battery is already voltage regulated other
        then a small internal resistance and gradually decreasing voltage as
        it is used. Any common silicon diode rated for 1 amp or more is
        suitable - 1N4001, 1N4002, 1N4003, 1N4004 etc. Ten in series will
        drop 7 volts for minimum speed (2 volts left for the loco from the 9
        volt battery), 5 in series drop 3.5 volts (5.5 volts left over for
        the loco) etc. An alligator clip wire can be used to select how many
        diodes are electrically in the string. If you want to get fancy you
        can connect each diode wire connection to a screw, a series of screws
        in the back of the cigar box let you select speed with the alligator
        clip. As the battery ages move the clip to the next screw. Not
        elegant, but for a small layout with grades this is the simplest form
        of constant voltage supply.

        Another use for diodes proposed and tested by Cliff Travis - series
        diodes used on a helix in the downhill polarity help maintain the
        speed so the same throttle setting results in the same speed both up
        and down. Neat idea.
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