Loading ...
Sorry, an error occurred while loading the content.

Re: [usa-tesla] The Master's Own Words... (Tesla's Notes on A Unipolar Dynamo)

Expand Messages
  • Michael Riversong
    Unfortunately Word 97 is not a standard format. Many of us can t read it. Generally a text file is always better, because that s the one thing everyone can
    Message 1 of 3 , Sep 1, 2000
    • 0 Attachment
      Unfortunately Word 97 is not a standard format. Many of us can't read it.
      Generally a text file is always better, because that's the one thing
      everyone can read.

      At 09:23 PM 8/31/00 -0500, you wrote:
      >NOTE: This was scanned by me, and there are 3 embedded figures (*.tif files),
      > and the article from 1891, is in Word 97 *.DOC format. There
      >are NO
      > viruses in this document! I hope that the figures open
      >correctly, within
      > the body of the document, but if they don't, I can send
      >higher resolution
      > tif files of the figures, separately. ENJOY... if you haven't
      >already read this!
      > The document will come as an attachment... so here goes.
      >later... ***jpm***
      >
      >
      > <html><br>
      >
      ><!-- |**|begin egp html banner|**| -->
      >
      ><table border=0 cellspacing=0 cellpadding=2>
      ><tr bgcolor=#FFFFFF>
      ><td colspan=2 width=470><!-- |@|begin eGroups banner|@| runid: 8987 crid:
      3729 -->
      ><a target="_blank"
      href="http://click.egroups.com/1/8987/18/_/522035/_/967775541/"><center>
      ><img width="468" height="60"
      > border="0"
      > alt=""
      >
      src="http://adimg.egroups.com/img/8987/18/_/522035/_/967775541/WarningOther4
      68x602E.gif"></center><center><font color="black"></font></center></a>
      ><!-- |@|end eGroups banner|@| --></td>
      ></tr>
      ><tr bgcolor=#FFFFCC valign=middle>
      ><td width=77><a href="http://www.egroups.com/"><img border=0
      src="http://www.egroups.com/img/logo/logo72.gif" width="72" height="32"
      alt="eGroups"></a></td>
      ><td width=388>
      ><font size="-1">
      ><a href="http://www.egroups.com/mygroups">My Groups</a> |
      ><a href="http://www.egroups.com/group/usa-tesla">usa-tesla Main Page</a>
      >| <!-- |@|begin eGroups banner|@| runid: 8150 crid: 4125 --><a
      target="_blank"
      href="http://click.egroups.com/1/8150/18/_/522035/_/967775541/">Start a new
      group!</a><!-- |@|end eGroups banner|@| --></font>
      ></td>
      ></tr>
      ></table>
      ><br>
      >
      ><!-- |**|end egp html banner|**| -->
      >
      ><p>
      >
      >
      ><font color="#FF0000"><b>NOTE: This was scanned by me, and there are 3
      >embedded figures (*.tif files),<br>
      >            
      >and the article from 1891, is in Word 97 *.DOC format. There are NO<br>
      >            
      >viruses in this document! I hope that the figures open correctly,
      >within<br>
      >            
      >the body of the document, but if they don't, I can send higher
      >resolution<br>
      >            
      >tif files of the figures, separately. ENJOY... if you haven't already
      >read this!<br>
      >            
      >The document will come as an attachment... so here goes. later...
      >***jpm***<br>
      ><br>
      ><br>
      >           
      ></font></b>
      >
      ></html>
      >
      >Attachment Converted: C:\EARTHL~1\EUDORA2\NOTESONA.doc
      >
      -- Michael Riversong **
      Professional Harpist, Educator, and Writer **
      RivEdu@... ** Phone: (307)635-0900
      http://home.earthlink.net/~mriversong
    • James P Moore
      ... I will try to send it as a text file with attachments Michael... should it be plain txt or enriched txt... sometime the conversion to txt will not preserve
      Message 2 of 3 , Sep 1, 2000
      • 0 Attachment
        >
        >Unfortunately Word 97 is not a standard format. Many of us can't read it.
        >Generally a text file is always better, because that's the one thing
        >everyone can read.

        I will try to send it as a text file with attachments Michael... should it
        be plain txt or
        enriched txt... sometime the conversion to txt will not preserve the
        format, but I
        can try. later...
      • James P Moore
        Ok.... for you plain txt folks... here it is again in plain txt format. jpm
        Message 3 of 3 , Sep 1, 2000
        • 0 Attachment
          Ok.... for you plain txt folks... here it is again in plain txt format. jpm
          ************************************************************************************************

          *NOTES ON A UNIPOLAR DYNAMO*

          Written by Nikola Tesla and published in:
          * The Electrical Engineer, N.Y., Sept. 2, 1891 *


          It is characteristic of fundamental discoveries, of great
          achievements of intellect, that they retain an undiminished
          power upon the imagination of the thinker. The memorable
          experiment of Faraday with a disc rotating bctwe'en the two
          poles of a magnet, which has borne such magnificent fruit,
          has long passed into every-day experience; yet there are certain
          features about this embryo of the present dynamos and motors
          which even to-day appear to us Striking, and are worthy of the
          most careful study.

          Consider, for instance, the case of a disc of iron or other
          metal revolving between the two opposite poles of a magnet,
          and the Polar surfaces completely covering both sides of the
          disc, and assume the current to be taken off or conveyed to
          the same by contacts uniformly from all points of the periphery
          of the disc. Take first the case of a motor.

          In all ordinary motors the operation is dependent upon some
          shifting or change of the resultant of the magnetic attraction
          exerted upon the armature, this process being effected either
          by some mechanical contrivance on the motor or by the action
          of currents of the proper character. We may explain the operation
          of such a motor just as we can that of a water-wheel.

          But in the above example of the disc surrounded completely by
          the polar surfaces, there is no shifting of the ;magnetic action,
          no change whatever, as far as we know, and yet rotation ensues.
          Here, then, ordinary considerations do not apply; we cannot even
          give a superficial explanation, as in ordinary motors, and the
          operation will be clear to us only when we shall have recognized
          the very nature of the forces concerned, and fathomed the mystery
          of the invisible connecting mechanism.

          Considered as a dynamo machine, the disc is an equally interesting
          object of study. In addition to its peculiarity of giving currents
          of one direction without the employment of commutating devices, such
          a machine differs from ordinary dynamos in that there is no reaction
          between armature and field. The armature current tends to set up a
          magnetization at right angles to that of the field current, but since
          the current is taken off uniformly from all points of the periphery,
          and since, to be exact, the external circuit may also be arranged
          perfectly symmetrical to the field magnet, no reaction can occur.

          This, however, is true only as long as the magnets are weakly
          energized, for when the magnets are more or less saturated, both
          magnetizations at right angles seemingly interfere with each other.

          For the above reason alone it would appear that the output of
          such a machine should, for the same weight, be much greater than
          that of any other machine in which the armature current tends to
          demagnetize the field. The extraordinary output of the Forbes
          unipolar dynamo and the experience of the writer confirm this view.

          Again, the facility with which such a machine may be made to
          excite itself is striking, but this may be due m besides to the
          absence of armature reaction -- to the perfect smoothness of the
          current and non-existence of self-induction.


          Page 2


          If the poles do not cover the disc completely on both
          sides, then, of course, unless the disc be properly subdivided,
          the machine will be very inefficient. Again, in this case there
          are points worthy of notice. If-the disc be rotated and the
          field current interrupted, the current through the armature
          will continue to flow and the field magnets will lose their
          strength comparatively slowly. The reason for this will at once
          appear when we consider the direction of the currents set up
          in the disc.

          Figure 1

          Referring to the diagram Fig. 1, d represents the disc with
          the sliding contacts B B' on the shaft and periphery. N and S
          represent the two poles of a magnet. If the pole N be above, as
          indicated in the diagram, the disc being supposed to be in the
          plane of the paper, and rotating in the direction of the arrow D,
          the current set up in the disc will flow from the centre to the
          periphery, as indicated by the arrow A. Since the magnetic action
          is more o.or less confined to the space between the poles N S,
          the other portions of the disc may be considered inactive.

          The current set up will therefore not wholly pass through the
          external circuit F, but will close through the disc itself, and
          generally, if the disposition be in any way similar to the one
          illustrated, by far the greater portion of the current
          generated will not appear externally, as the circuit F is
          practically short-circuited by the inactive portions of the disc.

          The direction of the resulting currents in the latter may be
          assumed to be as indicated by the dotted lines and arrows
          m and n; and the direction of the energizing field current
          being indicated by the arrows a b c d, an inspection of the
          figure shows that one of the two branches of the eddy current,
          that is, A B' m B, will tend to demagnetize the field, while
          the other branch, that is, A B' n B, will have the opposite
          effect.

          Therefore, the branch A B' m B, that is, the one which is
          approaching the field, will repel the lines of the same, while
          branch A B' n B, that is, the one leaving the field, will gather
          the lines of force upon itself. In consequence of this there
          will be a constant tendency to reduce the current flow in the
          path A B' m B, while on the other hand no such opposition will
          exist in path A B' n B, and the effect of the latter branch or
          path will be more or less preponderating over that of the former.

          The joint effect of both the assumed branch currents might be
          represented by that of one single current of the same direction
          as that energizing the field. In other words, the eddy currents
          circulating in the disc will energize the field magnet. This is
          a result quite contrary to what we might be led to


          Page 3

          suppose at first, for we would naturally expect that the
          resulting effect of the armature currents would be such
          as to oppose the field current, as generally occurs when
          a primary and secondary conductor are placed in inductive
          relations to each other.

          But it must be remembered that this result from the
          peculiar disposition in this case, namely, two paths being
          afforded to the current, and the latter selecting that path
          which offers the least opposition to its flow. From this we
          see that the eddy currents flowing in the disc partly
          energize the field, and for this reason when the field
          current is interrupted the currents in the disc will continue
          to flow, and the field magnet will lose its strength with
          comparative slowness and may even retain a certain strength
          as long as the rotation of the disc is continued.

          Figure 2 & 3 together

          The result will, of course, largely depend on the
          resistance and geometrical dimensions of the path of
          the resulting eddy current and on the speed of rotation;
          these elements, namely; determine the retardation of
          this current and its position relative to the field.

          For a certain speed there would be a maximum energizing
          action; then at higher speeds, it would gradually fall off
          to zero and finally reverse, that is, the resultant eddy
          current effect would be to weaken the field. The reaction
          would be best demonstrated experimentally by arranging the
          fields N S, N' S', freely movable o.on an axis concentric
          with the shaft of the disc.

          If the latter were rotated as before in the direction of
          the arrow D, the field would be dragged in the same direction
          with a torque, which, up to a certain point, would go on
          increasing with the speed of rotation, then fall off, and
          passing through zero, finally become negative; that is: the
          field would begin to rotate in opposite direction to the disc.

          In experiments with alternate current motors in which the
          field was shifted by currents of differing phase, this
          interesting result was observed. For very low speeds of
          rotation of the field the motor would show a torque of
          900 lbs or more, measured on a pulley 12 inches in
          diameter.

          When the speed of rotation of the poles was increased, the
          torque would diminish, would finally go down to zero, become
          negative, and then the armature would begin to rotate in
          opposite direction to the field.

          To return to the principal subject; assume the conditions
          to be such that the eddy currents generated by the rotation
          of the disc strengthen the field, and suppose the latter gradually
          removed while the disc is kept rotating at an increased rate.
          The current, once started, may then be sufficient to maintain
          itself and even increase in strength, and then we have the case
          of Sir William Thomson's "current accumulator."

          Page 4


          But from the above considerations it would seem that for the
          success of the experiment the employment of a disc not subdivided
          would be essential, for if there should be a radial subdivision,
          the eddy currents could not form and the self-exciting action would
          cease. If such a radially subdivided disc .were used it would be
          necessary to connect the spokes by a conducting rim or in any
          proper manner so as to form a symmetrical system of dosed circuits.

          The action of the eddy currents may be utilized to excite a machine
          of any construction. For instance, in Figs. 2 and 3 an arrangement
          is shown by which a machine with a disc armature might be excited.
          Here a number of magnets, N S, N S, are placed radially on each
          side of a metal disc D carrying on its rim a set of insulated coils,
          C C. The magnets form two separate fields, an internaY and an
          external one, the solid disc rotating in the field nearest the axis,
          and the coils in the field further from it.

          Assume the magnets slightly energized at the start; they could be
          strengthened by the action of the eddy currents in the solid disc
          so as to afford a stronger field for the peripheral coils. Although
          there is no doubt that under proper conditions a machine might be
          excited in this or a similar manner, there being sufficient
          experimental evidence to warrant such an assertion, such a mode of
          excitation would be wasteful.

          But a unipolar dynamo or motor, such as shown in Fig. 1 may be
          excited in an efficient manner by simply properly subdividing the
          disc or cylinder in which the currents are set up, and it is
          practicable to do away with the field coils which are usually employed.

          Such a plan is illustrated in Fig. 4.

          The disc or cylinder D is supposed to be arranged to rotate between
          the two poles N and S of a magnet, which completely cover it on both
          sides, the contours of the disc and poles being represented by the

          Figure 3 & 4 together


          But from the above considerations it would seem that for
          the success of the experiment the employment of a disc not
          subdivided would be essential, for if there should be a
          radial subdivision, the eddy currents could not form and
          the self-exciting action would cease. If such a radially
          subdivided disc were used it would be necessary to connect
          the spokes by a conducting rim or in any proper manner so
          as to form a symmetrical system of dosed circuits.

          The action of the eddy currents may be utilized to excite a
          machine of any construction. For instance, in Figs. 2 and 3
          an arrangement is shown by which a machine with a disc armature
          might be excited. Here a number of magnets, N S, N S, are
          placed radially on each side of a metal disc D carrying on its
          rim a set of insulated coils, C C. The magnets form two
          separate fields, an internal and an external one, the solid disc
          rotating in the field nearest the axis, and the coils in the
          field further from it.

          Assume the magnets slightly energized at the start; they could
          be strengthened by the action of the eddy currents in the solid
          disc so as to afford a stronger field for the peripheral coils.
          Although there is no doubt that under proper conditions a machine
          might be excited in this or a similar manner, there being
          sufficient experimental evidence to warrant such an assertion,
          such a mode of excitation would be wasteful.

          But a unipolar dynamo or motor, such as shown in Fig. 1 may be
          excited in an efficient manner by simply properly subdividing
          the disc or cylinder in which the currents are set up, and it
          is practicable to do away with the field coils which are usually
          employed.

          Such a plan is illustrated in Fig. 4. The disc or cylinder D
          is supposed to be arranged to rotate between the two poles N and S
          of a magnet, which completely cover it on both sides, the contours
          of the disc and poles being represented by the circles d and d'
          respectively, the upper pole being omitted for the sake of clearness.

          The cores of the magnet are supposed to be hollow, the shaft C of
          the disc passing through them. If the unmarked pole be below, and
          the disc be rotated screw fashion, the current will be, as before,
          from the centre to the periphery, and may be taken off by suitable
          sliding contacts, B B', on the shaft and periphery respectively.

          In this arrangement the current flowing through the disc and
          external circuit will have no appreciable effect on the field
          magnet. But let us now suppose the disc to be subdivided, spirally
          as indicated by the full or dotted lines, Fig. 4. The difference
          of potential between a point on the shaft and a point on the
          periphery will remain unchanged, in sign as well as in amount.

          The only difference will be that the resistance o,of the disc will
          be augmented and' that there will be a greater fall of potential
          from a point on the shaft to a point on the periphery when the same
          current is traversing the external circuit. But since the current
          is forced to follow the lines of subdivision, we see that it will
          tend either to energize or de-energize

          Page 5



          the field, and this will depend, other things being equal,
          upon the direction of the lines of subdivision. If the
          subdivision be as indicated by the full lines in Fig. 4,
          it is evident that if the current is of the same direction
          as before, that is, from centre to periphery, its effect
          will be to strengthen the field magnet; whereas, if the
          subdivision be as indicated by the dotted lines, the
          current generated will tend to weaken the magnet.

          In the former case the machine will be capable of exciting
          itself when the disc is rotated in the direction of arrow D;
          in the latter case the direction of rotation must be reversed.
          Two such discs may be combined, however, as indicated, the
          two discs rotating in opposite fields, and in the same or
          opposite direction.

          Similar disposition may, of course, be made in a type of
          machine in which, instead of a disc, a cylinder is rotated.
          In such unipolar machines, in the manner indicated, the usual
          field coils and poles may be omitted and the machine may be
          made to consist only of a cylinder or of two discs enveloped
          by a metal casting.

          Instead of subdividing the disc or cylinder spirally, as
          indicated in Fig. 4, it is more convenient to interpose one
          or more turns between the disc and the contact ring on the
          periphery, as illustrated in Fig. 5.

          A Forbes dynamo may, for instance, be excited in such a manner.
          In the experience of the writer it has been found that instead
          of taking the current from two such discs by sliding contacts,
          as usual, a flexible conducting: belt may be employed to advantage.

          The discs are in such case provided with large flanges, affording
          a very great contact surface. The belt should be made to bear
          on the flanges with spring pressure to take up the expansion.
          Several machines with belt contact were constructed by the
          writer two years ago, and worked satisfactorily; but for want
          of time the work in that direction has been temporarily suspended.

          A number of features pointed out above. have also been
          used by, the writer in connection with some types of
          alternating current motors.

          THE END
        Your message has been successfully submitted and would be delivered to recipients shortly.