P R ACTI C A L
DETAIL DRAWINGS AND INSTRUCTIONS FOR WINDING.
GIVING CORRECT SIZES OF
WIRE, DIMENSIONS OF IRON, ETC., ETC.
DIAGRAM FOR HOUSE WIRING.
L C. ATWOOD
NIXON -JONES PRINTING Co.
Entered according to Act of Congress in the year 1893, by
L. C. ATWOOD,
In the office of the Librarian at Washington, D. C.
Ever since electric lighting has become a practical success, there has
been a desire, on the part of the general public, to know the method of
construction of dynamos. There are many able works on the subject, but
far too deep and scientific to reach the class most deeply interested. This
work is gotten up especially for amateur builders and non-professional men.
All measurements and instructions for winding are taken from machines in
actual service. Particular attention has been given to every detail of
construction, that they may be thoroughly understood. This work will be
of great value, not only to those who wish to build dynamos, but to
superintendents, engineers and workmen who have the care of present
St. Louis, June, 1893.
TABLE OF CONTENTS.
The Construction and Winding of a Siemens Armature 4
How to Wind a Gramme Ring Armature 9
Four Light Dynamo 14
Ten Light Dynamo 21
Fifteen Light Dynamo 29
Thirty-five Light Dynamo 39
Sixty Light Dynamo 45
One Hundred and Fifty Light Dynamo 52
One Light Arc Dynamo 61
Method of Field Winding and House Wiring 67
Neutral Diameter 70
Charging of Dynamo 72
Magnetic Strength of Fields 72
Speed of the Dynamo 72
Lines of Force 72
Causes of Brushes Sparking 73
Commutator Segments , 75
Position of the Brushes 76
How to Test the Dynamo 77
Wiring for Lamp Circuits 78
Wiring Tables for Lamps 80,82,83
Table of Dimensions, Weight and Resistance of Bare Copper Wire 85
vi TABLE OF CONTENTS.
Table showing the Weight, Carrying Capacity and Loss in Volts of
Different Sizes Copper "Wire 84
Rules and Regulations of the New England Insurance Exchange and
Boston Fire Underwriters Union for Electric Lighting 86
Rules and Regulations of the New York Board of Fire Underwriters .... 101
How the Electric Current is Produced 110
History of Electricity and Electric Light 115
The Incandescent System 129
Storage Batteries 135
Economy of Electric Lighting 140
The time has come when the proper understanding of dynamo building
is just as essential as the knowledge of steam engines or any other mechanical
appliance. There is hardly any branch of industry but that electricity figures
in it in some form. Engineers are called upon to take charge of dynamos and
motors in connection with their engineering duties, and many times they are
compelled to take positions and run the chances of the machine not getting out
of order, and how often are they censured for the apparatus getting out of
order when the injunction has been placed upon them not to meddle with any
portion of the machine or its adjustments? ~No engineer can take charge of
an engine and boilers until he has passed a thorough examination as to his
fitness, still machinery far more delicate and liable to get out of order is
forced upon him. A mischievous person with a little smattering of electricity
can give him no end of trouble when, if the engineer thoroughly understood
the machine, he could easily locate or determine the cause. The construction
is purely mechanical and in cases of accidents, when the parts are returned to
the factory for repairs, those who repair them are perhaps no better workmen
than the engineer who had charge of the machine, only they have had a little
more experience in that particular line of work. From the mystery that is
thrown around that class of work, it is looked upon as something beyond the
reach of the ordinary mechanic. The object of this work is to dispel that
illusion, and to teach engineers, machinists, non-professional men and school-
boys that all that is required to build dynamos is the knowledge of the proper
dimensions of iron, correct sizes of wire and a little mechanical skill. The
2 PRACTICAL DYNAMO BUILDING.
principles involved in the generation or production of dynamic electricity are all
the same, even if each separate machine is known as a certain system. That
magic word has long gone into disuse, and one that thoroughly understands
one machine, knows them all, and all that is required to build dynamos for
any service, let it be arc or incandescent, continuous or alternating current,
high or low potential, is the knowledge of dimensions of iron, sizes of wire
and number of windings, for whatever service the machine is intended. If the
exact dimensions of iron, the sizes and correct number of windings of wire
on the armature and field magnets were given of a large lighting or power
generator, it would be impossible to reduce at a regular ratio and construct a
dynamo that would give satisfactory results, if any at all. As sizes and styles
change, conditions change also. Each machine has its own measurement and
sizes of wire for whatever service it is to be used.
What wonderful changes have been wrought within the last few years in
systems that were put on the market as perfect ! Form and quantity of iron
have been changed, sizes and quantities of wire have gone through the same
transformation, and the end is not yet. The future field is open as wide for
electrical developments as the past, and I fully believe that if the fundamental
principles of dynamo building were within easy reach of all, it would enable
those who are engaged in the care and management of electric plants, to give
the owners better service and the machines longer lives. Those who have a
desire to engage in the business can do so with a thorough knoAvledge of
Practical electric lighting is of very recent date. In 1878 Charles
Brush exhibited the first lamps burning in series, and in 1881 Edison installed
his first incandescent plant. But how many who are familiar with the workings
of dynamos understand their construction? In presenting this little volume to
the public, it is the writer's aim to give that information so much desired. The
fundamental principles will be so plainly laid down that any one skilled in the
use of tools should be able to build all the dynamos in this work, or, with the
information it gives, should be able to repair almost any of the present systems.
Every dynamo that this work contains has been built and thoroughly tested
by the writer, and only information gained by actual practice will be given.
PRACTICAL DYNAMO BUILDING. 3
Electricity will not be treated scientifically, and no attempt will be made to
explain its nature ; neither will we go back to Davenport and Page and rehearse
their experiments. No attempt will be made to explain the various systems
now in use, as there are but few who have any love for the study of
electricity, but have had the opportunity of seeing the different systems
working, or have books with cuts of the different machines in use ; but
none have given the information so much desired; that is, to tell just how a
dynamo is constructed ; how the armature and commutator are made ; how
much iron in the pole pieces, and field magnets ; what size of wire on the
armature and field magnets, and how many convolutions on each to produce a
given current and voltage. That information is the private property of dynamo
builders, and the writer will not infringe on their rights, but will confine himself
strictly to machines of his own building. While the machines given in this
work are small and of low voltage, the principles of construction are as
thoroughly incorporated in them as though they were the largest lighting or
power generators on the market to-day. It has been the writer's aim in getting
up this work to make it as plain as possible for amateur builders, and give
information which is of the greatest importance to that class. All technical
terms and mathematical formulas have been dispensed with and only plain
words and figures used, so that all parts can be readily understood. By
carefully following the instructions, there is no reason why any one building a
dynamo from this work should not get as good results as the writer. Good
workmanship, good material and good insulation are the essential features of
ST. Louis, Mo. L. C. AT WOOD.
THE CONSTRUCTION AND WINDING OF A SIEMENS ARMATURE.
When the armature core is finished, whether it is a spool of iron wire, or
is built up of iron discs, it should be spaced off into the number of sections
required. In each end of the core, and on lines parallel with the shaft should
be formed equi-distant slots 3 /i6 inch deep and about Vie inch wide. Into these
slots are driven pieces of hard wood or vulcanized fiber, which should project
sufficiently to keep the coils of copper wire in place, the length of pins varying
with the different sizes of wire used on the armature.
The armature core should now be covered over its entire surface with
rubber tape or two or three layers of thin muslin well saturated with shellac
varnish. The shaft for a proper distance from the core should also be covered
with the same thickness of insulation, and the armature is ready for the copper
In Fig. I, the wire starts from the commutator end of the armature
at 1 ; is carried along the surface of the core between two division pins
parallel with the shaft between the pins at the opposite ends ; across the
end of the armature core ; then between the pins diametrically opposite those
between which the coil started ; then across the commutator end of the core
and alongside of the first wire laid on. The wire is carried around the
armature core in this manner until the space between one set of pins is filled
one layer deep. If two layers of wire are required to each section, go around
the armature again in the same manner between the same set of pins, thus
winding back to the point of starting. The first layer can be laid all on one
side of the shaft and the second layer on the other side, or each coil may be
PRACTICAL DYNAMO BUILDING,
divided, one-half on each side of the shaft as shown in figure (1). Do not
cut the wire but leave a loop as shown at 2 sufficiently long to go to the
commutator. After making the loop and securing the wires together close
to the armature core, as shown at 2 (which may be done with strong thread,
or the wires may be twisted together) , the second section is started between the
6 PRACTICAL DYNAMO BUILDING.
next set of pins, and proceeded with as the first section until one-half of the
sections are laid on the core as shown in Fig. II. All the spaces are now filled,
but with only six loops to go to the commutator. The outer layer is now
started at 7, going between the pins in the next section and between wire 1
and loop 2, as shown in Fig. Ill on the opposite side continuing around the
armature core as in the first instance until the outer layer is laid on. The
ending wire of the last layer and the starting wire of the first layer joining
together and connecting to the same segment in the commutator. Only three
sections of the outer layer are shown in the diagram. If there are two layers
of wire to each section, there will be four layers between each set of pins with
the lead wires for each section on opposite sides of the armature core. The
object of leaving the loops between the sections instead of cutting the wire is
PRACTICAL DYNAMO BUILDING. 7
to prevent making a mistake in connecting the wires to the commutator, as
each loop from the armature connects to a segment in the commutator. To
prevent the copper wire from being thrown out against the pole pieces from
the centrifugal force, there should be bands of brass wire placed on the outside
of the armature ; the number of bands and the size of brass wire will depend
upon the size and length of the armature. For the small machines three bands
of No. 26 spring brass wire is large enough, but for the larger machines No.
20 or 22 should be used. Between the brass and copper wires should be placed
strips of mica, which not only serve as insulation but will prevent the insulation
on the copper wire being scorched as the bands are being soldered.
These cuts are made from a small armature in the course of construction
with only twelve sections and one layer of wire to each section. The core is a
g PRACTICAL DYNAMO BUILDING.
wooden spool filled with iron wire, the division pins are small smooth wire nails
with the heads removed. After the armature is wound, the bands placed on
the outside, and it is given a coat of shellac varnish, the pins are removed. If
the copper wire is well laid on the armature core, there is no danger of the wire
coming off, even at a high rate of speed, but in all large armatures the division
phis should be of wood or fibre and should remain in the armature.
HOW TO WIND A GRAMME RING ARMATURE.
The armature core should be first well insulated and spaced off into the
desired number of sections that the coils may all be of the same width. The
winding is a very simple process as far as the knowledge of the work is
concerned, as can be seen by referring to Fig. IV. Starting the first coil at 1,
the wire is passed through the interior of the armature core, returning across
the outer surface to the point of starting, ending the first section at 2. The
second section starts at 3 ending at 4, and so on around the core until the
surface of the core is covered. If two or more layers are required to each
section, wind back and forth until the desired number of convolutions are laid
on. The ending wire of one section and the starting wire of the next section
join and go to the same segment in the commutator. As the wires 2 and 3
connect and go to one segment in the commutator, 4 and 5 would connect to
another segment ; thus when the whole surface was covered, the ending wire
of the last section would connect with the starting wire 1 of the first section,
forming a complete circuit around the armature core. It is not convenient to
leave a loop between the sections to go to the commutator segments as in a
Siemens armature, as the wire has to be wound on a shuttle to get it in
convenient form to pass through the interior of the armature core. The length
of each section should be determined and cut off, for if there should be a few
convolutions short in a section, all the wire in that section would have to be
taken off again or the wire spliced, which is a dangerous piece of work, as a
splice in an armature is liable to come apart, which would open the circuit in the
PRACTICAL DYNAMO BUILDING.
armature, no doubt causing sufficient spark to burn the section in which the
break occurred and the adjoining one as well.
Figs. V and VI are cuts made from a four light armature, which is a
little more convenient to make than the one given in the drawings for a four
light dynamo. The armature core is made of iron wire wound on a wooden
spool with removable flanges on the ends. When the proper amount of wire is
wound on the spool the end of the wire is soldered; the flanges are then
PRACTICAL DYNAMO BUILDING.
12 PRACTICAL DYNAMO BUILDING.
removed and the wire ring slipped off the wooden spool. The iron ring is then
covered with two layers of adhesive rubber tape, then spaced off into eighteen
sections and wound four layers deep with "No. 20 double cotton covered magnet
wire (B. & S. Gauge). To secure the armature to the shaft, the shaft should
be threaded in the center the length of the armature or a little more ; two
taper wooden bushings with holes in the centers to admit the armature shaft are
placed in the interior of the armature ; with a nut and washer on each end of
the shaft, the bushings are forced into place, which will bring the armature
central with the shaft if care has been taken in winding the armature so that
the copper wire has not been piled up more on one side than the other. After
that is done the shaft should be placed in the lathe and turned down to the
proper size of the bearings.
Fig. VI shows the armature finished with commutator in place and
bearing turned down. No dimensions of the armature in Figs. V and YI need
be given here as they are given in drawing for four light dynamo. Only two
styles of armature will be given in this work, the Gramme ring and the
Siemens or drum armature, as they are the only ones that can be used with
this type of field magnets given. At one time there was quite a difference of
opinion as to the relative merits of the two armatures, but the difference
existed more in imagination than in the armatures themselves. The agents of
the different systems had as much, or in fact, more to do in forming the
opinions of users of dynamos than did the machines themselves. In early days
of electric lighting ever argument was used to convince a prospective purchaser
that theirs was the only system that could be used with any degree of success.
Those in favor of a Gramme ring would tell of the slow armature speed, of
the hollow core, thereby securing perfect ventilation, and that as each coil was
separate and distinct from its neighbor, in case of injury one could be removed
without disturbing the others. As all the wire on a Siemens armature is
laid on the outside of the armature core, each coil as it is laid on must
necessarily cross all previous ones at each end ; the ends of the armature
thereby become a perfect network of wires so when one coil burns out, it is
generally the first one laid on, and all the wire on the armature must be
removed to get to the injured coil.
PRACTICAL DYNAMO BUILDING. 13
If the wire is properly laid on the core, and is drawn down firmly across
the ends, and properly bound and shellaced that the wires may not be thrown
out of place from centrifugal force, there is no reason why a Siemens armature
of the same electrical output should not run as long and give as good servive as
a Gramme ring. When a coil on an armature burns out from fair play, let it
be Siemens or Gramme ring, it is time that all the wire on the armature was
removed and new wire put on in its place. It requires skill and good workmanship
to build either style of armature, and no pains should be spared if good results
are expected. As both armatures require the same mechanical horse power to
produce a given candle power, it resolves itself into a mere matter of choice
which armature is used.
These drawings are for a dynamo that will supply current for 4, 16
candle power, 35 volts lamps. The machine weighs 25 pounds, and occupies a
floor space of 8 x 12 inches ; armature speed 3,200 revolutions per minute, and
V2 horse power will be required to drive it.
Dynamos of this size are much harder to build than larger ones, and
the results obtained are not generally as satisfactory. In order to get the
required voltage, many turns of fine wire are used on the armature, and a slight
variation will cause trouble. If finer wire is used than given here, the armature
resistance will be increased. As the resistance of fine wire multiplies very
rapidly, that of itself would be sufficient to prevent the machine working.
Other obstacles that present themselves are the small polar surfaces and the
large air space, and the only way to overcome these difficulties is by a high rate
of armature speed and strong fields.
In Fig. I is shown the upper pole piece (1) ; lower pole piece (3) ;
field magnets (2) ; bolts (5) ; and cross section of pole piece extension for
supporting the bearings (4).
The pole pieces should be of soft gray cast iron ; the field magnet cores
can be of the same material, but it would be much better to make them of
wrought iron as it is very difficult to get solid castings where they are so small ;
also the iron is liable to chill, which makes it very hard, thereby increasing the
magnetic resistance of the iron, and reducing the efficiency of the machine.
Too much care can not be taken in putting the machine together.
Where the pole pieces join the field magnets the surfaces must be perfectly
16 PRACTICAL DYNAMO BUILDING.
true and smooth, that the whole surface of the iron may be in contact, for if
only half of the iron in the field magnets touches the pole pieces, the portion
that is not in contact may as well be left out of the machine. There is always
a loss at a joint, no matter how well it is made. The best way to put the
machine together is to bolt the field magnet cores to the lower pole piece, then
place the upper pole piece in position and examine carefully to see that the
whole surface is in contact ; if not, the high points should be taken off until
it is. Do not depend on the bolts to spring the pole pieces down to make a
The pole pieces are 7V2 inches long, 3 inches wide, and 3 / inch thick.
The field magnet cores are 4 inches long, 3 inches wide, and 3 /4 inch thick.
The gap between the pole pieces is ! 3 /4 inches. The diameter of the bore of
the machine is about 4 inches, but it should not be bored out until the armature
is finished for the reason that the armature may not have worked out to just
the size calculated ; if not, the pole pieces can be bored out to suit the
Fig. II shows the lower pole piece (3) with extensions (4 1 and 4 2 )
for supporting the bearings. The extension (4 1 ) on the pulley side is ! 3 /s
inches long ; 1V2 inches wide, and 3 /s inch thick. The extension (4 2 ) on the
commutator side is 2V2 inches long, ! J /2 inches wide, and 3 /s inch thick.
In Fig. Ill is shown the armature drum (1) which can be made of brass
or galvanized iron ; it consists of a tube 3 inches long, 2*/2 inches in diameter
with flanges on each end 1/2 inch wide. To support the tube is a brass hub
with 3 radial arms, as shown at 2 in Fig. IV. The hubs are first drilled, then
slipped on the shaft in their proper position ; a pin is then put through the hubs
and shaft to securely hold the armature in place. The shaft should then be
placed between the centers in a lathe and the ends of the arms turned off until
the core will slip over them ; then secure the core to the arms with screws or
pins as shown at 3 in Fig. IV.
The core between the flanges should now be wound full of No. IS
annealed iron wire with a layer of paper between each layer of wire. The
outer end of the wire should be soldered to prevent its unwinding. The core
should be placed on parallel strips and perfectly balanced before it is insulated.
PRACTICAL DYNAMO BUILDING. 17
This armature is a Gramme ring and as the wire has to pass between the shaft
and the core, the inside of the core must be insulated as well as the outside.
Great care must be taken in insulating the arms of the hubs where they join
the core ; if not, the copper wire will be drawn down so close in these corners
that it Avill come in contact with the core, so one-half of the sections in the
armature would be cut out, or in other words, the coils would be grounded on
the core. A machine in this condition would generate no current though all
the other parts were perfect.
The armature should be spaced off into 12 sections and wound 4 layers
deep, 22 convolutions per layer of "No. 20 double covered copper wire (Brown
and Sharp gauge). The method of winding and connecting the armature is
given in Figs. 4 and 5, page
The commutator (3) is an important feature ; the success of the machine
to a great extent depends upon its construction. The core is of vulcanized
fibre 1V4 inches long, and 1 inch in diameter ; a brass ring Vs inch thick is
forced over it. The ring is then spaced off into 12 sections, and a screw put
through the end of each section into the fiber, as shown at 3 in Fig. IV.
Then with a fine hack saw cut through the ring to the fibre between the rows
of screws. Be sure that the ring is cut through and all brass cuttings are
removed from the slots. The slots can then be filled with fibre, making the
commutator solid and smooth on the outside. If any of the brass cuttings are
allowed to remain in the slots, thus making a contact between two sections of
the commutator, one section of the armature would be cut out or short circuited,
reducing the efficiency of the armature. !S"ot only that, but there will be an