Professor of Electrical
Engineering (Emeritus), Stanford University
Paper presented at the
1986 meeting of the Society for Scientific Exploration (San
Francisco, June 21, 1986)
Revised February 1, 1987
Known for over 150 years,
the Faraday homopolar generator has been claimed to provide a
basis for so-called "free-energy" generation, in that
under certain conditions the extraction of electrical output
energy is not reflected as a corresponding mechanical load to
the driving source.
During 1985, I was invited
to test such a machine. While it did not perform as claimed,
repeatable data showed anomalous results
that did not seem to conform to traditional theory.
In particular, under certain
assumptions about internally generated output voltage, the
increase in input power when power was extracted from the
generator over that measured due to frictional losses with the
generator unexcited seemed to be either about 13% or 20% of
the maximum computed generated power, depending on
The paper briefly
reviews the homopolar generator, describes the tests on
this particular machine, summarizes and presents tentative
conclusions from the resulting data.
The Sunburst Homopolar
In July, 1985, I became
aware of and was invited to examine and test a so-called
free-energy generator known as the Sunburst N Machine.
This device, shown in
Figures 1a & 1b, was proposed by
Bruce DePalma and constructed by Charya Bernard of the
Sunburst Community in Santa Barbara, CA, about 1979.
The term "free-energy"
refers to the claim by DePalma  (and others ) that it
was capable of producing electrical output power that was not
reflected as a mechanical load to the driving mechanism but
derived from presumed latent spatial energy.
Apart from mechanical
frictional and electrical losses inherent in the particular
construction, the technique employed was claimed
to provide a basis for constructing a generator which could
supply the energy to provide not only its own motive power but
also additional energy for external use. From August 1985 to
April 1986 I made a series of measurements on this particular
machine to test these claims.
Details of the generator
construction are shown in Figure 2
and Figure 3.
It consists essentially of
an electromagnet formed by a coil of 3605 turns of #10 copper
wire around a soft iron core which can be rotated with the
magnetic field parallel to and symmetrical around the axis of
At each end of the magnet
are conducting bronze cylindrical plates, on one of which are
arranged (as shown in Figure 3) one
set of graphite brushes for extracting output current between
the shaft and the outer circumference and a
second set of metering brushes for independently
measuring the induced voltage between these locations.
A third pair of brushes and
slip rings supply the current for the electromagnet. A thick
sheath of epoxy-impregnated fiberglass windings allow the
magnet to be rotated at high speed.
The generator may be
recognized as a so-called homopolar, or acyclic machine, a
device first investigated and described by Michael
Faraday  in 1831 (Figure 4 & Figure 5) and shown schematically in Figure 6.
It consists of a cylindrical
conducting disk immersed in an axial
magnetic field, and can be operated as a generator with
sliding brushes extracting current from the voltage induced
between the inner and outer regions of the disk
when the rotational energy is supplied by an
external driving source.
The magnitude of the
incremental radial generated voltage is proportional to both
the strength of the magnetic field and the tangential
velocity, so that in a uniform magnetic field the total
voltage is proportional to the product of speed times the
difference between the squares of the inner and outer brush
The device may
also be used as a motor when an external
voltage produces an radial current between the sliding
There have been a number of
commercial applications of homopolar motors and generators,
particularly early in this century , and their operating
principles are described in a number of texts .
The usual technique is to
use a stationary magnet to produce the magnetic field in which
the conducting disk (or cylinder) is rotated.
Faraday found, however, (Figure 7) that it does not matter
whether the magnet itself is stationary or rotating with the
disk as long as the conductor is moving in the field, but that
rotating the magnet with the conducting disk stationary did
not produce an induced voltage.
He concluded that a magnetic
field is a property of space itself, not attached to the
magnet which serves to induce the field .
DePalma stated  that when
the conducting disk is attached to a rotating magnet, the
interaction of the primary magnetic field with that produced
by the radial output current results in torque between the
disk and the magnet structure which is not reflected back to
the mechanical driving source.
Lenz's law therefore does
not apply, and the extraction of output energy does not
require additional driving power. This is the claimed basis
for extracting "free" energy.
Discussions of the torque
experienced by a rotating magnet are also discussed in the
Because the simple form
shown in Figure 6 has essentially
one conducting path, such a homopolar device is characterized
by low voltage and high current requiring a large magnetic
field for useful operation.
Various homopolar devices
have been used for specialized applications  (such as
generators for developing large currents for
welding, ship degaussing, liquid metal magnetohydrodynamic
pumps for nuclear reactor cooling, torque motors for
propulsion, etc.), some involving quite high power.
These have been extensively
discussed in the literature, dealing with such problems as
developing the high magnetic fields required
(sometimes using superconducting magnets in air to avoid
iron saturation effects), the development of brushes that can
handle the very high currents and have low voltage drop
because of the low output voltage generated, and with
counteracting armature reaction which otherwise would reduce
the output voltage because of the magnetic field distortion
resulting from the high currents.
From the standpoint of prior
art, the design of the Sunburst generator is inefficient and
not suitable for power generation:
1. The magnetic field is
concentrated near the axis where the tangential velocity is
low, reducing the generated voltage.
2. Approximately 4 kilowatts
of power are required to energize the magnet, developing
enough heat so that the device can only be operated for
limited periods of time.
3. The graphite brushes used
have a voltage drop almost equal to the total induced voltage,
so that almost all of the generated power is consumed in
heating the brushes.
4. The large contacting area
(over 30 square inches) of the brushes needed for the
high output current creates considerable friction loss.
Since this machine was not
intended as a practical generator but as a means for testing
the free energy principle, however, from this point of view
efficiency in producing external power was not required or
DePalma's Results with
the Sunburst Homopolar Generator
In 1980 DePalma conducted
tests with the Sunburst generator, describing his
measurement technique and results in an unpublished report
The generator was driven by
a 3 phase AC 40 horsepower motor by a belt coupling
sufficiently long that magnetic fields of the motor and
generator would not interact. A table from this report giving
his data and results is shown in Figure 8.
For a rotational speed of
6000 rpm an output power of 7560 watts was claimed to require
an increase of 268 watts of drive power over that required to
supply losses due to friction, windage, etc., as measured with
the output switch open.
If valid, this would mean
that the output power was 28.2 times the incremental input
power needed to produce it. Several assumptions were made in
1. The drive motor input
power was assumed to be the product of the line voltage and
current times the appropriate factor for a three-phase machine
and an assumed constant 70% power factor.
There was apparently no
consideration of phase angle change as the motor load
increased. This gives optimistic results, since
consideration of phase angle is necessary for calculating
power in an AC circuit, particularly with induction motors.
It might also be noted that
the measured incremental line current increase of 0.5 ampere
(3.3%) as obtained with the analog clamp-on AC ammeter
that was used was of limited accuracy.
2. The output power of the
generator was taken to be the product of the measured output
current and the internally generated voltage in the disk less
the voltage drop due only to internal disk resistance.
Armature reaction was thus neglected or assumed not to be
3. The generated voltage
which produced the current in the main output brushes was
assumed to be the same as that measured at the metering
brushes, and the decrease in metered voltage from 1.5 to 1.05
volts when the output switch is closed was assumed to be
due to the internal voltage drop resulting from the output
current flowing through the internal disk resistance
that is common to both sets of brushes and calculated to
Of these, the first
assumption seems the most serious, and it is my opinion that
the results of this particular test were inaccurate.
Tim Wilhelm of Stelle,
Illinois, who witnessed tests of the Sunburst generator in
1981, had a similar opinion .
Recent Tests of the
Being intrigued by DePalma's
hypothesis, I accepted the offer by Mr. Norman Paulsen,
founder of the Sunburst Community, to conduct tests on the
generator which apparently had not been used since the
tests by DePalma and Bernard in 1979.
A schematic diagram of the
test arrangement is shown in Figure 9,
with the physical equipment shown in Figure
10a. The generator is shown coupled by
a long belt to the drive motor behind it, together
with the power supplies and metering both
contained within and external to the Sunburst power and
shows the panel of the test cabinet which provided power
for the generator magnet and motor field. The 4-1/2
digit meters on the panel were not
functional and were not used; external meters were
I decided to use an
available shunt-field DC drive motor to facilitate load tests
at different speeds and to simplify accurate motor input power
Referring to Figure 9, variacs and full-wave
bridge rectifiers provided variable d-c supplies for the
motor armature and field and the homopolar generator magnet.
Voltages and currents were
measured with Micronta model 11-191 3-1/2 digit meters
calibrated to better than 0.1% against a Hewlett
Packard 740B Voltage Standard that by itself was accurate to
better than .005%.
Standard meter shunts
together with the digital voltmeters were used to measure the
various currents. With this arrangement the generator speed
could be varied smoothly from 0 to over 7000 rpm, with
accurate measurement of motor input power, metered generator
output voltage Vg and generator output current Ig.
Speed was measured with a
General Radio model 1531 Strobotac which had a
calibration accuracy of better than 2% (as
verified with a frequency counter) and which allowed
determination of relative speed changes of a few rpm of less.
Small changes in either load
or input power were clearly evident because of the sensitivity
of the Strobotac speed measurement, allowing the motor input
power to be adjusted with the armature voltage variac to
obtain the desired constant speed with no acceleration or
deceleration before taking readings from the various meters.
Various tests were conducted
with the output switch open to confirm that generated
voltage at both the output brushes (Vbr) and metering brushes
(Vg) were proportional to speed and magnetic field, with the
polarity reversing when magnetic field or direction of
rotation were reversed.
Tracking of Vbr and Vg with
variation of magnetic field is shown in Figure
11, in which it is seen that the output
voltages are not quite linearly related to magnet current,
probably due to core saturation.
The more rapid departure of
Vg from linearity may be due to the different brush locations
as seen on Figure 3, differences in
the magnetic field at the different brush locations, or other
causes not evident. An expanded plot of this voltage
difference is shown in Figure 12,
and is seen to considerably exceed meter error tolerances.
also shows an approximate 300 watt increase in drive motor
armature power as the magnet field was
increased from 0 to 19 amperes.
(The scatter of input power
measurements shown in the upper curve of Figure
11 resulted from the great sensitivity of the
motor armature current to small fluctuations in power
line voltage, since the large rotary inertia of
the 400 pound generator did not allow speed
to rapidly follow line voltage changes).
At first it was thought that
this power loss might be due to the fact that the outer output
brushes were arranged in a rectangular array as shown in Figure 3.
Since they were connected in
parallel but not equidistant from the axis the different
generated voltages would presumably result in
circulating currents and additional power dissipation.
Measurement of the generated
voltage as a function of radial distance from the axis as
shown in Figure13, however, showed
that almost all of the voltage differential occurred between 5
and 12 cm, presumably because this was the region of greatest
magnetic field due to the centralized iron core.
The voltage in the region of
the outer brushes was almost constant, with a measured
variation of only 3.7% between the extremes, so that this did
not seem to explain the increase in input power. The other
likely explanation seems to be that there are internal losses
in the core and other parts of the metal structure due to eddy
currents, since these are also moving conductors in the field.
In any event, the increase
in drive power was only about 10% for the maximum magnet
current of 19 amperes.
typifies a number of measurements of input power and generator
performance as a function of speed and various generator
Since the generator output
knife switch procedure was very stiff and difficult to operate
the procedure used was to make a complete speed run from zero
to the maximum speed and descending again to zero with the
switch open, taking readings at each speed increment with the
magnet power both off and on.
The procedure was then
repeated with the switch closed. (It was noted that during the
descending speed run the input power was a few percent lower
than for the same speed during the earlier
ascending speed run; this was presumably due to
reduced friction as the brushes and/or bearings became
heated. In plotting the data the losses for both runs
were averaged which gave a conservative result since the
losses shown in the figures exceed the minimum values
The upper curve (a) shows
the motor armature input power with a constant motor field
current of 6 amperes as the speed is
varied with no generator magnet excitation and is seen to
reach a maximum of 4782 watts as the speed is increased to
represents the power required to overcome friction
and windage losses in the motor, generator, and drive belt,
and are assumed to remain essentially constant whether the
generator is producing power or not .
shows the increase of motor armature power over that of curve
(a) that results from energizing the generator magnet with a
current of 16 amperes but with the generator output switch
open so that there is no output current (and hence no
output power dissippation).
This component of power
(which is related to the increase of drive motor power with
increased magnet current as shown in Figure
11 as discussed above) might also be present
whether or not the generator is producing output current and
power, although this is not so evident since the output
current may affect the magnetic field distribution.
shows the further increase of motor armature input power over
that of curves (a) plus (b) that results when the output
switch is closed, the generator magnet is energized and output
current is produced.
It is certainly not zero or
negligible but rises to a maximum of 802 watts at 6500 rpm.
The total motor armature input power under these conditions is
thus the sum of (a), (b), and (c) and reaches a maximum of
6028 watts at 6500 rpm.
The big question has to do
with the generated output power. The measured output current
at 6500 rpm was 4776 amperes; the voltage at the metering
brushes was 1.07 volts.
Using a correction factor
derived from Figure 12 and assuming
a common internal voltage drop due to a calculated disk
resistance of 38 microohms, a computed internal generated
potential of 1.28 volts is obtained which if multiplied by the
measured output current indicates a generated power of 6113
All of this power is
presumably dissipated in the internal and external circuit
resistances, the brush loss due both to the brush resistance
and the voltage drops at the contact surfaces between the
brushes and the disk (essentially an arc discharge), and the
power dissipated in the 31.25 microohm meter shunt.
It still represents power
generated by the machine, however, and exceeds the 802 watts
of increased motor drive power due solely to closing the
generator output switch and causing output current to flow by
a factor of 7.6 to 1.
If the 444 watts of
increased input power that resulted from energizing the magnet
with the output switch open is assumed to have been converted
to generated output power and hence should be included as part
of the total increased drive motor power required to produce
generated output, the computed 6113 watts of generated power
still exceeds the total input power of 444 watts plus
802 watts by a factor of 4.9 to 1.
The computed output
power even slightly exceeds the total motor armature input
power including all frictional and windage losses of
6028 watts under these conditions (although the total system
effeciency is still less than 100% because of the generator
magnet power of approximately 2300 watts and motor field power
of about 144 watts which must be added to the motor armature
power to obtain total system input power).
It would thus seem that if
the above assumptions are valid that DePalma correctly
predicted that much of the generated power with
this kind of machine is not reflected back to the motive
summarizes the data discussed above.
To further examine the
question of the equivalence between the internally generated
voltage at the main output brushes and that measured at the
metering brushes, a test was made of the metered voltage as a
function of speed with the generator magnet energized with a
current of 20 amperes both with the output switch open and
closed. The resulting data is shown in Figure
The voltage rises to about
1.32 volts at 6000 rpm with the switch open (which is
close to that obtained by DePalma) and drops 0.14
volts when the switch is closed and the measured output
current is 3755 amperes, corresponding to an
effective internal resistance of 37 microohms.
Even if this were due to
other causes, such as armature reaction, it does not seem
likely that there would be a large potential drop
between the output and metering brushes because of the
small distance, low magnetic field (and radial
differential voltage), and large mass of conducting disk
Internal currents many times
the measured output current of almost 4000 amperes would be
required for the voltage difference between the outer metering
and output brushes to be significant and invalidate the
conclusions reached above.
A further method of testing
the validity of the assumed generated output potential
involved an examination of the voltage drop across the
graphite brushes themselves.
Many texts on
electrical machinery discuss the brush drop in
machines with commutators or slip rings. All of those examined
agree that graphite brushes typically have a voltage drop that
is essentially constant at approximately one volt per brush
contact when the current density rises above 10-15 amperes per
To compare this with the
Sunburst machine the total brush voltage was calculated by
subtracting the IR drop due to the output current in the known
(meter shunt) and calculated (disk, shaft, and brush lead)
resistances from the assumed internally generated output
voltage. The result in Figure17
shows that the brush drop obtained in this way is even less
than that usually assumed, as typified by the superimposed
curve taken from one text.
It thus seems probable that
the generated voltage is not significantly less than that
obtained from the metering brushes, and hence the
appropriateness of the computed output power is supported.
We are therefore faced with
the apparent result that the output power obtained when the
generator magnet is energized greatly exceeds the increase in
drive power over that needed to supply losses with the magnet
not energized. This is certainly anomalous in terms of
convential theory. Possible explanations?
1. There could be a large
error in the measurements resulting from some factor such as
noise which caused the digital meters to read incorrectly or
grossly inaccurate current shunt resistances.
If the measured results had
shown that the computed generated output power exceeded the
input drive power by only a few percent this explanation would
be reasonable and would suggest that more careful calibration
and measurements might show that the results described above
were due to measurement error.
With the data showing such a
large ratio of generated power to input power increase,
however, in my opinion this explanation of the results
(A later test showed that
the digital meters are insensitive to a large AC ripple
superimposed on the measured DC, but within their rated
accuracy of 0.1% give a true average value).
2. There could be a large
difference between the measured voltage at the metering
brushes and the actual generated voltage in the
output brush circuit due to armature reaction, differences
in the external metering and output circuit geometry, or
other unexplained causes.
As discussed above the
various data do not seem to support this possibility.
3. DePalma may have been
right in that there is indeed a situation here whereby energy
is being obtained from a previously unknown and unexplained
This is a conclusion that
most scientists and engineers would reject out of hand as
being a violation of accepted laws of physics, and if true has
4. Perhaps other
possibilities will occur to the reader.
The data obtained so far
seems to have shown that while DePalma's numbers were high,
his basic premise has not been disproved. While the Sunburst
generator does not produce useful output power because of the
internal losses inherent in the design, a number of
techniques could be used to reduce the friction losses,
increase the total generated voltage and the
fraction of generated power delivered to an external load.
DePalma's claim of
free energy generation could perhaps then be examined.
I should mention, however,
that the obvious application of using the output of a
"free-energy" generator to provide its own motive power, and
thus truly produce a source of free energy, has occurred to a
number of people and several such machines have been built.
At least one of these known
to me , using what seemed to be a good design techniques,
1. DePalma, 1979a,b,c, 1981,
1983, 1984, etc.
2. For example, Satellite
News, 1981, Marinov, 1984, etc.
3. Martin, 1932, vol. 1,
4. Das Gupta, 1961, 1962;
Lamme, 1912, etc.
5. See, for example, Bumby,
1983; Bewley, 1952; Kosow, 1964; Nasar,1970.
6. There has been much
discussion on this point in the literature, and about
interpretation of flux lines. Bewley, 1949; Cohn,
1949a,b; Crooks, 1978; Cullwick, 1957; Savage, 1949.
7. DePalma, op. cit.
8. Kimball, 1926; Zeleny,
9. Bumby, Das Gupta, op. cit.
10. DePalma, 1980.
11. Wilhelm, 1980, and
12. The increase
in motor losses with increased load are neglected in
this discussion because of a lack of accurate values for
armature and brush resistances, magnetic field distortion
resulting from armature reaction, etc. Such losses, while
small, would be appreciable, however; their inclusion
would further increase the ratio of generated to drive power
so that the results described are conservative.
13. Wilhelm, 1981, and
[Bewley, 1949] - L. V.
Bewley: letter re: [Cohn, 1949a]; ELECTRICAL ENGINEERING,
Dec. 1949, p.1113-4. (Claims error in Cohn's paper)
[Bewley, 1952] - L. V.
Bewley: FLUX LINKAGES & ELECTROMAGNETIC INDUCTION,
Macmillan, NY, 1952. (Explanation
of induction phenomena and the Faraday generator)
[Bumby, 1983] - J. R. Bumby:
SUPERCONDUCTING ROTATING ELECTRICAL MACHINES, Claredon
Press, 1983. (Homopolar designs, high current brushes
including liquid metal)
[Cohn, 1949a] - George I.
Cohn: "Electromagnetic Induction", ELECTRICAL ENGINEERING,
May 1949, p441-7. (Unipolar generator as paradox)
[Cohn, 1949b] - George Cohn:
letter re: [Savage, 1949]; ELECTRICAL ENGINEERING, Nov
1949, p1018. (Responds to criticism by Savage)
[Crooks, 1978] - M. J.
Crooks, et al.: "One-piece Faraday generator: A paradoxical
experiment from 1851", Am. J. Phys. 46(7), July
1978, p729-31. (Derives Faraday generator performance using
[Cullwick, 1957] - E. G.
Cullwick: ELECTROMAGNETISM AND RELATIVITY, Longmans
& Green, London, 1957. (Chapter 10, "A
Rotating Conducting Magnet", pp.141-60, discusses question of
flux rotation with magnet)
[Das Gupta, 1961] - A.
K. Das Gupta: "Design of self-compensated high current
comparatively higher voltage homopolar generators", AIEE
Trans., Oct 1961, pp. 567-73. (Discusses
very high current homopolar generator design)
[Das Gupta, 1962] - A. K.
Das Gupta: "Commutatorless D-C generator capable to supply
currents more than one million amperes, etc"; AIEE Trans.
Oct 1962, p399-402. (Discusses very high current low
voltage Faraday generators)
[DePalma, 1979a] - Bruce
DePalma: "EXTRACTION OF ELECTRICAL ENERGY DIRECTLY FROM
SPACE: THE N-NACHINE", Simularity Institute, Santa
Barbara CA, 6 March 1979. (Discusses homopolar
generator or N-Machine as free-energy source)
[DePalma, 1979b] - Bruce
DePalma: "The N-Machine", Paper given at the
World Symposium on Humanity, Pasadena, CA, 12 April 1979.
(Describes background, development of "free-energy" theories)
- Bruce DePalma: "ROTATION OF A
MAGNETIZED GYROSCOPE", Simularity Institute
Report #33, 16 July 1979. (Describes design of
Sunburst homopolar generator)
[DePalma, 1980] - Bruce
DePalma: "Performance of the Sunburst N-Machine", Simularity
Institute, Santa Barbara, CA, 17 December 1980.
(Description of tests and results)
[DePalma, 1981] - Bruce
DePalma: "Studies on rotation leading to the N-Machine",
DePalma Institute, 1981 (Transcript of talk; discusses
experiments with gravity that led to development of idea of
[DePalma, 1983] -
Bruce DePalma: "THE ROTATION OF
THE UNIVERSE", DePalma Institute Report #83,
Santa Barbara, CA, 25 July 1983. (Uses
Faraday disc to discuss universal principles).
[DePalma, 1984] -
Bruce DePalma: "THE SECRET OF THE FARADAY DISC", DePalma
Institute, Santa Barbara, CA, 2 Feb 1984. (Claims explanation
of Faraday disc as a free-energy device)
[Kimball, 1926] -
A. L. Kimball, Jr.: "Torque on revolving
cylindrical magnet", PHYS. REV. 28, Dec.
1928, pp.1302-8. (Alternative analysis of torque in a
homopolar device to that of Zeleny and Page, 1924)
[Kosow, 1964] - Irving L.
Kosow: ELECTRICAL MACHINERY & CONTROL,
Prentice-Hall, 1964. (Discusses high current homopolar
[Lamme, 1912] - B. G. Lamme:
"Development of a successful direct-current 2000-kW unipolar
generator", AIEE Trans. 28 June 1912,
pp.1811-40. (Early discussion of design of high power
[Marinov, 1984]- Stefan
Marinov: THE THORNY WAY OF TRUTH, Part II; Graz,
Austria, 1984 (Advertisement in NATURE). (Claims
free-energy generator proved by DePalma, Newman)
[Martin, 1932] - Thomas
Martin (ed): FARADAY'S DIARY, Bell, 1932, in 5 vols.
(Transcription and publication of Faraday's original diaries)
[Nasar, 1970] - S. Nasar: ELECTROMAGNETIC
CONVERSION DEVICES & SYSTEMS, Prentice-Hall,
1970. (Discusses principles and applications of acyclic
[Satellite News, 1981] -
"Researchers see long-life satellite power systems in 19th
century experiment", Research News, SATELLITE NEWS,
15 June 1981. (Reports DePalma's claim for
[Savage, 1949] - Norton
Savage: letter re: [Cohn, 1949a]; ELECTRICAL ENGINEERING,
July 1949, p. 645. (Claims error in Cohn's paper)
[Wilhelm, 1980] - Timothy J.
Wilhelm: "INVESTIGATIONS OF THE N-EFFECT ONE-PIECE HOMOPOLAR
DYNAMOS, ETC. (Phase I)", Stelle, IL, 12 Sept. 1980.
(Discusses tests on DePalma's N-Machine)
[Wilhelm, 1981] - Timothy J.
Wilhelm: "INVESTIGATIONS OF THE N-EFFECT ONE-PIECE HOMOPOLAR
DYNAMOS, ETC. (Phase II)", Stelle, IL, 10 June 1981.
(Design and tests of improved homopolar generator/motor)
[Zeleny, 1924] - John Zeleny
& Leigh Page: "Torque on a cylindrical magnet through
which a current is passing", PHYS. REV.
v.24, 14 July 1924, pp.544-59. (Theory and
experiment on torque in a homopolar device)
1a & 1 b ~ Not shown (poor quality image)
~ Sunburst Homopolar Generator (side view):
~ Sunburst Homopolar Generator; output (brush) end view:
/ Figure 5 ~ Transcription of Faraday's first experiment
showing generation of electrical power in a moving conductor
(Faraday's Diary, 28 October 1831):
99. Made many expts. with a
copper revolving plate, about 12 inches in diameter and about
1/5 of inch thick, mounted on a brass axle.
To concentrate the polar
action two small magnets 6 or 7 inches long, about 1 inch wide
and half an inch thick were put against the front of the large
poles, transverse to them and with their flat sides against
them, and the ends pushed forward until sufficiently near; the
bars were prevented from slipping down by jars and shakes by
means of string tied round them.
100. The edge of the plate
was inserted more of less between the two concentrated poles
thus formed. It was also well amalgamated, and then contact
was made with this edge in different places by conductors
formed from equally thick copper plate and with the
extreme end edges grooved and amalgamated so as to fit on to
and have contact with the edges of the plate. Two of
these were attached to a piece of card board by thread at such
~ Homopolar (Acyclic) Generator:
- Test of a rotating magnet by Michael
Faraday (December 26, 1831):
255. A copper disc was
cemented on the top of a cylinder magnet, paper intervening,
the top being the marked pole; the magnet supported so as to
rotate by means of string, and the wires of the galvanometer
connected with the edge and the axis of the copper plate. When
the magnet and disc together rotated unscrew the marked end of
the needle went west. When the magnet and disc rotated screw
the marked end of the needle went east.
256. This direction is
the same as that which would have resulted if the copper had
moved and the magnet been still. Hence moving the magnet
causes no difference provided the copper moves. A rotating and
a stationary magnet cause the same effect.
257. The disc was then
loosed from the magnet and held still whilst the magnet itself
was revolved; but now no effect upon the galvanometer. Hence
it appears that, of the metal circuit in which the current is
to be formed, different parts must move with different angular
velocities. If with the same, no current is produced, i.e.
when both parts are external to the magnet.
~ Test data from report by Bruce DePalma:
PERFORMANCE OF THE SUNBURST
when N machine
Voltage output of N
1.5 volts d.c.
Voltage output of N generator
Current output of N
m.v. across shunt @ 50 m.v./1600 amp.)
Power output of
watts = 10.03 H.p.
Incremental power ratio
watts out/watts in
Internal resistance of
Reduction of the above data
gives as the equivalent circuit for the machine:
R(internal) = 62.5
114.25 " "
= 31.25 " "
~ Schematic diagram of generator test arrangement:
10a & 10b ~ Sunburst power unit & test panel (Not
shown: poor image quality)
11 ~ Input power & generated voltage vs. magnet current:
12 ~ metering & output brush voltage difference vs.
13 ~ Radial voltage distribution:
14 ~ Input & output power vs. speed:
15 - Summary of test results at 6500 rpm:
HOMOPOLAR GENERATOR TEST -
BIG SPRINGS RANCH APRIL 26, 1986
16 ~ Metering brush voltage vs. speed:
17 ~ Calcualted output brush voltage drop vs. current: