Homopolar Generator

Robert Kincheloe Professor of Electrical Engineering (Emeritus) _Stanford University_

Paper presented at the 1986 meeting of the

Society for Scientific Exploration San Francisco

June 21, 1986

A bstract

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 exiraction of electrical output energy is not reflected as a corresponding mechanical load to the driving source.

During 1985 the author 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 fro.n the generator over that measured due to fric-'ional losses with the generator unexcited seemed to be about 26% of the maximum computed output power.

The paper briefly reviews the homopolar generator, describes the tests on this particular machine and summarizes the resulting data.

The Sunburst Homopolar Generator

In July, 1985, the author was invited to examine and test a so-called free-energy generator known as the Sunburst N Machine. This device was designed by Bruce DePalma and constructed with the support of the Sunburst Community in Santa Barbara, CA, about 1969. The term "free-energy" refers to the claim by DePalma1 (and others2) 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 energy of a spatial magnetic field.

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 a series of measurements were made by the author to test these claims.

Generator Description

Details of the generator construction are shown in Figs. 1 and 2. It consists essentially of an electromagnet formed by a coil of 3605 urns 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 rotation. At each end of the magnet are conducting bronze cylindrical plates, on one of which are arranged one set of graphite brushes for extracting output current between the shaft and the outer circumference, and a second set of metering brushes

Sunburst Homopolar Generator

The generator may be recognized as a so-called homopolar, or acyclic machine, a device first investigated and described by Michael Faraday3 in 1831 and shown schematically in Fig. 3. 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 resulting 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 radii. The device may also be used as a motor when an external voltage produces a radial current between the sliding brushes.

There have been a number of commercial applications of homopolar motors and generators, particularly early in this century4, $nd their operating principles are described in a number of texts.5. 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, 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.6

DePalma claimed7 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 literature.8 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 v indings allow the magnet to be rotated at high speed.

Because the simple form shown in Fig. 3 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 applications9 (such as generators for developing large currents for welding, ship degaussing, liquid metal magnetohydrodynamic pumps for nuclear reactor cooling, torquemotors 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, DePalma's 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.

Sunburst Generator

Figure 3 - Homopolar (Acyclic) Generator

2. Approximately 4 kilowatts is 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.

However, this machine was not intended as a practical generator but as a means for testing the free energy principle, so that from this point ¿>f view efficiency was not required.

DePalma's Results with the

Sunburst Homopolar Generator_

In 1980 DePalma conducted tests w ith the Sunburst generator, describing his measurement technique and results in an unpublished report10. The generator was driven by a 3 phase a-c 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 Fig. 4. 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 this analysis:

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