Critique of the N-Machine Zero Point

Adam TROMBLY // Joseph KAHN
Homopolar Generator

Critique of the N-Machine Constructed by Trombly & Kahn
by Bruce E. DePalma (11 October 1985)

Recently the International Patent Application of Trombly and Kahn (assigned to Acme Energy Co. of San Rafael, CA) has become public property under the Patent Cooperation treaty and can be obtained from the International Bureau of the World Intellectual Property Organization. A copy of this patent application is attached. The difference between the international patents and the US patent system is that in the US the material of the patent is secret until the patent is granted, while overseas the application itself is the basis of the patent, which stands until challenged by a third party.

Thus although Adam Trombly, the senior designer of the machine, has received two written gag orders from the Pentagon Department of Defense, forbidding him to reveal details of the machine --- upon threat of 10 years imprisonment for violating security relating to homopolar generator design -- through the very nature of life itself by a totally automatic process, the attache document falls into the public domain.

The attached patent application and drawings represent the result of the expenditure of $290,000 in two phases. The DOD-imposed secrecy has prevented any recompense whatsoever from accruing to the men who performed this work. What is described is a machine, an electrical generator whose output exceeds the input by a factor of 4.92.

Summary of Machine Parameters:
Rotor o.d: 14.0 inches 
Rotor Length: 9.25 inches 
Internal Rotor Diameter: 6 inches
Shaft Diameter (at widest point): 2 inches 
Speed: 7200 rpm 
Field: 15,000 gauss @ 150 watts field input 
Voltage Output: 2.9 volts C @ 15,000 amperes 
Drive Motor (DC) input (no load): 1.8 - 1.9 hp (1340-1470 watts) windage & friction 
Drive Motor input (loaded): 10.8 Kw, 14.5 hp 
Machine Internal Resistance: 6-10 micro-ohms 
Output Power: 43.7 Kw (maximum achieved 45.8 kw) 

Power gain of Machine: 45.8 / 9.3 (drag due to current withdrawal) = 4.92

In the above figure the 150 watts consumed in exciting the magnet is a negligible factor.

The numbers in the above list of machine parameters which were not included in the patent application have been obtained in private communication with Adam Trombly. The US patent application was rejected twice on the grounds of impossibility that the machine could work, and then the authors were warned not to publish any information on the basis of violation of secret homopolar generator work being done concurrently in the DOD.

Technical Comment:

Trombly and Kahn are two of the brightest young physicists in America today. Their work is of the very highest quality and is reflected in the enclosed report. Technically what was done represents the first stages of the development of the N-machine as an article of commerce. Particularly two items are important.

Closure of the magnetic field path in the Trombly machine allows for high magnetic field strength to be obtained with little effort, i.e., the 150 watts of excitation. Strong magnetism in the N-machine rotor results in high voltage output but at the expense of increased drag. Extraction of current from a machine of this type wherein current is taken out through holes in the magnets (Be-Cu shaft in iron rotor), as well as flowing radially outward (to the edge of iron rotor), as well as flowing radially inward (to the edge of the disk liquid metal contact), through the outer flux return path causes a reverse motoring action which increases the drag of the machine. If the gap between the outer rotor annuli were increased the flux in the central core would decrease but also would the drag of the machine brought about by the anti-motoring action.

Experience as well as design philosophy will decide the proper balance between drag and power gain in a particular machine. In the earlier "Sunburst" machine drag was minimized by not closing the flux path and operating the machine in a totally non-magnetic (brass and wood) environment. Here the measured power gain was 28:1 at 10 kw output (1.5 v.d.c @ 6700 amperes). However, much more power was consumed in exciting the magnet of this machine, i.e., 4 kw vs. 150 watts for the Trombly machine.

A major factor is the construction of the liquid metal brush system, which makes possible the power potential of a low voltage, very high current machine.

The solution described by Trombly seems to have been simultaneously invented by him, DePalma, and the DOD. Without necessarily having to add specific detail, it should be obvious how to enlarge the structure to handle more current. The liquid metal could be circulated to provide additional cooling. Different metals could be used, i.e., mercury. I estimate that the Trombly machine should be able to produce 100,000 amperes without difficulty.

Conversion of the low voltage d.c. output to the standard 110 and 220 volt a.c./60 cps requires innovative engineering. The easiest way is to run a Faraday disk motor at the low voltage and drive a conventional electrical generator to produce whatever voltage and current required. Conversion could also be attempted by interrupting the low voltage high current with some sort of liquid metal commutator and transforming the voltage directly without a transformer. These ideas are treated by Tesla in his patents for the design of liquid metal commutators and interrupters. The voltage could be transformed electronically but at this time is beyond the state of the art of low voltage high current transistors at the present time.

A larger diameter machine could be built. Voltage goes as the square of the machine radius.

The low internal resistance, 6-10 micro-ohms, reported for the Trombly-Kahn machine speaks to the quality of the liquid metal sliding contacts obtained with the construction method described. Low internal resistance is crucial to obtaining high power output and avoiding internal heating.

The Trombly-Kahn machine represents what bright young minds can accomplish given the right circumstances and support. The attempted suppression of this work only point up the feeblemindedness of the gerontocracy that rules science in the USA.

Building a useful N-machine is a high-technology accomplishment. Intelligent designers and craftsmen can take this information and scale it to appropriate needs. The wish is to cause this technology to flourish on Earth.

Bruce DePalma  - DePalma Institute

Closed Path Homopolar Machine

Inventors: Adam D. Trombly & Douglas Kahn
Acme Energy Company: 25 Mitchell Blvd, San Rafael,CA 94903

International Patent Application Number: PCT/US81/01588
International Patent Classification: H02K 31/00, 39/00 
International Publication Number: WO 82/021=6 
International Publication Date: 24 June 1982

Abstract -- A co-rotating homopolar generator has a rotor (12) comprising a disk conductor (30) and co-rotating coaxial electromagnets (32a and 32b) on either side, and achieves improved operation by utilizing a low reluctance magnetic return path for the magnetic flux that passes through the disk conductor (30). The low reluctance path permits the electromagnets (32a and 32b) to produce a high field with a relatively low value of coil excitation current. Thus overheating is avoided and the full potential of the homopolar generator is achieved. The low reluctance magnetic return path (220) is preferably provided by a relatively high permeability co-rotating enclosure (having enclosure halves 37a and 37b) of sufficient radial and axial dimensions to enclose the electromagnets and disk conductor of the rotor. The disk conductor (30) is preferably constructed from a high permeability, low resistivity material such as iron, and can indeed be integral with the electromagnet cores (35a and 35b).

Field of the Invention:

The present invention relates generally to electric generation, and more particularly to a homopolar machine having high efficiency.

Background of the Invention:

Electrical generation typically involves the conversion of mechanical work to electrical energy. In these energy conscious times, it is most important to achieve as high a conversion efficiency as possible.

It is well known that if a conducting disk is rotated about its axis in the field of a fixed magnet such that the magnetic flux lines intersect the plane of the disk, a voltage is induced between radially distinct portions of the disk. Such a device is known as a homopolar generator. Although less well known, it is also known that if the magnet is fastened to the disk, and the whole assembly co-rotated, a voltage is also induced between radially distinct portions of the disk. M. J. Crookes, et al., in a recent article in theAmerican Journal of Physics 46 (7): 729-731 (1978), note with amusement that while the co-rotating type of homopolar generator seemed to the authors to be a brilliant new invention, it was "belatedly discovered that Faraday got there first". According to the published results of an experiment performed by Michael Faraday in 1832, "a copper disk was cemented upon the end of a cylinder magnet, with paper intervening; the magnet and disk were rotated together and collectors (attached to the galvanometer) brought in contact with the circumference and the central part of the copper plate. The galvanometer needle moved as in former cases, and the direction of motion was the same as that which would have resulted, if the copper only had revolved, and the magnet had been fixed. Neither was there any apparent difference in the quantity of deflection. Hence, rotating the magnet causes no difference in the results; for a rotary and a stationary magnet produces the same effect upon the moving copper".

Bruce E. DePalma, in an article in Energy Unlimited 5: 16-23 (1980), makes the further statement that unlike a conventional generator which resists rotation when current is drawn, a homopolar generator having the magnet and disk conductor rigidly coupled to one another operates in a manner free of such rotational drag. More particularly, it is suggested that due to the fact that the torque is absorbed in the assembly, conversion efficiency beyond that normally achievable should be possible. To date, there have been attempts to build co-rotating homopolar generators, but the devices appear to have been troubled by overheating and other engineering difficulties that have tended to mask the potentially high efficiency.

Summary of the Invention:

The present invention provides a co-rotating homopolar generator that avoids the heating problems of prior machines and renders possible and convenient the generation of electricity at extremely high efficiency. The generator has a rotor comprising a disk conductor and co-rotating coaxial electromagnets on either side. The present invention achieves the improved operation by providing a low reluctance magnetic return path for the magnetic flux that passes through the disk conductor.

The low reluctance path permits the electromagnets to produce a high field (limited to 2.2 tesla by the saturation of iron) with a relatively low value of coil excitation current. Thus overheating is avoided and the full potential of the homopolar generator is achieved.

In the preferred embodiment, the low reluctance magnetic return path is provided by a relatively high permeability co-rotating enclosure (designated a "flux return enclosure") of sufficient radial and axial dimensions to enclose the magnets and disk conductor of the rotor. Additionally, the disk conductor itself is preferably constructed from a high permeability, low resistivity material such as iron, and can indeed be integral with the electromagnet cores.

Output power is drawn between the periphery of the disk conductor (within the flux return enclosure) and the rotor shaft through fixed disk and shaft brushes. The disk brush protrudes through an annular slot in the flux return enclosure, and is geometrically configured so as not to add a large amount of reluctance to the flux return path. To this end, the disk brush is formed with a relatively thin web portion that passes through the enclosure gap. The web portion still has sufficient thickness so that the mechanical strength o the brush is not compromised. Moreover, the web portion has sufficient thickness, and hence conductance, that the saving in magnet power is not offset by excessive ohmic heating in the web portion.

For a further understanding of the nature and advantages of the present invention, reference should be made to the remaining portion of the specification and to the attached drawings.

Brief Description of the Drawings:

Figure 1 is a sectional isometric view of a homopolar machine according to the present invention;

Figure 2 is an electrical/mechanical schematic view of the homopolar generator;

Figure 3 is a sectioned oblique view of the rotor and shaft;

Figure 4A is an isometric view showing the construction of the disk brush

Figure 4B is a fragmentary enlarged view showing a portion of the disk brush;

Figure 5A and Figure 5B are exploded isometric views of the shaft brushes;

Figure 5C is an isometric view of the magnet brush;

Figure 6 is a sectioned isometric view of the magnet brush;

Figure 7 is a sectioned oblique side view showing the brushes, bearings, and casing, with the rotor shown in phantom; and

Figure 8 is a sectioned isometric view of the shaft end seal.

Detailed Description of the Drawings:


Figure 1
is a sectioned isometric view showing a homopolar generator according to the present invention. Figure 2 is an electrical and mechanical schematic of the generator system incorporating generator 10. Generator 10 comprises a rotor 12 mounted to a shaft 15 journaled in bearing assemblies 17 and 18 for rotation within a casing 20. The casing maintains rotor 12 within a controlled atmosphere (slightly pressurized nitrogen). One end of shaft 15 protrudes outside casing 20 through a shaft seal assembly 21 and is provided a drive sheave 22 to communicate mechanical energy from a drive motor 25 of any conventional desired type. A shaft end bearing 27 takes up radial loading on drive sheave 22 due to the coupling with motor 25.

Broadly, rotor 12 comprises a central disk conductor portion 30, flanking electromagnet coils 32a and 32b with respective associated iron core portions 35a and 35b, and a flux return enclosure having enclosure halves 37a and 37b. When high currents are involved, the disk may more closely resemble a cylinder. However, the term "disk" will still be used for the conductor that corresponds to the disk of Faraday's experimental device. Electromagnet coils 32a and 32b are series connected between shaft 15 and an electrically isolated shaft portion 40. Excitation current is provided by a magnet excitation power supply 42 which is coupled between a magnet brush 45 which rubs on electrically isolated shaft portion 40, and a pair of parallel connected shaft brushes 47 and 48. An outer portion of disk conductor 35 engages a disk brush 5 and output power is drawn between disk brush 50 and shaft brushes 47 and 48. As will be described more fully below, generator 10 has the capability of operating at extremely high efficiency.

Rotor & Shaft:

Referring to the sectioned oblique view of Figure 3, the detailed construction of rotor 12 and shaft 15 may be seen. While there is no particular significance to absolute dimensions, the description that follows will be in terms of an illustrative generator whose rotor has an outer dimension of 14.0 inches and an axial length of 9.25 inches, with the rotor being being carried on a shaft of diameter 2.0 inches. Where practical, suitable proportions will be maintained in isometric and oblique views so that other dimensions may be ascertained from the drawings. Disk conductor portion 30 and electromagnet core portions 35a and 35b are constructed of high permeability, low resistivity material such as iron, and may be integrally formed as a single iron rotor core, designated 55. Rotor core 55 is brazed to shaft 15 which is preferably made of a copper-beryllium alloy. A suitable shaft material may be obtained from Brush Wellman Company under the name of Brush 3 Alloy. This is an alloy characterized by a high electrical conductivity (50% of copper standard) and a high module of elasticity. A circumferentially extending copper contact 57 is brazed to the outer surface of rotor core 55 at the axial midpoint thereof and contacts disk brush as will be described below.

Electromagnet coils 32a and 32b are wound with epoxy-impregnated wire which may be no. 12 size in the illustrative embodiment. Iron annuli 60a and 60b are bolted to opposite ends of rotor core 55 to define therewith a spool which axially confines the coils. The series connection between isolated shaft portion 40 and shaft 15 is defined by first, second, and third magnet conductors 62, 62, and 64. First magnet conductor 62 runs from shaft portion 40 along the axis of shaft 15, and then radially outward to coil 32b. Second magnet conductor 63 runs between coils32a and 32b, passing through brush contact 57. Third magnet conductor passes radially outward from coil 32a to shaft 15. Electromagnet coils 32a and 32b are provided with respective high tensile strength wrappings 65a and 65b, preferably fiberglass-epoxy tape, to prevent centrifugal destruction of the coils.

The flux return enclosure provides a low reluctance magnetic path for the magnetic flux lines passing through rotor core 55 and should therefore be made of relatively high permeability material. For example, enclosure halves 37a and 37b may be constructed of medium-high permeability, high tensile strength, forged silicon steel. Enclosure halves 37a and 37b are bolted to rotor core 55, and together define a cylindrical enclosure within which are located electromagnet coils 32a and 32b, rotor core 55, rotor core 55, copper brush contact 57, and magnet coil wrappings 65a and 65b. Facing portions of enclosure halves 37a and 37b are spaced apart to define a circumferentially extending slot 66 that permits disk brush 50 to engage copper contact 57. Slot 66 is approximately 9/32-inch thick in the region between enclosure halves 37a and 37b, but broadens to approximately 1.0 inch thick in the region between electromagnet coils 32a and 32b. Enclosure halves 37a and 37b are provided with respective high tensile strength wrappings 67a and 67b.

As stated above, shaft 15 is characterized by a 2-inch diameter in the rotor region. Axially away from rotor 12, shaft 15 is of lesser diameter, being reduced to 45 millimeters in the region of bearing assemblies 15 and 17. Proceeding axially away from rotor 12 in a first direction toward isolated shaft portion 40, shaft 15 is formed with radially relieved portions 68 and 69 to define therebetween a first annular collar 70 for engagement with shaft brush 47. Proceeding axially in the other direction, shaft 15 is formed with an annular groove 71 spaced from the shaft end to define a second annular collar 72 for engagement with shaft brush 48.


Figure 4A is an isometric view showing the construction of disk brush 50. Disk brush 50 comprises symmetrical halves 75a and 75b which, when bolted together in coplanar relationship, completely encircle rotor 12. Disk brush half 75b is shown only in phantom. Since disk brush halves 75a and 75b are similarly constructed, brush half 75a only will be described. Brush half 75a is in the form of a 1-inch thick rigid copper plate with a semicircular opening 77 along an edge thereof, opening 77 being adapted to cooperate with a similar opening in brush half 75b to form a circular aperture. A semi-annular web portion 80 of reduced thickness surrounds opening 77 in a spaced concentric relation thereto, and defines an inner brush portion 82 between opening 77 and web portion 80. Web portion 80 is approximately 1/4-inch thick while inner brush portion 82 is approximately 13/16-inch thick. Web portion 80 has a radial extent that is only slightly greater than the radial extent of the facing portions of flux return enclosure halves 37a and 37b and their associated wrappings 72a and 72b. At the same time, web portion 80 is sized to fit within slot 66 of rotor 12 with a small clearance (for example 1/64-inch on either side). Inner brush portion 82 is sized to fit within the broadened slot portion between electromagnet coils 32a and 32b, and engages brush contact 57. Axial clearances are somewhat broader than those surrounding web portion 80. A clearance of 3/32-inch on either side is suitable.

The outside dimensions of disk brush halves 75a and 75b are not critical, nor are the particular outside configurations. However, it is important that the brush halves have portions that extend sufficiently beyond the outside surface of rotor 12 to permit proper mechanical support with respect to casing 20. A height of 18 inches and a width of 20.5 inches (total brush width of 21 inches) is suitable.

As will be described below, generator 10 is operated under conditions of very high current so that brush resistance must be minimized. This is accomplished by wetting the brush contact areas with liquid metal, and providing a structure to hold the liquid metal in place. To this end, inner brush portion 82 carries a fixed contact assembly 85, which may be seen with reference to the fragmentary oblique sectional view of Figure 4B. More particularly, inner brush portion is formed with an inwardly opening recess 87 which broadens beneath the surface to define opposing lips 90 and 91 spaced to receive copper contact 57 therebetween. Lips 90 and 91 confine mixed contact assembly 85 which comprises a strip of ground braid material 92 (1/2-inch x 1/16-inch cross-section is suitable) and a copper strap 95 that is crimped around it to provide structural integrity. Strap 95 surrounds ground braid strip 92 to the same extent as lips 90 and 91, so that the inwardly facing portion between the lips is exposed ground braid material which engages contact 57. In use, ground braid strip 92 is wetted with a liquid metal such as a sodium/potassium eutectic (NaK-78). Operation is optimum with a small and precisely controlled clearance (e.g., 0.002 inches) between braid strip 92 and contact 57. This may be achieved by a break-in run that is carried out prior to wetting braid strip 92 with the liquid metal. The purpose of braid strip 92 is to hold the liquid metal in place and to alter its velocity characteristics so that it does not experience dynamic turbulent flow phenomena or migrate away from the surface of brush contact 57. While the use of ground braid material is a useful expedient, fixed contact assembly may utilize any construction that provides a finely convoluted surface. For example, screen material could be used.

Figure 5A and Figure 5B are exploded isometric views of shaft brushes 47 and 48. Turning first to Figure 5A, shaft brush 47 is of two-piece construction including an elongated rectangular bar member 100 (1-inch x 4-inch cross-section) and an abutting short member 102, members 100 and 102 having respective semicircular openings 105 and 107 along facing, abutting edges thereof. Thus, when brush members 100 and 102 are bolted together, as for example by bolts 110, they define a circular bore of a diameter corresponding to that of radially relieved shaft portions 68 and 69. The surface of the circular bore is recessed and houses a contact assembly 112 (which may comprise eutectic wetted braid) in the same manner as inner brush portion 82 houses contact assembly 85. If braid material is used, a 3/4-inch x 1/16-inch cross-section is suitable. Contact assembly 112 engages annular collar 70 to conduct current between shaft 15 and shaft brush 47. The outside dimensions of brush members 100 and 102 are not critical, but brush member 100 is preferably of sufficient length to extend outside casing 20.

Turning next to Figure 5B, shaft brush 48 includes cooperating brush members 120 and 125 which are generally the same as brush members 100 and 105 with the exception tht the semicircular bores do not extend all the way through, but rather terminate within the brush members. A contact assembly 127 engages annular collar 72.

Figure 5C is an isometric view of one of two identical support elements 130 for shaft brushes 47 and 48. Support element 130 is formed of insulative material and provides an electrically insulated mounting of the shaft brushes to housing 20. Support element 130 includes a rectangular channel section 131 for receiving and supporting a respective shaft brush and flange section 132 for mounting to housing 20.

Figure 6 is an isometric sectional view illustrating the construction of isolated shaft portion 40 and magnet brush 45. Magnet brush 45 is a cylindrical element of sintered copper-graphite or equivalent material. As described above, conductor 62 runs in an axial bore along shaft 15. The end of shaft 15 is formed with a cylindrical recess into which is epoxied an undersized metal cylinder 135 which is bored to receive an uninsulated metal cylinder 135 which is bored to receive an uninsulated end of magnet conductor 62. Isolated shaft portion 40 is a circular plate of the same diameter as the adjacent portion of shaft 15, an is soldered to cylinder 135 to form a mechanical and electrical coupling thereto.


Figure 7 is a side oblique view, sectioned vertically along the axis of rotor 12, with the shaft and rotor shown only in phantom. Figure 1 and Figure 7, taken together, show the construction of housing 20, bearing assemblies 17 and 18, and the mechanical support of the disk, shaft and magnet brushes. Housing 20 comprises a central rotor chamber 150 and axially outboard shaft brush chambers 152 and 153. Rotor chamber 150 includes a pair of end walls 155a and 155b, and pair of side panels 157a and 157b. Shaft brush chamber 152 includes a pair of side walls 160a and 160b, and an end panel 162, while shaft brush chamber 153 includes a pair of side walls 165a and 1665b, and an end panel 167. housing 20 further comprises a floor 170 and a roof 172. End walls 155a and 155b, side walls 160a and 160b, side walls 165a and 165b and floor 170 are preferably 1/2--inch stainless steel plate and are welded together to provide a rigid load-bearing assembly. Side panels 157a and 157b, end panels162 and 167 and roof 172 are of lighter material such as 1/8-inch stainless steel, and are bolted in place so as to be removable. Bolted connections are gasketed, using, for example, 1/8-inch thick cloth-impregnated butyl rubber gasketing material, chosen for its minimal outgassing characteristics. Disk brush halves 75a and 75b are supported between a lower brush support channel 175 and an upper brush support channel 177, both of which are fabricated from a fiber reinforced thermosetting plastic material. Lower brush support channel 177 is bolted to appropriate structural angle members, not shown. Shaft and bearing 27 is mounted to a housing extension 178 which carries a magnet brush support bracket 179. Magnet brush 45 is held in a cylindrical bore within an insulating brush support block 180, and is kept in contact with isolated shaft portion 40 by a spring 181.

Bearing assemblies 17 and 18 are mounted into, and supported by respective end walls 155a and 155b. Since the bearing assemblies are generally identical, only one will be described. Bearing assembly 17 includes a lightly preloaded duplex pair of angular contact ball bearings 180a and 180b mounted within a rectangular housing having a mounting flange 185 on three sides thereof. Suitable bearings may be obtained from Fafnir Company under the designation 2MM209 WI CR DUL. These are very high precision grade (ABEC-7) bearings characterized by a 1.7717-inch bore, a 3.3465-inch outer diameter, and a 1.4960-inch width. These bearings are able to run at 8000 rpm in grease under the loading imposed by rotor 12 and shaft 15. The bearings are held in place by opposed retaining plates 187a and 187b and a retaining collar 190. Shaft end bearing 27 may be a prehoused two-bolt flanged unit such as that obtainable from SKF under the designation FYTP-100. This is a bearing having a 1.000 inch bore and capable of operation at 8700 rpm in grease. Such a bearing has labyrinth seals which do not actually touch, thus avoiding problems of excessive wear and heating at high speeds.

Figure 8 is a partially cut away isometric view showing details of shaft seal assembly 21 which maintains a seal during operation when casing 20 is filled with slightly pressurized nitrogen. Shaft seal assembly 21 comprises an elastomeric seal 195 held in place within a shaft seal housing 196 by a retaining plate 197. A suitable elastomeric seal may be obtained from Johns-Mansville Company under the designation 10058LUP, which signifies a seal facbricated from buna-N material and characterized by a 2.0000-inch outer diameter, a 1.2500-inch bore, and a 0.3750-inch width. At the high angular velocity of operation, the elastomeric seal would rapidly wear away portions of the beryllium-copper material of shaft 15. Accordingly, shaft 15 is provided with a stainless sleeve 198, such as that obtainable from Chicago Rawhide under the designation 99125 Speedi-Sleeve. This is a sleeve characterized by a 1.250-inch bore, and a 0.010-inch wall thickness with a special outer finish designed expressly for efficient sealing action.

However, in order to fill housing 20 with pressurized nitrogen, the housing must first be evacuated and purged. Elastomeric seal 195 is incapable of maintaining a vacuum, so an o-ring sealing mechanism utilizing an axially movable gland 202 is provided. Moving gland 202, shown in its sealing position, has a frustoconical bore 205 adapted to engage a corresponding frustoconical portion 205 of shaft 15 (see also Figure 3). Movable gland 202 is grooved within its frustoconical bore to carry a first o-ring 210 for sealing to shaft 15, and is grooved on its face to carry a second o-ring 212 for sealing to shaft seal housing 197. After housing 20 is filled with nitrogen, gland 202 is moved away from shaft seal housing 197 so that o-ring 210 does not engage the shaft during operation.


Having described the structure of the present invention, suitable operating parameters may be set forth by way of example. By way of background, for a machine of the type described, it is readily shown that the voltage, V, generated between the shaft and the outer circumference of the rotor core is given by the following equation:

V = B w (r22 - r12) / 2 (in mks units)

Where B is the magnetic field strength, w is the angular velocity of the rotor, r2 is the motor core radius, and r1 is the shaft radius. For rotation at 7200 rpm (754 radians per second), a 1-inch radius shaft, a 3-inch radius rotor core, and a magnetic field of 1.5 tesla, the voltage may be shown to be equal to approximately 2.9 volts. In order to render the pattern of output current relatively symmetrical within the device, it is preferred to couple the load to both disk brush halves and both shaft brushes. If two similar loads are used, one may be coupled between disk brush half 75a and shaft brush 48 (which protrude through the casing on the same side) and the other between disk brush half 75b and shaft brush 47.

Due to the brush design, the total internal resistance of the generator is in the neighborhood of 6-10 micro-ohms. Assuming that the machine is capable of dissipating no more than 2.25 kilowatts of internal heating, the maximum test load current is about 15 kiloamperes. At this current, the power output is 43.7 kiloamperes. However, the anticipated load current permissible for continuous operation may be more realistically in the neighborhood of as low as 8 kiloamperes, which corresponds to a power output of 23.3 kilowatts. As stated above, motor 25 may be any suitable prime move, and for the operating conditions described herein, should be capable of developing approximately 15 horsepower.

In view of the present invention and the operation of generator 10, the advantages of the configuration of rotor 12 may be understood. In particular, it will be noted that enclosure halves 37a and 37b cooperate with rotor core 55 to provide a low reluctance magnetic circuit. That is, energization of coils 32a and 32b causes magnet flux lines, denoted schematically by loops 220 in Figure 3, that are contained within a low reluctance magnet circuit comprising a substantially closed path of high permeability material. The only high reluctance portion is slot 66 which is kept as narrow as possible consistent with web portion 80 of brush halves 75a and 75b having sufficient mechanical strength and electrical conductance. With this configuration, a total excitation input power of approximately 150 watts is sufficient to produce a 1.5 tesla field in portion 30 of rotor core 55. The excessive consumption of power in producing a high magnetic field level is eliminated, making possible sustained operation at high levels of magnetic induction (and therefore of output voltage).

In summary, it can be seen that a generator according to the present invention is characterized by high efficiency and low magnet power requirements, achieved by the use of a rotor configuration having a low reluctance path. While the above provides a full and complete disclosure of the preferred embodiments of the invention, various modifications, alternate constructions, and equivalents may be employed without departing from the true spirit and scope of the invention. For example, housing 20 could be constructed with a cylindrical configuration to minimize the internal volume. Moreover, while a brush geometry that encircles the rotor and shaft is desirable, other configurations could be used. Therefore, the above description and illustration should not be construed as limiting the scope of the invention which is defined by the appended claims.