Bruce Depalma December

Figure 4 - Test dala from report by Bruce DePalma

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 80^ power factor. There was apparently no consideration of phase angle change as the motor load increased. This is clearly incorrect, since inclusion of phase angle is essential in calculating power in an a-c circuit., particularly with induction motors. It might also be noted that the measured incremental line current increase of 0.5 ampere (3.3/?) was of limited accuracy as obtained with the analog clamp-on a-c ammeter that was used.

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 significant.

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 is assumed to be due to the internal voltage drop resulting from the output current tlowing through the internal disk resistance that is common to both sets of brushes and calculated to be 62.5 microohms.

Of these, the first assumption seems most serious, and it is the ipinion of this authoi that some of DePalma's numerical results .ire questionable. A similar conclusion was reached by Tim Wil-'telm of the Stelle Community in Illinois'1 who witnessed tests by DePalma in 1981.

Recent Tests of the Sunburst Generator by the Author

Being intrigued by DePalma's claims, the author accepted the offer by Mr. Norman Paulsen, founder of the Sunburst Community, to conduct tests on the generator which had not been used since the tests by DePalma.

Experimental Setup_

A schematic diagram of the test arrangement is shown in Fig. 5. The generator is coupled by a belt to the drive motor behind it, together with the power supplies and metering both contained within and external to the Sunburst power and metering cabinet. The panel of the test cabinet provided power for the generator magnet and motor field. Meters on the panel were n ot functional and were not used; external meters were supplied. It was decided to use a d-c drive motor, primarily to facilitate┬╗ load tests at different speeds and to simplify accurate motor input power measurements. The actual motor used was a surplus d-c generator from a DC-6 aircraft, rated at 400 amperes at 30 volts output from 3000 to 8000 rpm and capable of over 40 hp when used as a motor with appropriate forced air cooling. Half of the motor brushes were removed to reduce friction losses. Referring to Figure 9, variable d-c supplies for the motor armature and field and the homopolar generator magnet were provided by variacs and full-wave bridge rectifiers. Voltages and currents were mea-

sured with Micronta model 11-191 3Vi digit meters calibrated to better than 0.1% against a Hewlett Packard 740B Voltage Standard that 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 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 was accurate to better than 2%.

Armature \/&nac

Sunburst Homopolar Generator Test

M*fer

Bruce Depalma

Figure 5 - Schematic diagram of generator test arrangement htomepoUr

Figure 5 - Schematic diagram of generator test arrangement

Generator Tests

Various tests were conducted with the output switch open to confirm that generated voltage at both the output brushes (Vbr) and metering brushes were proportional to speed and magnetic field, with tne polarity reversing when magnetic field or direction of rotation were reversed. Tracking of Vg and Vt>r with variation of magnetic field is shown in Fig. 6, 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 Fig. 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 Fig. 7, and is seen to considerably exceed meter error tolerances.

Figure 6 also shows an approximate 300 watt increase in drive motor armature power as the magnet field is increased from 0 to 19 amperes. (The scatter of input power measurements shown in the upper curve of Fig. 6 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 does 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 Fig. 1. 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 Fig. 8. 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 o

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Responses

  • vera bass
    How did norman paulsen of sunburst farms die?
    7 years ago

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