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Output Switch Open

Output Switch Open

Continued explain the increase in input power. The other likely explanation seems to be that there are internal losses in the core and other par\f> of the metal sJructure due to eddy currents, since these are also moving conductors in the field. In any event, the increase in drive power was on!> about 10% for the maximum magnet current of 19 amperes.

Figure 9 typifies a number of measurements of input power and generator performance as a function of speed and various generator conditions. The upper curve (a) shows the motor armature input power for 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 6500 rpm. This presumably represents the power required to overcome friction and windage losses in the motor, generator, and drive belt, and could be expected to remain essentially constant whether the generator is producing power or not.

Curve 14b shows the increase of motor armature power 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 dissipation. This component of power (which is related to the increase of drive motor power with increased magnet current as shown in Fig. 6 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.

Curve 14c shows the further increase of motor armature input power over that of curves 14a and 14b 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 as predicted by DePalma, 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.

Figure 9 - Input and Output power vs speed

The big question has to do with the generated output power. The measured output current 6500 rpm was 4776 amperes; the voltage at the metering brushes was 1.07 volts. Using a correction factor derived from Fig. 7 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 results in an output power of 6113 watts. All of this power is 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 certainly exceeds the 802 watts of increased motor drive power by a factor of 7.6 to 1. It even exceeds the input motor armature power of 6028 watts, although the total system efficiency 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, DePalma correctly predicted much of the output power with this kind of machine is not reflected back to the motive source. Figure 10 summarizes the data discussed above.

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