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2 while phases 1 and 3 are reduced alike. This unbalance is not too serious and it appears only when capacitance balance has been made at no-load and load correction has been stretched to cover the whole power range of the motor. It should be noted in this connection that the motor load is 160 w under the conditions of Fig. 4 which is the same maximum power which this motor can deliver from a normal three-phase line.
Power Characteristics
Power output capacity sufficient to handle any motor or combination of motors would be desirable. Since this cannot be provided in a portable device, the maximum weight which can be carried by one hand (about 50 Ib) was used as a base, and as much power as possible was provided within this limitation rather than selection of some arbitrary value of power. The result of this approach is a power output of about 400 va; the real watts and available mechanical power being determined by the power factor and efficiency of the motor. The engineering model is shown in Fig. 5.
The single-phase input power factor is relatively good and varies from 50 to 95%, while the conversion efficiency from single-phase to three-phase varies from 30 to 75%; both factors depending on the characteristics of the motor load.
In terms of equipment which can be operated by the converter, the following motors or combinations of motors appear to be within the power handling range of the unit:
Standard camera, synchronous motor —
limited only by motor power Standard camera and portable recorder,
synchronous motors — above 50 F
ambient Standard camera and portable recorder,
multiduty motors — any weather
Technicolor camera — above 50 F ambient
As previously noted the load demand of most cameras varies widely with ambient temperature and the weather is thus noted as a limiting load factor in some cases. Multiduty motors * operated in the synchronous mode function at relatively high efficiency and good power factor and thus heavier loads and/or more motors are operable from the converter than is the case with the usual variable reluctance synchronous type. It should be noted that the inclusion of this converter in a multiduty equipped channel adds singlephase, 115-v supply to the existing battery and three-phase power sources frpm which such channels can operate.
Conclusion
The development of a portable, nonrotary converter to supply three-phase, 230-v from a single-phase, 115-v source has seemed desirable in order to realize the inherent advantages of three-phase motors, particularly on motion picture cameras, while utilizing the convenience and availability of single-phase source of supply. Good phase-voltage balance is essential in such a device under variable load conditions, and it has been possible to obtain this by providing a simple form of indication together with a ready means of correction.
Discussion
William P. Kruse: Approximately what is the primary voltage on your resonant transformer during some various normal loads?
(Communicated by} A, L. Holcomb: The primary voltage of T2 is maintained essentially constant at 135 volts by adjustment of the Variac, as described, to meet the various load conditions.
* A. L. Holcomb, "Motor systems for motion picture production," Jour. SMPE, 42: 9-33, Jan. 1944.
A. L. Holcomb: Three-Phase From Single-Phase
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