| 摘要 |
PROBLEM TO BE SOLVED: To prevent the number of revolutions of the motor of a motor-driven hoist, etc., from significantly exceeding its rating when the hoist lowers a hung load. SOLUTION: In the circuit of a motor-driven hoist, etc., a motor is inversely driven through a bridge rectifier circuit, and a magnet switch is operated by means of a lifting switch and a lowering switch. Such a means is adopted that connects the bridge rectifier circuit to the magnet switch so that a full-wave rectified current may flow to the motor when a load is lifted and a half-wave rectified current may flow to the motor when a load is lowered, and, in addition, a power generation braking circuit which operates when the load is lowered in parallel with the motor. In the power generation braking circuit, in addition, such a means is adopted that connects the contact of a latch relay in series with the coil for lowering operation of the lowering switch and, at the same time, the reset coil of the latch relay to the braking resistor of the braking circuit.
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