Abstract: An input-side rectifier (4), a smoothing capacitor (6), an inverter (8), a transformer (10) and an output-side rectifier (12) operate together to convert an AC voltage supplied from an AC power supply to a DC voltage. The DC voltage is coupled through a DC-to-AC converter (16) to a workpiece (18) and a torch (20). An auxiliary voltage supply (28) supplies the workpiece (18) and the torch (20) with a negative voltage for a short time following the transition of the AC voltage supplied to the workpiece (18) and the torch (20) from positive to negative. The negative voltage has a negative peak value larger than the negative peak value of the AC voltage supplied to the workpiece (18) and the torch (20), and rapidly changes from the negative peak value.

Abstract: An input-side rectifier (4), a smoothing capacitor (6), an inverter (8), a transformer (10) and an output-side rectifier (12) operate together to convert an AC voltage supplied from an AC power supply to a DC voltage. The DC voltage is coupled through a DC-to-AC converter (16) to a workpiece (18) and a torch (20). An auxiliary voltage supply (28) supplies the workpiece (18) and the torch (20) with a negative voltage for a short time following the transition of the AC voltage supplied to the workpiece (18) and the torch (20) from positive to negative. The negative voltage has a negative peak value larger than the negative peak value of the AC voltage supplied to the workpiece (18) and the torch (20), and rapidly changes from the negative peak value.

Abstract: A cooling apparatus for electrical equipment having heat-generating components, air-intake apertures and air-outlet apertures includes a fan, a forward-rotation power control circuit, a reverse-rotation power control circuit, an indicator, a long-term timer and a short-term timer. The forward-rotation power control circuit rotates the fan in a forward direction such that air flows in through the air-intake apertures, over the heat-generating components and away through the air-outlet apertures, in response to a forward-rotation command signal. The reverse-rotation power control circuit rotates the fan in the opposite direction. The long-term timer continuously applies the forward-rotation command signal to the forward-rotation power control circuit during a first predetermined period. The indicator indicates the expiration of the first predetermined period.

Abstract: An AC voltage applied among power input supply terminals is rectified by a rectifier, and the rectified voltage is adapted to be reduced in a voltage-reducing converter with a switch connected in parallel with it. A switching circuit connect smoothing capacitors in series or parallel to the voltage-reducing converter. Inverters are connected in parallel with the respective smoothing capacitors. The output voltages of the inverters are voltage-transformed by transformers. The transformed voltages from the transformers are converted to DC voltages by converters. A control unit renders the voltage-reducing converter operative and causes the switching circuit to connect the smoothing capacitors in series when a third AC voltage is applied among the power supply input terminals.

Abstract: A DC power supply apparatus includes a rectifier circuit for rectifying an input AC voltage to develop a rectified voltage between two output terminals thereof. First and second smoothing capacitors are connected in series between the output terminals of the rectifier circuit. First and second voltages developed across the first and second capacitors are applied to first and second inverters which convert the applied voltages to high-frequency voltages, which, in turn, are applied to a transformer. The transformer develops a transformed high-frequency voltage which is converted to a DC voltage by a converter. A voltage detector detects the first and second voltages, and the detected first and second voltages are compared in a microprocessor. An inverter control circuit controls the first and second inverters in accordance with the result of comparison, in a sense to make the voltages across the first and second smoothing capacitors equal.

Abstract: An arc welder includes an inverter for converting a DC voltage to a RF voltage which, then, is rectified by a rectifier. The output of the rectifier is smoothed by a DC reactor. A RF generator provides RF current to flow between a workpiece and a main electrode of the welder forming a welder load, which initiates arcing between the workpiece and the main electrode. Initiation of arcing causes output current from the DC reactor to be supplied to the welder load, so that steady-state arcing is established. The DC reactor has a relatively small inductance which permit the output current from the DC reactor to reach a value required for establishing the steady-state arcing within a time period during which the RF generator provides RF current. The RF voltage from the inverter has a relatively high frequency so that the output current from the DC reactor can sustain the steady-state arcing.

Abstract: An air plasma arc cutter includes spaced apart front and rear panels. A partition wall has its opposed two edges coupled to the front and rear panels to divide the space therebetween into upper and lower regions. An AC-to-DC voltage converter is disposed in the upper region and converts an AC voltage to a DC voltage to be applied between a torch electrode of a torch of the cutter and a workpiece. An air compressor supplies compressed air around the torch electrode and is disposed in the lower region. The air compressor has a threaded bolt which extends through the partition wall from the lower into upper regions. A nut is screwed onto the bolt in the upper region to thereby secure the air compressor to the partition wall. Shock absorbing members are disposed between the nut and the partition wall and between the air compressor and the partition wall.

Abstract: A power supply apparatus for a plasma arc cutter includes an inverter which converts DC power to high-frequency power. An output developing circuit rectifies and smooths the high-frequency power for application between a torch electrode and a workpiece which form together a plasma load. A current detecting unit detects current flowing through the plasma load. A reference signal generating unit generates a reference signal including a preset DC signal and a predetermined AC signal superposed on the DC signal. A control units control the inverter, in accordance with the difference between the output of the current detecting unit and the reference signal, so that the output current to be supplied between the electrode and the workpiece has a predetermined constant DC current and a predetermined AC current superposed on the DC current.The reference signal generating unit can vary the frequency and amplitude of the AC signal in the reference signal.

Abstract: A plasma-arc power supply apparatus includes a main electrode terminal, a nozzle electrode terminal and a workpiece terminal which are respectively coupled to a main electrode, a nozzle electrode and a workpiece of a plasma-arc apparatus. A DC power supply has its first output terminal coupled to the main electrode terminal, and a second output terminal. A pilot arc path is coupled between the second output terminal and the nozzle electrode terminal. A switch is connected in the pilot arc path. A plasma-arc path is coupled between the second output terminal and the workpiece terminal. A current detector has its first input coupled to the plasma-arc path, has its second input coupled to the pilot arc path, and produce a detection signal corresponding to the values of pilot arc and plasma-arc currents in the pilot arc and and plasma-arc paths, respectively.

Abstract: An inverter controlled DC arc welder of consumable electrode type includes an input rectifier for rectifying AC input power, an inverter for converting the rectifier output to high frequency AC power, an output transformer for stepping down the inverter output voltage, and an output rectifier for rectifying the transformer output voltage to provide a DC output voltage to be applied to a welder load. The welder further includes means for detecting current flowing through the welder load to produce a detection signal, a differentiator circuit for differentiating the detection signal, and correction means for correcting a predetermined reference voltage in accordance with the differentiator output voltage. Feedback control means controls the inverter in accordance with the difference between the transformer output and the corrected reference voltage.

Abstract: An arc welder provided with a low frequency square waveform a.c. power supply as a main power supply for welding in order to improve its power of recovering an arc which may go out at the time of polarity transition of a welding load and an auxiliary d.c. power supply for super-posing its output upon the input of the main power supply to further improve the recovering power, in which a switching element is inserted in a supply path of the output of the auxiliary d.c. power supply and the switching element is put in conduction by a suitable control device only for a necessary shortest arc recovery time in order to reduce a power loss due to continuous supply of the auxiliary d.c. output.

Abstract: A d.c. arc welder which can use either a high voltage power supply of a certain voltage such as 400 volts or a low voltage power supply of about a half voltage thereof such as 200 volts and is arranged to effect automatic switching between low and high voltage power supply states not only when the power supply is switched from one to the other but also when the input voltage gradually rises from zero voltage to the above-mentioned high voltage, thereby constantly providing an adequate d.c. output for welding. It is provided with a circuit breaker in a stage next to its input terminals for sensing a high voltage of the power supply to temporarily shut off the input from the power supply and closing the circuit after its initialization.

Abstract: An invertor controlled D.C. arc welder of consumable electrode type which is arranged to rectify an a.c. power from a commercial power supply, convert it into a high frequency a.c. power by an invertor, rectify it again to obtain a d.c. power output for welding and stabilize the output voltage by feedback control of the invertor based upon the output voltage and provided with means for discriminating shorting and arcing periods of its welding load from the output voltage and additionally controlling the invertor based upon a resultant discrimination signal to raise the output voltage during the early time of the arcing period, thereby preventing defective welding due to insufficient output current.

Abstract: An arc welder which can be used with either a high voltage a.c. power supply of a certain voltage or a low voltage a.c. power supply of about a half of said voltage, such as 400 or 200 volts, for example, and which is provided with a circuit configuration in which an input a.c. voltage is rectified by a rectifier and smoothed by a pair of capacitors and the resultant d c. power is converted by an invertor into a high frequency a.c. power which is reduced in voltage by an output transformer and then rectified again, and arranged to discriminate the input a.c. voltage and switchingly connect these capacitors in series or parallel between both ends of the input rectifier, thereby automatically conforming the circuit to both high and low supply voltages.