Electricity: circuit makers and breakers – Interlocking – Between plural switches
Reexamination Certificate
2002-01-18
2004-06-15
Friedhofer, Michael A. (Department: 2832)
Electricity: circuit makers and breakers
Interlocking
Between plural switches
C200S00100B, C200S04800A, C200S334000
Reexamination Certificate
active
06750409
ABSTRACT:
The present invention relates to the art of electric arc welding and more particularly to an input power switch for a welder and/or plasma cutter.
BACKGROUND OF INVENTION
Industrial electric arc welders include a power source that must be connected to and disconnected from a line power supply, which is a single phase or three phase network. To make the connection between the power source and power supply, a manually operated toggle switch is normally used to toggle between a closed condition wherein the switch electrically connects the power source to the power supply and an open condition where the power source is disconnected from the power supply. The main power toggle switch is well known in the electric arc welding field; however, it must be designed to have long life and acceptable temperature limits during operation. To assure long term operation, such main power switches must be certified as meeting standards, such as passing a life test of 6000 cycles at 6 cycles per minute with a one second minimum time delay between cycles. When the output power source is shorted, the compliance test requires 100 cycles without failure. The mechanical toggle switch needs to have a maximum contact temperature rise of 40° C., as well as meeting the 100 cycle shorted output switching test. To assure compliance with these operating conditions, it has been common practice to replace the input line switch of a welder with an expensive input line connector relay with an overcurrent protected pilot transformer having a low current pilot switch. By activating and deactivating the power connector coil the input power is turned on and off. In other words, simple mechanical toggle power switches, that have been used for many years in lower capacity power sources, do not provide the heat and arcing protection meeting the demands of the larger electric arc welders. Consequently, very expensive contact or relays have been suggested and used to comply wit the switching requirements. Such relays require a power supply that demands a separate and distinct auxiliary power supply to operate the relay mechanism. These relays complicate the welder design and increases the cost and complexity over standard mechanical toggle switches used for years.
THE INVENTION
The present invention relates to the an improved mechanical power switch for an electric arc welder. As is well known, such welders often include an override protection circuit having thermostats for sensing temperature levels of the transformer windings, chokes and other electrical components subjected to temperature rises. The power source, such as an inverter or SCR rectifier, is deactivated when one of the thermostats of the override protection circuit detects an overheat condition. These thermal shut down conditions are communicated to the operator, usually by a panel light which is activated when the override heat sensing circuit has sensed an overtemperature condition. When the thermostat resets, the panel light is extinguished. The improved mechanical power switch of the present invention is designed to utilize the existing override circuit of a welder. The override circuit normal in welders is used to substantially extend the switching life of the input main power switch of the electric arc welder. A standard toggle main power switch is provided with a normally opened microswitch mounted on the power switch so the mechanical operation of the toggle lever of the power switch closes the normally opened contacts of a microswitch. After the power contacts are closed to provide input power to the power source, the microswitch is operated to close its normally open contacts. In a like manner, the microswitch is released so the normally opened switch is shifted to the normal position before the power switch contacts are opened. Thus, the power source is deactivated before the main contacts are opened. By putting the normally opened contacts of the microswitch in series in the override temperature sensing protection circuit of the welder, the welder power supply is deactivated or disabled by opening the normally opened contacts when the toggle switch is toggled toward the opened condition of the contacts. After the lever of the toggle switch is toggled into the closed contact condition, the microswitch actuator is depressed to close the normally opened contacts of the microswitch and enable the power supply. By connecting the normally opened microswitch contacts in series with the thermostats contacts of the override protection circuit, the welder output will shut down whenever the microswitch contacts are opened. If the main toggle switch opens the normally opened contacts of the microswitch without following through to open the line contacts, the thermal light panel indicator will turn on to indicate the welder shut down. Conversely, when the main toggle switch toggle lever closes the power contacts, the thermal light momentarily blinks on to indicate the short delay in activating the output. The microswitch contacts are initially opened They are closed after the main line contacts are closed. Thus, there is a slight delay in welder start. By using the present invention, main power toggle switches that have previously been unsuccessful in passing the cycle life and temperature requirements for certification have easily exceeded the cycle life test requirements with substantially less arcing and virtually no contact erosion. Consequently, by the mere addition of the auxiliary microswitch onto the standard mechanical power switch, the power switch is converted into a mechanical switch meeting all requirements of temperature and arcing.
The present invention involves the addition of a microswitch with a normally opened contact placed in series in the standard thermostat override or protection circuit of an electric arc welder. An extension or finger on the toggle lever of the toggle switch engages and depresses the actuator of the microswitch to close the normally opened contacts in the override circuit when the main switch is closed. As the main switch is opened, the extension of the toggle lever releases the actuator of the microswitch. This immediately opens the normally open contact in the override circuit to disable the power source. This first movement releases the microswitch before opening the line contacts. Thus, the power source is initially deactivated as the toggle switch is moved into the disconnect condition. Consequently, disconnection of the line contacts is accomplished at a deactivated or low input level of the power source. Deactivation means both off or low input level to the power source. This opening of the line contacts at low input prevents overheating and drastically reduces arcing. This is the main feature of the present invention. The microswitch used in the present invention has a benefit during closing of the line contacts of the main power switch. As the toggle lever is moved into the closed condition for the line contacts, the toggle first closes the snap-action contacts. Then full movement of the extension or finger engages the microswitch which closes the override circuit allowing activation at full power for the power source. In both opening and closing of the main contacts, there is a delay during which the power source is disabled, so the contacts actually switching the supply to and from the power source are first to close, but last to open relative to the enabled power source.
In accordance with the present invention there is provided a power switch for selectively connecting a power source to an input power supply where the power source has an override circuit to deactivate the power source when in a first condition and allowing activation of the power source when in a second condition. The power switch of the present invention has snap-acting electrical contacts movable between an open condition with the power source electrically disconnected from the power supply and a closed condition with the power source electrically connected to the power supply and an operating lever movable between a first position w
Fay Sharpe Fagan Minnich & McKee
Friedhofer Michael A.
Lincoln Global Inc.
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