Power switch for welder

This application claims the benefit of provisional application No. 60/340,136, filed Dec. 14, 2001.

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 with the switch contacts in the open condition and a second position with the switch contacts in the closed position. The power switch also has, in accordance with the invention, an auxiliary switch in the override circuit with a movable element having a first orientation to shift the override circuit into the first disenabled condition and a second orientation to shift the override circuit into the second enabled condition. The lever of the main power switch causes the movable element of the auxiliary switch to move into the first orientation before the lever of the power switch moves to the first position during the movement of the lever from the second position connecting the power source to the first position disconnecting the power source. In accordance with an aspect of the invention, the auxiliary switch is a microswitch with a normally open contact in series in the protection circuit of the welder. The power switch is, in the preferred embodiment, the input power switch for an electric arc welder or plasma cutter. In accordance with the invention, the main power switch has a standard toggle lever so that the switch toggles between the open condition and closed condition of the input main power contacts.

In accordance with another aspect of the present invention there is provided a power switch for selectively connecting a power source to an input power supply. The power switch has an operating lever movable between a connecting position and disconnecting position. In accordance with the invention, an auxiliary switch with a first switch condition disabling the power source and a second condition enabling the power source. The auxiliary switch is provided with an element or actuator for shifting between the two conditions. The power switch has a lever with an extension or finger engaging the movable elements or actuator of the auxiliary switch. When the lever is in the line contact connecting position, the lever shifts the element into the second condition activating or enabling the power source. The element or actuator is released when the lever is moved from the connecting position toward the disconnecting position. This shifts the contacts in the protective circuit into the disabling normally open condition.

The primary object of the present invention is the provision of an improvement in a standard input toggle switch of a power source of the type used for electric arc welders, which input power switch includes an auxiliary switch for deactivating the power source before the main switch is disconnected.

Another object of the invention is the provision of a main mechanical power switch for a welder and/or plasma cutter, which main power switch deactivates or disables the power source prior to shifting the main switch from the connected condition to the disconnected condition.

Yet another object of the present invention is the provision of a power switch, as defined above, which power switch allows a standard toggle switch to cause reduced arcing and have reduced heating as it is shifted many times between the connected condition and the disconnected condition.

These and other objects and advantages will become apparent from the following description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1

is a wiring diagram showing the preferred embodiment of the present invention;

FIG. 2

is a pictorial view of a standard input toggle power switch used in electric arc welders and provided with a microswitch used in the present invention;

FIG. 3

is a side view of the pictorial view shown in

FIG. 2

illustrating the toggle lever in a solid line condition connecting the power source to the input power supply and a dashed line toggle position disconnecting or disabling the power source from the input supply,

FIG. 4

is a current graph illustrating the turn-on sequence of a switch using the present invention; and,

FIG. 5

is a current graph showing the turn-off sequence of a power switch utilizing the present invention.

PREFERRED EMBODIMENT

Referring now to the drawings, wherein the showings are for the purposes of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same,

FIG. 1

shows a welder A having an input reconnect panel

10

with an output transformer

12

directing current controlled by an SCR bridge

16

through a polarity switch network

14

. Standard controller

20

has a control or command line

22

that determines the operation of SCR bridge

16

for performing an electric arc welding operation between electrode E and workpiece W. Electrode E is a welding wire provided by spool

24

in this embodiment. SCR holding resistor

30

is connected in parallel between electrode E and workpiece W in accordance with standard welding technology. Choke

32

controls current flow. Controller

20

receives a current signal from current shunt

34

as indicated by line

36

. A standard override or temperature protection circuit

40

controls the logic on line

42

to enable controller

20

. In accordance with standard technology, circuit

40

includes normally closed contacts

50

,

52

operated by thermostats

60

,

62

in accordance with the heat from transformer

12

or other components in the welder. As so far described, welder A involves normal welding technology. The invention is in the area of the mechanical main input switch

100

, shown in

FIG. 1

as a dashed line box. The switch connects the power supply shown as a single phase line voltage having lines L

1

, L

2

. This supply is to be connected to input reconnect panel

10

forming the input of the power source of welder A. Switch

100

is illustrated as having contacts

102

,

104

for connecting input lines

110

,

112

with output lines

120

,

122

, respectively. As shown in

FIGS. 2 and 3

, lines

120

,

122

are directed to panel

10

forming the input stage of the power source. Referring now more particularly to

FIGS. 2 and 3

, main power switch

100

is standard snap-action toggle switch commonly used in the welders. It includes a mounting insulator plate

140

having contacts

142

,

144

. The contacts

142

,

144

are connected or disconnected by swinging segment

150

having internal arcuate copper contacts to engage and disengage spaced copper blades extending into the switch from the contacts at the back of insulator plate

140

. Both input line L

1

and L

2

have contacts

142

,

144

as represented in FIG.

3

. Segment

150

(two are used on switch

100

) is shifted between a connecting and non-connecting position by manually moving toggle lever

160

supported by a metal front plate or bracket

162

. As so far described, toggle switch

100

is standard. Lever

160

is shifted by a snap-action between a solid line position with contacts

102

,

104

closed to the dashed line position with these contacts opened. Segment

150

pivots back and forth to either connect the line contacts or disengage the line contacts. Plate or bracket

162

of the toggle switch is provided with an upwardly extending flange

164

forming the mounting platform for microswitch

210

that converts standard switch

100

to an improved mechanical switch in accordance with the invention. Turning back to

FIG. 1

, a normally opened contact

200

can connect leads

202

,

204

in series with switches

50

,

52

of standard protective circuit

40

. An auxiliary switch in the form of microswitch

210

is mounted on flange

164

. As shown in

FIG. 3

, and schematically in

FIG. 1

, switch

210

includes a standard actuator

212

that is a movable element. It is depressed to close contact

200

and released to open this contact Contact

200

is not operated directly with contacts

102

,

104

. An extension or finger

220

on toggle lever

160

engages actuator or movable element

212

for the purposes of closing normally closed contact

200

, as shown in FIG.

3

.

In operation, when toggle lever

160

is in the solid line position shown in

FIGS. 2 and 3

, actuator

212

is depressed by extension or finger

220

. This closes contact

200

causing the logic on line

42

to SCR bridge

16

through controller

20

and control line

22

. As toggle lever

160

is moved downwardly as shown in

FIG. 3

, the first action is for finger

220

to release actuator

212

. This opens contact

200

and deactivates or disables SCR bridge

16

through controller

20

. Further movement of the toggle lever into the dashed line position shown in

FIG. 3

opens contacts

102

,

104

. Thus, release of actuator

212

of microswitch

210

to deactivate or disable the power source including bridge

16

. The power source is then disconnected from the input power supply at a low current. This reduces the temperature and prevents arc. The depressed position of actuator or movable element

212

is a second condition of circuit

40

enabling the power source. The released position is a first condition of circuit

40

disabling the power source. This is done in unison with snap-action of toggling lever

160

between a down first position disconnecting the line contacts and an up position connecting the line contacts. As switch

100

is toggled into the closed position, lever

160

moves up to depress actuator

212

. Contact

200

is closed to enable operation of welder A.

The current graph during operation of switch

100

to connect the power source to the input power supply is shown in FIG.

4

. In area

240

the power source or bridge

16

is disconnected. Contacts

102

,

104

are opened and contact

200

is opened. Lever

160

is down. Then toggle lever

160

is moved upwardly as shown in

FIG. 3

until the snap-action contacts close to allow idle input current to flow. This is shown in area

242

of FIG.

4

. Full upward movement of toggle lever

160

causes extension or finger

220

to close contact

200

by extension

220

engaging and depressing actuator

214

. This enables the output load current of welder A and is shown in area

244

of FIG.

4

. The main contacts

102

,

104

are closed and the welder is at full power. Thereafter, the welder operates in accordance with standard technology to perform a welding operation between electrode E and workpiece W with welding wire from spool

24

. To disconnect the power source of welder A, toggle lever

160

is moved downwardly releasing finger

220

from actuator

212

. This sequence is shown in FIG.

5

. Area

244

of

FIG. 4

is the initial area of FIG.

5

. Contact

200

is opened when actuator

212

is released. This deactivates the power source of welder A due to the logic on line

42

directed to controller

20

to shut off SCR bridge

16

to cause only idle input current. This is area

250

. Further movement of toggle lever

160

into the dashed line position shown in

FIG. 3

, opens the contacts

102

,

104

to disconnect the power source of the welder, as shown in area

252

. Consequently, the activation and deactivation of the standard main input power switch

100

is accomplished at a low current determined by deactivation of the power source using a normal protection override circuit

40

. Since low current exists when connecting and disconnecting the power source of the welder from the main power supply, reduced temperature and arcing is obtained.