Abstract:
A system and method to control the power supplied to heating elements of a conveyor oven. The conveyor oven includes a plurality of heating elements to evenly distribute heat in an oven compartment. During peak-loads, the current draw of the heating elements may exceed available power of a power supply. Therefore, a system and method to reduce the total current draw of the plurality of heating elements is provided. The system includes a controller configured to perform the methods disclosed herein. The methods effectively lower the total current draw by rapidly cycling a plurality of relays connected to each of the plurality of heating elements to achieve even distribution of heat and reduced current draw during peak-loads.

Description:
BACKGROUND 
       [0001]    Embodiments of the invention relate to power and control systems for conveyor ovens. 
         [0002]    A conveyor oven often includes multiple heating elements positioned in an oven compartment and a conveyor that passes through the oven compartment. 
       SUMMARY 
       [0003]    During peak-loads, for example, on a cold startup of the conveyor oven, the current draw of the heating elements may exceed the available power of a power supply. Therefore, a conveyor oven and a method for controlling a conveyor oven that controls the current draw during peak-loads are desirable. 
         [0004]    In one embodiment, the invention provides a conveyor oven including an oven compartment with a conveyor extending through the oven compartment and a motor that drives the conveyor. The conveyor oven includes a first heating element and a first relay that controls the current flow to the first heating element. A power input module receives external power and distributes power to components within the conveyor oven. A controller includes an input/output module, a user interface, and a memory that stores instructions for the controller. The controller is configured to receive an input control signal from the user interface. The input control signal may represent a temperature setpoint for the oven compartment. The controller is also configured to send a heating element control signal to the first relay based on the input control signal. The heating element control signal is pulsed such that the first relay is repeatedly actuated to reduce an average current to the first heating element. 
         [0005]    In another embodiment, the invention provides a conveyor oven including a first heating element, a second heating element, and a third heating element connected to a first relay, a second relay, and a third relay respectively. The conveyor oven includes a controller configured to actuate the first relay, the second relay, and the third relay such that the second heating element and the third heating element are energized for a first period of time during which the first heating element is de-energized. The controller actuates the second relay to de-energize the second heating element for a second period of time. Next, the controller actuates the first relay to energize the first heating element for a third period of time. The controller actuates the third relay to de-energize the third heating element for a fourth period of time, and actuates the second relay to energize the second heating element for a fourth period of time. The controller then actuates the first relay to de-energize the first heating element for a fifth period of time, and lastly, actuates the third relay to energize the third heating element for a sixth period of time. 
         [0006]    In another embodiment, the invention provides a conveyor oven including a first heating element, a second heating element, a third heating element, and a fourth heating element connected to a first relay, a second relay, a third relay, and a fourth relay respectively. The conveyor oven includes a controller configured to actuate the first relay, the second relay, the third relay, and the fourth relay such that the second heating element, the third heating element, and the fourth heating element are energized for a first period of time during which the first heating element is de-energized. The controller is configured to perform the following steps. The controller actuates the second relay to de-energize the second heating element for a second period of time. The controller actuates the first relay to energize the first heating element for a third period of time. The controller actuates the third relay to de-energize the third heating element for a fourth period of time. The controller actuates the second relay to energize the second heating element for a fourth period of time. The controller actuates the fourth relay to de-energize the fourth heating element for a fifth period of time. The controller actuates the third relay to energize the third heating element for a sixth period of time. The controller actuates the first relay to de-energize the first heating element for a seventh period of time. Lastly, the controller actuates the fourth relay to energize the fourth heating element. The controller is configured to repeat the above-listed steps until the controller determines that the oven compartment is at a desired temperature setpoint. 
         [0007]    In another embodiment, the invention provides a method for controlling a conveyor oven including a first heating element, a second heating element, and a third heating element. A first relay is connected to the first heating element, a second relay is connected to the second heating element, and a third relay is connected to the third heating element. A controller operates the relays by actuating the first relay, the second relay, and the third relay such that the second heating element and the third heating element are energized for a first period of time while the first heating element is de-energized. The controller actuates the second relay to de-energize the second heating element for a second period of time. Next, the controller actuates the first relay to energize the first heating element for a third period of time. The controller actuates the third relay to de-energize the third heating element for a fourth period of time, and actuates the second relay to energize the second heating element for a fourth period of time. The controller then actuates the first relay to de-energize the first heating element for a fifth period of time, and lastly, actuates the third relay to energize the third heating element for a sixth period of time. The controller is configured to repeat the above-listed steps until the controller determines that the oven compartment is at a desired temperature setpoint. 
         [0008]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a sectional view of a conveyor oven. 
           [0010]      FIG. 2  is a block diagram of a controller of the conveyor oven of  FIG. 1 . 
           [0011]      FIG. 3  is a circuit diagram of an embodiment of the conveyor oven of  FIG. 1  that uses single-phase power and four heating elements. 
           [0012]      FIG. 4  is a circuit diagram of an embodiment of the conveyor oven of  FIG. 1  that uses three-phase power and four heating elements. 
           [0013]      FIG. 5  is a circuit diagram of an embodiment of the conveyor oven of  FIG. 1  that uses single-phase power and three heating elements. 
           [0014]      FIG. 6  is a circuit diagram of an embodiment of the conveyor oven of  FIG. 1  that uses three-phase power and three heating elements. 
           [0015]      FIG. 7  is a block diagram of a heating element control method for embodiments of the conveyor oven shown in  FIGS. 3 and 4 . 
           [0016]      FIG. 8  is a block diagram of a heating element control method for embodiments of the conveyor oven shown in  FIGS. 5 and 6 . 
           [0017]      FIG. 9  is a graph illustrating a timing sequence for actuation of relays for the method of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0019]    It should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components may be used to implement the invention. In addition, it should be understood that embodiments of the invention may include hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic based aspects of the invention may be implemented in software (e.g., stored on non-transitory computer-readable medium) executable by one or more processors. As such, it should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components may be utilized to implement the invention. For example, “controllers” described in the specification can include one or more processors, one or more memory modules including non-transitory computer-readable medium, one or more user interfaces, and various connectors connecting the components. 
         [0020]      FIG. 1  is a sectional view of an exemplary conveyor oven  100 . In the illustrated embodiment, the controller  110  is located in a control cabinet  115  adjacent to an oven compartment  120 . The controller  110  and various electrical components are mounted to a frame  125  on an interior portion of the control cabinet  115 . The frame  125  is connected to an insulated panel  130 , which separates the oven compartment  120  from the control cabinet  115 . The controller  110  is electrically connected to components within the control cabinet  115 . The components may include, for example, circuit breakers, fuses, transformers, cooling fans, manual switches, and conveyor controls. A user interface  135  is connected to the controller  110 . The oven compartment  120  includes a conveyor  140  that transports items through the conveyor oven  100 . 
         [0021]    One embodiment of the conveyor oven  100  is illustrated in  FIG. 2 . The controller  110  includes a processor  215 , a memory  220 , a relay driver  225 , and a user interface  235 . The processor  215  is electrically connected to a number of modules or components of the controller  210 . For example, the processor  215  is connected to the memory  220 , the user interface  235 , and the relay driver  225 . The controller  110  includes combinations of hardware and software that are operable to control the operation of the conveyor oven  100 . In addition, the controller  110  includes a plurality of electrical and electronic components that provide power, operational control, and protection to the components and modules within the controller  110  and/or within the control cabinet  115 . 
         [0022]    The user interface  235  may include a graphical user interface or other input/output device that enables an operator to control and configure the controller  110  and that enables the controller  110  to present an output to the user. The user interface  235  may be located externally to the controller  110  or be integrated with the controller  110 . For example, the user interface  235  may be mounted on an exterior surface of the control cabinet  115  for ease of access by an operator. The user interface  235  allows an operator to adjust the temperature setting of each individual heating zone and to set the conveyor speed. Temperature setpoints and conveyor speed setpoints may be programmed and saved as multiple presets. Presets allow an operator to recall the temperature setpoints and conveyor speed setpoints with a single button on the user interface  235 . The user interface  235  displays messages to the operator including, for example, an active preset, a time and date, and error messages. 
         [0023]    The memory  220  includes, for example, a program storage area and a data storage area. The memory  220  can include combinations of different types of memory or computer readable medium, such as read-only memory (“ROM”) and non-volatile random access memory (“RAM”). The processor  215  is connected to the memory  220  and executes instructions stored therein. Instructions stored in the memory  220  and executed by the controller  110  may include, for example, firmware, one or more applications, filters, rules, one or more program modules, and other executable instructions. The controller  110  is configured to retrieve from memory and execute, among other things, instructions related to the control processes and methods described herein. For example, the controller  110  executes the methods illustrated in  FIGS. 7 and 8  when one or more thermocouples measure a temperature in the conveyor oven  100  that is less than the temperature setpoint of the oven compartment  120 . In other constructions, the controller  110  includes additional, fewer, or different components. 
         [0024]      FIG. 3  illustrates a single-phase, four-heating-element embodiment of the conveyor oven  100  of  FIG. 1 . A power supply  300  provides current to heating elements  305  and to a controller  310 . The controller  310  includes the components of the controller  110 . The power supply  300  includes an L1 line  315  and an L2 line  316 . The current to the heating elements  305  is actuated by relays  320 . The relays  320  include a first relay  325 , a second relay  330 , a third relay  335 , and a fourth relay  340 . The L1 line  315  connects to an input of the first relay  325  and an input of the second relay  330 . The L2 line  316  connects to an input of the third relay  335  and an input of the fourth relay  340 . An output of the first relay  325  connects to a first terminal  349  of the zone 1 heating element  350 . A second terminal  351  of the zone 1 heating element  350  connects to the L2 line  316 . Similarly, the second relay  330  connects to a first terminal  354  of the zone 2 heating element  355 , and a second terminal  356  of the zone 2 heating element  355  connects to the L2 line  316 . An output of the third relay  335  connects to a first terminal  359  of the zone 3 heating element  360 , and a second terminal  361  of the zone 3 heating element  360  connects to L1 line  315 . Similarly, an output of the fourth relay  340  connects to a first terminal  364  of the zone 4 heating element  365 , and a second terminal  366  of the zone 4 heating element  365  connects to L1 line  315 . The relays  320  may be solid-state relays. Alternatively, the relays  320  may be mechanical relays (e.g., contactors) or alternative forms of automated switches. It should be noted that the zone 1 heating element  350 , the zone 2 heating element  355 , the zone 3 heating element  360 , and the zone 4 heating element  365  are collectively referred to as heating elements  305 . The heating elements  305  may be grouped in the conveyor oven  100  in configurations other than in zones as described herein. In addition, the heating elements  305  may be infrared or resistive heating elements and may include multiple bulbs or coils controlled by a single relay. 
         [0025]    The conveyor oven  100  is configured to operate with either single-phase power or three-phase power in a single-phase configuration or a three-phase configuration. When connected to single-phase power, all of the heating elements  305  and the relays  320  are connected between the line  315  and the line  316 . When connected to three-phase power and configured to operate in single-phase, two phases of the three-phase power are used to supply power to the heating elements  305 . When connected to three-phase power and configured to operate with three-phase power, the heating elements  305  are connected between the different phases of the three-phase power. Thus, a load evenly balanced between phases may be achieved with a conveyor oven  100  that operates on three-phase power with a multiple of three heating elements  305 . 
         [0026]      FIG. 4  is a circuit diagram that illustrates a three-phase, four-heating-element embodiment of the conveyor oven  100 . A three-phase power supply  400  is connected by three power lines, an L1 line  415  (a first phase), an L2 line  416  (a second phase), and an L3 line  417  (a third phase) to the conveyor oven  100 . The L1 line  415  connects to an input of a first relay  425  and to an input of a second relay  430 . An output of the first relay  425  is connected to a first terminal  449  of a zone 1 heating element  450 . A second terminal  451  of the zone 1 heating element  450  is connected to the L2 line  416 . An output of the second relay  430  is connected to a first terminal  454  of a zone 2 heating element  455 , and the second terminal  456  of the zone 2 heating element  455  is connected to an L3 line  417 . The L2 line  416  is connected to an input of a third relay  435  and to an input of a fourth relay  440 . An output of the third relay  435  is connected to a first terminal  459  of a zone 3 heating element  460 , and a second terminal  461  of the zone 3 heating element  460  is connected to the L3 line  417 . Similarly, an output of the fourth relay  440  is connected to a first terminal  464  of a zone 4 heating element  465 , and a second terminal  466  of the zone 4 heating element  465  is connected to the L3 line  417 . 
         [0027]    In the embodiment of  FIG. 4 , the controller  410  includes the components of the controller  110 . The controller  410  is connected to relays  420  at each of the respective control inputs of the relays  420 . Even though the zone 4 heating element  465  and the fourth relay  440  are illustrated across the L2 line  416  and the L3 line  416 , the zone 4 heating element  465  and the fourth relay  440  may positioned across any two of the three phases. Since the zone 4 heating element  465  and the fourth relay  440  are located parallel to the zone 3 heating element  460  and are positioned across the L2 line  416  and the L3 line  417 , removing the zone 4 heating element  465  may provide an evenly distributed load. Alternatively, additional heating elements and associated relays may be added to the design without departing from the scope of the invention. 
         [0028]      FIG. 5  is a circuit diagram that illustrates a single-phase, three-heating-element embodiment of the conveyor oven  100 . In this embodiment, heating elements  505  include a zone 1 heating element  550 , a zone 2 heating element  555 , and a zone 3 heating element  560 . A two-phase power supply  500  is connected to an L1 line  515  and an L2 line  516 . The L1 line  416  is connected to the relays  520 . The relays  520  include a first relay  525 , a second relay  530 , and a third relay  535 . An output of the first relay  525  is connected to a first terminal  549  of the zone 1 heating element  550 , and a second terminal  551  of the zone 1 heating element  550  is connected to the L2 line  516 . An output of the second relay  530  is connected to a first terminal  554  of the zone 2 heating element  555 , and a second terminal  556  of the zone 2 heating element  555  is connected to the L2 line  516 . Similarly, an output of the third relay  535  is connected to a first terminal  559  of the zone 3 heating element  560 , and a second terminal  561  of the zone 3 heating element  560  is connected to the L2 line  516 . The L2 line  516  provides a neutral or ground connection to the heating elements  505 . A controller  510  is connected to a control input of the relays  520 . As in the other embodiments, the controller  510  may include the components of the controller  110 . The controller  510  actuates the relays  520  to reduce current draw in the L1 line  515 . 
         [0029]      FIG. 6  is a circuit diagram that illustrates a three-phase, three-heating element embodiment of the conveyor oven  100 . A power supply  600  provides three-phase power including an L1 line  615 , an L2 line  616 , and an L3 line  617 . The L1 line  615  is connected to an input of a first relay  625  and also a second terminal  661  of a zone 3 heating element  660 . An output of the first relay  625  is connected to a first terminal  649  of a zone 1 heating element  650 . A second terminal  651  of the zone 1 heating element  650  is connected to the L2 line  616 . The L2 line  616  is also connected to an input of a second relay  630 . An output of the second relay  630  is connected to a first terminal  654  of a zone 2 heating element  655 , and a second terminal  656  of the zone 2 heating element  655  is connected to the L3 line  617 . The L3 line  617  is also connected to an input of a third relay  635 . An output of the third relay  635  is connected to a first terminal  659  of the zone 3 heating element  660 . Relays  620  include the first relay  625 , the second relay  630 , the third relay  635 , and the fourth relay  640 . Similarly, heating elements  605  include the zone 1 heating element  650 , the zone 2 heating element  655 , and the zone 3 heating element  660 . A controller  610  may include the components of the controller  110 , and the controller  610  is connected to a control input of each of relays  620 . As illustrated, the heating elements  605  are connected in a delta-load configuration. However, in other embodiments, the heating elements  605  may be connected in a Y-load configuration. 
         [0030]    For the embodiments of the conveyor oven  100  illustrated in  FIGS. 3 and 4 , the respective controller  310 ,  410  performs a method  700 , as illustrated in  FIG. 7 . The method  700  reduces the total current draw of the heating elements  305 ,  405  during peak-loads (e.g., cold startup) of the conveyor oven  100 . The method  700  is performed for embodiments of the conveyor oven  100  with four heating elements  305 ,  405  and four relays  320 ,  420 . For purposes of illustration and discussion, the component numbering in the method  700  corresponds to the embodiment as illustrated in  FIG. 3 . However, the method  700  is also performed by the controller  410  in the embodiment of  FIG. 4 . The controller  310  performs the method  700  as described below. 
         [0031]    The controller  310  actuates the second relay  330 , the third relay  335 , and the fourth relay  340  to energize the zone 2 heating element  355 , the zone 3 heating element  360 , and the zone 4 heating element  365  for a first period of time (e.g., 1 second) (step 705). The zone 1 heating element  350  is de-energized during this step. After the first period of time, the controller  310  actuates the second relay  330  to de-energize the zone 2 heating element  355  for a second period of time (e.g., 20 ms) (step  710 ). After the second period of time, the controller  310  actuates the first relay  325  to energize the zone 1 heating element  350  (step  715 ). After a third period of time, the controller  310  actuates the third relay  335  to de-energize the zone 3 heating element  360  for a fourth period of time (step  720 ). Next, the controller  310  actuates the second relay  330  to energize the zone 2 heating element for a fifth period of time (step  725 ). After the fifth period of time, the controller  310  actuates the fourth relay  340  to de-energize the zone 4 heating element  365  for a sixth period of time (step  730 ). The controller  310  actuates the third relay  335  to energize the zone 3 heating element  360  for a seventh period of time (step  735 ). The controller  310  actuates the first relay  325  to de-energize the zone 1 heating element  350  for an eighth period of time (step  740 ). After the eighth period of time, the controller  310  actuates the fourth relay  340  to energize the zone 4 heating element  365  (step  745 ). Once the fourth relay  340  is actuated, the position of the relays  320  corresponds to a state that is the same as in step  705 . If the desired temperature has not been reached, the method  700  then repeats steps  710 - 745  until the desire temperature has been met (step  750 ). Step  750  is illustrated at the end of one heating cycle. However, step  750  may be performed at any point during the cycle. Once the controller  310  receives a signal indicative of adequate temperature in the conveyor oven  100 , the controller  310  may immediately halt the method  700 , may halt the method  700  after step  750 , or halt the method  700  after a preprogrammed time delay. 
         [0032]    In the method  700 , the first, third, fifth, and seventh periods of time may be set to the same predetermined value. Similarly, the second, fourth, sixth, and eighth periods of time may also be set to an equal value. The first, third, fifth, and seventh periods of time correspond to the time when three of the heating elements  305  are energized. The second, fourth, sixth, and eighth periods of time correspond to the time when the controller  310  is actively switching the relays  320 . Accordingly, the second, fourth, sixth, and eighth periods of time are set to a shorter period of time (e.g., one-tenth) than that of the first, third, fifth, and seventh periods of time. The second, fourth, sixth, and eighth periods of time ensure that the heating elements  305  are not energized simultaneously. 
         [0033]    For the embodiments of the conveyor oven  100  illustrated in  FIGS. 5 and 6 , the respective controller  510 ,  610  performs a method  800 , as illustrated in  FIG. 8 . The method  800  is performed on the embodiments of the conveyor oven  100  with three heating elements  505 ,  605 . As in the method  700 , the method  800  is used for both single-phase and three-phase power configurations. For purposes of illustration and description, the method  800  is described in reference to  FIG. 5 . However, the method  800  is also performed for the embodiment illustrated in  FIG. 6 . 
         [0034]    The controller  510  actuates the second relay  530  and the third relay  535  to energize the zone 2 heating element  555  and the zone 3 heating element  560  (step  805 ). The first relay  525  remains open. After a first period of time (e.g., 1 second), the controller  510  actuates the second relay  530  to de-energize the zone 2 heating element  555  (step  810 ). At step  810 , the zone 3 heating element  560  is the only heating element  550 ,  555 ,  560  that is energized. After a second period of time (e.g., 20 ms), the controller  510  actuates the first relay  525  to energize the zone 1 heating element  550  (step  815 ). After a third period of time, the controller  310  actuates the third relay  535  to de-energize the zone 3 heating element  560  (step  820 ). After a fourth period of time, the controller  510  actuates the second relay  530  to energize the zone 2 heating element  555  (step  825 ). After a fifth period of time, the controller  510  actuates the first relay  525  to de-energize the zone 1 heating element  550  (step  830 ). After a sixth period of time, the controller  510  actuates the third relay  535  to energize the zone 3 heating element  560  (step  835 ). After the third relay  535  closes, the position of the relays  520  is identical to step  805 , and the method  800  repeats if the conveyor oven  100  is still requesting heat (step  840 ). The controller  510  cycles through the steps  810  through  835  until the call for heat of the conveyor oven  100  is finished. Step  840  is illustrated at the end of one heating cycle. However, step  840  may be performed at any point during the cycle. Once the controller  510  receives a signal indicative of adequate temperature in the conveyor oven  100 , the controller  510  may immediately halt the method  800 , may halt the method  800  at step  840 , or halt the method  800  after a preprogrammed time delay. 
         [0035]      FIG. 9  is a graph  900  illustrating the energization state of the heating elements  305  for the method  700 . The graph  900  includes an x-axis  905  corresponding to time and a y-axis  910  corresponding to a number representing each of the heating elements  305 . For each of the heating elements  305 , an energized or de-energized state is charted over time. The zone 1 heating element  350  is represented by line  915 , the zone 2 heating element  355  is represented by line  920 , the zone 3 heating element  360  is represented by line  925 , and the zone 4 heating element  360  is represented by line  930 . Each line  915 ,  920 ,  925 , and  930  is labeled with a respective zone number. When each line  915 ,  920 ,  925 , and  930  is in an upper position, each corresponding heating element  350 ,  355 ,  360 , and  365  is energized. When each line  915 ,  920 ,  925 , and  930  is in a lower position, each corresponding heating element  350 ,  355 ,  360 , and  365  is de-energized. The graph  900  illustrates how the energization state of each of the heating elements  350 ,  355 ,  360 , and  365  relate to each other. The graph  900  illustrates one and one-half cycles, and the pattern illustrated by the graph  900  repeats as the method  700  repeats. 
         [0036]    As illustrated by each previously described method  700 ,  800 , the controller  310 ,  410  actuates the relays  320 ,  420  to limit the maximum time that each of the heating elements  305 ,  405  are energized. In  FIG. 9 , each of the heating elements  305  is energized in a duty cycle of 70% on and 30% off. The on/off cycles are distributed in time by the controller  310  to ensure that at most three of the heating elements  305  are energized at any given time and that at least two heating elements of the heating elements  305  are energized at any given time. This cycling reduces average current draw by each of the heating elements  305 . For example, the zone 1 heating element  350  is energized for 70% of a cycle. Therefore, 70% of the time the zone 1 heating element  350  draws full current while 30% of the time the zone 1 heating element  350  draws no current. This achieves an average current draw and power usage for each of the heating elements  305  less than the maximum current draw available. 
         [0037]    It should be noted that the controller  310 ,  410 ,  510 , and  610  is adjustable to modify the duty cycles. In a four-heating-element configuration, as shown in  FIGS. 3 and 4 , the controller  310 ,  410  actuates each of the relays  320 ,  420  at less than three-fourths of continuous operation. The controller  310 ,  410  can alter the duty cycle to range between one-half and three-fourths of a full cycle. Ideally, the controller  310 ,  410  will set the duty cycle near to the three-fourths duty cycle (e.g., 70% duty cycle). At this duty cycle, not all of the heating elements  305 ,  405  will be active at any given time. A 70% duty cycle ensures a margin of safety corresponding to the second, fourth, sixth, and eighth times in the method  700 . The margin of safety ensures that the total current draw of the conveyor oven  100  is less than its potential continuous amperage draw during peak-times of the conveyor oven  100 . At no point in time are four of the heating elements  305 ,  405  energized. 
         [0038]    In a three-heating element configuration, as shown in  FIGS. 5 and 6 , the controller  510 ,  610  actuates the relays  520 ,  620  such that energization of the heating elements  505 ,  605  gives a maximum current draw of two-thirds continuous operation. Generally, the controller  510 , 610  actuates each of the relays  520 ,  620  at less than two-thirds of continuous operation to allow each of the relays  520 ,  620  time to actuate. The duty cycles for each of the heating elements  505 ,  605  are adjustable from a range of two-thirds to one-third of continuous operation. At a two-thirds duty cycle, two of the heating elements  505 ,  605  are energized while one of the heating elements  505 ,  605  is de-energized. At a one-third duty cycle, one of the heating elements  505 ,  605  is energized while the other two heating elements  505 ,  605  are de-energized. Ideally, the controller  510 ,  610  actuates the heating elements  505 ,  605  closer to the two-thirds duty cycle (e.g., 60% duty cycle) with a margin of safety to ensure that at no point in time are three of the heating elements  505 ,  605  energized at the same time. This ensures that the average current draw will be, at maximum, two-thirds of the continuous current draw. 
         [0039]    Thus, embodiments of the invention provide, among other things, a conveyor oven and a method for controlling the conveyor oven such that the current draw to the heating elements is reduced during peak-loads. Various features and advantages of the invention are set forth in the following claims.