Electric resistance heating devices – Heating devices – Convection space heater
Reexamination Certificate
1998-02-13
2001-05-15
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Convection space heater
C219S477000
Reexamination Certificate
active
06233397
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electric heaters, and more particularly relates to an heater with automatic switching of series and parallel heating element connections capable of operating at a first power rating and a second power rating.
BACKGROUND AND DESCRIPTION OF THE PRIOR ART
Portable electric heaters must presently be limited to an electrical capacity of 1500 watts. This limit for continuous operation is set to reduce the risk of fire associated with continuous use heating devices operating at capacities beyond this power rating. This limit is also enforced by product certification laboratories such as Underwriters Laboratories.
However, in an enclosed space to be heated, the operation of a heater at 1500 watts or less results in extended heating times. Therefore, there is a need for an electric heater which operates at a higher power rating during the initial heating cycle when the space is at its coldest and then operates at a lower power rating for the remaining continuous heating operation.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electric heater which will rapidly heat a given space without increasing the risk of fire.
It is another object of the present invention to provide a two-stage electric heater which operates at an initial high power level at the beginning of a heater cycle, then automatically drops to a lower power level for continuous operation.
In accordance with one form of the present invention, a heater is formed having two resistive heater elements and an automatic switching device. The switching device initially selects the heater elements to provide a first, reduced resistance for the initial a predetermined operating time of the heater, then selects a higher resistance for the remaining continuous operation of the heater.
In accordance with another form of the present invention, a heater is formed with a first resistive heating element and a second resistive heating element connected to form a series circuit. The heater further includes a thermally responsive switch coupled across the second resistive heating element. The thermally responsive switch initially presents a short circuit across the second resistive heating element, thereby reducing the total resistance of the series circuit. Upon detection of a predetermined temperature, the thermally responsive switch opens, thereby increasing the resistance of the series circuit. In the presence of a substantially constant voltage applied to the series circuit, the operation of the switch results in a first operating power and a second, lower operating power. In accordance with a preferred embodiment of the present invention, the thermally responsive switch latches after the predetermined temperature is reached and remains latched until the voltage is removed.
In accordance with another form of the present invention, a heater is formed with a first resistive heating element and a second resistive heating element connected to form a series circuit. The heater further includes an electrically controllable switch coupled across the second resistive heating element. The electrically controllable switch initially presents a short circuit across the second resistive heating element, thereby reducing the total resistance of the series circuit. Upon receipt of a control signal, the electrically controllable switch opens, thereby increasing the resistance of the series circuit. The heater includes a timer circuit which generates the control signal upon initial detection of a voltage applied to the series circuit. In the presence of a substantially constant voltage applied to the series circuit, the operation of the switch results in a first operating power for an initial time period and a second, lower operating power for the remaining time of operation.
In accordance with yet another form of the present invention, a heater is formed with a first resistive heating element and a second resistive heating element connected to form a parallel circuit. The heater further includes a thermally responsive switch coupled in series with the second resistive heating element. The thermally responsive switch initially presents a short circuit, thereby reducing the total resistance of the parallel circuit. Upon detection of a predetermined temperature, the thermally responsive switch opens, thereby increasing the resistance of the parallel circuit. In the presence of a substantially constant voltage applied to the parallel circuit, the operation of the switch results in a first operating power and a second, lower operating power. In accordance with a preferred embodiment of the present invention, the thermally responsive switch latches after the predetermined temperature is reached and remains latched until the voltage is removed.
In accordance with yet another form of the present invention, a heater is formed with a first resistive heating element and a second resistive heating element connected to form a parallel circuit. The heater further includes an electrically controllable switch coupled in series with the second resistive heating element. The electrically controllable switch initially presents a short circuit, thereby reducing the total resistance of the parallel circuit. Upon receipt of a control signal, the electrically controllable switch opens, thereby increasing the resistance of the parallel circuit. The heater includes a timer circuit which generates the control signal upon initial detection of a voltage applied to the parallel circuit. In the presence of a substantially constant voltage applied to the parallel circuit, the operation of the switch results in a first operating power for an initial time period and a second, lower operating power for the remaining time of operation.
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Hoffmann & Baron , LLP
Marino Francis E.
Robinson Daniel
The Holmes Group, Inc.
Walberg Teresa
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