Electric heating – Heating devices – With protective means for heater
Reexamination Certificate
2002-03-05
2003-11-11
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
With protective means for heater
C219S497000, C219S505000, C392S449000
Reexamination Certificate
active
06646237
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control circuit for an electric water heater, and more particularly to a safety control circuit for electric water heater to detect the dry heating of an electric water heater at ceasing of water supply.
2. Description of the Prior Art
Water heaters are common used home appliances and can be generally divided into two types, namely, gas-fired water heaters and electric water heaters. The electric water heaters are convenient, safe, ready for use and are therefore widely adopted. For a place at where a large volume of hot water is to be supplied, a thermal storage type of electric water heater is normally adopted.
The electric water heater usually includes a heating element made of nickel-chrome wire which is continuously heated whenever power supply to the water heater is maintained , even if water supply to the water heater is terminated. Thus, the electric water heater is subjected to damage that may cause a fire.
The currently commercially available electric water heaters have many shortcomings. They generally lacks good safety designs. For example, the control circuits in some of the commercially available electric water heaters include a mechanical or an electronic timer to control on and off of the electric water heaters at preset time. However, these mechanical or electronic timers are unable to detect whether a water heater that is under drying heating without water supply.
Moreover, the control switch of commercial water heater cannot provide overcurrent protection. In case of overcurrent, the electric water heaters will be damaged and it easily causes fire.
Furthermore, the control circuits do not include the delay power-on function. When the power supply is recovered from a power failure, the electric water heaters and other indoor electric appliances are re-started and powered on almost at the same time to possibly cause an instantaneous overcurrent that would result in tripped breakers.
Also, the control circuits have a switch that is turned on or off as soon as the power is supplied or cut off respectively, and it will generate surge current at the switch which will reduce its shelf life thereof.
It is therefore desirable to develop a control circuit for the electric water heater to provide multiple safety protections thereof.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a safety control circuit for electric water heater, which can detect whether the water heater is at a state of dry heating without water supply while power supply is still maintained, and which can automatically cut off power supply to the water heater when dry heating is detected.
Another object of the present invention is to provide a control circuit for electric water heater adapted to automatically power off the electric water heater when its circuit or element is damaged and results in an abnormal overcurrent.
A further object of the present invention is to provide a control circuit for electric water heater, which can provide time-control to reduce power consumption of the electric water heater.
A still further object of the present invention is to provide a control circuit for electric water heater enabling delay power-on of the electric water heater, so that power may be supplied to the electric water heater at a delayed time after a power failure.
A still further object of the present invention is to provide a control circuit for electric water heater enabling elimination of surge current at on and off of a switch of the electric water heater, so that the shelf life of switch may be prolonged at reduced frequency of maintenance.
REFERENCES:
patent: 4523084 (1985-06-01), Tamura et al.
patent: 5552998 (1996-09-01), Datta
patent: 6080973 (2000-06-01), Thweatt, Jr.
patent: 2-203152 (1990-08-01), None
patent: 9-178265 (1997-07-01), None
Jeffery John A.
Rosenberg , Klein & Lee
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