Pulsed power-based dry fire protection for electric water heaters

摘要

A water heater having an electric heating element therein is provided with apparatus for preventing dry firing of the heating element. The apparatus is operative to (1) power the heating element with electrical test pulses having first predetermined durations and being separated by rest periods of second predetermined durations during which the heating element is depowered, (2) determine the average electrical current flow through the element during each of the test pulses, and (3) preclude energization of the heating element if the average current flow therethrough during an electrical test pulse subsequent to the first test pulse is less by a predetermined magnitude than the average electrical current flow through the heating element during the first electrical test pulse.

主权项

1. Liquid heating apparatus comprising:
a tank for storing liquid to be heated; an electric heating element extending through the tank interior and being energizable to heat tank liquid within which it is immersed; an AC electrical power circuit coupled to said electric heating element and operative to energize it; and an electrical dry fire protection circuit coupled to said AC electrical power circuit and operative to:
utilize AC power from said AC electrical power circuit to power said electric heating element with a plurality of electrical test pulses having first predetermined durations and being separated by rest periods of second predetermined durations during which said electric heating element is depowered;determine an average of a representative value corresponding to an electrical current flow through said electric heating element during each of said plurality of electrical test pulses; andpreclude the operative energization of said electric heating element if the average of the representative value corresponding to the electrical current flow through said electric heating element during an electrical test pulse subsequent to the first electrical test pulse is less by a predetermined amount than the average of the representative value corresponding to the electrical current flow through said electrical heating element during said first electrical test pulse.