Portable spa monitoring and control circuitry

摘要

Control circuitry for controlling a spa water heater, wherein a microcontroller is configured to detect zero crossings of an A.C. line voltage from a voltage sense signal, to cause closing of a first heater relay and a second heater relay, to detect the time at which heater current is initially sensed by a current sensor after the initial closing of the second heater relay, to measure a time delay between the time that the second heater relay is closed and the time at which heater current is initially sensed, and to adjust the time at which a second closing of the second heater relay occurs such that zero crossings of the heater current occur at the same time as zero crossings of the voltage waveform. The control circuitry further includes a voltage sense circuit comprising a first diode connected in series with a current limiting resistance connected in series with a Zener diode, which is in turn connected in series with an optical coupler LED.

主权项

1. Control circuitry for controlling a spa heater comprising:
first and second heater relays closeable to supply current to said heater; a current sensor for sensing heater current and generating a current sense signal; a voltage sensor for generating a voltage sense signal; and a microcontroller supplied with the current sense and voltage sense signals and configured to:
(a) detect zero crossings of a voltage waveform from the voltage sense signal;(b) cause a first closing of the first heater relay;(c) cause a first closing of the second heater relay;(d) measure a time delay TD where TD is the time delay between the time that the second heater relay is closed and a time at which heater current is initially sensed by the current sensor after the first closing of the second heater relay; and(e) employ the measured time delay TD to adjust the time at which a subsequent closing of the second heater relay is caused to occur so that a zero crossing of the heater current occurs closer in time to a zero crossing of the voltage waveform.