Direct ignition system for gas appliance with dc power source

Abstract

An ignition system for use with a source of dc (or full-wave-rectified) power without the need for an inverter includes a flame sensing relay and a checking relay interlocked to achieve lockout if the proper starting sequence or timing are not met or if a flame-out occurs during operation. The checking relay is energized in response to a call-for-heat signal to isolate the flame detection circuitry from its source and commence a trial-for-ignition period in the flame detection circuitry which includes a timing circuit. The timing circuit actuates the flame-sensing relay during the trial-for-ignition period. The flame sensing relay energizes the fuel valve and a spark generator to ignite the fuel. If a flame is detected during the trial-for-ignition period by a flame probe, the timing circuit is disabled and operation continues until the call for heat is terminated as long as the flame is sensed. Another circuit senses flame at the spark gap and disables the spark gap generator after a flame is established. If a flame-out or fuel interruption occurs, the spark generator is re-energized, and the timing circuit is enabled to commence a re-ignition timing period, after which the flame relay is disabled and the system is locked out if ignition is not proved. Once locked out, the system can be re-started only by cycling the thermostat or a remote switch. A minimum re-cycle time is defined by a charging circuit connected to the timing circuit when either switch is re-cycled.