ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Hi- the flame circuit needs to read a ground path through the flame-which is flame rectification. this is a mA circuit that, when not present whether because of a poor ground or a dirty sensor, will present itself exactly as you describe-3 tries and a lockout. this sensor usually resembles a spark igniter electrode and is at the opposite end of the burner assy. from the igniter. While the unit is on the grid, you could disconnect this sensor and see the same behavior. That being said, there must be something about the gen-sine. Perhaps a small ups/conditioner would do upstream from the control board, so it wouldn't need to be sized for the fan motor. Have you checked the frequency of genset output?

"High speed" {sub-cycle} voltage changes cannot reliably be measured with a voltmeter. That's what oscilloscopes and related power-quality instruments [and consequent bird-dogging] are for.

I suspect that a ferroresonant transformer will have a faster response time than a furnace and should resolve the problem. The advantage over a UPS is that the transformer doesn't need the maintenance of that a battery requires.

<< A ferroresonant transformer, also called a constant voltage transformer, will give a constant AC voltage output when the input voltage varies within the rated input voltage range. Typical response for output regulation is plus or minus 3% for input voltage swings that are within the rating of the transformer. Typical response times are 8 millseconds for a 5% line or load variation, and 16 milliseconds for a 10% variation. Generated harmonic distortion will be less than 3%. >>
http://www.powerqualityanddrives.com/sag_correction_without_ups/