Originally Posted by VinceU
Most regulators will allow no more than 10% droop usually less. Swing is caused by a defective regulator, also called hunting.
Have measured the sag of a dual Inverter setup It does take time to go from idle current of 2 to 5 amps of fan load to 20 amps of AC Compressor load? Faulty regulator aside the engine has to speed up to match the voltage required to meet the load on the output.