Hi all, I have a 1 HP capacitor start motor (old, c.1950) that runs an air compressor in my little workshop. When it's running, the lights in the shop and the whole house dim and brighten rhythmically, at about 5 Hz. This, of course, is related to the compression cycles of the compressor, but how is such a low power appliance having such an effect on the line voltage? I have researched power factors and realise that the old motor is likely to have a low one, but I have two questions: 1. Is the brightness of the house lights oscillating between normal and low, or becoming brighter than normal then dimmer, oscillating about the normal? 2. Would inserting a capacitor in series with the run windings help, or is this too simplistic? Our house supply is UK standard, i.e. 230V AC 50Hz.