Ek's Home   |   Forum   |   Chat   |   Electrical Links   |
	Subject - How does I lag V in a split-phase motor? DanoChunk hello all, I am writing a technical report on split-phase motors for school and have been reading up on them very much. I only have one problem, when ever they are explaining how the motor does start, they always say that the initial push is created by the start and run windings being 90 electrical degrees apart. They always refer to this as being current lags voltage. I was wondering if somebody could explain to me or direct me to a website where they explain how this happens. What I was taught was that current happens when voltage is induced, then how can it lag? thank you for your time! DANO JimmyDee I'll take a try at it. To get starting torque for a motor, you need a rotating magnetic field. With a 3 phase motor, it is a smooth rotating field produced by 3 sets of poles that are 120° apart from each other. In any single phase motor, we don't have this situation but we can create a rotating field with 2 sets of poles. The trick is to get one of these poles to rise and fall 90° apart from each other. By putting a capacitor in series with the starting winding, that will delay the energizing of the start winding by 90°. We can achieve this same but opposite current shift by doing the same trick but running through an inductor instead of a capacitor. I'm not sure how technically correct this is with a split phase but it is close. Jim blackrd the starting winding contains few turns of small wore. The run winding contains a larger number of turns of large size wire. Few turns mean reduced inductive reactance, larger wire and more turns and inductive reactance is higher comparatively higher. Inductive reactance is kind of like the abiliity to take a soaking of current, to initially resist and then become charged while voltage remains constant. This current lagging voltage is the inductive reactance of a given piece of electrical equipment (a motor). A split phase motor splits a phase to what appears to be two phase current.the start winding is in series with a switch that opens when the motor hits 75% speed. A cap start motor is a type of split phase motor with a cap in series with the start winding.(Taken from Industrial Electricity, 3rd Edition Adams/Rockmaker.I hope all that was correct.