Design a single-phase induction motor by moving sliders.
One phase makes a field that only pulses, so at rest there is no torque at all — and everything interesting about this machine is the second winding that gets it moving. Set the output and the starting method, and the main winding, the starting winding, the capacitor and the performance are worked out live.
This is an interactive design studio and needs JavaScript to run. Here is what it does.
Two windings, and the one that matters
A three-phase motor starts itself, so its textbook chapter never discusses starting. A single-phase motor has no starting torque whatever, so its chapter is mostly about the auxiliary winding that provides it — capacitor-start, capacitor-start capacitor-run, split-phase resistance start, or a shaded pole.
The studio treats that as the subject rather than an appendix. The readings carry a whole group for starting: the turns ratio, the starting winding’s turns, wire gauge and resistance, the capacitor and its reactance, the voltage the capacitor must stand, the phase split, the starting current and torque with their ratios, and the torque the running winding alone gives at the moment the centrifugal switch drops the starting winding out.
The field you can watch pulsing
The 3D view draws the real thing: B(φ,t) = B̂·cos(p(φ−φ_axis))·cos(ωt) — a standing wave whose poles never move, swelling, vanishing and returning reversed. It genuinely goes to nothing at the zero crossing rather than leaving a faint ring, because that vanishing is the whole reason the machine cannot start itself.
A toggle splits it into the two counter-rotating half-amplitude fields whose sum it is. The legend says in words that this is a decomposition and not extra fields, and spells out the consequence: equal and opposite at standstill, so no starting torque; nudge it forward and the forward field wins.
Method
Closed-form classical design after A. K. Sawhney, A Course in Electrical Machine Design, Chapter 11, pinned in CI against the chapter’s worked Design Problem. That example contains ten arithmetic and typesetting errors, including one in Veinott’s own column; each is pinned twice — what the page prints and what the page’s own inputs give — so nobody later "fixes" the engine to match a typo. Results are analytical, not finite-element.
Common questions
Why does a single-phase induction motor not start on its own?
A single winding on one phase makes a field that pulses in place instead of rotating: it swells, dies to nothing and returns reversed, twice per cycle, with its poles never moving (Art 11.2). By the double-revolving-field theorem that standing wave is the sum of two counter-rotating fields of half the amplitude, and at standstill they are exactly equal and opposite — so the net torque is zero. Nudge the rotor and the field turning with it wins, which is why the whole of the chapter is about the second winding.
How is the starting capacitor of a single-phase motor sized?
The capacitor has to put the starting winding’s current far enough out of phase with the main winding’s to make a rotating field. The studio works out the turns ratio, the starting winding’s turns, wire and resistance, the capacitance and its reactance, the phase split it achieves against the book’s expected band, and the starting torque and current with their ratios to full load.
Why must the capacitor be rated above the mains voltage?
Because the capacitor and the starting winding form a series circuit that part-resonates, the voltage across the capacitor at starting is routinely higher than the supply (Sawhney p. 710). A capacitor bought for line voltage fails in service. The studio states the voltage the capacitor must actually stand as a figure in its own right, not a note.
How is the performance of a single-phase motor calculated?
Not from a circle diagram — from Veinott’s 38-step method (§11.15.2), repeated at each speed. The studio plots the speed–torque curve by calling the same function the engine uses for the full-load figures at 120 speeds, so the curve and the full-load row cannot disagree. That curve correctly starts at zero torque, because it is the running winding alone.
What about a shaded-pole motor?
Shaded pole is offered and says plainly what the book does: Art 11.7 describes the construction without giving winding equations. So the design stops after the main dimensions, the air gap lg = 0.007·D/√p and the flux, Table 11.1’s expectations are shown for orientation, and nothing is invented to fill the gap.
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