The Single-Phase Motor/Generator

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The Real Story:

OK, I'll be honest, I only built a model single-phase motor/generator because I didn't know what the hell I was doing and screwed up my first attempt at building a model three-phase motor/generator. From my junior encyclopedia understanding of such things, it seemed you could match the armature frame coils with rotor magnets placed at 60 degree intervals around the rotor disc and wire up a three phase machine. Nope! At least I couldn't make it work. (I could get voltage from neutral across all three phases, but only voltage across two of the phase pairs, regardless of how I tried to wire things up for three-phase use.) None the less, it makes a nice single-phase machine. And, I know a bit more of such things now.

Motor/Generator Assembly:

The single-phase motor/generator armature consists of six 250 turn coils of 24 AWG magnet wire mounted in notches made every 60 degrees along the edge of a circular hole cut into a wooden armature frame. Each coil was wound on a piece of 1/4" polystyrene tube which was left inside the coil. The coils are mounted with 6-32 machine screws which pass through their polystyrene center tubes and extend through the armature frame. A wing nut on each screw clamps the coils in place. A metal washer with inner hole ID small enough so that it rests on the end of the polystyrene tube in the coil center hole was placed on both ends of each coil. A square washer cut from 0.010" polystyrene sheet was placed between the metal washer and the end of each coil from which the coils' leads extend, (the metal washer closest to the armature frame), to protect the coil lead insulation. "U" pieces cut from 0.04" polystyrene sheet were placed between the armature frame and the washer closest to the frame to adjust each coil's spacing from the rotor.

The rotor is a wooden disc with shallow holes drilled along its circumference every 60 degrees, into which six 1/2" diameter neodymium disc magnets are inserted so that they alternate poles on the faces exposed at the rotor circumference. The magnets are fixed in place with hot-melt glue. The armature frame is mounted on a base assembly frame, and the rotor disc spins within the armature frame on a 3/8" polystyrene tube axle. The rotor disc center hole is drilled so it fits very snugly on the shaft and the rotor is also hot-melt glued to the axle. The axle spins in two bearings which fit into circular pockets (cut with a Forstner bit) in two pieces of lexan material. The lexan pieces are mounted on the base assembly frame, one on either side of the opening in the armature frame, with the shaft fixed in place between them by two pieces of thin wall brass tubing which press the center of the bearings into the pockets in their respective lexan mounts. The thin wall brass tubing pieces are are held in place by washers cut from 0.08" polystyrene sheet which fit tightly on the rotor shaft. A drive gear was fixed on one end of the shaft via a wood screw screwed into a wooden plug driven into the polystyrene tube, and it was also hot-melt glued in place.

The armature frame, rotor disc, and base assembly frame are all cut from 3/4"x12"board. The mounting blocks are cut from 2"x4" board.

The armature coils are wired to two 6-screw barrier strips, one on either side of the base assembly frame, so that three coils are connected to each strip in the order they are mounted on the armature frame. There are two ganged six-pole double-throw switches used to change the coil wiring configuration from generator mode to motor mode. The switch common pins are connected to the barrier strips so that each pair of wires from a coil is connected to an adjacent pair of the ganged switches, one on the inside edge of the switch body, and one on the outside edge of the switch body. Each switch is connected to only one for the barrier strips. The configuration wiring connections are made on the top of the switches themselves. Both switches must be set in the same direction to change configuration.

In generator mode, the unit can be hand cranked through an approximately 8:1 gear up pair made from parts of a model car differential. For motor mode, the generator crankshaft drive gear can be pulled back from the rotor shaft drive gear so the handle won't spin while the motor is running. The crank consists of a piece of 1/4"-20 threaded rod bent to form a handle. The straight portion of the crank is inserted though a piece of 3/8" polystyrene tubing, and that tubing is inserted through a hole in its mounting block which has been sleeved with thin wall brass tubing. The crankshaft drive gear was fixed on the end of the straight portion of the crank by threading its center hole and screwing it on to the crank.

A 1.5 V, 25 mA bulb was wired directly across the generator terminals, so it uses the straight AC voltage output. By turning the hand crank the bulb can be made to glow continuously a fairly bright orange color. Flipping the end of the shaft between thumb and forefinger causes the lamp to glow every bright white for a moment before the resulting rotation stops. The rotation from flipping the end of shaft is much faster than what can be achieved using the hand crank, even with the one stage of gear up. Actually spinning the shaft at that speed or faster for very long would likely burn out the bulb.

Armature and Base Frame Assemblies:

[single phase m/g] [single phase m/g]

Rotor Assembly:

[single phase m/g] [single phase m/g] [single phase m/g] [single phase m/g]

Completed Generator:

[single phase m/g] [single phase m/g] [single phase m/g] [single phase m/g]

Ooooh, pretty light:

[single phase m/g]

Gear train disengaged for motor mode:

[single phase m/g]

Adding the Motor Driver:

[single phase m/g] [single phase m/g] [single phase m/g] [single phase m/g] [single phase m/g] [single phase m/g] [single phase m/g] [single phase m/g] [single phase m/g]

How's It Work?:

Click here for the explanation section on the polyphase motor generator page.

Last updated 03August2008
Alan Swithenbank,