AC Single Phase Alternators and Motors Study Guide

= Provide the low friction support for the rotor. Holding the rotor coil(s) location relative to the stator coils for optimal mutual induction

bearings/bushings

Reversing a single-phase induction motor is done by swapping the polarity of the start winding leads if accessible.

how to reverse a single-phase motor

Normal CCW nameplate rotation is viewed looking at rear of motor, so CW rotation looking at motor shaft. Nameplate direction is achieved by connecting T5 of start winding to T1 of run winding. Swap T5, T6(8) position to reverse.

how to view and reverse CCW and CW rotation in a single-phase motor

No they do not.

Are single phase motors self starting

our book called Resistive-start/inductive-run: secondary winding is more resistive then the more inductive run (main) winding (causes around 30-degree phase difference between the two). Will require a switch to disconnect the aux. winding after ~70% speed is reached (this means you cannot run this motor any slower than the switch cutout point or you will damage the aux. windings). Not an efficient way to start a motor (high inrush current of 7 to 10 time's normal run current level). Much greater staring torque than shaded pole (100 to 200% full load torque). Start winding has double or triple the resistance of the run winding

Induction-start/induction-run

to change number of poles on the fly (then speed can change greatly like 3600, 1800, 1200, 900, ... so maybe a motor built with 8 poles that can be switched to 4 poles thus 1800 or 900 sync. speed) Common Split Phase

another option to change speed is to

the name for the output coil, as shown above the armature could be on the rotor or in the stator.)

aramature

The brush rides on the slip ring to transfer electrical current to/from the rotating rotors windings and the external circuit. The slip ring is part of the rotor. The brush is part of the frame

brush and sliprings

Can run a stepper motor off AC for continuous rotation instead of stepping.

can you run a steeper motor off of AC?

same as above except the cap is in series with the aux. winding creates a phase shift much closer to 90 degrees so better starting torque (400 to 600%) and less in rush starting current as well (2 to 4 times normal run current). Still needs a switch to cutout start circuit after ~70% speed is reached (this means you can't run this motor any slower that the switch cutout point or you will damage the aux. windings) start caps are going to be in the higher micro farad range like hundreds or thousands of micro. Again start winding has double or triple the resistance of the run winding

cap start induction run

like PSC but actually have a switch and two caps. One start cap parallel with run cap but switched out near run speed (higher farad one) and one run cap to stay in series with aux. winding (lower farad value). Switch would again mean you could not really vary speed much. A combination of the PCS and Cap start so the best of both. Start torque of the Cap start and inrush current of the PSC. Cons: switch and also most expensive

cap start/run motors

The support structure for the parts listed above

frame/endplate

Our book called these Permanent-Split Capacitor: They are a form of Cap-start/cap-run. Since cap stays in circuit no need for a switch in aux. winding. However, because cap and aux. winding are always energized, they must be able to withstand continuous operation (typically metal cased oil filled cap to handle higher voltage and continuous operation). Run caps are going to be in the lower 10's of microfarad range. No switch also means it can be run at lower than 70% of rated speed (multi-tapped run winding). Aux. winding also heaver gauge wire to handle continuous current. Starting torque not as great as cap start at30-150% and in rush current is less at or below 2 times run current.

permanent start cap motor

The source of mechanical energy that the alternator will convert to electrical energy. The thing that rotates the rotor.

prime mover

predated cap start motors. Similar to universal motor except armature is not connected to the line voltage. The armature does have brushes but the brushes are shorted out and not set to neutral position (15 degrees either way gives good starting torque but, 0 or 90 degrees will not start). Transformer action induces current into armature and magnetic field in armature then spins do to repulsion against the field instead to attraction to it like all the other motors. Direction of rotation is changed by moving brushes to other side of neutral. Excellentstarting torque. Other single-phase motor types

repulsing motors

A physical location in a motor/generator. It is the rotating shaft (will have a coil but it might be the field coil or the output coil)

rotor

(think cheap small fans in bathrooms and small appliances) very low starting torque (25-75% of full load torque). One winding only, no auxiliary winding needed as each pole is split. The small split portion has a shorted loop or band to cause a phase delay in the magnetic field in that section of the pole piece. Inefficient motor type at only 20% or less. Throw away motors, as in cheaper to buy new instead of fix. *Could vary speed by varying voltage to motor or having a multi-tapped winding.

shaded pole

A physical location in a motor/generator. The stationary motor case a.k.a. the frame (will have a coil but it is the opposite coil from the rotor) Not mentioned by name in our book but an alternator needs to have an output coil.

stator

Dual voltage motor windings are wired in series for high voltage lines and parallel for low voltage installations.

what are dual voltage windings wired in vs low voltage?

Multispeed (slower than normal) available for most types listed below by switching in additional inductor windings in series with run winding. This increases XL which lowers current through the run winding and increases slip. Does not reduce speed by much (example: 1625, 1500, 1350 for high, med. and low)

what is Multispeed

AC series motor (typically wired like a DC series motor) has an armature, field, and interpole or compensating winding and can run from AC or DC. Used in small variable speed appliances like blenders, drills etc. Switch the armature winding polarity to reverse. Physically wired field and armature so those do not rely on induction. (compensating winding may be wired or inductive) Pros: Good torque, variable speed with inexpensive rheostat control Cons: more mechanical parts to go wrong like brushes, poor speed regulation

what is a Universal motor

"Inverter" Generators are actually DC generators that include a DC to AC Inverter onboard

what is an inverter

Output frequency = 𝑅𝑃𝑀 𝑥 # 𝑜𝑓 𝑝𝑜𝑙𝑒𝑠/120

what is the output frequency formula

If replacing a capacitor match farad value as close as possible to maintain phase shift. Also, meet or exceed voltage rating of old capacitor. (voltages applied to capacitor can exceed line voltage because of the coils collapsing electromagnetic field which is out of phase with the capacitors collapsing electrostatic field)

what should you do if replacing a capacitor