E2 Motors and Motor Starting #1 Fan Motors - Homesteadhvacrknowlagecenter.homestead.com/E2_Subject1_Fan_Motors_.pdf© 2005 Refrigeration Training Services - E2#1 Fan Motors v1.1

E2 Motors and Motor Starting

#1 Fan Motors

© 2005 Refrigeration Training Services - E2#1 Fan Motors v1.1 2

Basic Electric Motor

• Stator– Stationary electromagnet

• Rotor– Rotating magnet

• Movement of the rotor– Rotates by repulsion and attraction of stator


ROTOR(with shaft)

STATOR(with windings)

Exploded View of Motor


Two-pole stator motor

NN S

_+

SN S

Stator(Stationary)

When stator is energized the rotor will make a half turnwith each half of current cycle

Rotor(Rotates)

Polarity reverses (N to S) on stator

Stator repels & attracts rotor into

motion


Second half of cycle

NS

+ _

N S

The alternating current nowchanges direction

NSPolarity reverses (N to S) on stator

Stator continues motion by repelling

and attracting


Motor Starting

All motors need a phase shift to start rotation


Stator

S

N

Stator

Rotor

S

NEqual and opposite attraction

Equal and opposite attraction

Opposite attractionRotor will NOT move

Power applied to stators

Motor Tries to Start


Stator

S

N

Stator

Rotor

S

NA magnetic field isformed at a slightlydifferent angle

This phase shift can be caused by:A shaded poleA start windingA capacitor3 separate phases

A phase shift causes rotation

A Phase Shift is Needed


Shaded-Pole Motors

• Low starting torque• Low efficiency• Low cost


Examples of Shaded-Pole Motors


Starting a Shaded-Pole Motor

• Each pole has a copper band attached– The shaded-pole provides the phase shift

needed to start rotation• Usually impedance protected

– A stalled blade will not cause burned windings


Rotation toward the Shaded Pole

S NN S


Shaded-Pole Motor Wiring

GREEN GROUND

BLACK LINE


Changing Motor Rotation

• Shaded-pole motors can be reversed:– First, turn stator around– Second, turn blade around


Interesting Motor Fact

Motor efficiency:A 100 watt 50% efficient motor will put out

50 watts of work, and 50 watts of heat.


Shaded-pole C-frame Motor


To Reverse Rotation

Turn Stator Around


Turn fan bladearound

Rotation is now reversed


Multi-speed Shaded-Pole Motors• Speed depends on winding resistance

– Low speed: most resistance– High speed: least resistance

• Motor speed is based on where power is connected into the winding

CommonHigh

SpeedMedium Speed

Low Speed


BLACK LINE

Shaded-Pole 3-Speed Motor Wiring

GREEN GROUND

BLACK-HIGH

BLUE-MED

RED-LOW

LINE

Common Wire is White (115v) or Black (230v)


Split Phase Motors

• Have two separate windings, a run and a start

• The start winding provides the phase shift for starting

• More efficient and have more torque than shaded pole motors


Start

Start

A Split Phase Motor is a Two-pole stator motor …

RunRun

with Start Windings added

TO RUN WINDINGS

TO STARTWINDINGS

R

CS


ΩΩΩ

Start & Run Winding Resistances

RS

C

COM V/Ω

Ω VAC

DC


Windings of a split phase motor


Split Phase Motor

LINE

RUN WINDINGSTART WINDING

C RS

This motor needs power to the run winding

to run

This motor needs power to the start winding to start

This motor needs a start winding for

a phase shift


Fan Motor with Centrifugal Switch

• A mechanical switch is used to de-energize the start winding

• The switch is attached to the motor shaft• After the motor starts, centrifugal force opens

the switch• The start winding circuit remains open as long

as the motor is running


Split Phase Motor with Centrifugal Switch

LINE

RUN WINDINGSTART WINDING

S C R

Centrifugal switch opens start winding


Fan Motor with Centrifugal Switch

• The next slide is a picture of a fan motor with the motor cover removed

• The centrifugal switch is attached to the motor shaft

• The switch contacts are attached to the end bell (motor cover)


To Start Winding

Motor with Centrifugal Switch

Start winding energized

Motor Speed Increases

Weights shift, disk moves back

Centrifugal SwitchFrom Run

Winding

Contacts Open

Disk

Before starting, disk pushes bar, closing contacts


Permanent Split Capacitor Motors

• A run capacitor is “permanently” wired into the start winding circuit

• The capacitor provides partial voltage to the start winding, during start and run


PSC Motor with run capacitor

Low Starting Torque

Low to Medium Cost

Medium Efficiency


Split Phase Motor + Run Cap = PSC Motor

R

C

S

Run Capacitor



A PSC motor with a bad run capacitor will act like an overloaded motor


PSC Motor Wiring Diagram

GREEN GROUND

BLACK LINE

BROWN

CAPACITOR


Motor Speeds

• The synchronous, or “nominal” speed of a motor can be determined by the number of its poles

• The more poles, the lower the speed


Courtesy ofCopeland7200 ÷ 2 = 3600 RPMTw

o Po

le M

otor

Win

ding

s


Calculating Motor Speeds

• One cycle has two current flow reversals• 60 cycles has 120 flow reversals• Speed = (60 Hz x 120 reversals) ÷ PolesExample: 7200 ÷ 2 Motor poles = 3600 RPM


Courtesy ofCopeland

1

2

3

4

2

34

1

7200 ÷ 4 = 1800 RPM

Four

Pol

e M

otor


Actual Motor Speed

• Slippage is the loss of speed from motor load• The actual speed is less than the calculated

speedCommon motor speeds: Calculated: Actual:

2 Pole motor: 3600 34504 Pole motor: 1800 17506 Pole motor: 1200 10508 Pole motor: 900 850


Multi-Speed Split Phase Motors

• Actually they are “Multi-horsepower”• The windings are tapped so the motor is

weaker, running slower under load• Example of a 3-speed 1/3 HP motor:

– High speed is 1/3 HP– Medium speed is 1/4 HP– Low speed is 1/6 HP


Single-Speed PSC Motor

R

C

S

Run Capacitor


Single-Speed PSC Motor

R

C

S

Run Capacitor


Multi-speed PSC Motor

RL

RM

R

C

S

RH

High Speed

Medium Speed

Low Speed


3-Speed PSC Motor Wiring Diagram

GREEN GROUND

BROWN

BLACK LINEBLACK-HIGH

BLUE-MED

RED-LOW

LINE

Single-Speed CSCR Motor


R

C

SRun Capacitor

Start Capacitor


Multi-speed CSCR Motor

RL

RM

R

C

S

RH

High Speed

Medium Speed

Low Speed

Capacitor Start Capacitor Run




• Multi-speed motors must be under a load to change speeds– Example: A multi-speed blower removed from

the blower compartment will run at high speed, no matter which speed tap is used


Common WireHigh

Speed (black)

Medium Speed (blue)

Low Speed (red)

PSC 3-speed Motor

Leads for changing motor

rotation

Run Capacitor

Leads


Three Phase Motors

• High starting torque• High efficiency• Medium to high cost


Three Phase Motors


Three Phase Motor Starting

• No start windings or capacitors needed• High torque because the windings are

120° out of phase

© 2005 Refrigeration Training Services - E2#1 Fan Motors v1.153

3Ø Motor – Wye Connections

208 V

208 V

208 V

T1

L1

L3

L2T2T3

© 2005 Refrigeration Training Services - E2#1 Fan Motors v1.154

3Ø Motor – Delta Connections

T1

T3 T2

L1

L3

240 VL2

240 V

240 V


Describing Common Motors

• Motor descriptions include the following information:– Type– Enclosure– Mounting


Common Motor Types


Motor Enclosure Types

• Open• Dripproof• Totally enclosed • Totally enclosed fan cooled


Open Enclosure Types

Open Dripproof Totally Open

Clean and Dry Locations

Note: Prevents direct entry of moisture

Clean and Mostly Dry Locations


Enclosed Type Motors

Totally Enclosed Air Over

Totally Enclosed Fan Cooled

Cooling from system air passing over the motor body

Cooling from fan forced air passing over the motor body

Totally Enclosed are good for wet and dirty conditions


Motor Mounting

• Some of the more common mounts:– Rigid – Cradle – Belly band– Stud– C-frame– Unit bearing


Cradle Mount


Rigid Mount

Motor housing is welded to the base


Belly Band Mounting

Motor slides into ring. Then band is tightened


Stud Mounts

Studs are bolted to fan guard or

housing.


Other Motor Mounting Styles

Unit bearingC-frame


Motor Nameplate

• Nameplates contain essential information

© 2005 Refrigeration Training Services - E2#1 Fan Motors v1.1 67Motor Nameplate explained


Motor Nameplate wiring diagram


Interesting Motor Facts

• An overloaded motor (too small for the job):– Lower speed, amperage above 10% of RLA, and

overheating• An under-loaded motor (too big for the job):

– Little change in speed, amperage 25% below RLA, and overheating


Documents

E2 Motors and Motor Starting #1 Fan Motors - Homesteadhvacrknowlagecenter.homestead.com/E2_Subject1_Fan_Motors_.pdf© 2005 Refrigeration Training Services - E2#1 Fan Motors v1.1