Closed-Loop Rotational Speed

Control of Cooling Fan

David Choi Jay Gainer

Shad Laws Karl Stensvad

Objectives

• Closed-loop control of cooling fan based on desired speed

• Fine tune LabVIEW parameters to quickly and accurately adjust between speeds

• To plot power usage and efficiency at different fan speeds

• To plot power usage and efficiency with different intake restricting

Overview

• Use small light bulb and photoresistor to create encoder

• Encoder relays fan speed to DAQ

• LabVIEW interprets encoder input and varies voltage across fan to maintain desired RPM

• Read current to the fan to calculate power usage and fan efficiency

Logic Overview

Mechanical Features• Cooling fan housing

• Encoder

• Airflow resistor plates

• Circuit board

Electronics•Tachometer

•Proto-board

•Circuit Board

User Interface

Software

Setting Trial Speed

Determination of Speed

Changing Output Voltage

Determination of Error

Calculating Power

Demo

Results and Analysis

• Fan Rotational Speed

• Power Draw

• Efficiency

• Error

Fan Rotational Speed

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 20 40 60 80 100 120 140 160

Time (sec)

Actual RPMDesired RPM

Power Draw

0

0.5

1

1.5

2

2.5

3

3.5

4

0 17.5 35 52.5 70 87.5 105 122.5 140 157.5

Time (sec)

Wat

ts

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Act

ual

RP

M

Power

Actual RPM

Efficiency

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

200001

301

601

901

1201

1501

1801

2101

2401

2701

3001

3301

3601

3901

4201

4501

4801

Iteration

RP

M o

r R

elat

ive

Eff

icie

ncy

Actual RPM

Average Efficiency

Error

0

500

1000

1500

2000

2500

3000

3500

4000

4500

1 501 1001 1501 2001 2501 3001 3501 4001 4501

Iteration

RP

M

0

20

40

60

80

100

120

140

Per

cen

t E

rro

r

Desired RPM

Observed Error

Power Draw with Varying Airflow Resistance

y = 4E-07x2 - 0.0009x + 1.0062y = 3E-07x2 - 0.0008x + 0.8191

y = 3E-07x2 - 0.0009x + 0.9306

y = 3E-07x2 - 0.0008x + 0.8150

0.5

1

1.5

2

2.5

3

3.5

1250 1750 2250 2750 3250 3750 4250

RPM

1 square inch

3 square inches

2 square inches

9 square inches

0 square inches

Effiency

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

1250 1750 2250 2750 3250 3750 4250

RPM

1 square inch

2 square inches

3 square inches

9 square inches

0 square inches

Error

0

2

4

6

8

10

12

14

1250 1750 2250 2750 3250 3750 4250

RPM

9 square inches

2 square inches

3 square inches

1 square inch

0 square inches

Conclusion• We successfully wrote a program that controls the fan speed

• We verified that power draw increases as airflow restriction and RPM increase

• We found that efficiency decreases as airflow restriction increases