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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