icon Cordless Drills


In looking for the efficiency and maximum voltage and power available from cordless drills used as DC generators the following measurements were preformed. One drill was powered to turning another of the same type hooked up as a generator. There was a short bolt put in the chuck of each unit to mechanically tie them together. Both were turning at the same speed. Several conditions were measured. The input current and voltage used under no load as a single drill was measured. The input current and voltage was measured while tuning another drill under no load was measured. Then the input current and voltage was measured while tuning another drill while generating output power was measured. From these measurements the efficiency of each type of unit was then determined. See the table below for a summary of the average measurements and calculated results.

Type of# ofInputInput InputOutput Output Output
TestsDrillsvolts Current Power VoltsCurrent power
12 volt drill 500 rpm max3 cells
Off OC

0.00

13.37

0.00

0.00

4.10

0.00

0.00

No load

1.00

12.30

1.65

20.23

0.00

0.00

0.00

Open Circuit

2.00

11.87

3.60

42.68

8.73

0.00

0.00

Generating

2.00

11.05

7.42

81.99

5.32

2.50

13.30

14 Volt drill 550 rpm max 4 Cells
Off OC

0.00

15.46

0.00

0.00

5.46

0.00

0.00

No load

1.00

15.50

1.17

18.14

0.00

0.00

Open Circuit

2.00

14.26

2.14

30.52

11.40

0.00

0.00

Generating

2.00

12.75

6.94

88.42

7.09

3.13

22.16

18 Volt drill 900 rpm max4 Cells
Off OC

0.00

20.20

0.00

0.00

5.46

0.00

0.00

No load

1.00

19.20

1.81

34.75

0.00

0.00

Open Circuit

2.00

18.60

4.81

89.47

15.40

0.00

0.00

Generating

2.00

17.25

11.89

205.10

8.12

5.1

41.62

OutputPowerPercentages
PowerLossesResults and Description
12 volt drill

20.97

0.44

average /drill gear train power loss

13.37

0.28

average /drill electrical power loss

0.28

efficiency generating at max speed
14.4 Volt drill

16.22

0.29

average /drill gear train power loss

16.92

0.3

average /drill electrical power loss

0.40

efficiency generating at max speed
18 Volt drill

41.41

0.34

average /drill gear train power loss

40.34

0.33

average /drill electrical power loss

0.34

efficiency generating at max speed

Summary of the results:
12, 14.4, and 18 Volt drills at rated speed output a maximum of 8.7, 11.4, and 15.4 open circuit Volts. This is to say the output voltage is roughly 74, 80, and 83 percent of the input volts when acting as a motor generator set. The suggested maximum rated output generated power at rated speeds of 500, 550, and 900 is 13.3, 22.2, and 41.6 watts. The electrical output generating efficiency is about 28, 40 and 34 percentage of the total input power. This to say that the 14.4 Volt drill is slightly more efficient at generating power than the other two.

Offered by Mike.

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