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Sensors, Actuators, and Robotics » My weird personal fan motor

December 10, 2010
by Wheresmind
Wheresmind's Avatar

Hello all,

I have salvaged a motor from a personal fan that I had lying around. I wanted to control that fan using one of the 2N7000 Transistors that came with my nerdkit.

First thing I did was to test the fan by connecting it to the nerdkit's 9V battery and nothing happened. The motor didn't move or anything. I thought it was broken until I connected it to 3 D-batteries in series (approx 4.7 V) and it worked fine. So I kept working with those 3 batteries.

To test the transistor setup I first used a LED and a resistor. I did the following setup with my breadboard.

Transistor + LED

The led turned on when I connected the Gate to 4.7V. I measured the voltage from my LED to my resistor and it was 4.7 V (approx). At this point I knew my transistor was working and I had setup everything correctly.

The next step was to replace the resistor and LED with my motor and a 1N4004 fly back diode.

Transistor + Motor

When I connect the Gate to 4.7V nothing happens. The motor does not want to move. When I measure the voltage I get 600 mV.

Can anyone explain to me why this is happening ?



PS: When I connect the motor and the diode to the batteries directly it works fine... Motor on batteries

December 10, 2010
by mongo
mongo's Avatar

It appears that the fan draws more current than the FET is capable of handling.If it would not run with a 9V battery but will with three D cells, I would say the motor is just too much for it. A 9V battery might have higher voltage, but if the load is too much, it just can't push enough current to make a difference. The D cells are capable of a lot more current and though a lower voltage, there is enough current to be of use. This probably applies to the FET. It is probably too small to handle the load.

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