Science Buddies: "Ask an Expert"

I am following your directions on using a dc powered fan to generate electricity. I have tried two different motors and cannot seem to get them to produce a current when the fan blade spuns. Is there some kind of device in the motor that may prevent the current from going out of the motor? An advice regarding this project would be appreciated.

robatkinson wrote:I am following your directions on using a dc powered fan to generate electricity. I have tried two different motors and cannot seem to get them to produce a current when the fan blade spuns. Is there some kind of device in the motor that may prevent the current from going out of the motor? An advice regarding this project would be appreciated.

This project was called "using a fan to generate electricity', I thougt, but I can't find it. robatkinson, could you post the link when you post back?


There are two likely problems:
1) Your circuit has a problem- something is shorted out or loose. Make sure nothing is touching that shouldn't be and all your connections are good

2) You are not spinning the fan fast enough to generate enough electricity to power the LED. If you can use a power drill to spin the fan (yeah, this seems silly to me... you use electricity to power the drill to spin the fan to make electricity to power the LED... but you can use this to troubleshoot the problem) then you can get it going pretty fast.

As for your hypothesis, I am not aware that there is a device that would prevent current from leaving the fan. Other people have gotten this experiment to work with a computer fan. I think the problem is probably (2) above. Let me know if this works!

Louise

Quick thought. LEDs are light emitting DIODES. As in unidirectional devices. If the polarity is backwards, they won't light.

Have you tried reversing the LED? Or, I guess, spinning the fan in the opposite direction.

Is the LED intact? Have you tried it with an appropriate battery (and limiting resistor, if necessary with your LED, to avoid destroying it)?

Have you connected a volt meter to the fan to be sure that it is producing electricity (this can also be used to confirm which polarity is correct.)

zzzzdoc wrote:Quick thought. LEDs are light emitting DIODES. As in unidirectional devices. If the polarity is backwards, they won't light.

Have you tried reversing the LED? Or, I guess, spinning the fan in the opposite direction.

Is the LED intact? Have you tried it with an appropriate battery (and limiting resistor, if necessary with your LED, to avoid destroying it)?

Have you connected a volt meter to the fan to be sure that it is producing electricity (this can also be used to confirm which polarity is correct.)

I had thought the (original) instructions were pretty specific about the polarity part. This is a good point, and worth checking.


robatkinson- If you decide to make a circuit with a battery and a resistor to check your LED, please google for instructions. Without a resistor, it is VERY easy to blow out the LED. There should also be diagrams indicating which lead of the LED is which, so you can check the polarity is correct.

Louise

If you are using a nominal T1 20MA @ 2V LED called for, you should be using somewhere between a 180 ohm and 270 ohm resistor with a 6 volt battery for testing purposes. The longer square pin is the anode (positive) pin (goes to + battery terminal or red wire on DC fan).