# Funky fan?



## agentRed (Nov 7, 2006)

Yeah...um...I have an old 80mm case fan that I don't use anymore. It's got 4 LED's and when I turn the blades, the lights light up?? Why?? There's no power being applied to it and the thing lights up. Is there maybe a generator in it??


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## Fr4665 (Nov 18, 2004)

well if you look at it. any electric motor u operate backwars will generate electricity. so a motor is basically a generator. 

like for example if u take a small servo motor electrical one for an RC car and start turning it, itl generate electricity and if u touch the wires that go to the regular batery youll get shocked.


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## agentRed (Nov 7, 2006)

That's odd  Thanks for the info though. 

I'm guessing the gearing in one of those servos, when reversed, makes the motor spin a whole lot faster than it should, right?


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## carsey (Aug 19, 2006)

My fans dont light up. Maybe the LEDs are on a different circuit.


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## agentRed (Nov 7, 2006)

Well...I spun the fan with a jet of co2 and it spun so fast, the LED's lit up, and then popped D:


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## Fr4665 (Nov 18, 2004)

maybe that was a little toooo fast depends how the motors are configured in the fans. some do it some dont.


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## nick.rambo (Jan 11, 2007)

There are a lot of LED fans that will light up if you spin the blades quickly. I'm not sure if all LED fans will.. but all three of mine do. (2 80mm, 1 120mm)

I just assumed that the power from the case spun the fan blades, and the spinning acted as a means of energy for the LED's to light up.


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## Ralck (Dec 10, 2004)

The power from your power supply normally powers both the fan spinning and the LED's.

However, spinning the fan is manually turning the motor (instead of letting the electric current doing it). Basically, energy is conserved. This means that the electric energy is converted into mechanical energy to make the fan spin. Vice Versa, mechanical energy can be converted to electric energy, such as through a generator. When you blow the compressed air over the fan blades to make it spin, this is actually turning the motor into a generator, which makes a small electric current usually refered to as Back EMF. That is why when you spin the fan, the LED's light up.

However, *NEVER* spin the fan blades on an LED fan. LED's are designed to have current pass through them in a certain direction. If you manually spin a fan, two bad things could happen. First, you could spin it so fast that too much current goes through and breaks the LED's. Second, and the more likely, the Back EMF generated could cause the current to go through the LED's backwards, which would make them pop. In fact, this Back EMF could actually go back to your motherboard and damage that as well.

This is why, with an LED fans, you always want to unplug it from your system and hold the blades when blowing compressed air on them so they don't spin. With non-LED fans, you should at least unplug those from your computer as well, because their Back EMF could damage your motherboard as well.


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