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I just broke a 120mm computer fan in name of science and now I'm pissed; can anyone explain why this doesn't work? :

enter image description here

The battery should create a potential difference across the motor, causing the fan to spin up, right?

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closed as off-topic by akhmeteli, David Z Sep 22 '13 at 16:06

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firstly, you hooked up the red wire to negative and the black wire to positive--you got it backwards.

secondly, computer fans operate at 12V, so you are short of several batteries. with luck, some fans might start spinning at 7V .

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  • $\begingroup$ Would it not spin very slowly however? $\endgroup$ – Shaun Wild Sep 22 '13 at 14:21
  • $\begingroup$ Also, if I spin the fan itself, will it create a PD? $\endgroup$ – Shaun Wild Sep 22 '13 at 14:22
  • $\begingroup$ the magnetic force produced from such a low EMF is surely not sufficient to overcome the inertia of the fan blades. but if you spun the blades manually, you might find that they spin for a while longer than if a battery wasnt hooked up at all--but with only 1.5V i'm doubtful it will be perceptible. $\endgroup$ – gregsan Sep 22 '13 at 14:27
  • $\begingroup$ what about my other question? $\endgroup$ – Shaun Wild Sep 22 '13 at 14:41
  • $\begingroup$ see the 4 coils inside the rotor? those are in series, and connect to the controlling electronics with 2 wires. you need to tap those two if you want to use the fan as a generator--you cant use the red and black wires as those are inputs to the electronics. $\endgroup$ – gregsan Sep 22 '13 at 14:41

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