did u make the ac generator or buy it I think there is no change in magnetic flux done by the coil your voltage depends on the number of turns and change in flux according to faraday
E = N (change in flux / change in time)
so if the coil rotation is greater it means that rate of change in flux is greater so more is the voltage and in your case I think the wind is not enough to rotate the coil. Please give the feecback to my e mail
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