> Ever > notice a ceiling fan Humm that has a variable speed control as the voltage > is turned down.All electric motors will do this When my fuel pump gets noisy (even happens with moderately warm fuel now), the pitch (not necessarily volume) changes according to system voltage. John, you are correct that motors running on insufficient voltage may make more noise, but your example is wrong. A ceiling fan will make more noise when fed through a variable speed control because of what the control does. It does not actually lower voltage (peak, not average). Instead it has a switching transistor that rapidly switches the voltage on/off. The potentiometer varies the duty cycle that the transistor switches at. The lower the duty cycle, the slower & noisier the fan is. This technique when used in light dimmers also can also make light bulb filaments noisy. That's your electronics lesson for the day. Walt To unsubscribe from this group, send an email to: DMCForum-unsubscribe@xxxxxxxxxxxxxxx _____ Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/DMCForum/ * To unsubscribe from this group, send an email to: DMCForum-unsubscribe@xxxxxxxxxxxxxxx <mailto:DMCForum-unsubscribe@xxxxxxxxxxxxxxx?subject=Unsubscribe> * Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> .
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