Also what happens when you change the polarity of a DC or an AC motor?
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I missed the first part. The "polarity" is which wire is made positive and which wire is made negative.
For an AC motor "polarity" has no meaning. It is alternating so it is changing polarity many times every second anyway. Hence switching wires is quite pointless.
And there are true DC motors in which reversing the polarity makes the motor run backwards but otherwise there is no "right" way to connect it.
But there are"DC" motors that are actually AC motors that require a DC input which is converted electronically into a quasi AC current.
In this case reversing the polarity destroys the transistors and ruins the motor.
The correct wire MUST be connected to positive at all times.
For an AC motor "polarity" has no meaning. It is alternating so it is changing polarity many times every second anyway. Hence switching wires is quite pointless.
And there are true DC motors in which reversing the polarity makes the motor run backwards but otherwise there is no "right" way to connect it.
But there are"DC" motors that are actually AC motors that require a DC input which is converted electronically into a quasi AC current.
In this case reversing the polarity destroys the transistors and ruins the motor.
The correct wire MUST be connected to positive at all times.
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http://forum.allaboutcircuits.com/forumdisplay.php?f=6
http://www.nfphampden.com/1phmotor.pdf
http://www.nfphampden.com/3phmotor.pdf
http://www.nfphampden.com/1phmotor.pdf
http://www.nfphampden.com/3phmotor.pdf