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Do-It-Yourself (DIY) Question & Answer Forum
A Thought Experiment
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<blockquote data-quote="apprentice87" data-source="post: 349755" data-attributes="member: 13534"><p>Hi there,</p><p></p><p>Say all the windings had a resistance of 10 Ohms.</p><p></p><p>Now taking delta first. measure the resistance between two of the wires, it will be 6.6667 Ohms. If you then linked two of the wires and then measured the resistance from the linked wire to the third one, you would have a reading of 5 Ohms.</p><p></p><p>Now divide the 6.6667 by 5. You will end up with the ratio between the two of 1.333</p><p></p><p>Now do exactly the same, but for the windings in star.</p><p></p><p>The resistance between two wires will be 20 Ohms. The resistance between two linked wires and the third one will be 15 Ohms. Divide 20 by 15 and you will get the ratio between the two, it is exactly the same at 1.3333 ******!!!</p><p></p><p>What you have discovered though, is that whichever way you measure it, the motor in star will have readings exactly 3 times higher than the delta one.</p><p></p><p>So, look at motors with the same shaft and keyway size, and same foot dimensions. Compare your readings with one of the "new" ones. If your readings are roughly the sameish, your motor is wired the same. If yours are about THREE times higher or lower, your motor is wired the "other" way.</p><p></p><p>Only thing i can think of..</p><p></p><p>john..</p></blockquote><p></p>
[QUOTE="apprentice87, post: 349755, member: 13534"] Hi there, Say all the windings had a resistance of 10 Ohms. Now taking delta first. measure the resistance between two of the wires, it will be 6.6667 Ohms. If you then linked two of the wires and then measured the resistance from the linked wire to the third one, you would have a reading of 5 Ohms. Now divide the 6.6667 by 5. You will end up with the ratio between the two of 1.333 Now do exactly the same, but for the windings in star. The resistance between two wires will be 20 Ohms. The resistance between two linked wires and the third one will be 15 Ohms. Divide 20 by 15 and you will get the ratio between the two, it is exactly the same at 1.3333 ******!!! What you have discovered though, is that whichever way you measure it, the motor in star will have readings exactly 3 times higher than the delta one. So, look at motors with the same shaft and keyway size, and same foot dimensions. Compare your readings with one of the "new" ones. If your readings are roughly the sameish, your motor is wired the same. If yours are about THREE times higher or lower, your motor is wired the "other" way. Only thing i can think of.. john.. [/QUOTE]
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A Thought Experiment
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