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Forum Index : Electronics : F&P Inductance
| Author | Message | ||||
Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I measured the inductance of each of the 3 different stators this afternoon. Used a series Resistor Inductor circuit shown below.... 
The resistor is there to reduce current. The stator is measured from the center of the star to the output of one phase, so we are measuring 14 coils in series. By feeding in AC, we can measure the circuit current and voltage across the inductor and use ohms law (R=V/A)to find its impedance ( resistance at a certain frequency ). My AC frequency was 50 Hz, so I used L = Z / ( 2 * Pi * f ) where L=Inductance in Henry, Z=Impedance in ohm, Pi=3.14, and f=frequency in Hz. These are my results. 
Now this gives me the inductance of 14 poles in series. To work out the L of each coil, just divide the figure by 14 ( there's actually a bit more to inductors in series calculations, but this will do for now ). So each pole of a 60 series is 5.65mH, 80 series are 2.5mH, and the 100 series are 0.4mH. Glenn PS. I think my maths are right, be gentle if they are wrong. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Megawatt Man Senior Member  Joined: 03/05/2006 Location: AustraliaPosts: 119 |
G'day Gizmo, please ignore my question on the rms thread, thanks very much for the info on this thread re inductances. Good work! Megawatt Man |
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| RossW Guru  Joined: 25/02/2006 Location: AustraliaPosts: 495 |
Glenn, I was looking at your calculations, and my measurements, and wondering why the difference. I think you've made one small oversight in your calculations which would account (I think) for (a) the difference, and (b) why your calculated inductance is higher (rather than lower) than mine. You have determined from ohms law the resistance of the coils at 50Hz, but have attributed the complete resistance measured to inductance. Given you have a relatively small (5.7R) series resistor, you should have also measured the DC resistance of the stator under test (at the same temperature, so probably immediately after your AC test) and subtracted that from the calculated value to work out PURELY the inductive component of the "resistance" measured. IF the DC resistance was approximately half of the calculated value, that would reduce the inductance to about half your calculated figure.... or about what I measured. Any chance you can easily measure or estimate the DC resistance and recalc? RossW |
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| Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119 |
Hello Glenn, Could you please turn on my ability to send only one e-mail about inductance etc, then turn it off again? Megawatt Man |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Megawatt Man. You've lost me there, not sure what you mean. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119 |
Thanks Gizmo, I have prepared a letter for you on inductance before I post it generally but was not able to send it to you, presumably because of settings on the Forum. It might need a massage. I don't want to know anybody's e-mails, so the facility looked as if I could send a private e-mail but it denied me. Megawatt Man |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Thats a little strange, but you know what computers are like. There are no settings to turn that off, usually you just go to Memberlist ( at the top of the page ), then go to G, and click on Gizmo. The next page has a email icon you can use to send me the message. If that dont work, my email is gizmo(at)thebackshed.com, just replace the (at) with @. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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