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Old 06-04-2012, 05:34 PM   #1
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Default magnatek century run/start cap motor wiring

I have a Magnatek single phase 230V 7.5hp run/start cap motor, 3480 rpm and I was wondering if anyone knew of a source for wiring schematic. I wired it up to what I thought was correct, but it seems to start very fast. I hear the centrifugal switch trip only after I cut the power to it, as it is slowing down. The leads are P1, 1, 4, 5, 7, 8, 9. It has 4 capacitors. The start caps 815-970 mfd/ 165VAC are wired in series, as are the run caps 30uf/ 370VAC. Both are fed from #8, the start caps have lead 9 going into the housing, the run caps have lead 7 going into the housing. The others are wired up like this(L1-P1), (4-8-L2), (1-5). At some point after I cut the power the motor slowly slows down, but at some point it seems like brakes are applied. I don't have a lot of experience with motors, and any help would be appreciated. Thank you.

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Old 06-04-2012, 06:28 PM   #2
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Well, in my efforts to dig up a wiring diagram all I have been able to turn up is this tidbit of info: "Magnetek no longer makes motors, and sold out to A O Smith. They no longer make a single phase motor this large." I'll keep scrounging though and let you know if I find something.

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Old 06-04-2012, 07:19 PM   #3
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Here is a Square D wiring book.

http://ecatalog.squared.com/pubs/Mac...0140CT9201.pdf
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Old 06-04-2012, 07:28 PM   #4
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Oh man! I forgot about that. I first downloaded a copy of it back in November 2010. Thanks Wirenuting.
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Old 06-04-2012, 08:08 PM   #5
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Are you starting the motor with no load? It doesn't sound like anything is wrong with it. It's normal for the single phase motor to do that when the centrifugal switch closes as it slows down. I'll look in my collection of diagrams but it sounds like you have it wired correctly. #1 should be coming from the overload protector as should P1 .
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Old 06-04-2012, 10:02 PM   #6
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Thank you all for your responses. Wirenuting, that manual will come in handy, I'm sure, and Wendon, the motor is being started with no load, so I guess that would explain the hyper-speed when starting. I appreciate the feedback.
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Old 06-04-2012, 11:55 PM   #7
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Capacitor run motors usually don't coast to a stop. They stop quickly; the run capacitor interacts with the inductance of the winding and acts like a brake.
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Old 06-05-2012, 09:10 AM   #8
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That would explain the way that it is stopping. Thanks for the clarification, Micromind.
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Old 07-16-2013, 07:13 PM   #9
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Google found this old thread, I have the same motor (Magnetek 7.5HP single phase) on an old air compressor. On applying power for the first time (no load), the motor groaned and turned slowly. On opening the cap enclosure, I found one start cap has a failed connector, the other looks like it will break at any time. I can't locate the exact caps (Aero M 815-970 MFD, 165 VAC), but have located Mars # 11983, 810-972 MFD. Will these be a suitable replacement?

Would you recommend also replacing the run caps, as they are the same vintage, 1992, and the unit looks like it has plenty of hours on it.

Thanks!
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Old 07-16-2013, 09:27 PM   #10
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The mfd rating of start capacitors need to be within about 10% of existing, voltage needs to be the same or higher, not lower.

Run capacitors are pretty much the same, but +or-5% is better.
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Old 07-16-2013, 09:35 PM   #11
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Quote:
Originally Posted by Packard8 View Post
Google found this old thread, I have the same motor (Magnetek 7.5HP single phase) on an old air compressor. On applying power for the first time (no load), the motor groaned and turned slowly. On opening the cap enclosure, I found one start cap has a failed connector, the other looks like it will break at any time. I can't locate the exact caps (Aero M 815-970 MFD, 165 VAC), but have located Mars # 11983, 810-972 MFD. Will these be a suitable replacement?

Would you recommend also replacing the run caps, as they are the same vintage, 1992, and the unit looks like it has plenty of hours on it.

Thanks!
Should work fine.
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Old 07-17-2013, 12:40 PM   #12
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Thanks for your help! Parts on order.

Cheers,

John

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