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Just a curious question, Rotor/Stator


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  #1  
Old 11-21-2017, 01:28:47 AM
nothingbutdarts nothingbutdarts is offline
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Default Just a curious question, Rotor/Stator

Today I pulled the rotor and stator off an extended stack 15.0, 12 wire JC.
I'm not getting any younger in life, both were a tad heavy. I beleive they also make a 17KW RJC. The JC units have the taper shaft crank and rotor is held on with the thru bolt.

My question is on the bigger units like the 20, 30 and 40KW units, like on a 20KW Onan, how is the rotor connected to the engine? Taper shaft or bolted to a flex plate like maybe like the SK I have.

On the bigger units, how does one get the stator off the rotor? Can a guy lift a 20KW stator or rotor?

I just ask out of curiosity, as there are quite a few here who do or did this for a living and I wasn't sure how you got the bigger "medium sets" apart for repairs.

As usual Thank You!
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Old 11-21-2017, 02:12:00 AM
Birken Vogt Birken Vogt is online now
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Default Re: Just a curious question, Rotor/Stator

Larger units have a kind of flex plate that fits into a precisely machined well in the engine flywheel and a bunch of bolts.

They are standard SAE sizes.

You take off the finger/bug guard screen thingy and undo all the flex plate bolts.

Then you support the whole generator with a fork lift.

Then you unbolt all the bolts between the generator stator/housing and the engine bell housing and drive the fork lift away with the generator on it.
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Old 11-21-2017, 09:16:41 AM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Just a curious question, Rotor/Stator

Plus you have a good supply of band aids on hand.
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Old 11-21-2017, 09:40:18 AM
Jack Hottel Jack Hottel is offline
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Default Re: Just a curious question, Rotor/Stator

The manual on my 25 KW states, "The rotor weighs over 100 pounds, so use care when sliding it in the stator." Very good advice!
Jack Hottel
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Old 11-21-2017, 09:50:45 AM
Troll Troll is offline
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Default Re: Just a curious question, Rotor/Stator

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Originally Posted by Jack Hottel View Post
The manual on my 25 KW states, "The rotor weighs over 100 pounds, so use care when sliding it in the stator." Very good advice!
Jack Hottel
With anything larger than about 10hp I slide 1/16" phenolic plastic strips between the rotor and the stator after pulling the end bell or access panels from the motor/generator to preclude damaging either.
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Old 11-21-2017, 12:57:07 PM
len k len k is offline
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Default Re: Just a curious question, Rotor/Stator

1/16" phenolic plastic strips ........WOW didn't know the magnetic gap was that large. But that gap sounds reasonable for tolerance buildup reasons.
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Old 11-21-2017, 01:01:52 PM
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Default Re: Just a curious question, Rotor/Stator

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Originally Posted by len k View Post
1/16" phenolic plastic strips ........WOW didn't know the magnetic gap was that large. But that gap sounds reasonable for tolerance buildup reasons.
I have several boxes of differing sizes of these strips which are insulators for differing purposes. I used that as example as they fit most applications. I've never had an Onan generator apart but several antique Hobart welders and such and 1/16" is the most common strip to use. Three of these shoved in, (on at the bottom, and two at opposing sides) and the rotor does not roll, nor really shift during transport. Onan generators could be built to a closer tolerance as I can't say for certain.
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Old 11-21-2017, 02:02:53 PM
Newoldstock Newoldstock is offline
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Default Re: Just a curious question, Rotor/Stator

Depending on who made the machine its size and if it is a rewind the tolerance can be larger or smaller.
The 1/16 is quite reasonable.

I used a sheet of a material called DMD, the same stuff they use to make the slot liners ( also off the same roll )

Taper lock between shafts and couplings can be very strong and handle a lot of power.
Large ones are done in a shop to specific tolerances and require heating.

Installed in the field, this usually ends badly...
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Old 11-21-2017, 02:05:56 PM
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Default Re: Just a curious question, Rotor/Stator

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Originally Posted by Newoldstock View Post
Depending on who made the machine its size and if it is a rewind the tolerance can be larger or smaller.
The 1/16 is quite reasonable.

I used a sheet of a material called DMD, the same stuff they use to make the slot liners ( also off the same roll )

Taper lock between shafts and couplings can be very strong and handle a lot of power.
Large ones are done in a shop to specific tolerances and require heating.

Installed in the field, this usually ends badly...
Yup. Some of those are damned hard to get apart as most cannot be heated for expansion.
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Old 11-21-2017, 02:18:06 PM
len k len k is offline
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Default Re: Just a curious question, Rotor/Stator

I was just used to hearing spark magnetoes were .010 inch air gap, ( in 1/2" instruments we ran ~.0023 " gap)

In a magnetic circuit an air gap is dominant magnetic drive loss of whole magnetic circuit. So you design gap as small as you can without parts hitting each other as they rotate. Otherwise to have same magnetic flux ( similar to current) you have to compensate by increasing magnetic drive (excitation).

That's why dropping a magneto gap to ~ zero sometimes "fixes" a weak spark, (mag flux might be 10X higher).

Last edited by len k; 11-21-2017 at 02:43:29 PM.
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Old 11-21-2017, 08:15:25 PM
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Default Re: Just a curious question, Rotor/Stator

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Originally Posted by len k View Post
I was just used to hearing spark magnetoes were .010 inch air gap, ( in 1/2" instruments we ran ~.0023 " gap)

In a magnetic circuit an air gap is dominant magnetic drive loss of whole magnetic circuit. So you design gap as small as you can without parts hitting each other as they rotate. Otherwise to have same magnetic flux ( similar to current) you have to compensate by increasing magnetic drive (excitation).

That's why dropping a magneto gap to ~ zero sometimes "fixes" a weak spark, (mag flux might be 10X higher).
Very accurate in most any motor type application also. It's why bearing failure on single bearing motors or generators can be so expensive to repair. A bearing gets loose or comes apart and parts that shouldn't make contact do.
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