Two speed motor winding 1

[joebems]

I have a 15 HP, 1800/1200 RPM motor. It needs rewinding. I never use the 1200 RPM speed. My question is: Can it be rewound for just the one speed 1800 RPM? Thanks, joebems

 

[aolalde]

Yes!
Since your motor has two windings the 6 pole could be eliminated.
You have two options.
1- Fill the empty space increasing the copper wire but keeping the very same turns per coil, span and connection.
2- Use insulation slot fillers and duplicate the original 4 pole winding.

Loose windings will lead to premature insulation failure due to vibration.

 

[edison123]

I once got a 750/1500 rpm (in the 50 hz world) where the client wanted it converted to just 1500 RPM. I found that the stator slots/rotor slots ratio would not allow the motor to start if designed purely for 1500 RPM. To prove the theory right, I rewound the motor to 1500 rpm (at my cost) and sure enough, the motor would not start. So, I changed it back to to 750/1500 RPM. Costly but valuable lesson.

Since your speed ratio is not 2:1, the motor should be having two windings.

So, yes, rewind it for 1800 rpm with more copper as aolalde suggested. It will result in a much cooler motor with a longer life with considerably less losses.


*Why a man thinks he outrun a chasing dog when it has twice as many legs?*

 

[oldfieldguy]

Before you foot the bill for a rewind, why not look at a NEW motor of the 1200-RPM variety. Unless you're dealing with some really odd-ball frame or mechanical need, you'll save money.

One of my former employers stopped rewinding ANYTHING below about 75 horsepower because it didn't pay: the cost of the rewind, the loss of efficiency, etc.

old field guy

 

[ScottyUK]

Hi edison,

Can you explain why the motor would not start - was it the load characteristic, or something inherent in the motor? This is a little out of my normal field so I'm interested to learn if you have time to explain it.


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Sometimes I only open my mouth to swap feet...

 

[jraef]

Slots to bars ratio perhaps? In the 2 speed config, the un-used windings were still getting magnetically induced from the others so the effect on starting the rotor was the same, but when re-wound where those slots were empty, the ratio was insufficient to induce rotation? Just a SWAG though, I'm curious too.

 

[edison123]

Scotty and Jeff

It was a consequent pole, single winding, two speed.

I am abroad now. Will post the details here once I get back home.

*Why a man thinks he outrun a chasing dog when it has twice as many legs?*