# Limitations of overdriving a motor with a VFD



## John Valdes (May 17, 2007)

Don't rewind a motor this small unless the motor is special and cannot be replaced.
I would be looking at replacing the motor and buying a drive for the voltage present.

If this motor is special, rewind it to your nominal voltage (single voltage makes easy for motor shop) and buy a drive to match it.
Use motor current to size the drive.


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## micromind (Aug 11, 2007)

Depending on whether the motor is two-winding or consequential pole, this could be fairly easy. 

If it's two-winding, and it's wound wye, it's possible to disconnect the splices (if you can get to them) at the center of the wyes (inside the frame) and bring out all 12 leads. Then connect the leads ∆, and you'll have a 240 volt motor. 

The way to tell is see if there's continuity between the low and high speed leads. If so, then it's consequential pole; if not, then it's two-winding.


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## Bootss (Dec 30, 2011)

I have rewound two speed Motors and they are a headache to wind.


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## Miller13 (Aug 7, 2014)

micromind said:


> Depending on whether the motor is two-winding or consequential pole, this could be fairly easy.
> 
> If it's two-winding, and it's wound wye, it's possible to disconnect the splices (if you can get to them) at the center of the wyes (inside the frame) and bring out all 12 leads. Then connect the leads ∆, and you'll have a 240 volt motor.
> 
> The way to tell is see if there's continuity between the low and high speed leads. If so, then it's consequential pole; if not, then it's two-winding.


Yes there is continuity so must be consequential pole. It is originally wound in delta for 1400rpm and double star for 2800.

I did manage to fish out the extra leads and I could possibly reconfigure it. Is the 3rd picture in my diagram correct?


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## Miller13 (Aug 7, 2014)

Lep said:


> I have rewound two speed Motors and they are a headache to wind.


I wouldn't even dream to rewind at 2 speeds :no:


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## Jhellwig (Jun 18, 2014)

I would wire it up for low speed and use a transformer to step up the voltage to the vfd unless you can find a vfd that will step it up to 415 volt from 240. And you could use a contactor after the vfd and still be able to use the high and low speed for greater speed control and torque.

No need to have it rewound.


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## micromind (Aug 11, 2007)

Miller13 said:


> Yes there is continuity so must be consequential pole. It is originally wound in delta for 1400rpm and double star for 2800.
> 
> I did manage to fish out the extra leads and I could possibly reconfigure it. Is the 3rd picture in my diagram correct?


I couldn't see the pic. I haven't worked with consequential pole motors in a long time, so I can't say for sure if it'd work on 240. 

I do know however, that the vast majority of 50HZ motors that are dual voltage have 6 leads. They are connected ∆ for low voltage and Y for high. 

This is how their power systems are arranged, they use only 240 volt transformers and connect them ∆ for 240 3Ø systems and Y for 415 3Ø.


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## Bootss (Dec 30, 2011)

Miller13 said:


> I wouldn't even dream to rewind at 2 speeds :no:


I was an electric motor rewinder in a previous life.actually worked in a motor shop
:thumbup:


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## Miller13 (Aug 7, 2014)

I've uploaded the pict again. Is the wiring correct Micromind? In my limited knowledge I woud say I get 207V per coil in delta, 240V per coil in double star and again 240V per coil in the third diagram.


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## micromind (Aug 11, 2007)

Miller13 said:


> I've uploaded the pict again. Is the wiring correct Micromind? In my limited knowledge I woud say I get 207V per coil in delta, 240V per coil in double star and again 240V per coil in the third diagram.
> 
> View attachment 38136


Not completely sure, but it certainly looks like it would work. 

It would still be 2 pole (high speed), and the HP would be the same. 

If you have access to a 240 3Ø source, it'd be worth it to connect it across the lines and see what happens. I'd use fuses as protection; if it doesn't work, they'll blow before the motor is damaged. 

The current with the double ∆ connection would be 3.6 amps. 5 amp dual-element fuses (slow blow) would be ok.


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## Miller13 (Aug 7, 2014)

micromind said:


> Not completely sure, but it certainly looks like it would work.
> 
> It would still be 2 pole (high speed), and the HP would be the same.
> 
> ...


Great stuff, I'll go ahead and test it soon. The VFD will be my 'fuse', I'll set it to go into fault mode if anything over 3.6A is drawn.


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