# Dual Voltage Motors



## pudge565

Ok if you have a dual voltage motor with the windings connected for low voltage operation but hook it up for high voltage what will happen to the speed of the motor?


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## RIVETER

pudge565 said:


> Ok if you have a dual voltage motor with the windings connected for low voltage operation but hook it up for high voltage what will happen to the speed of the motor?


Eventually, it will stop.


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## pudge565

Well I know that it will eventually burn the windings up. But before it does will it run faster slower or at the same speed? I would figure it will run at a slower speed. Due to it would be stuck in the start winding?


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## RIVETER

pudge565 said:


> Well I know that it will eventually burn the windings up. But before it does will it run faster slower or at the same speed? I would figure it will run at a slower speed. Due to it would be stuck in the start winding?


I hate to admit that I totally don't know the answer because I have never wired a motor wrong...my bad,I guess. What I can say is that if you run a motor at a slower speed than it was built for it may not be able to overcome the initial CEMF and the struggle will burn up the windings. I am going to try, on purpose, today to make a mistake...that way, maybe I'll learn something.


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## Innovative

RIVETER said:


> I hate to admit that I totally don't know the answer because I have never wired a motor wrong...my bad,I guess. What I can say is that if you run a motor at a slower speed than it was built for it may not be able to overcome the initial CEMF and the struggle will burn up the windings. I am going to try, on purpose, today to make a mistake...that way, maybe I'll learn something.


You have NEVER wired a motor wrong?? You must be the only person that can be able to say that, if you have wired alot of motors. Like guys that say " I have never gotten a red tag" or similar violation sticker.
I dont make a habit of wiring motors wrong, but have certainly done it a few times before.


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## RIVETER

Innovative said:


> You have NEVER wired a motor wrong?? You must be the only person that can be able to say that, if you have wired alot of motors. Like guys that say " I have never gotten a red tag" or similar violation sticker.
> I dont make a habit of wiring motors wrong, but have certainly done it a few times before.


Not me...NEVER, but then I've only wired a couple of hundred. My secret of success is read the name plate...and double check.


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## Navyguy

Well I agree, I can’t say for sure but I will put this out there. It depends on what the motor ratings are. What their purpose is, etc. I have wired 1000 volt motor to 600 volt often without any consequence, but the tolerance was acceptable for that range. I have also wired numerous 440 volt motors on 600. Now they don’t last long and seem to have lower starting torque, but they work

Lower voltage generally will have larger windings because the current draw is larger, so if they are using different windings for the different voltages, I would suspect that the winding will burn up.

Speed / Control is not related to voltage but to frequency in AC motors. DC motors is a different story.

Motor type is also a factor. Different motors react to the proportional values of current / voltage, some will speed up on voltage drop and other will slow down, I honestly remember which ones do what, but that is easy enough to search out.

Cheers


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## Toronto Sparky

Capacitor (assuming your talking single phase) will explode... Speed will not change but windings will fry quickly..

This a class room question? Theory always works great in theory.


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## pudge565

Yes I should have specified, we were discussing a 208/480 motor. This is a classroom question that the instructor does not know. It was posed to him by the HVAC teacher after it appearing on a test.


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## micromind

The speed of an AC induction motor is governed by the frequency, not voltage. It would turn at very close to its synchronous speed, based on the number of poles.

A 2 pole motor at 60HZ would turn slightly less than 3600 rpm, a 4 pole 1800, a 6 pole, 1200. 

The core would be saturated though, and even at no load, the current would be in the stratosphere! It'd burn up in about 10 seconds. It'd actually last longer if it were under load, the core wouldn't be quite as saturated, and some of the current would be used to drive the load, instead of heating the windings.

Rob


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## CEC_king

micromind said:


> The speed of an AC induction motor is governed by the frequency, not voltage. It would turn at very close to its synchronous speed, based on the number of poles.
> 
> A 2 pole motor at 60HZ would turn slightly less than 3600 rpm, a 4 pole 1800, a 6 pole, 1200.
> 
> The core would be saturated though, and even at no load, the current would be in the stratosphere! It'd burn up in about 10 seconds. It'd actually last longer if it were under load, the core wouldn't be quite as saturated, and some of the current would be used to drive the load, instead of heating the windings.
> 
> Rob


could not have said it better myself


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## pudge565

Thank you very much Micromind for that wonderful explaination!


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## John Valdes

micromind said:


> The speed of an AC induction motor is governed by the frequency, not voltage.


The speed of the AC induction motor is governed by the frequency AND the voltage applied proportionally.


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## Nephi

thankyou john. variable frequency drives most certainly change frequency in step with voltage thats why they are often reffered to as variable voltage frequency drives


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## pudge565

Nephi said:


> thankyou john. variable frequency drives most certainly change frequency in step with voltage thats why they are often reffered to as variable voltage frequency drives


Yes but they can only supply up to the incoming line potential. If you want to run it higher than base speed it only increases the frequency after it gets to line potential.


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## miller_elex

You will have to reset your OL's.


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## John Valdes

pudge565 said:


> Yes but they can only supply up to the incoming line potential. If you want to run it higher than base speed it only increases the frequency after it gets to line potential.


When a voltage is applied to a VFD, the voltage is rectified to DC at a much higher value than the nominal voltage being applied. At 480 volts input nominal you will have over 800 volts DC (DC Bus Voltage) available for operation. That is why you can over speed motors with a VFD.



miller_elex said:


> You will have to reset your OL's.


VFD's today come with electronic overloads and are set in the programming section of the parameters. When a motor is overloaded on a VFD, the VFD will either try to over come the overload or shut down the motor.
There are no overloads to reset.


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## micromind

VFDs do indeed vary the voltage along with frequency, but the original question was about raising the voltage while still at 60HZ. 

In this case, the speed will still be close to nameplate.

Rob


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## Nephi

the question was about what would happen if high voltage was applied to the low configuration of a dual voltage motor


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## knomore

There are two ways to change the speed of a motor, change the number of polls, or change the frequency...

If you hooked it up wrong it might move, but it's going to heat up like crazy and your going to fry the motor in a hurry. Moral of the story is look at the nameplate and triple check your tap connections, and you can claim you have never hooked up a motor wrong...


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## RIVETER

knomore said:


> There are two ways to change the speed of a motor, change the number of polls, or change the frequency...
> 
> If you hooked it up wrong it might move, but it's going to heat up like crazy and your going to fry the motor in a hurry. Moral of the story is look at the nameplate and triple check your tap connections, and you can claim you have never hooked up a motor wrong...


Right on...that's the way I do it.


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## noyesdb

the speed is not a factor if you hook it up wrong, replacing the motor (sooner or later) is


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## John Valdes

knomore said:


> There are two ways to change the speed of a motor, change the number of polls, or change the frequency...


There are other ways to change motor speed.
First. You don't change the number of poles. You buy the correct motor. You are correct that the number of poles indicates base speed. But this is not adjustable. 
Second. Adjusting the speed using Hz alone will not work. You must adjust frequency and voltage proportionally. 

You can also buy multi-speed speed motors or adjust speed mechanically.


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