Should a single phase shaded pole motor run on 2 phase?

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Hello. This is my first post.

I do maintenance at a manufacturing facility. We have been having problems with small shaded pole motors burning out. They are intermittent duty rated, 230V single phase, 50/60Hz. They run for a few seconds at a time with a few seconds rest in between, and one longer rest every minute. They also run basically 24hrs a day. After a few months they start blowing fuses and show very low resistance on the coil (5 ohms when they should read 60 ohms brand new).

One of our senior electricians said it would be fine to connect these to 208V 3-phase and just use 2 phases instead of single phase 230V and neutral. But I suspect that this is the reason why they keep burning out after a few months. The shaded pole motor creates it's own second phase, so wouldn't using 2 phases create a frequency problem, or perhaps eddy currents that are damaging the winding insulation? Either that, or they are starting and stopping too frequently.

Thanks!
 

LarryFine

Master Electrician Electric Contractor Richmond VA
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Welcome to the forum!

Between any two conductors, there can be only one "phase" or waveform. It's 208v instead of "230v" because of the timing; the two lines in question do not reach their individual, opposing peaks at the same time (because they're not opposed (180 deg), they're offset (120 deg)).

You need to find whether the motors are suitable for 208v from the manufacturer; they may have 208v motors if not.
 

GoldDigger

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The manufacturer should also have more complete profile information on the "intermittent" use in terms of duty cycle and number of starts. That may also take into account whether the motor is mechanically loaded while starting and how much of its rated power it is being called on to deliver.
Your load profile may just be abusing the motor. In that case either provide external cooling or use a larger motor.
But definitely first check whether you are providing too low a voltage (208 instead of 240) to the motor.
 

mbrooke

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Both 208 phase-phase and 230 volt L-N give a single sign wave and thus produce in a single phase field in the motor winding.


The phase angle and voltage may be different phase to ground on the 208 volt supply, but the motor does not see or experience it as there are no windings connected phase to ground.
 
Ahhh. I get it now!:jawdrop:

I had always thought of 3-phase as 3 separate sine waves 120 degrees phase shifted (that's what the diagrams show in trade school). But I was thinking about it the wrong way.

I should have thought of how voltage is difference in potential "electrical pressure" between 2 points. So measuring between 2 phases results in just 1 voltage (the potential difference between the 2), not 2 voltages.:slaphead:

I am enlightened. Thank you.
 

ActionDave

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Ahhh. I get it now!:jawdrop:

I had always thought of 3-phase as 3 separate sine waves 120 degrees phase shifted (that's what the diagrams show in trade school). But I was thinking about it the wrong way.

I should have thought of how voltage is difference in potential "electrical pressure" between 2 points. So measuring between 2 phases results in just 1 voltage (the potential difference between the 2), not 2 voltages.:slaphead:

I am enlightened. Thank you.

Now that we got that straightened out, I agree with Golddigger that you may be abusing your motors with the way you are using them.
 

Jraef

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.... They run for a few seconds at a time with a few seconds rest in between, and one longer rest every minute. ...
That is NOT an application for a shaded pole motor! Well, unless the IDEA was to go ahead and burn them out and replace them constantly because they are dirt cheap.

Shaded pole motors are only between 15 and 30% efficient. That's right, not 15-30% losses, but 15-30% efficiency, meaning 70-85% LOSSES in the motor! They are designed to be turned on and left on for light loads like fans and little circulating pumps, or if seriously over sized, they can be used when cheap speed control is wanted, like on old sewing machines with a rheostat foot pedals. if a 230V rated SP motor were given 208V, all it means is that it will be on the lower end of it's efficiency scale, so the 15% end. That's actually how they work for variable speed, you just reduce the voltage and the slip increases.

SP motors are not the type that you use on applications like this unless, as mentioned regarding the sewing machines, you grossly over size them, as in 3-4x the mechanical power rating you need.
 

synchro

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Chicago, IL
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EE
That is NOT an application for a shaded pole motor! Well, unless the IDEA was to go ahead and burn them out and replace them constantly because they are dirt cheap.
.

Agree completely. A permanent split capacitor (PSC) motor might fit the bill for a replacement because they make them in sizes down to 1/30 HP or less. They don't have a lot of starting torque but it's still more than a typical shaded pole.
 

scottbott

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Hello. This is my first post.

I do maintenance at a manufacturing facility. We have been having problems with small shaded pole motors burning out. They are intermittent duty rated, 230V single phase, 50/60Hz. They run for a few seconds at a time with a few seconds rest in between, and one longer rest every minute. They also run basically 24hrs a day. After a few months they start blowing fuses and show very low resistance on the coil (5 ohms when they should read 60 ohms brand new).

One of our senior electricians said it would be fine to connect these to 208V 3-phase and just use 2 phases instead of single phase 230V and neutral. But I suspect that this is the reason why they keep burning out after a few months. The shaded pole motor creates it's own second phase, so wouldn't using 2 phases create a frequency problem, or perhaps eddy currents that are damaging the winding insulation? Either that, or they are starting and stopping too frequently.

Thanks!

Your idea about motors going out after a short time may be because of the phase angle they are getting. While i agree with other posts about duty cycle, the way a split phase motor starts is dependent on phase shift within the motor its self. three phase power is at 120 degrees between lines therefore the starting torque is way advanced from where it should be given the power source. Also this type of use in a cheap split phase motor causes the winding to physically move chafing the insulation inside the motor. the windings will run hot. Also beware of the effects of high harmonics in power lines of industrial sites, you will need a power quality meter to see them.

I think you should look in to a three phase motor with a 100 percent duty cycle, inspect that the winding are vacuum packed against movement and thermal overloads installed in wingdings and a proper [solid state], current overload relay is installed, say, a Siemens ESP 200 series,
 
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Jraef

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I edited that previous post to correct the all caps typing, it is very difficult to read. Also corrected punctuation and spelling errors, but I did not alter the content.

I however disagree with some of the content. Shaded Pole is not Split Phase, different technologies.
 

mike_kilroy

Senior Member
Location
United States
Of course Jraef is correct, this is the wrong motor design for an application that "run for a few seconds at a time with a few seconds rest in between, and one longer rest every minute. They also run basically 24hrs a day."

Correct solution is to replace them with equiv size AC permanent magnet servo motors and drives. those ARE designed for that duty. Google "servo motors" to find manufacturers, then go to their websites, click on find local distributor, contact a few. Some will come look at your application and pick proper replacements for you that should then run this way for 5-10 years before you need maintenance on them.
 
Just to follow up, we contacted the manufacturer and they are not designed to run on 208. We installed small transformers on each one to change to the correct voltage and make single phase. This was cheaper than buying all new units. They have been running 2 years now with no further issues.
 
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