Rotary phase converter rotor problems

[rons]

I’ve personally never seen one with a pony motor and we work with rotary phase converters up to 50 hp started on caps

Are you using start caps with black plastic cases? The oval shaped tin can caps last longer but more are needed.

 

[billymx48]

Pretty good friends with a motor shop owner talked to him and he said manufacturers usually don't sell just rotors.

Cutting a shaft off a idler motor has been done and you should Dynamically balance it after while doing that you could lighten it up also for better performance in a RPC.

I have had three different brand RPCs and replaced bearings in all of them, I seen nothing special about their rotors besides the shaft being machined off so it doesn't stick out.

I would think that you would have to replace the motor in this situation. Just my two cents.

 

[Mook1004]

Pretty good friends with a motor shop owner talked to him and he said manufacturers usually don't sell just rotors.

Cutting a shaft off a idler motor has been done and you should Dynamically balance it after while doing that you could lighten it up also for better performance in a RPC.

I have had three different brand RPCs and replaced bearings in all of them, I seen nothing special about their rotors besides the shaft being machined off so it doesn't stick out.

I would think that you would have to replace the motor in this situation. Just my two cents.

That’s what I’ve been finding, that manufacturers won’t sell a rotor. And rebuilding a rotor isn’t cost effective in this situation either. I talked to a competitive rpc shop and they said they have in the past bought motors both ways with shafts machined off and shafts still sticking out. Think my best option is hopefully find, if even possible, rotor dimensions from the motor I think it is and compare. Ultimately I could separate a new motor and use the rotor and take the case to rewind shop and they could tell if winding internals are the same. If internals are the same just set it on the floor and sell it for one that needs rewound.

 

[rons]

Corrosion could be forming between the sheets of steel in the rotor. Producing a weak flux region.
Wonder if dipping the whole thing to dissolve rust would fix it. Then clear coating with two-part clear.

 

[Mook1004]

Corrosion could be forming between the sheets of steel in the rotor. Producing a weak flux region.
Wonder if dipping the whole thing to dissolve rust would fix it. Then clear coating with two-part clear.

What would dip sauce need to be. Something like an aluminum brightner? What kind of clear coat?

 

[dalmatiangirl61]

If you could find an exact replacement motor, same mfr, same frame, same HP, same voltages, same rpm, then yes the rotors would most likely be the same and you could swap rotors. But bearings may not be the same so you would have tp swap endbells too. Of course at that point you might as well swap out the whole motor, unless you know for sure the windings are bad in the replacement. Odds of finding a new replacement rotor are slim to nil, best to just look for a new/used motor.

 

[markz528]

Bad rotors are rare. And it takes a significant rotor problem to really cause a problem. This is for motors used as a motor - I know nothing about phase converters, but a lot about motors.

I have no idea about the test you described.

Common methods for finding bad rotor bars:
Motor current signature analysis - measuring rotor side band frequencies - cons - need to be at least at 50% load to see the sidebands, the more the better. Pros - very accurate.

Single phase test - apply single phase at rated current (approx 25% voltage) and rotate shaft. Cogging indicates bad rotor bars and no more than 3% current swing when shaft is rotated. Fairly accurate test.

Growler - hit or miss in my experience. Preferably using magnetic paper. Doesn't find voids in end rings, even if real bad. Will see broken rotor bars with magnetic paper.

Then there is snake oil like trying to measure magnetic peaks and valleys........

 

[Rob F.]

And im not telling him he needs two new matching ones. But he also wants something that works. I’m on here asking for help trying to save my customer money. But this is the 4th one that’s started doing this and the shop that’s making them can’t figure it out. Their response is to just sell them a brand new one.

Have you seen these large single phase motors? They say up to 100hp single phase. Maybe you can remove the need for the rpc's with these motors?

SPPS Written-Pole® single-phase motors...

THIS IS THE SINGLE-PHASE SOLUTION YOU'VE BEEN LOOKING FOR! Single Phase Power Solutions is the manufacturer of the world’s only large horsepower

singlephasepowersolutions.com

 

[Mook1004]

Bad rotors are rare. And it takes a significant rotor problem to really cause a problem. This is for motors used as a motor - I know nothing about phase converters, but a lot about motors.

I have no idea about the test you described.

Common methods for finding bad rotor bars:
Motor current signature analysis - measuring rotor side band frequencies - cons - need to be at least at 50% load to see the sidebands, the more the better. Pros - very accurate.

Single phase test - apply single phase at rated current (approx 25% voltage) and rotate shaft. Cogging indicates bad rotor bars and no more than 3% current swing when shaft is rotated. Fairly accurate test.

Growler - hit or miss in my experience. Preferably using magnetic paper. Doesn't find voids in end rings, even if real bad. Will see broken rotor bars with magnetic paper.

Then there is snake oil like trying to measure magnetic peaks and valleys........

The single phase test you describe is exactly what I did. Granted my shop said to test voltage and not current. But ohms law would apply as voltage and amps would correlate but they would be inverse. You tell me. You rotate rotor to a spot where it has a low mv rating it won’t start but put it to a place of high mv and it does start. I agree that rotor failures are rare. We service thousands of electric motors from vertical hollow shafts, submersibles and Rotophase and these are the only ones we can’t figure out. But these problem ones all have one thing in common. Being flooded for up to months when the Missouri River broke the levee. So I think that’s also a very rare occurrence.

 

[Mook1004]

Are you using start caps with black plastic cases? The oval shaped tin can caps last longer but more are needed.

Both. We call the oval tin cans run cap as the are about 40mf to balance manufactured leg and black plastic are our starts at 330mf

 

[Mook1004]

Have you seen these large single phase motors? They say up to 100hp single phase. Maybe you can remove the need for the rpc's with these motors?

SPPS Written-Pole® single-phase motors...

THIS IS THE SINGLE-PHASE SOLUTION YOU'VE BEEN LOOKING FOR! Single Phase Power Solutions is the manufacturer of the world’s only large horsepower

singlephasepowersolutions.com

I haven’t seen those. We sell Arco brand Rotophases and very happy with em. We’ve had hardly any trouble with them but I think that comes with a premium also.

 

[rons]

What would dip sauce need to be. Something like an aluminum brightner? What kind of clear coat?

Something that dissolves rust but doesn't attack aluminum. I have used EdFed from Ace Hardware on steel. Works the best.
I think it brightens aluminum. Soaking for a long time will etch. I have used vinegar too. Even 30% grade vinegar.
I have some Nason-496 clear with 483-78 hardener.

At first I was throwing out a guess about this. But you are describing a total immersion in water.
Are the end bearings rubber shielded? If not they get the water too.

Expensive explosion proof (totally closed) motors would resist a flood.

 

[rons]

Both. We call the oval tin cans run cap as the are about 40mf to balance manufactured leg and black plastic are our starts at 330mf

I have not studied what happens when black plastic case start caps are immersed in water. Are they vented? I don't use them.
The oval caps can be used as start caps but the largest size I can get is 100 uF. But they are totally sealed.

 

[Mook1004]

Something that dissolves rust but doesn't attack aluminum. I have used EdFed from Ace Hardware on steel. Works the best.
I think it brightens aluminum. Soaking for a long time will etch. I have used vinegar too. Even 30% grade vinegar.
I have some Nason-496 clear with 483-78 hardener.

At first I was throwing out a guess about this. But you are describing a total immersion in water.
Are the end bearings rubber shielded? If not they get the water too.

Expensive explosion proof (totally closed) motors would resist a flood.

Yea I’ve used some stuff called alumabrite that’s for aluminum and it eats rust. I was figuring a total immersion. We could rebearing it. We are just hoping it doesnt flood again.

 

[Mook1004]

I have not studied what happens when black plastic case start caps are immersed in water. Are they vented? I don't use them.
The oval caps can be used as start caps but the largest size I can get is 100 uF. But they are totally sealed.

I’m not worried about them flooding today and hopefully doesn’t in the future. They have a paper top and space would become and issue. And changing caps sizes is a weird deal in the set up as they have banks wired in parallel and the banks a wired series to each other. And capacitors wired series diminishes to total capacitance of all capacitors wires in that series but multiplies the voltage and the parallel wiring of capacitors adds capacitance but does nothing to voltage. So it gets tricky to replace to OEM with out using replacements at that are close in uf.

 

[Mook1004]

I’m not worried about them flooding today and hopefully doesn’t in the future. They have a paper top and space would become and issue. And changing caps sizes is a weird deal in the set up as they have banks wired in parallel and the banks a wired series to each other. And capacitors wired series diminishes to total capacitance of all capacitors wires in that series but multiplies the voltage and the parallel wiring of capacitors adds capacitance but does nothing to voltage. So it gets tricky to replace to OEM with out using replacements at that are close in uf.

And I wrote that backwards. The bank of start capacitors are wired in series and The two banks are wired parallel to with windings.

 

[BT Fabrication]

And that’s were I think I’m at. The company that made these were specifically made for phase conversion. Im not trying create my own version or reinvent the wheel. Would be hard to put a number of how many of these where made but there were a lot. The motor tags little information and like I said the new owners seem to just not know. Is there a way to distinguish a rotor by characteristics to find a replacement. This particular one we think we have narrowed down to a weg just by frame shape. But it’s also not the only style the used as I’ve seen others that have fins on the motor frame like many other motors and not a smooth frame like the pictured weg. This particular set up is parallel 40hp phase converters and going to be very costly to replace.

Just find a motor rewinding shop, that is 1/2 the cost of new and will be much more economical to do and easily save thousands

 

[rons]

What about the temperature change. Cab repeated freeze and thaw events make rotor laminations crack or disperse due to water expanding to ice.
If so, would a new motor be better off having a complete sealing job done. Wouldn't have to spray, just brush with no mask.

 

[Mook1004]

Just find a motor rewinding shop, that is 1/2 the cost of new and will be much more economical to do and easily save thousands

It’s not a winding issue so rewind wouldn’t help in this situation.

 

[Mook1004]

What about the temperature change. Cab repeated freeze and thaw events make rotor laminations crack or disperse due to water expanding to ice.
If so, would a new motor be better off having a complete sealing job done. Wouldn't have to spray, just brush with no mask.

So after the flood all motors were taken to rewind shop and cleaned, inspected and new bearings. I’m thinking more along the lines of corrosion of sitting in under water for months and then at the rewind shop for months as there was a massive back log of work.