# Is it possible for an AC induction motor to lose torque due to age.



## sparkywannabee

Been working on fixing some issues on a big mill. This 2 HP motor pumps coolant through the spindle, the bit and keeps chips flushed out. Lately bits have been getting jammed up as if coolant pressure not strong enough, should be able to get 240psi max, gauge reads about 90. They said the pump has been rebuilt and filters changed. Of course a rebuilt pump does not mean a good pump, probably first thing i'll check, but I did notice the motor is original, which makes it 17 yrs old, running about 16 hrs, 5-6 days a week. I've changed quite a few AC 3 ph motors and that is serious mileage, but usually its cause overloads start tripping, or bearings lock up etc. I'll megger, thermal, rpm check, but what i wanted to ask was if a motor could just get tired, loose torque, any way to possibly measure that, or even lose RPM's. I'll check amp draw when I go in monday, maybe that will tell me something. Tried uploading picture of motor info, I think file might be too big, it is a 2 HP made by US motors, 3.2 amp at 460, 1740 rpm.


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## Black Dog

sparkywannabee said:


> Been working on fixing some issues on a big mill. This 2 HP motor pumps coolant through the spindle, the bit and keeps chips flushed out. Lately bits have been getting jammed up as if coolant pressure not strong enough, should be able to get 240psi max, gauge reads about 90. They said the pump has been rebuilt and filters changed. Of course a rebuilt pump does not mean a good pump, probably first thing i'll check, but I did notice the motor is original, which makes it 17 yrs old, running about 16 hrs, 5-6 days a week. I've changed quite a few AC 3 ph motors and that is serious mileage, but usually its cause overloads start tripping, or bearings lock up etc. I'll megger, thermal, rpm check, but what i wanted to ask was if a motor could just get tired, loose torque, any way to possibly measure that, or even lose RPM's. I'll check amp draw when I go in monday, maybe that will tell me something. Tried uploading picture of motor info, I think file might be too big, it is a 2 HP made by US motors, 3.2 amp at 460, 1740 rpm.


Yes just like anything that gets old.


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## Bootss

Is that motor a special frame motor if not just go buy a new motor and see what happens.If it's not an off-the-shelf motor take it to motor shop and have them recondition the motor ,dip and bake the stator put new bearings in it see what happens.


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## wildleg

friction, dirt, filings, etc. cause degradation over time.

but from 240 to 90 is excessive (that's less than 40% of the pressure you had before), so I'd look for other things. major slippage, and the pump itself. Sounds like there's issues.


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## Jhellwig

Squirrel cage motors don't get weak they get dead. If it megs good and the winding ohm good and runs unhooked from the load there is nothing wrong with the motor electricly. There are ways that a motor can fail and still test good with a meter but a pdma test will find issues. Even then it will either run or not. No in between.

Bearings can drag small motors down though so that is worth checking.

There are some issues that can happen that will make motors do odd things. Those are very very rare though. 

Remember when checking amps that if it is a centrifugal pump, blocking flow will lower the amps. If it is a positive displacement pump the amps will go up if flow is blocked.


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## sparkywannabee

Blackdog, so you have personally seen old AC motors not work as well without tripping o/l, fuses, breakers etc.
Lep, motor looks like sumpun you would buy from Grainger in Baldor gold for about $500. I have only worked at this place for 3 weeks, they have 20-30 million of sales a month, go through $30,000 of wire a month, they say the big mills have to run all the time, but they sound as if changing one motor that might not need it will break the bank.Last place I worked we were broke but we stocked all these motors and once they got old and started acting up we just changed them, like a wear item.
Wildleg, i did notice in the prints that op can select 3 different pressure settings, i am sure they entered highest setting on their CNC screen but maybe the valve is stuck, or maybe a bad I/O.
Jhell, my experience with these motors is the same as yours, they just die, bearings I can usually hear or feel when bad, that will also increase amp draw, cause o/l's to trip, pump might be something new to me, looked like a centrifugal but they said it had diaphragms in it that got ripped, only diaphragms i have changed are in air operated pumps.
But I will get to the bottom of it and post what I find out. Mucho thanks for the feedback.


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## Jhellwig

If it would make them happy get some way to see what rpm the motor is turning. That might prove to them that it isn't the motor.

I have had to do all sorts of things to prove to dumb engineers and operators that it isn't the motors fault it is your process or mechanical.


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## John Valdes

I agree with Jhellwig.
Its either a good motor or its not.
It might need cleaning and or bearings, but if it runs its good.
I say this for simple 3 phase ac induction motors. Rotor and stator. Nothing more.


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## NC Plc

First thing I would do is check the RPM of the motor with a non-contact tool, then I would look at the bearings. Most of the motor issues I come across are the result of a bad VFD or bad bearings.

Or, just a bad motor that we replace.


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## oliquir

if rpm was not ok, current draw would become very high and should trip overloads


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## Wirenuting

Here is a 2hp diaphragm pump. Rated 2.9 amp and only pulled 1 when running full bore. It pumped water/oil waste to a separation tank. 
These style are long in the Tooth if kept up. 

This one lasted less then 6 months before it ripped the diaphragm and no one here wants to repair it. Our repair crew boss doesn't want to admit his buddy can't replace a diaphragm correctly so I have 2 of these new pumps sitting idle. Good thing I had replaced the back-up submersible pumps. The hi-level alarms have been lite up for months. 

The o/l was set at 3 amp on the old ones. They only tripped when the bearings or pivot points would seize. I replaced them down to 1.2 amp so as to catch the damage before it destroyed the units. 

I normally set the o/l's to just higher then the work the motor performs. Then I'll write it down in the starter for the next guy. 

Bearings, check valves, over greasing, couplings are all things to check. To bad you don't know the original amp draw. But a motor that lasts for 17 years is a good thing.


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## JRaef

Motors can get "weak" with age, yes. What happens is that the winding insulation starts to leak to the frame, so not all of the power going to the motor is performing useful work. Thats what a megger tells you. BUT, that can amount to a few percent before it makes the motor fail completely or the protection system take it off line. What often happens there is that the OL relay starts nuisance tripping, so someone puts in larger heaters or turns up the dial to make the problem go away, then the motor fails. So as previously mentioned, a 40% loss of pressure is way too much to be accounted for by motor age.

If there are 3 different pressure settings in the CNC and there is no speed controller on the pump, like a VFD, that can only be accomplished by valves. If it's a centrifugal pump, then it's a throttling (variable flow) valve that gets an analog signal, likely from the CNC controller, telling it how far to open. If its a positive displacement pump, then it can only be accomplished with an accumulator / recirculation bypass type system, where the pump puts out maximum flow all of the time, but for the lower pressures some of it is bypassed back into its reservoir.

Read the amps, and check to see if anyone in the past recorded the amps when it was working properly. If the amps are lower, it's probably a centrifugal pump and there is a flow blockage somewhere, or the variable flow valve is stuck or the analog signal is lost, so the valve goes to its minimum setting. If it is a positive displacement pump, you could tell because regardless of what pressure the CNC asks for, the motor current would remain close to normal regardless of pressure. If you find that, then there is a problem with one of the valves, likely stuck open at the lower pressure setting so that the flow is constantly bypassed.


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## sbrn33

You may check and make sure rotation didn't get changed somewhere along the line.


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## Bootss

JRaef said:


> Motors can get "weak" with age, yes. What happens is that the winding insulation starts to leak to the frame, so not all of the power going to the motor is performing useful work. Thats what a megger tells you. BUT, that can amount to a few percent before it makes the motor fail completely or the protection system take it off line. What often happens there is that the OL relay starts nuisance tripping, so someone puts in larger heaters or turns up the dial to make the problem go away, then the motor fails. So as previously mentioned, a 40% loss of pressure is way too much to be accounted for by motor age.
> 
> If there are 3 different pressure settings in the CNC and there is no speed controller on the pump, like a VFD, that can only be accomplished by valves. If it's a centrifugal pump, then it's a throttling (variable flow) valve that gets an analog signal, likely from the CNC controller, telling it how far to open. If its a positive displacement pump, then it can only be accomplished with an accumulator / recirculation bypass type system, where the pump puts out maximum flow all of the time, but for the lower pressures some of it is bypassed back into its reservoir.
> 
> Read the amps, and check to see if anyone in the past recorded the amps when it was working properly. If the amps are lower, it's probably a centrifugal pump and there is a flow blockage somewhere, or the variable flow valve is stuck or the analog signal is lost, so the valve goes to its minimum setting. If it is a positive displacement pump, you could tell because regardless of what pressure the CNC asks for, the motor current would remain close to normal regardless of pressure. If you find that, then there is a problem with one of the valves, likely stuck open at the lower pressure setting so that the flow is constantly bypassed.




Jraef
we used to steam clean small motors I guess larger motors also bake them out dip and bake them twice new bearings.what's your feelings on that?


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## Wirenuting

Lep said:


> Jraef we used to steam clean small motors I guess larger motors also bake them out dip and bake them twice new bearings.what's your feelings on that?


I've never seen any good come from steam cleaning a motor and not baking it. 

I've also seen motors get weak over time. But it's so rare I never give it much a thought as it was air handlers and they can hide it for years. Over greasing and wash downs cooked them.


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## JRaef

Lep said:


> Jraef
> we used to steam clean small motors I guess larger motors also bake them out dip and bake them twice new bearings.what's your feelings on that?


All motor winding insulation is "hygroscopic" meaning it absorbs and releases water, to varying degrees. Over time, microscopic cracks and fissures form in the insulation material that allow more moisture in, then when the motor heats up that moisture vaporizes and expands, accelerating the deterioration process. Steam cleaning can be the final straw in a cascading failure to destruction unless the motor is thoroughly baked out prior to ever being energized.

Dipping and baking helps, and is a good strategy in between rewinds, but is not the same. When dipping and baking, the varnish doesn't get all the way into each and every nook and cranny of every winding conductor, but it can form a barrier to help prevent further incursion of moisture. Vacuum impregnation is even better than simple dipping because it also helps to remove air bubbles (that can lead to corona discharge issues) and gets the varnish material deeper into the coils, but still, it's not a replacement for damaged insulation.


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## JRaef

sbrn33 said:


> You may check and make sure rotation didn't get changed somewhere along the line.


This is an excellent point that I forgot, especially if it in a centrifugal pump. A lot of times when the pump portion is rebuilt, the pump (mechanical) guys remove it without thinking of marking the conductor phasing. Then when they reconnect it, they check rotation, see that the pump is pumping, and they are done. They might not realize that a centrifugal pump will show flow in either rotation, just not enough if it's backward. So that could indeed explain this as well. Good catch sbrn33.


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## Bootss

Jraef
I worked at two electric motor shops and their practice was to steam clean bake out,dip & bake.This was 30 years ago is that still the practice?.I guess this is the poor mans repair.

I know this for a fact because I was the" crumb bum" steam cleaning the Stators. Lol


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## JRaef

Like I said, it's usually done as an intermediate step between rewinds, where the insulation still tests out as good when the motor is sent in for a PM overhaul, but they want to keep it that way. So for instance in some really nasty places like sawmills, they will periodically swap out motors during scheduled shutdowns and send them into the shop for PM overhaul, then put them on the shelf until the next time to be the one that is swapped-in. But after 3 or 4 of those cycles, maybe 25 years later for instance, they end up rewinding them. I doubt that many places still keep long term records like they used to, but that was the way it was 20 years ago when I was in the Northwest and Western Canada doing a lot of lumber mill work.


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## sparkywannabee

You guys are not going to believe this, when i asked the machine op. if he had punched in code for higher pressure setting he did'nt know what I was talking about, nobody over there including maintenance knew this could be done and i've only been there 3 weeks.I just happened to read the stupid manual on this machine. And what do you know, both machines had low pressure selected. Btw, Jraef, it is the second kind of setup you mentioned, 2 regulaters, valves etc, when it runs wide open its 200psi, med is 100, low is 50.


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## JRaef

LOL, it came down to "RTFM"!

Good job tracking it down for them, you are now a hero in their eyes!

Side note, I've recently toyed with the idea of adding "R.T.F.M. to the end of my title on my business cards, as if it's some sort of acronym for a special degree or skill certificate. if it makes just one person ask so that I can tell them that half of what I do for a living is instruct people on reading their F'ing manuals, it will be worth it. I got the idea from an old A-B salesman who had "V.L.G.D." printed at the end of his title, which made everyone ask what it meant. He then had an excuse to explain the virtues of Vertical Lift Gravity Dropout contactors!


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## sparkywannabee

Hero in some people's eyes maybe, some of the others seemed little upset. Machines are run by ancient GE Fanuc plc and drives, trying to get them to upgrade to controllogix and AB drives, program is written in C, I assume Rockwell would be able to convert that over for us. Can you shed some light on that Jraef, or anybody.


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## DriveGuru

sparkywannabee said:


> Hero in some people's eyes maybe, some of the others seemed little upset. Machines are run by ancient GE Fanuc plc and drives, trying to get them to upgrade to controllogix and AB drives, program is written in C, I assume Rockwell would be able to convert that over for us. Can you shed some light on that Jraef, or anybody.


 It is definitely possible for a motor to lose torque over time depending on its life, although I agree with others that the issue would normally lie elsewhere. A motor can only be rewound a finite number times before core losses make it too inefficient. Normally any type of core loss would be due to extreme overheating. Or in the case of a servo be demagnetized. Your local EASA shop should be able to test the windings for you, and most can also perform a core loss test as well.


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## Bootss

DriveGuru said:


> It is definitely possible for a motor to lose torque over time depending on its life, although I agree with others that the issue would normally lie elsewhere. A motor can only be rewound a finite number times before core losses make it too inefficient. Normally any type of core loss would be due to extreme overheating. Your local EASA shop should be able to test the windings for you, and most can also perform a core loss test as well. Or in the case of a servo be damaged.


How about if you're able to press new slot laminations in the frame for the windings ,then reuse the frame?Do the stator frames wear down somehow? Then install all new windings bearings?
maybe the motor frame gets tweeked after years.I guess the rotor laminations would wear down magnetically conducting ability


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## DriveGuru

Lep said:


> How about if you're able to press new slot laminations in the frame for the windings ,then reuse the frame?Do the stator frames wear down somehow? Then install all new windings bearings? maybe the motor frame gets tweeked after years.I guess the rotor laminations would wear down magnetically conducting ability


 That's conceivably possible, but not economical by any means. Any more ... Unless it's a special frame...it's hardly economical to rewind a motor under 40-50hp...let alone manufacture new core laminations (there are allot of them in a stack)...even if the OEM was willing to give you the data. Laminations don't really "wear " down magnetically, but they can short causing eddy currents, on large motors I've seen them re-insulated and re-stacked. Anytime a metal is heated greatly(as in burning out the old winding) then cooled, the metal hardens. The more a metal hardens, the higher its reluctance (or its ability to conduct magnetic lines of flux).


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## JRaef

sparkywannabee said:


> Hero in some people's eyes maybe, some of the others seemed little upset. Machines are run by ancient GE Fanuc plc and drives, trying to get them to upgrade to controllogix and AB drives, program is written in C, I assume Rockwell would be able to convert that over for us. Can you shed some light on that Jraef, or anybody.


Rockwell services (CSM) can be contracted with to convert your GE/Fanuc PLC system to Logix, in fact our group out here is doing one right now. The separation of GE and Fanuc is creating a lot of confusion with customers now. But I doubt you can get someone to do it for free if that's what you were thinking.


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## sparkywannabee

Absolutely not for free. Last controllogix upgrade from Automax was first project I was given, back in '08. Me and our plant guys did all the wiring and I/O install, there were 8 remote bases, almost a thousand I/O's, the old enclosures were too small for Controllogix I/O's so we had to install 3 x 3 cabinets and run wires to that cabinet. Rockwell had one engineer doing the software all week and his boss part of the week, and they had been working on converting even before that. Between Rexel, Rockwell and AB software we were well into 6 figures. This project might be harder softwarewise cause its 2 486's, yes, a 486, remember that, talking to each other. The I/O's and plc I can physically install, even if I have to install a larger cabinet for the I/O's. The project you are doing would'nt be like a huge ass CNC would it. Window would be extremely tight and this company will happily pay what it takes, they have orders for new presses thru 2016.


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