my plant was built in the late 50's and we have alot of old u frame motors still running. Most of the bigger fans have been replaced with T frame high efficiency motors, but there is still lots of U frames in service. Replacing the U's with a T takes alot of work, and I'm wondering if it is cost effective in the long run. The U frames seem far more substantial than the T's. Most of the 40hp blowers use 5 belt sheaves, and the T's just don't seem to have the shaft to handle them. The U's also seem to have more starting torque and also a longer life in harsh conditions.
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Pros and cons of U frame motors 2
- Thread starter Thedroid
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- #2
Look up a frame size for a 10 HP U frame motor. Then look up the same frame size as a T frame motor. The T's are a rerate of the U's. More HP out of the same basic frame size. The U frames will take punishment that would kill a T frame in a shift.
Bill
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"Why not the best?"
Jimmy Carter
Bill
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"Why not the best?"
Jimmy Carter
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- #3
I agree the U frames we have around here are pretty bulletproof. I would like to have a few new ones around as spare's instead of replacing them as they go out with a T frame.
The newer motor's just don't seem to have the same durability as the old U's.
The boss thinks that they are too expensive, but by the time we retrofit the appication for a T frame, I think they come close in price.
Are there any advantages to going with one over the other besides initial purchase price?
The newer motor's just don't seem to have the same durability as the old U's.
The boss thinks that they are too expensive, but by the time we retrofit the appication for a T frame, I think they come close in price.
Are there any advantages to going with one over the other besides initial purchase price?
I am a ME but I do make observations about what people do sucessfully. I had a client that would use an U frame motor ever chance he got instead of a T frame. He bought up every used U frame he could get his hands on in the ranges that he needed. He only used T frames when he had outdoor applications. He ran a large sawmill operation and the service on the motors was brutal.
rmw
rmw
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- #5
LionelHutz
Electrical
The big disadvantage of the old U frames is the efficiency.
To easily find something fairly equivalent, you can look up the U frame motor size and then pick the T frame motor with the same frame size.
To easily find something fairly equivalent, you can look up the U frame motor size and then pick the T frame motor with the same frame size.
These old motors were designed with plenty of safety factor to last a lifetime. The present day designers seem to design them to last until warranty period.
I always pack more copper in these old monsters (by using thinner and better modern insulation materials) so that the copper loss is reduced. Depending on the age and the OEM, I could stuff with the winding with 10 to 30% more copper. Not great strides have been made in the reduction of iron loss in the past 50 years and this loss is typically low (1 to 2 %) to begin with.
So, I would recommend that these old work-horses be rewound to class H by a good rewind company, may be with new bearings.
I always pack more copper in these old monsters (by using thinner and better modern insulation materials) so that the copper loss is reduced. Depending on the age and the OEM, I could stuff with the winding with 10 to 30% more copper. Not great strides have been made in the reduction of iron loss in the past 50 years and this loss is typically low (1 to 2 %) to begin with.
So, I would recommend that these old work-horses be rewound to class H by a good rewind company, may be with new bearings.
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- #9
Strictly speaking, a U frame motor is simply a motor built into an extremely rugged, beefy, extra heavy frame.
In practice, most U frame motors also were built as NEMA Design D which translates into a high slip motor with virtually no breakdown point in the toruq-speed characteristic curve and very high starting toruq. Also, for the very high starting torque they had relatively low starting inrush currents.
Today, for mechanically demanding jobs, the U frame is a plus and is still occasionally seen on rock crushers and other heavy duty applications. Unfortunately, the NEMA D design is a big negative since the the efficiency is so poor.
Maybe the motor guys can answer this: Is it possible to buy a high-efficient or premium-efficient Design A or B motor in a U frame?
In practice, most U frame motors also were built as NEMA Design D which translates into a high slip motor with virtually no breakdown point in the toruq-speed characteristic curve and very high starting toruq. Also, for the very high starting torque they had relatively low starting inrush currents.
Today, for mechanically demanding jobs, the U frame is a plus and is still occasionally seen on rock crushers and other heavy duty applications. Unfortunately, the NEMA D design is a big negative since the the efficiency is so poor.
Maybe the motor guys can answer this: Is it possible to buy a high-efficient or premium-efficient Design A or B motor in a U frame?
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- #11
I have seen them in several different manufacturers catalogs, they are described as automotive duty, and listed as design B. I've compared their spec sheets with similiar rated T frames, and they are very similiar in there efficiency and power factor ratings. They weigh more and they also cost more. If the newer U frames are built as durable as the older one's, I feel that the cost premium would be offset by our labor to install a T frame in it's place, and also the long life and durability.
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- #12
Thedroid, that's a question that's impossible to answer unless we know what the extra ruggedness is worth in your application.
So, if an ordinary T frame motor is plenty good enough, then a U frame is largely a waste of money.
If you are running a concrete crusher or some other machine that vibrates and bangs around, the U frame motor might be a bargain.
So, it depends!
So, if an ordinary T frame motor is plenty good enough, then a U frame is largely a waste of money.
If you are running a concrete crusher or some other machine that vibrates and bangs around, the U frame motor might be a bargain.
So, it depends!
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2
- #14
There is no doubt the old U frames are bulletproof but inefficient.
I would advise working with your motor suppliers. They should be able to provide you with sound reasoning on their recommendations. If not, find another.
For instance, if you are concerned about bearings, you can go with a crusher duty T frame with roller DE bearings. Be prepared to do the research, as they will need to know sheave radius, number of belts, etc. to qualify a good replacement.
If heat is a concern, especially where air flow across the motor will be minimal or soon plugged with crap and no maintenance for long periods of time, you might want to stay with the old U.
I do want to point out that the total cost of changing to T frames is more involved than simply tit for tat. Standardization is THE big reason for changing to T frames. Another is efficiency. Another is off the shelf availability. If you have spares for every U frame presently, you may be in good shape, but consider the future. Everyone wants to reduce inventory. Some companies work with their suppliers to minimize what they have to carry on hand. For instance if you have six 75 HP NEMA 444T frame motors in your plant, how many spares do you need? If you carry one on hand and can get another same or next day, you would be smart to add another 444T frame to this equation instead of carrying a U frame bastard (which will take several days to rewind at best.) Suppliers will sometimes carry a motor (T frame) for you for a very small "insurance cost" that they can spread out over many other facilities like yours. U frames are getting harder to find and more expensive. This will only worsen. The future is upon us. Embrace and work with it.
I would advise working with your motor suppliers. They should be able to provide you with sound reasoning on their recommendations. If not, find another.
For instance, if you are concerned about bearings, you can go with a crusher duty T frame with roller DE bearings. Be prepared to do the research, as they will need to know sheave radius, number of belts, etc. to qualify a good replacement.
If heat is a concern, especially where air flow across the motor will be minimal or soon plugged with crap and no maintenance for long periods of time, you might want to stay with the old U.
I do want to point out that the total cost of changing to T frames is more involved than simply tit for tat. Standardization is THE big reason for changing to T frames. Another is efficiency. Another is off the shelf availability. If you have spares for every U frame presently, you may be in good shape, but consider the future. Everyone wants to reduce inventory. Some companies work with their suppliers to minimize what they have to carry on hand. For instance if you have six 75 HP NEMA 444T frame motors in your plant, how many spares do you need? If you carry one on hand and can get another same or next day, you would be smart to add another 444T frame to this equation instead of carrying a U frame bastard (which will take several days to rewind at best.) Suppliers will sometimes carry a motor (T frame) for you for a very small "insurance cost" that they can spread out over many other facilities like yours. U frames are getting harder to find and more expensive. This will only worsen. The future is upon us. Embrace and work with it.
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