7 HP motor

[digr]

The shop recently threw out a newer 7 hp single phase air compressor motor because it would not start every time it called for air. They said it had a dead spot and when it wouldn't start you had to shut it off and turn the motor by hand and it would start after you turned it back on. It just happened to end up in the back of my truck. Is there any way to fix this motor or is just junk?

[Sandy]

This is one of those this that could be discussed eternally but the short answer is yes, it probably can be fixed. Without argueing the merits of repairing one versus replacing one, a couple of things can be determined by you right off the git-go. 1) Availability of parts. Is there a motor repair shop in your area that can get common components. 2) Time and talent. If you have a propensity for these tedious little tasks it's an easy job.

There probably will be a contactor plate in the motor that acts as the interface between the start and run windings. This guy gets burnt spots in it or the contacts are burnt. That'll need replaced and while you're in there bearings bla bla bla. Just as well replace the start capacitors also. One capacitor if it's a 120v and two if it's 230v.

For the guy that likes messing with these things there are some savings to be had. For a company labor costs back and forth to the shop as well as repair costs override the purchase price of a new one. Not a lot of motor repair shops left anymore because of that.

Have fun.

[digr]

This is one of those this that could be discussed eternally but the short answer is yes, it probably can be fixed. Without argueing the merits of repairing one versus replacing one, a couple of things can be determined by you right off the git-go. 1) Availability of parts. Is there a motor repair shop in your area that can get common components. 2) Time and talent. If you have a propensity for these tedious little tasks it's an easy job.

There probably will be a contactor plate in the motor that acts as the interface between the start and run windings. This guy gets burnt spots in it or the contacts are burnt. That'll need replaced and while you're in there bearings bla bla bla. Just as well replace the start capacitors also. One capacitor if it's a 120v and two if it's 230v.

For the guy that likes messing with these things there are some savings to be had. For a company labor costs back and forth to the shop as well as repair costs override the purchase price of a new one. Not a lot of motor repair shops left anymore because of that.

Have fun. That sounds good I will take a look as soon as I get time. One thing I forgot to mention is that the motor is only a year or so old. Our shop only has about 208 volts to run single phase motors. This was the second motor on that air compressor. It now has a three phase motor and is working fine. I asked the power company about the low voltage and they said that it was above their minimum so they would not do anything about it. We also had trouble with a plasma cutter running on single phase. We have changed it to three phase and it is working fine. Could the low voltage have caused all these problems? And we have a motor repair shop that is very anxious to do business with us. We have five rock crushers and two blacktop plants. all with big motors.

[Sandy]

One thing I forgot to mention is that the motor is only a year or so old. Our shop only has about 208 volts to run single phase motors. This was the second motor on that air compressor. It now has a three phase motor and is working fine. I asked the power company about the low voltage and they said that it was above their minimum so they would not do anything about it. We also had trouble with a plasma cutter running on single phase. We have changed it to three phase and it is working fine. Could the low voltage have caused all these problems? And we have a motor repair shop that is very anxious to do business with us. We have five rock crushers and two blacktop plants. all with big motors.

Yeh they are a little low by what most consider standard. There are no real hard standards they have to follow in absolute. In current years most utilities have had to file with their respective states so called service agreements that they will run within certain nominal voltages plus or minus ten percent. Excessive brown outs brought this to the front. Cooking too many microwaves, TV's, HVAC compressors and such. Take 230 volts minus 10% would be 207, LOL. I've seen as low as 196 but that's plain not healthy for electronics. Most stuff is manufactured for a 220-240 range. higher is better than lower.

In the old days if you knew you were going to have a steady diet of 208 you could by equipment that was strappable for the lower range. Not so anymore. Another possibility is that your shop is by an older 208 three phase transformer.

In a shop environemnt it could be these motors were coming off the start winding a little slow as well as running hotter and burning little pits each time.

You could measure yours at home several times over a seasonal period and see how it compares.

[smithboy]

Here is a question that is in the same area...
I was looking at new compressors at the local Tractor Supply. One was a big mutha and had a three phase motor (at least it said so on the motor), but the power input was single phase 220. It was an ingersol-rand. It had a box on the side that I assumed was a small solid state phase converter, but it had no markings or stickers that indicated what it was. Is this common? and, is it viable over the long term? The reason I ask is that I have never seen a 7hp single phase motor and was wondering if that motor might actually be 3-phase running off a similar setup. Could this affect starting? Just wondering.

[digr]

Here is a question that is in the same area...
I was looking at new compressors at the local Tractor Supply. One was a big mutha and had a three phase motor (at least it said so on the motor), but the power input was single phase 220. It was an ingersol-rand. It had a box on the side that I assumed was a small solid state phase converter, but it had no markings or stickers that indicated what it was. Is this common? and, is it viable over the long term? The reason I ask is that I have never seen a 7hp single phase motor and was wondering if that motor might actually be 3-phase running off a similar setup. Could this affect starting? Just wondering. No sir this is a single phase motor, It is 7.5 H.P. motor actually.I think they make them up to 10 HP. This has a box on the top which houses the capacitors. This motor is a Ingersoll Rand also.

[halbritt]

Here is a question that is in the same area...
I was looking at new compressors at the local Tractor Supply. One was a big mutha and had a three phase motor (at least it said so on the motor), but the power input was single phase 220. It was an ingersol-rand. It had a box on the side that I assumed was a small solid state phase converter, but it had no markings or stickers that indicated what it was. Is this common? and, is it viable over the long term? The reason I ask is that I have never seen a 7hp single phase motor and was wondering if that motor might actually be 3-phase running off a similar setup. Could this affect starting? Just wondering.

It is likely that you were looking at a three-stage compressor with a single-phase motor. I was in TSC just the other day looking at the same compressors. "Three-stage" is in reference to the compressor pump. A three-stage pump will output more CFM at a higher pressure than a single-stange pump for a given HP rating.

[smithboy]

Halbritt,
It's possible I misread the label or misinterpreted it. I live really close to that store, so I will look more carefully next time. It was over $1000, so it was way out of my price range anyway. But I was curious, because I was under the impression that there was sort of a design limitation on the possible size of a single phase motor (like around 5 or 6 hp) and that label on the compressor I saw seemed to re-inforce that (now obvious) misconception.

Digr,
I didn't mean to imply that you didnt read the label on the motor or anything like that, so I hope you didnt take my question that way, and thanks for the pictures. Like I said, I have never seen a single phase motor that large. Wow! 3-phase, sure...I have seen very, very large 3-phase motors (100hp or more). In fact, big 3-phase motors are probably more common than the small ones. I now wonder if the box I saw on the side of the tank was just a remote bank of capacitors. I'll have to go to TSC and use one of their screw drivers to take it apart in the store. I am sure they will let me, maybe... Thanks for the eye-opener.

Another myth dispelled.

[digr]

Its apart. The fan was a bit of trouble but its off in one piece.

[Sandy]

Armeture looks good.

Backend looks good.

Contacts looks baaaaad!!

Pitted looks baaaaad!!!

Shaft end looks good.

Looks like your shop has a lot of heavy dirty air drifting around or that compressor was in a bad spot. Lot of caked on stuff there. Especially for the contactor area. Part of the short life span issue maybe???

[digr]

Armeture looks good.

Backend looks good.

Contacts looks baaaaad!!

Pitted looks baaaaad!!!

Shaft end looks good.

Looks like your shop has a lot of heavy dirty air drifting around or that compressor was in a bad spot. Lot of caked on stuff there. Especially for the contactor area. Part of the short life span issue maybe???
The compressor has been moved out of the shop because of the noise but it is in a lot cleaner environment. What do you think clean up these contacts or try to find a new set?

[Sandy]

The compressor has been moved out of the shop because of the noise but it is in a lot cleaner environment. What do you think clean up these contacts or try to find a new set?

For the effort I would get a new set. Those two that are sticking outward in the pics are plain wore out and wouldn't last long. The other two that are pitted, if they are like most important contacts, come with a semi-precious metal surface for long life and positive contact. Once they are pitted filing them down is temporary at best.

Look at it from this perspective; if you put it into service and happened to be away from it during one of those start failures------it's going to set there and hum till the windings get hot and cook the whole thing.

So to maximize on your efforts, get a complete set. They used to come as a whole kit anyway. You've worked hard on this, make it last. :)

[digr]

For the effort I would get a new set. Those two that are sticking outward in the pics are plain wore out and wouldn't last long. The other two that are pitted, if they are like most important contacts, come with a semi-precious metal surface for long life and positive contact. Once they are pitted filing them down is temporary at best.

Look at it from this perspective; if you put it into service and happened to be away from it during one of those start failures------it's going to set there and hum till the windings get hot and cook the whole thing.

So to maximize on your efforts, get a complete set. They used to come as a whole kit anyway. You've worked hard on this, make it last. :)
Thanks for all the info. Thats what I was thinking I don't need the motor right now so I have a lot of time to replace the parts. I filled the contacts and put it back together so I wouldn't lose any parts and it runs fine.