7.5HP Air Compressor Burning Up Motors?

[mgb1974]

I recently purchase a used Paletek Sullivan M7.5 Screw Air Compressor. 220V Single Phase with 80 Gallon tank. It has 25K hours on it. I got a ok deal on it and seemed to be in good shape.

I run 5 axis Machining center in my garage, it is a Air hog. The machine uses air to keep the linear guides clean. Its a constant flow when the machine is powered up (Even if its running or not). I burnt up a Husky 3HP compressor and then my backup Craftsmen 1.7HP 33 Gallon Compressor.

I haven't been happy with the compressor, it is noisy over 80DB and runs constantly. It also runs constantly due to how the motor will continue to turn the compressor for 10 minutes after it last unloads, then it will shut off but only if it does not reload within the 10 minutes.

My main issue is the motor stopped working after about 300 hours of my use, blew a fuse. I took the belt off of the motor and tried to start it with same issue of not able to fully get to RPM. So I replace the motor with another Vevor 7.5HP motor. VEVOR 7.5HP Air Compressor Electric Motor 230V 30A CW/CCW Rotation 184T Frame, which was the same brand and model that was on the compressor.

So compressor worked fine for about 100 hours and the new motor stopped working.

The pulley on the screw compressor side seems to spin freely/normal.

Any ideas what is causing this or what to look for?

 

[finn]

Vevor wasn’t the motor brand original to the compressor. Rather, it’s an inexpensive importer and rebrander of Asian generic commodities, akin to Harbor Freight.

I doubt you will find a motor shop that will touch it, but perhaps it’s worth a try.

Another thing to check is what the voltage is at the motor when it’s running. Low voltage will kill the motor. Kind of hard to do with a broken motor, though.

Indo have some Vevor products, and they work, for whatever that’s worth, but definitely not professional quality.

 

[micromind]

Vevor wasn’t the motor brand original to the compressor. Rather, it’s an inexpensive importer and rebranded if Asian generic commodities, akin to Harbor Freight.

I doubt you will find a motor shop that will touch it, but perhaps it’s worth a try.

Another thing to check is what the voltage is at the motor when it’s running. Low voltage will kill the motor. Kind of hard to do with a broken motor, though.

Indo have some Vevor products, and they work, for whatever that’s worth, but definitely not professional quality.

I agree. A chintzy motor won't last very long when it's operated at full HP.

Since it's 7 1/2HP and 184T frame, it's almost certainly a bit less that 3600 RPM. That's not a real common thing, most 7 1/2HP motors are 213T frame.

How hot is it where the motor is located? Does it have fresh air for cooling? Clean or dusty? Is there any oil mist around it?

 

[BillK]

M7.5 Screw Air Compressor

I recently purchase a used Paletek Sullivan M7.5 Screw Air Compressor. 220V Single Phase with 80 Gallon tank. It has 25K hours on it. I got a ok deal on it and seemed to be in good shape.

I run 5 axis Machining center in my garage, it is a Air hog.

What is the cfm requirements of your cnc machine ? I just looked up a Haas UMC750 and it calls for 9.9 cfm @ 120 psi Your compressor is rated at 26 cfm @ 125 psi so it would be more than enough for the Haas.

I have a friend who has 2 Haas cncs in his shop. I have been there when both of them were running production and I can t remember his Kaeser screw compressor running continuously.

 

[Junker]

I'm assuming you dialed in the compressors settings already? What's your piping like? As others have said that motor is **** and you shouldn't be running that hard. You've got a massive resistance somewhere or some really dirty power. Screw compressors are supposed to be quiet.

Is your oil separator in good condition? Filter? Drains working? Too many unknowns to say for sure

 

[mgb1974]

My machine needs 3-15cfm, I think it’s more on the lower end. The Issue is it’s 3-5cfm constantly. Its a dumb design with Hurco to keep the linear rails clean. I asked if I can lower it or turn it off, the tech said no…
I only hear the air blowing when everything is off after I completely power down the machine and phase converter.

im running a regular air hose to the machine, I haven’t got around to hard pipping it in yet. the gage on the regulator before the cnc and on the cnc all are at 80psi.

oil/filters all were changed with the new motor. I got the exact oil that Sullivan recommended.

Clean air, no dust or oil, it’s sitting in the corner of my 40x26x16 insulated garage. It puts out some heat when running but garage doesn’t get above mid 70s after I replaced the motor.

 

[micromind]

With the new motor, it'd be a good idea to replace the motor pulley with on that's one size smaller. That will reduce the load on the motor.

Also, ensure that the motor is properly protected, even if you have to add an overload block.

 

[LXCam]

I imagine it has magstarter? On top the previous advice have you checked the contacts? I’d suggest inspecting those to see if they’re burned up. That’ll take out a motor in short order.

 

[The Cobbler]

I think you should look at a better quality motor . as said, Vevor is not high end , meant for production quality

 

[CraigStu]

How is the motor wired? What gauge wire is used? I know it isn't the same but I once burned up the motor on my Craftsman radial arm saw. Took it to be repaired, the guy took a quick look and asked if I was running it on an extension cord. Uh yeah, at times I have to. Get a bigger cord or I will see you again.

 

[Mainiac Mat]

Random thoughts.... worth what you're paying to read them:

Our company runs 7 Schulz screw compressors and they are all in the 10-15 HP range and are wicked loud (none have sound boxes on them)... so we have them in dedicated compressor rooms. All get hot and have fans blowing on them continuously. The rooms are all on exterior walls and in the summer, we vent the rooms through the wall with fans, as heat kills these things. In the winter we vent them into the shops to augment the heat.

We finally stopped buying cheap motors when we replace them. Now we only buy Baldor or Leeson.

We stood up a new facility in 2021and I finally managed to get the boss to do it right... a 30 HP variable speed (VFD) compressor on a 100 gal tank. cycles on and off with a soft startup, and runs at the lowest rpm that can supply the load. For distribution we have a 2" Copper loop with 1.25" lines running out to the far corners. I put in for energy credits, which paid for the difference between the VS model and the old style that runs pretty much non-stop.

We have a CNC router with a similar set up in that it has air jets blasting the rack and linear rails to clear debris. But it's controlled by a solenoid valve that turns the air on/off when the program starts/stop, so it's demand isn't so bad. Me thinks the designer who planned your machine with non-stop air to the rails didn't ever run one in a production setting.

 

[karoc]

May check into Service Factor of motor, I just can’t remember much about Service Factor to make guess. Which has to do with run time of motor.

 

[micromind]

May check into Service Factor of motor, I just can’t remember much about Service Factor to make guess. Which has to do with run time of motor.

Service factor is a measurement of how much reserve is built in to the motor.

For example, a 10HP motor with a 1.0 service factor is a 10HP motor.

A 10HP motor with a 1.15 service factor is a 11.5HP motor that is sold as 10HP.

 

[HAP]

I would bet you have undersized wiring for your needs.

R,
HAP

 

[u3b3rg33k]

I recently purchase a used Paletek Sullivan M7.5 Screw Air Compressor. 220V Single Phase with 80 Gallon tank. It has 25K hours on it. I got a ok deal on it and seemed to be in good shape.

I run 5 axis Machining center in my garage, it is a Air hog. The machine uses air to keep the linear guides clean. Its a constant flow when the machine is powered up (Even if its running or not). I burnt up a Husky 3HP compressor and then my backup Craftsmen 1.7HP 33 Gallon Compressor.

I haven't been happy with the compressor, it is noisy over 80DB and runs constantly. It also runs constantly due to how the motor will continue to turn the compressor for 10 minutes after it last unloads, then it will shut off but only if it does not reload within the 10 minutes.

My main issue is the motor stopped working after about 300 hours of my use, blew a fuse. I took the belt off of the motor and tried to start it with same issue of not able to fully get to RPM. So I replace the motor with another Vevor 7.5HP motor. VEVOR 7.5HP Air Compressor Electric Motor 230V 30A CW/CCW Rotation 184T Frame, which was the same brand and model that was on the compressor.

So compressor worked fine for about 100 hours and the new motor stopped working.

The pulley on the screw compressor side seems to spin freely/normal.

Any ideas what is causing this or what to look for?

if the motor itself is dying out, then either you're exceeding it's HP rating, or it's starts per hour rating. this typically is part of the service factor.

10 minutes seems like a long time for unloaded running, my 10hp VFD compressor defaults to 60 seconds, and the VFD says it takes about 1kW to spin at 30Hz, unloaded. the point being that running properly unloaded is just going to give your motor and compressor time to cool down, and should not be cause for burning up.

I would suggest you buy an ebay baldor/hitachi/WEG/marathon motor long before you buy vevor. worst case you'll need to throw new bearings at it before putting it in service, but that's not hard.

also get some data. put a clamp ammeter on your motor and make sure you're in-spec before you go changing things. maybe you've got a clogged discharge line and you're pumping way more head pressure than you think. I've seen it happen with microchannel aftercoolers.

 

[GrayFlattop]

How is the motor wired? What gauge wire is used? I know it isn't the same but I once burned up the motor on my Craftsman radial arm saw. Took it to be repaired, the guy took a quick look and asked if I was running it on an extension cord. Uh yeah, at times I have to. Get a bigger cord or I will see you again.

100% What gauge wire is used and how far are you from the service entrance panel? If you have a long run that's going to present more voltage drop.

Have you measured the line voltage before start-up and while starting / running?

I have a feeling that you may not have a "real" 7.5 HP motor. Generally speaking single-phase motors top out at 5HP, but they are made in 7.5 and 10 HP, just more costly. FLA on a 7.5 motor should be closer to 33 Amps.

 

[Firstram]

100% What gauge wire is used and how far are you from the service entrance panel? If you have a long run that's going to present more voltage drop.

Have you measured the line voltage before start-up and while starting / running?

I have a feeling that you may not have a "real" 7.5 HP motor. Generally speaking single-phase motors top out at 5HP, but they are made in 7.5 and 10 HP, just more costly. FLA on a 7.5 motor should be closer to 33 Amps.

Different compressor but, my 7.5hp 208v single phase Baldor motor FLA is 42. I think that's the same as 37ish at 230v.

 

[GrayFlattop]

Different compressor but, my 7.5hp 208v single phase Baldor motor FLA is 42. I think that's the same as 37ish at 230v.

I believe you. I just checked the Grainger catalog for reference.

My 5 hp compressor motor Is 23 or 24 amps at 240, so logically 30 amps seems light for a full 7.5 hp

 

[Monza Harry]

I'm with the low voltage scenario called by others, so a thorough check of wiring, and voltage/amperage at the motor, and did you mention a phase convertor? Which style and is it fed with enough power?
Under powering the motor is #1 cause of burn up! Motor slows, amps raise, [less counter EMF] this heats the wire, which increases resistance and then that restart that loop, no win for the motor. The piping issue is a possible cause or serious contributing factor. Harry

 

[Firstram]

I'm with the low voltage scenario called by others, so a thorough check of wiring, and voltage/amperage at the motor, and did you mention a phase convertor? Which style and is it fed with enough power?
Under powering the motor is #1 cause of burn up! Motor slows, amps raise, [less counter EMF] this heats the wire, which increases resistance and then that restart that loop, no win for the motor. The piping issue is a possible cause or serious contributing factor. Harry

This is why I specifically ordered a 208v motor when I ordered my compressor. I set up shop in random old buildings with 3 phase power and 230v motors don't do well with the voltage drop.

One of the places we spent 2 years in was 1600' from the panel. They ran 480 to a transformer 300' away from our shop giving us a stated 100 amps of 208 3 phase. Heaven forbid if the compressor kicked on while you were using the plasma, voltage drop is a killer!

I have a Buck/Boost transformer to drop the Voltage when we do end up with a 240 service.

 

[mgb1974]

Thanks everyone for the feedback. I talked to Sullivan Paletek. They said I for sure have a aftermarket and wrong motor on the compressor. They wanted $3300 for a replacement. That's not feasible since I have $4k already into this used compressor.

So I am looking for a decent motor to replace my burnt up one. Once I get it replaced I will check amps on start and such.

I do believe that I may have low voltage, the motor I put on there is a 230V. I see motors that are 208V which is a better fit.

What RPM should I get? The motor on it was a 3450. The spec for the machine says 3530.

So get a quality single phase 7.5hp 208v motor, ensure amps and volts are good.

 

[pancho400cid]

Don't worry about the "exact" RPM as long as it is within a couple of percent of the "factory" motor design RPM . Induction motor RPMs vary by manufacturer / design / applied load / voltage, etc. If the original factory-installed motor was a two-pole, as it appears, the actual RPM will be a couple of percent under 3600 RPM. Just don't try to put a 2 pole motor in place of a 4 pole or something... you'll be WAY off speed-wise and sure to have issues.

Many 230 VAC motors will have a note on the rating nameplate that says something like "useable on 208 VAC". Often there will be current values, etc. for both 230 VAC and 208 VAC. The current at 208 VAC will be higher than that for 230VAC and you have to size any breakers, conductors, etc. for the 208 VAC current values.

...

 

[micromind]

The small difference in RPM doesn't matter.

A motor designed to NEMA standards is required to produce its rated HP with the voltage at + or - 10%. This means that a 230 volt motor can operate anywhere from 207 to 253 volts.

If the 240 voltage is lower than 207, contact the power co. and have them fix it......it'll be free.