7.5 HP Compressor Shutting Off - 3 Capacitor Testing & Identifying & Grease Fitting Question

[cloves]

Hi all, I have a 80g 7.5 NorthStar compressor 1 phase w/ mag starter (sold via northerntools). I have had it for about 3+ years. I probably have run it maybe 80-100 hrs total. Weekend warrior but occasional sandblasting and grinding under the car. Anyways the compressor started shutting off before hitting its 175 psi target. It turns on at (0-150psi and off at 175psi)

Action/Question 1:
I replaced the pressure switch as per tech support and it wasn't the problem. Figured it was something electrical so decided to check the capacitors on the Baldor motor. Can't find wiring diagram online. Motor is a 36LYH282 model. It has 3 capacitors, sure enough one of them is out of spec with the microfarads (uf) printed on it. This capacitor has 2 soldered 10k resistors, and I am not sure if those resistors would cause my multi-meter test result numbers to be incorrect?
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This capacitor is the same as one of the other ones. Baldor EC1216C06. Since I have 3 capacitors, I am assuming 1 is start cap, 1 is the run cap, and the other the thermal cap? Anyway to figure which one of these it is?
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Is it normal for capacitors to go bad? The center one is showing 456uf and should be 216-259uf. My multimeter has the uf setting to test.

Question 2:
I thought I was going nuts but I think this Baldor motor has grease zerks on it. I found a diagram of it on their site (https://www.baldor.com/api/products/L1509T/drawings/36LYH282). Are we suppose to grease these? Nothing in the manual about that.

 

[rlitman]

Multimeters aren't the best capacitor testers, so it's no surprise to me to see it skewed with the bleeder resistors in parallel. But those resistors look like they're on the QD. Can't you slide one side off? Anyway, failing capacitors don't go up in capacitance (at least, that's a failure mode I've never heard of). If you really want to test a capacitor, you want an LCR meter, preferably with ESR capability (or an oscilloscope and knowledge of what you can do with one), but again, there's nothing here to indicate a capacitor issue.

Both of the capacitors with black shells and brown tops are start caps, and you're using the pair in series. The silver one the run cap.

Also, shutting down before it reaches pressure is not a capacitor related issue. If the caps were going bad, it would fail to start. This is an issue with your pressuretrol.

 

[BillK]

Does it do it every single time ? If so it should be easy to monitor the voltage on the pressure switch to make sure that isnt the problem. Yes I know you replaced it but that does not mean anything nowdays.

One more thing . . . . are you sure the gauge is correct ? What pressure is it stopping at ?

 

[micromind]

When it stops early, what do you need to do to get it running again?

Yes, the bearings need to be greased but be careful.....

1) For every motor I've seen fail because of lack of grease, I will see about 50 fail because of too much grease.

2) It needs to be the proper grease. Most motors have either Shell Dollium or Mobil Polyrex from the factory. If you use any other type of grease the end result will be a sticky gooey mess the doesn't lubricate anything. The nameplate will usually state what the factory used.

3) There is a specific procedure to greasing a motor. As a rough idea though, if you squirt a pump or 2 of the proper grease into the zerks every 2 - 3 years, it'll be close enough.

 

[mm08822]

Remove the PS cover and attach VOM across the terminals. When PS is closed, VOM should read 0, when it opens, it will read 240v.

Around what pressure is it opening?

Has anyone messed with the Setpoint or differential?

 

[BillK]

As far as the grease fitting go it probably wont hurt but just make sure to use the proper grease. i would check with Baldor. To be honest with you my compressor at the shop runs 19 hours every day 5 days a week. Its over 35 years old and I cannot ever remember greasing the motor

 

[wyliesdiesels]

as said above, caps have nothing to do with cutting out before reaching pressure.

have you checked the overloads in the starter along with measuring the current the motor is pulling? as the pressure goes up its possible its pulling more amps above the overload setting causing it to trip

can you post a picture of your starter and overload relay block. also post a pic of the motor nameplate.

 

[cloves]

Thanks for all the reply fella's, already learned a few new things.
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Symptom & Details: Updating for clarity. The compressor is turning off before it hits the pressure switch target of 175 psi (turn back on is set to 150) but it might not pressure related could be thermal. Last week it ran through at least 3 good cycles hitting 175 while I was working then the 4th it cut out early. If I hit the "reset" button on the Eaton mag switch box it starts back up. I installed a cooler and dryer on this unit and its been on there since the start (see photos). Instead of the copper line going from the head to the compressor tank, I have it going to a cooler at the back and then through a dryer and then to the tank.

• Q/A @rlitman : The quick connects on one starting capacitors, have heavy soldering on them to hold the resistors I think (see photo) This is the one with high values. I did disconnect all the wires from all three to test. After of course discharging them using a screw driver.
  
  
• Q/A @BillK : Today it's shut off before hitting 175, and I believe it was about 140 another time 160. Last week I was able to run at least 3 cycles without issue (all showed 175 on gauge) while I was working outside continuously. Used up the 25 psi before restart about 20 minutes apart. The compressor comes with an oil filled gauge, not sure how I would test that out. One thing I will say, I had it stop pretty fast after starting up with no air a week or so ago. Hit the reset switch and it started right back up. So if it starts up after shutting off, using the reset switch, that tells me the pressure switch is confirming that it hasn't hit 175 (that's just me thinking though)
  
  
• Q/A @micromind : Reset button on mag switch starts it right back up. This is why I am leaning toward electric issue either thermal or motor vs pressure. Thanks for the grease heads up. I'll back seat that till I can figure out the first issue.
  
  
• Q/A @mm08822 : I'll check the the voltage. The new switch came factory preset on 0-150 and off 175.
  
  
• Q/A @wyliesdiesels : I updated the symptoms. Motor is cutting out but it might not have anything to do with the psi, that was my error in thinking. No I have not checked the overloads in the starter or measured the current the motor is pulling. I have multi-meter just need to figure out how to do what you mentioned now. All new photos attached. Let me know if I guessed what the starter and overload relay block are correctly.

Photo of starting caps. One has 2 resistors soldered onto terminals. Odd thing, so both caps show the same model numbers and info on the stickers. But the one with the resistors shows 25 in the brown center and the other 20. Not sure if that is even worth mentioning.


20 and 25



This is from the NorthStar manual: I am "assuming" my motor overload on the mag switch is tripping. Why I am not sure. I have had no issues for 3 years so ruling out "D" and "G". Checked grounds in the mag switch to see if they got lose. :


Name plate from online easier to see:



Mag switch no cover:

 

[Chris_Hamilton]

Don't have much to add other than to say I have never seen any compressor rated at 175 psi turn off at that. Or turn on at 150. I've been around a fair amount of compressors in my life and most are going to cut off at 150, turn on at 125. My 7.5 HO IR is set that way as are most (all?) the others I've fooled with working in a Body Shop environment. Much easier on the compressor and motor than how you have it set.

Whether that has anything to do with your problem IDK. My gut says it's the pressure switch assembly. That would be most logical. Like was said above a bad capacitor it's not going to start.

 

[BillK]

Just want to add that you absolutely cannot check the capacitors with the resistors attached. You have to at least unsolder one side.

 

[micromind]

This might be an incredibly dumb question but does the pump have oil in it?

If it starts, the 2 black capacitors are ok. If the silver one is bad, the motor will run but draw too much current.

It's also possible that the overload relay has gone bad. Those cutler-Hammer/Eaton ones are known for failing earlier than most others. I see that it's set for 36.5 amps and trips, this is an indication that it's bad.

If possible, measure current while it's running. If it's 30 or less, the relay is bad.

 

[cloves]

@Chris_Hamilton yup, I confirmed those numbers with tech and also in the manual later on.

@BillK - Ok good to know, not sure I want to desolder those things, they look like a pain the a$s to align back on

@micromind - Yup, oil is good. As far as the caps, makes sense. I was thinking perhaps one was starting to go bad, based on my cap test, but the resistors are throwing my numbers off as per BillK.
That's an interesting note on Eaton, thought they were a good brand. You mentioned "it's set for 36.5 amps and trips" where do you see that? I am looking at the eaton box but don't see it. I need to figure out how to test.

This is from the manual, the mag starter isn't shown in this diagram:

 

[mm08822]

When this early shutoff happens, what must be done for it to restart?

 

[35Ford]

Doesn't sound like it's the pressure switch.
If you're pressing the reset button to get it to restart, its stopping on thermal and could be caused by an overload or poor connection.
Does it stop on run up? Mechanical issue, low voltage, bad run capacitor, poor connection, motor or compressor problem.
Does it trip on restart? Bad check valve / unloader.

 

[wyliesdiesels]

If I hit the "reset" button on the Eaton mag switch box it starts back up.

This is whats causing your compressor to shutoff NOT the pressure switch. Return the replacement pressure switch…

First, you need to check the solid state overload relay setting and make sure it matches your motor FLA plus 15% (1.15 service factor).

If that is good, then you need to check motor current draw as you could have a bad capacitor or something else that is causing the motor to work harder (drawing excess current). This in turn causes the overload to trip to protect the motor.

You will need a clamp meter to check this. A multimeter cannot do so…

Its odd the manual mentions a poor ground as a possible reason for motor issues. No, not even close. The EGC is for preventing the frame from becoming energized. has nothing to do with motor operation. who writes these manuals?

 

[wyliesdiesels]

My gut says it's the pressure switch assembly. That would be most logical. Like was said above a bad capacitor it's not going to start.

Nope. The pressure switch wouldn't cause the overload relay to trip. And he already replaced the pressure switch which didnt fix the issue. Also, this compressor motor has start caps and run caps so a bad run capacitor could cause issues while it’s running.

 

[wyliesdiesels]

When this early shutoff happens, what must be done for it to restart?

In post #8 he says he has to push the reset on the overload relay

 

[u3b3rg33k]

When it stops early, what do you need to do to get it running again?

Yes, the bearings need to be greased but be careful.....

1) For every motor I've seen fail because of lack of grease, I will see about 50 fail because of too much grease.

2) It needs to be the proper grease. Most motors have either Shell Dollium or Mobil Polyrex from the factory. If you use any other type of grease the end result will be a sticky gooey mess the doesn't lubricate anything. The nameplate will usually state what the factory used.

3) There is a specific procedure to greasing a motor. As a rough idea though, if you squirt a pump or 2 of the proper grease into the zerks every 2 - 3 years, it'll be close enough.

coming back to greasing motors, do not just grease them. you need to KNOW what kind of bearings/seals it has. and you need to remove the drain plug. greasing motors wrong often kills bearings faster than not greasing them. just because it has zerks on it does NOT mean the bearings aren't 2RS.

 

[micromind]

double post

 

[micromind]

@Chris_Hamilton yup, I confirmed those numbers with tech and also in the manual later on.

@BillK - Ok good to know, not sure I want to desolder those things, they look like a pain the a$s to align back on

@micromind - Yup, oil is good. As far as the caps, makes sense. I was thinking perhaps one was starting to go bad, based on my cap test, but the resistors are throwing my numbers off as per BillK.
That's an interesting note on Eaton, thought they were a good brand. You mentioned "it's set for 36.5 amps and trips" where do you see that? I am looking at the eaton box but don't see it. I need to figure out how to test.

This is from the manual, the mag starter isn't shown in this diagram:

These overloads were Cutler-Hammer when Eaton bought them out. They never were all that great, I've seen a number of them fail.

The overload blocks have current ratings for A,B,C and D. There is a rotary switch labeled A,B,C and D.

 

[mm08822]

The heat exchanger used to cool the pump output air is raising the temp of the motor windings. You will shorten the life of the motor windings and/bearings doing this.

Is the motor starter enclosure exposed to this higher ambient? Heaters have a current range and time delay that is affected by the ambient temp they are subjected to.

When did you add this H/E and was the room temp much cooler than now?

Bypass the h/e and see if problem is eliminated.

On second look, the elevated air flow temp is impacting the compressor. It's oil life will be reduced causing higher bearing wear long term.

 

[wyliesdiesels]

Is the motor starter enclosure exposed to this higher ambient? Heaters have a current range and time delay that is affected by the ambient temp they are subjected to.

He doesn’t have heaters. It’s a solid state overload relay

 

[cloves]

This is whats causing your compressor to shutoff NOT the pressure switch. Return the replacement pressure switch…

First, you need to check the solid state overload relay setting and make sure it matches your motor FLA plus 15% (1.15 service factor).

If that is good, then you need to check motor current draw as you could have a bad capacitor or something else that is causing the motor to work harder (drawing excess current). This in turn causes the overload to trip to protect the motor.

You will need a clamp meter to check this. A multimeter cannot do so…

Its odd the manual mentions a poor ground as a possible reason for motor issues. No, not even close. The EGC is for preventing the frame from becoming energized. has nothing to do with motor operation. who writes these manuals?

@wyliesdiesels : Makes sense, so the thermal cut off is shutting off the compressor and not the pressure switch. I keep saying multi-meter when I should be saying clamp on meter (old habits). I have a Klein CL800 which has the cap setting dial.
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Solid State Overload Relay: You mentioned checking, I have had the compressor for 3+ years now and haven't touched the settings dial, would that change? Assume I need to figure out how to test it to see if its failing. @micromind mentioned he has seen a number of them fail.
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Amp Check (Photo of where I am testing below): So I'll put my clamp on each leg and see what numbers I get. Plate shows 29-32 assume that it will be a bit higher when it starts up but should fall into this range after.

The heat exchanger used to cool the pump output air is raising the temp of the motor windings. You will shorten the life of the motor windings and/bearings doing this.

Is the motor starter enclosure exposed to this higher ambient? Heaters have a current range and time delay that is affected by the ambient temp they are subjected to.

When did you add this H/E and was the room temp much cooler than now?

Bypass the h/e and see if problem is eliminated.

On second look, the elevated air flow temp is impacting the compressor. It's oil life will be reduced causing higher bearing wear long term.

@mm08822 :
I put on the radiator to cool the air and moisture trap water separator as soon as I got the unit (a week later) It was the summer so temps were around 70s when I first started using it all the way till fall so temps were easily low 50s. No issues for 3+ years.
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We are in PA so weather varies, right now we are around the 60s in the day at night its still getting cold 40s. Why would adding an air cooler and water separator cause issues with the motor windings and bearings?
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Could you also touch on how air flow temp is impacting the compressor?
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Photos: Amp Test:

 

[micromind]

If the actual current is 29 - 32, and the overload relay is set to 36.5 and it trips, then the relay is bad but the pump and motor are both ok.

 

[62civa]

This might be a dumb comment, but the wiring into and out of the compressors electrical box looks to be either 10 or maybe 8 AWG. Then I see three short bare copper jumpers between the circuit breaker and the contractor….which look much smaller like maybe 12 AWG? Could this be causing a voltage drop which I turn is causing the motor to overheat as the air pressure goes up? Those three small bare copper jumpers just don’t look right to me. I know they are very short, so the voltage drop may be negligible, but maybe not.

 

[Norcal]

He doesn’t have heaters. It’s a solid state overload relay

They are "heater packs" that you have to select based on motor data, why Eaton went that route I have no idea, other then there is more flexibility over having to replace because of needing to replace the O/L relay because of needing a different ampere range.

 

[Norcal]

This might be a dumb comment, but the wiring into and out of the compressors electrical box looks to be either 10 or maybe 8 AWG. Then I see three short bare copper jumpers between the circuit breaker and the contractor….which look much smaller like maybe 12 AWG? Could this be causing a voltage drop which I turn is causing the motor to overheat as the air pressure goes up? Those three small bare copper jumpers just don’t look right to me. I know they are very short, so the voltage drop may be negligible, but maybe not.

The current rating for conductors are mostly based on insulation type, the 'ho made jumpers have nothing to do with it, but the Romex® supplying is a bit on the sloppy side.

 

[cloves]

@62civa : My subpanel is supplying power via a 6-2 cable off a 50amp breaker. Anything inside the Eaton box is stock. Top part of that is the starter, the bottom is the overload (See pic below)

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Amp Test 1: (motor name plate shows 32-29 amps)
1. Testing white wire going to motor from mag starter (amp1 in photo above). Tank empty. Started at 20 amps and climbed to 28 amps by the end of the filling cycle.
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2. Used air triggering motor to turn back on at 150 setpoint. Amps started at 23.59 and headed up till 28-29.1. Early on it moved up faster then toward the end.
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3. Used air triggering motor to turn back on at 150 setpoint. Amps started at 24 and headed up till 28-29.1.
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Is it normal to start way below what the name plate is showing? So far everything seems normal. Should I fully empty the tank and try the other leg?

 

[PCustoms]

How old is this compressor, and how long have you been using it before this issue happened?

 

[rlitman]

Just want to add that you absolutely cannot check the capacitors with the resistors attached. You have to at least unsolder one side.

A multimeter cannot check a capacitor in-curcuit, though some devices can. Anyway, caps aren't the issue.

If I hit the "reset" button on the Eaton mag switch box it starts back up.

100% sure that's the problem now, and wyliesdiesels pointed it out first.

 

[Jim greengo]

Have you tried running it without the belt?

 

[cloves]

@PCustoms compressor has been running fine for 3+ years as is. No issues till last month. Something is starting to fail and seems to be electrical in nature.

@Jim greengo no I haven't. This this has 2 steel belts and a cage and would require me shifting the engine.

I'll do some more runs on the compressor see if I get a thermal shut off again.

 

[PCustoms]

@PCustoms compressor has been running fine for 3+ years as is. No issues till last month. Something is starting to fail and seems to be electrical in nature.

I'm not so sure about that. Seems like, mechanically, you can't hit the pressure setting and that is why the electrical safety/cutoff is kicking in.

 

[walta]

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Amp Test 1: (motor name plate shows 32-29 amps)
1. Testing white wire going to motor from mag starter (amp1 in photo above). Tank empty. Started at 20 amps and climbed to 28 amps by the end of the filling cycle.
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2. Used air triggering motor to turn back on at 150 setpoint. Amps started at 23.59 and headed up till 28-29.1. Early on it moved up faster then toward the end.
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3. Used air triggering motor to turn back on at 150 setpoint. Amps started at 24 and headed up till 28-29.1.

The overload should not trip unless more than 36 amps has been flowing for 15 seconds or more.

Your tests prove the problem is with the overload and not the motor or pump.

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Is it normal to start way below what the name plate is showing? So far everything seems normal. Should I fully empty the tank and try the other leg?

Yes it is normal for an air compressor to pull fewer Amps when the pressure is lower and pull the most Amps just before the pump cut off at the highest pressure because the motor is working harder and more work equals more Amps.



Walta

 

[micromind]

According to post #28, the motor current readings are all within spec. There is nothing mechanically wrong with the compressor. The starter overload is set at 36.5 amps and is tripping at less than 30. Obviously, this is the problem.

I see Walta beat me to it........lol.

 

[cloves]

I'm not so sure about that. Seems like, mechanically, you can't hit the pressure setting and that is why the electrical safety/cutoff is kicking in.

It has a new pressure switch and I inspected the check valve at the tank top. So not sure what mechanical variables are left . Seems like either something is wrong in the mag switch box or the electric motor is failing. Still have to do a few more cycles till I get a failure. Need to see if the electric motor draws higher amps which would cause the "overlay relay" below the starter to trip.

 

[walta]

Before you order a replacement moto started / overload, disconnect each wire make sure the wires are shiny and retighten them also move all the adjustment controls thru every possible setting several times and back to the original setting to polish the contacts.

Walta

 

[PCustoms]

It has a new pressure switch and I inspected the check valve at the tank top. So not sure what mechanical variables are left . Seems like either something is wrong in the mag switch box or the electric motor is failing. Still have to do a few more cycles till I get a failure. Need to see if the electric motor draws higher amps which would cause the "overlay relay" below the starter to trip.

Big question my kind is what's the pressure doing when it trips

 

[cloves]

Ok so just to reiterate, in today's tests the compressor didn't trip. It ran normal.
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@micromind @walta Just to wrap my head around this. You think the "overload relay" is going bad. Today during my test on the one hot leg, I didn't get any trips. If the motor or pump was bad or going bad I should have seen my amps jump past 36 for 15 secs and trip? So a motor or pump going bad wouldn't be intermittent pointing to the "overload relay"?
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@PCustoms when it has tripped in the past? It seems to be climbing and then just cuts off. I thought it was a psi issue but the smart guys here pointed me toward thermal shutdown.

 

[walta]

Ok so just to reiterate, in today's tests the compressor didn't trip. It ran normal.
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@micromind @walta Just to wrap my head around this. You think the "overload relay" is going bad. Today during my test on the one hot leg, I didn't get any trips. If the motor or pump was bad or going bad I should have seen my amps jump past 36 for 15 secs and trip? So a motor or pump going bad wouldn't be intermittent pointing to the "overload relay"?
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Intermittent pump and motor problems are possible but they would both make the Amp reading exceed 36 before the overload should trip.

I thought you that you saw the over load trip while pulling less than the set current. Apparently, I misunderstood.

Keep testing until it fails while you are looks at the meter.

Note it is generally a bad idea to push the reset button on the overload without allowing the motor time to cool off. 30 minutes would be a very safe number. If the overload is working as intended you risk over heating the motor and damaging the motor beyond repair.



Walta