Baldor Air Compressor Motor Issues

Hi all,
I have a Baldor motor (L1430T) 5hp single phase I’m planning on using to run my Champion air compressor (HR5-8). Problem is, the motor makes a loud humming noise, the same ugly sound a motor makes when the start caps go bad and the motor tries to start, but cant. The only difference is, this motor starts right up and runs, but makes that same awful sound while running. It pulls about 30 amps using a clamp-on meter running with no load on a bench top . Name plate says 20.6 amps, but with no load, I would expect something much less. I thought maybe the internal start switch was not disengaging the caps, so I took it apart, but its working fine. I then suspected a bad run cap, so I pulled the one from my other Baldor motor (L1410T) and put in the (L1430T). This made no difference what so ever. Thing is, can’t read the label of the run cap in the (L1430T), but the (L1410T) has a run cap value of 50 mfd 370VAC. Not sure if it would make much difference using a run cap with a value of 10 mfd higher or lower since the two motors are virtually identical.
Any ideas what else might cause this problem?
Thanks in advance.

Bad start cap that stays in the circuit because the motor does not actually get up to speed? Measure the RPM. Fix is easy. Call Baldor for parts and data.

Bearings? compare run down times.
Bill D

If you have a megometer, measure the windings. If not, take it to a motor shop that can measure it. It is pulling too many amps.

Joe Gwinn said:

Bad start cap that stays in the circuit because the motor does not actually get up to speed? Measure the RPM. Fix is easy. Call Baldor for parts and data.

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Hi Joe, Thanks for your response.
The start caps are new and the motor starts up fine. Not sure what rpm the motor reaches, but the centrifugal switch is opening, you can also hear it close when the motor winds down after power is removed.

Bill D said:

Bearings? compare run down times.
Bill D

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Hi Bill,
The bearings are good; the shaft spins nice and easy by hand with no noise.

Bob-J-H said:

If you have a megometer, measure the windings. If not, take it to a motor shop that can measure it. It is pulling too many amps.

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Hi Bob,
I only have a digital ohm meter, so I measured the resistance between the windings just for the heck of it. Don’t know what they should read, or if these values reveal any problems or not, 2.4 ohms on the start winding, 1.6 on the Run. There is an infinite reading between each winding and the motor case, so at least it’s not shorted to ground.
Attached is a diagram.

S.C. said:

Hi Joe, Thanks for your response.
The start caps are new and the motor starts up fine. Not sure what rpm the motor reaches, but the centrifugal switch is opening, you can also hear it close when the motor winds down after power is removed.

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Hmm. Is the supply voltage correct for the motor wiring configuration?

Can you measure the capacitor capacitance? Actually, there are two capacitors. Are they both good? Many digital multimeters can measure capacitance.

The other possibility is a partly shorted winding.

Joe Gwinn said:

Hmm. Is the supply voltage correct for the motor wiring configuration?

Can you measure the capacitor capacitance? Actually, there are two capacitors. Are they both good? Many digital multimeters can measure capacitance.

The other possibility is a partly shorted winding.

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Joe,
Yes, the supply voltage is correct for the motor wiring configuration
The 2 start caps measure out at 230-235MFD each. The label says they are 216-259 MFD 250V, so they should be good. The old run cap is around 53MFD, but I can't read the label and don’t know what its value should be.

I called Baldor today and talked with a service tech, I told him about my motor issues and he was happy to answer questions. After giving him the motor serial number and spec. number, he gave me the correct values for the caps; he also gave me the motor winding ohm values. He even told me the exact day, month and year the motor was made, I thought that was pretty cool. Another thing he mentioned was that the run cap must match the values of the original, no deviations. The bad news, he said the very same thing Joe Gwinn mentioned about a possible shorted winding.

Later, after talking with him, I decided to recheck all my previous readings since mine were different. As I started checking the windings, I again came up with different readings, so I got my el cheapo meter out and rechecked. Ok, great, my new readings are now very close to what Baldor’s specs are. Apparently, my expensive meter (Fluke) is having issues now, go figure.

Since the winding values are close to what’s considered factory new and not shorted to the case, I’m just going to order out new caps and see what happens. I’m hoping it’s just a bad run cap.

If anyone is interested, attached is the updated wiring diagram with the Baldor specs along with my new readings.

I will throw my in my .02 FWIW.
The capacitor check function on the bog standard DVM is quick dirty check. A cap can read okay using this method but if tested it with dedicated capacitor tester a lot of times you find it leaky as hell. As capacitors age they essentially turn into resistors. As we are not dealing with the front end of a radio receiver, caps are cheap just replace them.
I would also suggest megging the motor, again your standard DVM only uses about 1.5 VDC to measure resistance. You need voltages in 1000 volt and up range to perform PI and DAR (dielectric absorption ratio)tests which will give a much better indication of the state of the insulation on the windings. But all that said a motor shop is probably your best bet cause a good megger will cost serious coin. There are low cost ones available from usual scum bags. Problem with them is they don't carry UL and other stamps of approval. I don't know about you but I want a piece of gear that can believe the readings and if I make a mistake and hook something up wrong it will not blow up in my hand.
Apologies for going OT but I feel it is important to realize the limitations of the test gear you are using. Both from a safety stand point and acquiring data that is accurate enough for what you are attempting to do.

Only other thing is measure voltage at line and load side of start control whether it is a contactor or a pressure switch. Bad contacts can make all the difference.

S.C. said:

Yes, the supply voltage is correct for the motor wiring configuration.
The 2 start caps measure out at 230-235MFD each. The label says they are 216-259 MFD 250V, so they should be good. The old run cap is around 53MFD, but I can't read the label and don’t know what its value should be.

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Even if 53 MFD isn't what the factory ordered, it should work well enough.

My suspicion is that one of the two windings has a shorted turn or three. This can be impossible to detect with an ohmmeter.

So, I'm thinking that this problem requires specialized tools to figure out. As others have said, I'd talk to a motor shop.

If it is in fact a failed winding, I'd guess that buying a new motor is cheaper than rewinding the old motor.

Joe Gwinn said:

. . . I'd guess that buying a new motor is cheaper than rewinding the old motor.

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Maybe not. The 5hp US made Baldors list for around $1000 these days.

Did you ever figure anything definite out. I have a similar issue. Motor hums when starting, I replaced both capacitor and have unhooked from compressor. Sometimes it will take off and others it will do nothing. It’s also a single phase baldor that is 1 month out of warranty

doug8cat said:

I will throw my in my .02 FWIW.
The capacitor check function on the bog standard DVM is quick dirty check. A cap can read okay using this method but if tested it with dedicated capacitor tester a lot of times you find it leaky as hell. As capacitors age they essentially turn into resistors. As we are not dealing with the front end of a radio receiver, caps are cheap just replace them.
I would also suggest megging the motor, again your standard DVM only uses about 1.5 VDC to measure resistance. You need voltages in 1000 volt and up range to perform PI and DAR (dielectric absorption ratio)tests which will give a much better indication of the state of the insulation on the windings. But all that said a motor shop is probably your best bet cause a good megger will cost serious coin. There are low cost ones available from usual scum bags. Problem with them is they don't carry UL and other stamps of approval. I don't know about you but I want a piece of gear that can believe the readings and if I make a mistake and hook something up wrong it will not blow up in my hand.
Apologies for going OT but I feel it is important to realize the limitations of the test gear you are using. Both from a safety stand point and acquiring data that is accurate enough for what you are attempting to do.

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This is 100% correct.

Voltmeter is the wrong tool for this, it doesn't tell you much and more often than not will give a false good reading.

This is what a megger is for. If you work on stuff with motors and wires you should own a megger. A new cheap one is around $100. An older used one on craigslist is often $20.

Megger tells you the whole story and gives you a for sure it's good/mediocre/bad.

I've had several motors that test borderline bad with a megger, but still run fine when humidity is low. One of my bandsaws has one. Been that way for a decade now and still going. Voltmeter says it's fine, megger says it's bad, but it still starts.

This sounds like a bad run cap to me, with the easy start but high running amperage draw and the windings checking out okay. I had a very similar issue with my 20 year old (bought new by me) Ingersoll compressor. It would pop the thermal overload several times a day, and running amps were measuring about 20% higher than nameplate. I checked the run cap for ESR and it was very high. There were no identifiable markings on the run cap that I could read (years of vibration had rubbed them off) so I looked at a few other similar compressors and was able to get a ballpark capacitance. I ordered about 5 caps off eBay that encompassed the likely range, then tried each one on the compressor, checking the running amperage under load for each. I kept the one installed that got me to the least amps and it was pretty close to right on the nameplate FLA.

The Fluke meter problem may be bad leads - I have had several older sets go high resistance on me - probably internal conductor strand breakage or corrosion, or both...

Regarding the voltmeter being the wrong tool for the job, right on. Capacitors are a little tricky to measure. Think of capacitance as being like the amount of energy the capacitor will hold. That's a useful thing to know but there are other just as important things involved. For one, ESR - this is the series resistance through the cap. If this is too high, the cap won't be able to charge and discharge fast enough, limiting the voltage/capacitance it's able to build in the time available during AC cycles. There's also leakage, which is how fast the cap self-discharges, and a few other things. But anyway, yeah, a voltmeter is of limited use.

Rick2752 said:

Did you ever figure anything definite out. I have a similar issue. Motor hums when starting, I replaced both capacitor and have unhooked from compressor. Sometimes it will take off and others it will do nothing. It’s also a single phase baldor that is 1 month out of warranty

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Since the original poster has only made 7 posts, 6 of which were in this thread, has no recent activity, it is doubtful he is monitoring the thread almost 2 years later to give you a update.

Too bad posters that come up with these type of questions rarely come back with the solution once they have found it.

Rick2752 said:

Did you ever figure anything definite out. I have a similar issue. Motor hums when starting, I replaced both capacitor and have unhooked from compressor. Sometimes it will take off and others it will do nothing. It’s also a single phase baldor that is 1 month out of warranty

Click to expand...

Yours could be the centrifugal switch. On certain motor lines Baldor uses a SyncroSnap mechanism from Torq (Centrifugal Switch, Stationary Switch Components and Motor and Switch Replacement Parts- Bedford, Ohio - Torq Corporation).
I've had two of these fail while almost new, one on a 7.5hp SP motor and the other on a 5hp. The engineers at Torq said there was a fairly recent design change to the plastic disc because the old discs were cracking and disintegrating. They sent me a new mechanism with a re-designed disc and my problem was solved.

Even though your problem is intermittent, it can still the contact board for the centrifugal mechanism. It is easily examined and replaced by taking the back end bell off the motor.

like the one poster was saying the run cap could be bad or your running two start caps or you have the caps mixed up