Compressor motor keeps burning out 1

[LeadF00T]

I have burned out two compressor motors in a very short period of time and want to know if anyone has any ideas on what to check, I would greatly appreciate the help.

The compressor motor is a Leeson Air Compressor Electric Motor — 5SPL HP, Model# 116845. I replaced the motor about 3 weeks ago and it the second motor to go out withing a short time period. I have checked my connections and everything appears to be up to par.

I have tested the wall receptacle and it is putting out approximately 120v per side of a single phase outlet. I have also tested the power to both sides of the switch and at the motor to ensure it is receiving power. The compressor pump also spins normally, so I do not think it is overworking the motor.

I would greatly appreciate any input.

 

[BrianE22]

Is the pressure (in the cylinder head) unloading valve working properly?

 

[Skogsgurra]

The 5SPL HP, Model# 116845 is a 230 V motor. You mention 120 V. That doesn't sound right. Have you checked voltage across motor? It should be somewhere between 207 and 253 volts.



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[LeadF00T]

I mentioned that I checked approximately 120v on each side of the plug, combines for about 240. The voltage at the motor is also about 240v.

The unloader valve is working as it is supposed to. The compressor is cutting out at it's pre set 120psi as advertised.

 

[Skogsgurra]

Yes, I noticed that you mentioned 120 V on each side. But, if there is a phase angle from Neutral to each of these 120 V, they will not add up to 240 V. That's why I asked about voltage across the motor.

This may sound odd to some of you. But I have seen so many different distribution schemes all over the world that I am prepared to accept the weirdest things.

What part of the world are you in?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[rbulsara]

A motor rewinder or a repair shop should be able to analyze the burnt motor and tell you much more about possible cause of the failure or at least mode of the failures. That is if it motor shorting out to ground or between phases. How many winding are affected. Or it is due to simple overheating (overload).

What type of starting this motor has? May be the start winding remains in the circuit, which it should not.

Rafiq Bulsara

http://www.srengineersct.com

 

[itsmoked]

I have seen compressors that were dying of heat stroke mounted in small enclosed closets. Where's yours?

A lot of small compressors are only rated intermittent duty, able to run perhaps a few minutes at a time and expecting to be off at least half the time. Is yours rated continuous duty? Is it running for long periods?

Also you state the voltage. At this point you have to measure the voltage at the motor with the compressor actually running.

Does the motor have a start capacitor and a centrifugal switch in it or does it have an external start relay?

The replaced motor came with another start capacitor didn't it?

When does the motor fail? As it's running merrily along or during a start?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Explaining where I think some of the above questions are leading...

Just because you read the correct voltage at the receptacle when nothing is plugged into it and running, doesn't mean you have enough power available at that receptacle. A very common occurrence is that the load is too heavy for the size of wire you have running to the receptacle and it is causing a voltage drop as soon as the current starts to be drawn by the compressor. That motor draws 15A at 230V when fully loaded. If you have 14ga wire running to your receptacle, that may be fine as long as the run length is short and there is nothing else running on that wire at the same time. But if it is part of another circuit with other loads, and/or the distance is over a few yards, voltage drop may be causing your motors to burn up. Even with heavier gauge wire, the starting current may be so high that it causes an immediate voltage drop and the motor is never getting to full speed, so it ends up running on the starting capacitors the entire time, which would also affect a premature death.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[wayne440]

After looking at the subject motor's specifications, I think it is closer to a 3 HP motor than a 5 HP one, hence the ""5SPL" rating. My experience with "SPL" rated air compressor motors indicates that "SPL" must be shorthand for "we are giving this motor a grossly inflated rating". At 230V, 15A, your motor doesn't even draw 5 electrical HP, much less produce 5 HP at the shaft.

Consider getting rid of that 36 pound, 15 amp, "5SPL" HP rated motor and installing one that is actually "5" HP (It will probably weigh considerably more and draw more than 15A).

 

[LeadF00T]

I am in the US, the compressor is in a large open room, the capacitors are external, start capacitor is mounted to the top of the motor and it did come with new capacitors, the wire is 14 gauge, about 2 ft in length, the only thing on the circuit, and the cord is about 5 ft.

I will make sure to check voltage with the motor running when the new motor arrives.

When this motor arrived, I had immediately noticed it was smaller and lighter than the original. It is still under warranty, and I will see if I can upgrade as opposed to direct replacement.

Thank you all for your input.

 

[LionelHutz]

Try checking the current while the motor is running.

 

[potteryshard]

Rather than checking voltage phase to neutral and phase to neutral, check phase to phase. Very often, single phase loads are fed from two phases of a three phase system, resulting in 208 V phase to phase, even though they are 120 V phase to neutral in each case. If that is the case, a 200 V motor would be more appropriate.

Also, when installing, carefully check the internal connections; 115/230 V motors may come from the factory connected for 115 V, or may come connected for 230 V. The actual connection must match the applied voltage; wrong in either direction results in smoke.

A note on usage: The SPL motors use a part of the overload capacity inherent in a general purpose motor as part of the predicted load cycle. What would normally be marketed as a 2 HP motor can thus be called a 5 HP motor. It can produce 5 HP, for only for a very limited time. Because an air compressor has a load that increases toward the end of the cycle, under normal circumstances the motor only needs to produce the 'rated' 5 HP for a few minutes.

However, if one is heavily using a small air compressor so that it runs continuously, the compressor remains continuously in the end-of-cycle state where the actual load has risen to the 5 HP level, so the motor is forced into overload conditions (remember that it is really a 2 HP motor...) on a near continuous basis. No surprise that motor life is negligible.

 

[electricpete]

Frequent starting without adequate cooling can be another factor that can kill motors or capacitors.

I don't know what SPL means (splashproof?) but I wouldn't read too much into the current rating of a single phase motor... can vary widely depending on things like whether there are some caps that remain in the circuit while running.

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[electricpete]

I agree 15A at 230volt sounds low for 230vac single phase even with caps. Even with 1.0 pf and 1.0 efficiency (impossible) we get 16A. Hmm.

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[ccjersey]

Smaller and lighter???????

Maybe it's a 3450 rpm replacing a 1725?

That would do it!

 

[jraef]

That Leeson part number was a 3450HP motor, 56H frame. If the replacement was 1750RPM and the same HP, it would be larger, not smaller; probably a 184T frame.

SPL means "Split Phase" as opposed to Cap-Start/Cap-Run or PSC. Split Phase motors have relatively low starting torque, so they MUST be used with an unloader on a compressor, otherwise they stall really easy. As to whether or not it is truly "5HP", that's a subject of much debate when it comes to consumer products. Mfrs get away with a lot of "poetic license" when it comes to marketing statements. SPL motors have high breakdown torque, which means if you measure the speed and torque AT THAT MOMENT, it likely calculates out to be 5HP, if only for a very brief time.

I just noticed a potential subtlety in the way you worded this:

The unloader valve is working as it is supposed to. The compressor is cutting out at it's pre set 120psi as advertised.

It sounds like maybe you are describing the pressure switch. The unloader valve is different. Typically on small consumer type compressors like this the pressure switch is what would cut out at 120PSI (if that's where it's set), and kill power to the motor AND THE UNLOADER VALVE. When that happens, the unloader should open and you will hear a brief "Pssssss" noise as the cylinder pressure releases. Then when the pressure switch calls for the compressor again, the unloader stays open for a second or two so that there is no pressure in the cylinder head until after the motor gets to full speed. On larger industrial high volume compressors, the motor runs basically all the time and the unloader cycles on and off to charge the pressure vessel.

If the compressor motor turns on and off via the pressure switch, and the unloader is not working like I stated above, that may be the root of your problems.



"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[ccjersey]

I don't think the SPL in the HP block means anything other than "special" (whatever that means). I saw that myself several years ago. In that case, it was a 3450 rpm replacing a 3450 rpm original equipment compressor motor under warranty. Neither of those "SPL" motors lasted very long, but longer than a few weeks, more like a few months to a year each time.

I doubt the original motor was a 1750 rpm, just because we had a compressor with the SPL hp 3450 rpm motor, but I was saying a 3450 replacement of an OEM 1750 motor of similar hp would not last long without a pulley ratio change.

 

[starkopete]

Hi, you might find this intresting:

http://www.wisedan.com/aircomp

Thanks

 

[electricpete]

Good link Pete. Now I know what SPL stands for (Someone Probably Lied!)

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