# Stumped on 5hp compressor motor(s)



## scallyWags (Sep 22, 2014)

I have a brand new 208-230v single phase 5hp iron horse compressor. I just purchased a shop with a 208 3phase supply/panel. I'm reading 124 to ground on one leg and 125 on the other and across both 249v at the compressor outlet. All this motor will do is grunt for a quick second then nothing, no overload trip on the motor and no circuit breaker trip in the panel. After a couple seconds I turn the breaker off. The motor has dual caps that both are taking a charge and discharge from my fluke by reading then reversing leads. Seemed as if the motor was faulty so I contacted the seller and they sent me a new motor that is doing the exact same thing. What gives ? Tonight I will measure the mf of the caps and meg out both motors to rule out those items for sure. The motor wiring looks straight forward and not interchangeable for dual voltages. Any suggestions would be fantastic.


Thank you,


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## scallyWags (Sep 22, 2014)

Also forgot to mention that, the wiring from the panel is correct, I'm not using the "wild" leg , I've hooked up the line and load thru the pressure bypass switch and completely bypassed the switch to rule it out and I can also turn the pump wheel by hand so I'm assuming there's not too much resistance on the motor (from say a seized pump) to cause it from turning.


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## Wirenuting (Sep 12, 2010)

Do you have a 3 phase 208 system and a single phase compressor? Are your o/l's set correctly?


Is the unloading valve stuck?


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## scallyWags (Sep 22, 2014)

That is correct the service is 208 3phase and the compressor motor is listed 208-230v single phase. I've completely bypassed the unloader and pressure switch with the same exact results as feeding thru it. The ol is of the push button type on the end of the motor with internal wiring.


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## Wirenuting (Sep 12, 2010)

scallyWags said:


> That is correct the service is 208 3phase and the compressor motor is listed 208-230v single phase. I've completely bypassed the unloader and pressure switch with the same exact results as feeding thru it. The ol is of the push button type on the end of the motor with internal wiring.


If all she does is grunt and stall sounds like a dead hi piston, mashed valve or bad motor. 
If it's a belt driven unit, take the belt off and see what happens. 

What brand & model #


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## scallyWags (Sep 22, 2014)

Wirenuting said:


> If all she does is grunt and stall sounds like a dead hi piston, mashed valve or bad motor.
> If it's a belt driven unit, take the belt off and see what happens.
> 
> What brand & model #


It's an iron horse with 5hp motor. 
I can spin the pump pulley by hand so pretty sure the motor should be able to turn it over. Since all signs seemed to be motor in my HO, I called the company and they sent out a new motor that is acting the exact same way.
I will pull the belt off and try that as well as bringing my meggar home to check motors.


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## Hmacanada (Jan 16, 2014)

Pics would help.
Sounds like contactor not wired correctly . Our bad over load / contact or something.
Wire it across the line with out contactor and try it with just the breaker and under no load,
Or test voltage at motor leads if it's not tripping breaker.




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## Wirenuting (Sep 12, 2010)

Hmacanada said:


> Pics would help. Sounds like contactor not wired correctly . Our bad over load / contact or something. Wire it across the line with out contactor and try it with just the breaker and under no load, Or test voltage at motor leads if it's not tripping breaker. Sent from my iPhone using electriciantalk.com


I tried to look it up online. If the one I found is correct it doesn't have a contactor, just a pressure switch. It says rated at 5hp and can deliver up to 7hp. There wasn't a wiring diagram and I don't know who makes this brand.


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## Hmacanada (Jan 16, 2014)

Oh , ok I just did the same.
It's not a true 5 hp.
They rate them funny.
20 amp 240 volt likely .
Probably pressure switch not making contact or terminal not crimped on wire . Insulation under it or something.



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## gnuuser (Jan 13, 2013)

a single phase motor rated for 208 to 230 volts is generally connected to a split phase panel 
if your supply panel is 3 phase you will need to install a transformer to split a phase into the 2 separate hot legs the motor requires

otherwise it would be better to install a 3 phase motor on the compressor

one other thing to check though is look to see if the starter lead is correctly and securely connected
ive seen poor termination make a motor buzz and quit with out rotating


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## Hmacanada (Jan 16, 2014)

gnuuser said:


> a single phase motor rated for 208 to 230 volts is generally connected to a split phase panel
> if your supply panel is 3 phase you will need to install a transformer to split a phase into the 2 separate hot legs the motor requires
> 
> otherwise it would be better to install a 3 phase motor on the compressor
> ...



??? Are you saying a single phase motor won't run on two phases of a three phase system?


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## MXer774 (Sep 1, 2014)

Are you sure you have a 208/120v 3phase service in that shop? If you are indeed reading over 240v at the device as you say, that voltage couldn't be correct unless there was another xfmer creating that higher voltage.


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## Service Call (Jul 9, 2011)

gnuuser said:


> a single phase motor rated for 208 to 230 volts is generally connected to a split phase panel if your supply panel is 3 phase you will need to install a transformer to split a phase into the 2 separate hot legs the motor requires otherwise it would be better to install a 3 phase motor on the compressor


Um no.


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## gnuuser (Jan 13, 2013)

if you read in my post it says generally 
with out a diagram to go by its difficult to say accurately
anyhow the company he got the motor from should have sent some documentation with the motor


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## Hmacanada (Jan 16, 2014)

Just stopped at a TSC store here and they sell iron horse compressors.
Likely one of these two motors.
My guess is pressure switch problem!


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## farlsincharge (Dec 31, 2010)

15 years ago if a new part didn't fix it, that meant the problem was elsewhere.
In todays world it can just as easily mean you have two duds. I wonder if the start switches aren't stuck. Give it a spin by hand when it is trying to start.
What does the line voltage go to when it is trying to start?


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## Ultrafault (Dec 16, 2012)

gnuuser said:


> a single phase motor rated for 208 to 230 volts is generally connected to a split phase panel
> if your supply panel is 3 phase you will need to install a transformer to split a phase into the 2 separate hot legs the motor requires
> 
> otherwise it would be better to install a 3 phase motor on the compressor
> ...



You do not know what you are talking about.


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## Ultrafault (Dec 16, 2012)

Op you have a high leg delta 120/240.
You do not have a 208/120y.

You can confirm this with your meter.
Based on your other readings one leg will have about 214v to ground.

Check your line to line voltage at the motor during startup. I think you have a voltage drop problem. Probably from a bad connection or contact.


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## DriveGuru (Jul 29, 2012)

First of all I read a few post talking about single and three phase panels. Two phases of a 3 phase circuit IS single phase power. As long as you are sure the voltage supply isn't dropping, then the issue sounds like either the start cap, the centrifugal switch inside the motor, or the connections between the cap/switch/and power.


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## Hmacanada (Jan 16, 2014)

???? Did you find out the issue?


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## Bad Electrician (May 20, 2014)

Use trouble shooting skills not a bunch of wild guesses.

Trouble shoting is not one test or another it is a series of test to discern the issue.

Use an amp clamp on Min, Max.
Use a DMM on VAC with Min, Max

Try to start the motor. Check maximum Current, check minimum voltage
Remvoe the belt (as noted above) Check maximum Current check minimum voltage.
With belt off try to spin the compressor by hand


Discern the issues from above.


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## karl_r (Nov 5, 2012)

scallyWags said:


> I just purchased a shop with a 208 3phase supply/panel. I'm reading 124 to ground on one leg and 125 on the other and across both 249v at the compressor outlet.


if panel is 208 3 phase where do you get 249 from?

I had the same problem few months ago and it was OL at fault.


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## DriveGuru (Jul 29, 2012)

karl_r said:


> if panel is 208 3 phase where do you get 249 from? I had the same problem few months ago and it was OL at fault.


A "buck/boost" transformer is a cheap and easy way to increase voltage by 24v. That would bring 208 to 232.


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## sparky970 (Mar 19, 2008)

gnuuser said:


> a single phase motor rated for 208 to 230 volts is generally connected to a split phase panel
> if your supply panel is 3 phase you will need to install a transformer to split a phase into the 2 separate hot legs the motor requires
> 
> otherwise it would be better to install a 3 phase motor on the compressor
> ...


What are you talking about?:no:


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## Big John (May 23, 2010)

I agree with the guys who say you've likely got a high-leg delta. But that doesn't sound like your problem.

Have you taken any current measurements? _Every time_ you try to start it, do you get the exact same results? I.e., a quick hum and then nothing? What happens to voltage and current before during and after?

How many leads are brought out of this thing? Can we get a nameplate?


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## karl_r (Nov 5, 2012)

DriveGuru said:


> A "buck/boost" transformer is a cheap and easy way to increase voltage by 24v. That would bring 208 to 232.


user didn't mention about any transformer. I was confused why he read 249V when his panel is 208V :001_huh:


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## gnuuser (Jan 13, 2013)

sparky970 said:


> What are you talking about?:no:


my bad 
I should know better than to answer posts with a migraine headache:001_huh:


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## Bad Electrician (May 20, 2014)

DriveGuru said:


> A "buck/boost" transformer is a cheap and easy way to increase voltage by 24v. That would bring 208 to 232.


With a center tapped or high leg delta,

You have 120 VAC, 208 VAC and 240 VAC,


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## JRaef (Mar 23, 2009)

scallyWags said:


> That is correct the service is 208 3phase and the compressor motor is listed 208-230v single phase. I've completely bypassed the unloader and pressure switch with the same exact results as feeding thru it. The ol is of the push button type on the end of the motor with internal wiring.


Your voltage is a red herring in that it must be 120/240 3 phase 4 wire with a "high" leg to get those readings, but it doesn't really matter because your motor is rated for either.

This is either a bad motor, which you have likely ruled out (because 2 bad motors in a row is astronomically bad luck) or a problem with the compressor. So in the beginning, wildleg asked if you checked the unloader, and you responded that you BYPASSD the unloader. What did you mean by that?

Because an unloader valve is usually a NORMALLY OPEN valve that you energize to close, so that the compressor starts with the chambers open to atmosphere, then once it gets to speed, the valve closes so that they can compress. If the valve is PHYSICALLY stuck closed, bypassing it electrically so that it's solenoid does not function to close it would be pointless. If by "bypassed" you meant that you directly energized the solenoid, that would be exactly the OPPOSITE of what you needed to do.

If your bypass valve is closed, your compressor is essentially a locked rotor and the motor will not spin. EVENTUALLY your overload relay would trip, but you are not likely giving it that long (rightfully so).

REMOVE the unloader valve so that it is just an open hole, then try to start it. If it starts, you have a bad valve. Common problem.


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## Wirenuting (Sep 12, 2010)

JRaef said:


> Your voltage is a red herring in that it must be 120/240 3 phase 4 wire with a "high" leg to get those readings, but it doesn't really matter because your motor is rated for either. This is either a bad motor, which you have likely ruled out (because 2 bad motors in a row is astronomically bad luck) or a problem with the compressor. So in the beginning, wildleg asked if you checked the unloader, and you responded that you BYPASSD the unloader. What did you mean by that? Because an unloader valve is usually a NORMALLY OPEN valve that you energize to close, so that the compressor starts with the chambers open to atmosphere, then once it gets to speed, the valve closes so that they can compress. If the valve is PHYSICALLY stuck closed, bypassing it electrically so that it's solenoid does not function to close it would be pointless. If your bypass valve is stuck closed, your compressor is essentially a locked rotor and the motor will not spin. EVENTUALLY your overload relay would trip, but you are not likely giving it that long (rightfully so). REMOVE the unloader valve so that it is just an open hole, then try to start it. If it starts, you have a bad valve. Common problem.


He could have a mechanical unloader attached to the pressure switch. Bypassing the switch doesn't do anything to a bad unloader valve. 
It just sits and waits for the next fool to try a new motor.


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## Jlarson (Jun 28, 2009)

Sounds like he's got an unloading pressure switch and he just took the whole thing off and tried to run it. 

Those combo switches are cheap crap and get flakey and stop triggering the valve. I replaced 2 just last night, the squeal of V belts and smell of burning rubber through the plant told me something might be up. :laughing:

We fix a lot of them that have buggered up unloader because the check valve failed or clogged and then someones solution was just to kink, flatten or plug the line to the unloader.


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## 3DDesign (Oct 25, 2014)

What happens when you remove the belt?


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## don_resqcapt19 (Jul 18, 2010)

Does the unloader valve make much of a difference when the storage tank is empty? The OP said it was a new compressor, so I expect the tank is empty.


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## garfield (Jul 30, 2009)

The motor could be tapped incorrectly. He needs to confirm correct taps are connected then get volts and amps at the peckerhead while starting.


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## A Little Short (Nov 11, 2010)

Just a shot in the dark here, but........
It seems the OP joined and posted this thread about the same time.
Since he has not reported back with any results, I'm guessing he got his compressor running and doesn't want to tell us something.
Since he also didn't appear to know the difference between a 3Ø 208/120V service and a 3Ø 240/120V high leg delta, I'm guessing something wasn't wired right and he didn't want to tell us.

He also said in his "new member" post that he often joins forums to get answers to problems.

Nothing wrong with any of that. I'm just saying that's probably why we haven't heard back from him.


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