# Bad Starter



## erics37 (May 7, 2009)

What is the coil voltage of the starter? If it's only getting 50V and it needs 120 or whatever then I'd go check the control transformer.

Putting some line breaks and stuff into your post would make it easier to read


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## captkirk (Nov 21, 2007)

did you meg out the coil to the case..? there can be a short in it that your regular ohm meter wont pick up..


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## erics37 (May 7, 2009)

Also, what was making the fuses for the compressor blow? Was there a phase missing or anything?


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## ericg2000 (Oct 25, 2010)

there's no control transformer. i thought about that initially, and mentioned it, but was told it gets 480v. my coworker/trainer is more mechanic than electrical. he picked up his electrical knowledge on the job. 

i did not meg out the coil to case. 

i have idea if they had a phase issue at some point. the initial problem occurred a few weeks ago. they replaced the fuses i think once (maybe twice) and have been using a screwdriver to hold the contacts in ever since. 

sorry for no line breaks in my post. i got carried away typing.


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## erics37 (May 7, 2009)

ericg2000 said:


> there's no control transformer. i thought about that initially, and mentioned it, but was told it gets 480v. my coworker/trainer is more mechanic than electrical. he picked up his electrical knowledge on the job.
> 
> i did not meg out the coil to case.
> 
> sorry for no line breaks in my post. i got carried away typing.


A 480 volt starter coil? 480V control stuff gets pretty spendy, I understand. Are you sure?


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## jlmran (Feb 25, 2011)

Use em all the time. Very common here.


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## ericg2000 (Oct 25, 2010)

yes. there was no transformer to be found inside the enclosure. i looked. in fact, there was no room for one. 

this was my first encounter with this type of issue. i used my class knowledge as much as i could, but it only goes so far in the real world.


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## erics37 (May 7, 2009)

ericg2000 said:


> i have idea if they had a phase issue at some point. the initial problem occurred a few weeks ago.


Well that's probably the place to start then. Meg the motor and the starter coil and stuff. If the motor is blowing fuses cause it's single-phasing and someone keeps putting new fuses in, that's like putting quarter after quarter into a vending machine that eats quarters.


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## jlmran (Feb 25, 2011)

What pulls the coil in..pressure switch?


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## ericg2000 (Oct 25, 2010)

i don't access to a megger, nor does my shop

no, the pressure and temp switches are inline with 2 of the 3 lines bringing in power. they are both NC switches, and if there is low oil pressure or an over temp on the motor, they open, breaking power. 

i took both of them out of the circuit, tested their continuity, and applied voltage with them out. while we were there, we didn't blow any fuses. i measures 480v on line 1-2, 1-3 and 2-3, but not at the coil (a1-a2).


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## captkirk (Nov 21, 2007)

are you certain the coils are ac not dc..?


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## varmit (Apr 19, 2009)

It COULD be a bad overload block causing either, or both, of two problems: The coil circuit, that goes through the overload block, could be open. The power through one or more of the overloads may be open causing the motor to single phase. The electronic O/L blocks are much more prone to failure than the "old" NEMA overloads. But any type O/L can fail.

Also, you really need to meg the motor. It could have a insulation breakdown. It could also have a motor winding open. A megger will help find a short. A regular ohm meter can be used to check the windings, but you will need to disconnect all of the motor leads, at the pecker head, and check each of the windings.


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## jlmran (Feb 25, 2011)

ericg2000 said:


> i don't access to a megger, nor does my shop
> 
> no, the pressure and temp switches are inline with 2 of the 3 lines bringing in power. they are both NC switches, and if there is low oil pressure or an over temp on the motor, they open, breaking power.
> 
> i took both of them out of the circuit, tested their continuity, and applied voltage with them out. while we were there, we didn't blow any fuses. i measures 480v on line 1-2, 1-3 and 2-3, but not at the coil (a1-a2).


The failsafes open line power directly?? Or the control circuit?


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## ericg2000 (Oct 25, 2010)

there are no inverters switching the ac to dc power. 

we pressed the reset button on the OL. but like i said, once we got incorrect voltage at the coil, i was told to stop, that's as far as we go. 

the failsafes open line power directly. one is wired in after the one/off switch before a fuse, the other is wired in after a fuse but before the starter.

my problem is what if we get the new starter, install it and run into more problems. that's why i started this thread. on one hand i was told to stop looking because it beyond what we do. but on the other hand, i want to know everything i can possibly look for, A) for my personal knowledge B) what if it happens again.


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## jlmran (Feb 25, 2011)

You are stating that you have a failsafe which opens one leg BEFORE the starter. Are you certain?


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## ericg2000 (Oct 25, 2010)

now that i picture it in my head, one is between the on/off switch and a fuse, the other is between line voltage and the coil (A1 lead). sorry for the wrong info.


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## jlmran (Feb 25, 2011)

Hmmmmmm...Glad your head got clear.

Test the control circuit to answer why it won't start.


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## ericg2000 (Oct 25, 2010)

it was a long week... i've had a few beers this evening.

all voltages were ok, except the coil. when we go back, i'll re-examine the circuit drawing inside the cover and try to narrow down the problem before we install the new starter.


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## JRaef (Mar 23, 2009)

Many issues...



480V control is VERY common on air compressor circuits, because typically they don't have control signals from anywhere else, they just run 480 from one leg, through the pressure switch, oil switch, temperature switch etc. to the starter. It's done all the time that way in that industry, it's cheaper than having a large control power transformer. A 480V coil for a starter is exactly the same price as a 120V coil by the way.
I would hazard a guess that the first event was a fuse blowing and single phasing the motor. That most likely caused the Over Load Relay to trip, because when a motor is single phased and run under load, the current draw is immediately 1.732X normal, and air compressor motors are almost always sized "close to the bone" so there would be little room for error. Then when the user replaced the fuses, he was not smart enough to know that he had to hit the reset button on the starter too, so it would not work. Pushing the "go" button on the contactor with a screw driver accomplished the immediate task, so why bother calling someone to fix it, right?
The "50V" you are reading on the coil is probably just leakage, the OLR aux contact is probably still open, but has arced enough to leave a slight carbon trace that allows 50V to show across a very low impedance measuring circuit like a DMM. I'd bet if you put a Wiggy on that it would read nothing. Sometimes there is a reason to stick with the old fashioned tools, they can show you things (or not show you things) that DMMs can be fooled by.
In the act of pushing that button (actually the top of the armature of the movable contacts), he has almost assuredly destroyed his contacts. When a set of contacts is closed, there are magnetic fields that form around the current carrying components. The mfr designs the current path so that these magnetic fields around the stationary and movable contacts oppose each other, trying to force them apart from each other. That way if the contactor is opening under load (as it almost always is), these fields aid in separating the contacts faster. So the coil must be designed to pull the armature in AND to overcome this rather substantial magnetic field strength. In any contactor over about 50A, the average person pushing in with their finger or a screw driver is only able to express about 75% of the mechanical force necessary to keep the contacts from forcing each other open, it gets worse with size. So what happens, on a microscopic level, is that you push, the contacts make, they push back, unmake, the field strength drops and because you are still pushing, they make again, repeat ad infinitum. But unfortunately it's not really ad infinitum, because every time this occurs, there is an arc across the tiny little gap in the separating contacts, so in relative short order the contacts are melted and if hey don't weld, they vaporize. I have seen it happen on a 400HP contactor in about 2 seconds!
The first thing to investigate s the reason for the fuse having blown. But before you get excited, get the sequence of events correct. For instance if the entire plant had a single phasing event, and AFTER that the fuse blew, then there may be no other contributing factor in the motor circuit. But for that to have happened, the user would have had to try to re-start with the blown fuse, and THEN the OLR tripped. Because if the OLR had tripped when the initial plant wide single phase event happened, then the fuse would not have blown.
You have more stuff to investigate if you want to improve your understanding, but I like how you have taken it upon yourself to not just blindly accept the replacement of the starter as the only solution. Chances are, as I said above, it needs to be replaced now anyway, but you are right to try to learn from this.


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## pudge565 (Dec 8, 2007)

JRaef said:


> Many issues...
> 
> 
> 
> ...


We had that happen the other weekend. The power went out at our plant (480V) The lights came back on but the motors wouldn't start (they would hear the starter click but no motion. 

So my boss (who was on call) got a phone call and explained it to the supervisor what was wrong (he still didn't understand) and went in to verify.

He reset the motor OLR on the shredders but forgot the well pump OLR. He also wants to find a way to wire the compactor (on timers to auto cycle) to not run if the OLR is tripped as it got jammed up because the PLC saw that it was running as everything was working properly but the OLR was tripped preventing the compactor from actually compacting. I haven't had a chance to look at the diagram (if there is one) to see how it could be done.


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## PsiMan84 (Oct 29, 2010)

is this compressor a Reciprocating or Rotary Screw?


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## ericg2000 (Oct 25, 2010)

Reciprocating


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## JRaef (Mar 23, 2009)

pudge565 said:


> We had that happen the other weekend. The power went out at our plant (480V) The lights came back on but the motors wouldn't start (they would hear the starter click but no motion.
> 
> So my boss (who was on call) got a phone call and explained it to the supervisor what was wrong (he still didn't understand) and went in to verify.
> 
> He reset the motor OLR on the shredders but forgot the well pump OLR. He also wants to find a way to wire the compactor (on timers to auto cycle) to not run if the OLR is tripped as it got jammed up because the PLC saw that it was running as everything was working properly but the OLR was tripped preventing the compactor from actually compacting. I haven't had a chance to look at the diagram (if there is one) to see how it could be done.


You have some problems in that control design that need serious investigation. When your OLs trip, the motor starter should not pull in, so you should not have heard any "clicks" etc., and the PLC should not have "seen" anything was running. Sounds to me as though your interlocks are not wired properly.


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## lefleuron (May 22, 2010)

> We had that happen the other weekend. The power went out at our plant (480V) The lights came back on but the motors wouldn't start (they would hear the starter click but no motion.
> 
> So my boss (who was on call) got a phone call and explained it to the supervisor what was wrong (he still didn't understand) and went in to verify.
> 
> He reset the motor OLR on the shredders but forgot the well pump OLR. He also wants to find a way to wire the compactor (on timers to auto cycle) to not run if the OLR is tripped as it got jammed up because the PLC saw that it was running as everything was working properly but the OLR was tripped preventing the compactor from actually compacting. I haven't had a chance to look at the diagram (if there is one) to see how it could be done.


 Tell your boss that you can program N.O. contacts in the plc- these are wired as inputs through the OLs on the motor starters. If he does this, neither machine will start/run without both starters having their over-loads pulled in.


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## pudge565 (Dec 8, 2007)

lefleuron said:


> Tell your boss that you can program N.O. contacts in the plc- these are wired as inputs through the OLs on the motor starters. If he does this, neither machine will start/run without both starters having their over-loads pulled in.


Well we will see if we get around to it. We only have til Friday possibly, due to well I won't get into it here but If you are curious send me a PM.


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## bereawouldworker (Dec 10, 2010)

when these tyoe of issues come up, it is important to remember that blown fuses indicate a short while open overloads incidate a load issue. just by knowing what tripped can immediately point you in the right direction. one fuse blown is a short to ground while two fuses blown is a short between two phases. when an overload is opened, the load issue is not neccesarily electrical. this may be a misaligned motor, spent bearings, improperly sized motor, etc.


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## nitro71 (Sep 17, 2009)

"Kept blowing the fuses" First problem to figure out. 

Is the circuit, over current and motor overload protection sized properly? That's the first thing I would check. If so, there is a problem because that thing is blowing fuses. Check connections, meg the motor, check winding continuity. Measure inrush current. Measure running current.

After you find the problem I would want to take a look at the contacts on the starter. Make sure they aren't damaged. I'd also want to inspect the termination points on the run. Holding the contactor in till the fuses blow isn't a good idea.


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## pudge565 (Dec 8, 2007)

JRaef said:


> You have some problems in that control design that need serious investigation. When your OLs trip, the motor starter should not pull in, so you should not have heard any "clicks" etc., and the PLC should not have "seen" anything was running. Sounds to me as though your interlocks are not wired properly.


Sorry had my info wrong. Complaint was heard click but motors did not start. Did not have to reset OLR as they did not trip. Supervisor shut them down when they did not start.


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