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Old 06-26-2020, 06:44 PM   #1
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Default Chattering Contactors

Had an interesting thing at work today. A 25 HP bucket had a contactor chattering. To me this has always been a pretty clear indicator that the contactor is done. Changed the bucket and had the exact same thing happen. I had my apprentice stand by the motor, it sounded awful and the gear box seems to be done. Amp draw would shoot up 300% for a second and go back down.

At the risk of sounding dumb, how is this gearbox/motor affecting the contactor? Even if there was a slipping issue and the motor was working too hard, how is the overload letting this thing chatter and spark? With no load the bucket works just fine, no noise or sparks. It seems like the breaker/overload tripping would make sense, but not everything else.
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Old 06-26-2020, 06:47 PM   #2
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Maybe the replacement bucket had the same issue. What about changing the contactor or checking the coil voltage


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Old 06-26-2020, 06:50 PM   #3
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Bad/open shading ring? Dirt? Loose connections in the control circuit? Low voltage?
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Old 06-26-2020, 07:00 PM   #4
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Coil voltage is what engages the starter and holds it in.

Why would you change a starter without checking the coil voltage that keeps it engaged?
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Old 06-26-2020, 07:07 PM   #5
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Coil voltage is what engages the starter and holds it in.

Why would you change a starter without checking the coil voltage that keeps it engaged?

Also chattering weeds to contact surfaces breaking down


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Old 06-26-2020, 07:13 PM   #6
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That was my first post here, I obviously left out a bunch of the details. Both of these buckets work fine with other motors. Both were tested and ran no problem. I switched the bucket not the contactor simply because it is much faster and they needed the plant up. The motor megs out just fine. No damage in the peckerhead and in Ohms good. The only common denominator that is broken is the gearbox, which makes zero sense.

Ask me more questions please, things to try or troubleshoot. I still think its impossible, but I don't know what else to say is the issue. When on another motor everything is electrically fine in the buckets. Will be interesting to see what happens when they change the gearbox.
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Old 06-26-2020, 07:18 PM   #7
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Low voltage protection or low voltage release?

Cheers
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Old 06-26-2020, 07:34 PM   #8
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If it's safe to do so, power the coil from another source; this will tell you if it's a control voltage problem or something else.

If the coil is 120AC, powering it from an outlet will work, if it's a different voltage, you'll need to be creative........
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Old 06-26-2020, 07:51 PM   #9
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Quote:
Originally Posted by joebanana View Post
Bad/open shading ring? Dirt? Loose connections in the control circuit? Low voltage?
Especially with a 300% overcurrent. I'd start with micromind's suggestion.
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No, seriously!
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Old 06-26-2020, 07:57 PM   #10
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The increased load causes the voltage to drop at the coil which causes the contactor to drop out raising the voltage causing the contactor to close and so on and on
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Old 06-26-2020, 08:03 PM   #11
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Lots of different buckets and lots of different control setups.

If the bucket has a built in control transformer (480 to 120) and the starter/breaker/wiring is on the small size for a locked rotor 25hp motor then a buzzing on start up isn't all that surprising. Once running it should be quite.

contactors can buz, chatter or jerk off

chattering is either low voltage or dirty pole faces. Cleaning the contactor isn't that big of a deal. A little rust between the pole faces will make it chatter.

Jerking is more violent than a fast rattle and is normally due to a controls problem which is rapidly turning the contactor on and off.
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Old 06-26-2020, 11:19 PM   #12
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The motor and gear reducer aren't causing the starter chatter, the starter chatter is causing the motor and reducer noise. A good analog VOM [Simpson] on the coil terms while it's running will tell the tale. Chances are you have a intermittent connection on the control causing this, think a low oil level switch or a limit switch or a cabinet safety switch.
I run into this often enough on air compressors on r-mix plants, as it's running the pressure switch will try to open but close then open then close in rapid succession. This causes spike after spike of inrush current that the breaker or fuses and overloads see as a huge continuous overload. The start and stop will cause backlash in couplings and reducers to make all manner of noise.
If you listen carefully, you can hear the boyyyt boyt boyt of the inrush current and the 60 cycle magnetic noise as this is happening. If you have 50 cycle current insert the burt sound effect instead lol.
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Old 06-26-2020, 11:31 PM   #13
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Another problem I run into is broken pole face coils. This is a useless looking loop of wire either across the face or wrapped around the side. They flatten the magnetic field. If they break it sits too far away to pull in so it rattles.

I’ve also seen a blown diode in a rectifier on a DC coil cause this.
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Old 06-26-2020, 11:44 PM   #14
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Quote:
Originally Posted by paulengr View Post
Another problem I run into is broken pole face coils. This is a useless looking loop of wire either across the face or wrapped around the side. They flatten the magnetic field. If they break it sits too far away to pull in so it rattles.

I’ve also seen a blown diode in a rectifier on a DC coil cause this.
That's one of the shortest and least interesting posts I've seen you make. Everyone expects better from you!

You been drinking?
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No, seriously!
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Old 06-27-2020, 05:21 AM   #15
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Quote:
Originally Posted by joebanana View Post
Bad/open shading ring? Dirt? Loose connections in the control circuit? Low voltage?
I experienced this on a huge fan motor in a green house... did indeed turn out to be low voltage.
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Old 06-27-2020, 07:16 AM   #16
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That's one of the shortest and least interesting posts I've seen you make. Everyone expects better from you!

You been drinking?
Everyone killed the "low voltage" answer. Just pointing out a couple others.


A glass plant customer had a 4160 GE Limitamp contactor that probably would work better if they didn't swap out the 120 V coil for a 220 V one. That better?
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Old 06-27-2020, 11:58 AM   #17
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Originally Posted by paulengr View Post
Another problem I run into is broken pole face coils. This is a useless looking loop of wire either across the face or wrapped around the side. They flatten the magnetic field. If they break it sits too far away to pull in so it rattles.

I’ve also seen a blown diode in a rectifier on a DC coil cause this.
Is that the thing that looks like a epoxy white square on the pole faces. I know on AB if that epoxy is old and broken (missing chunks) then its time to replace the horse shoes or it will never quieten down. I just presumed it was a shock absorbed.
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Old 06-27-2020, 12:26 PM   #18
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Is that the thing that looks like a epoxy white square on the pole faces. I know on AB if that epoxy is old and broken (missing chunks) then its time to replace the horse shoes or it will never quieten down. I just presumed it was a shock absorbed.

Yes. On bigger ones there is an actual wire.
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Old 06-27-2020, 12:54 PM   #19
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https://www.retekool.com/HOW-IS-A-ST...id3097364.html

Electrolytic capacitors. On DC types you can get away with making one side of the aluminum the insulator. Not on AC.

It is filled with an electrolyte such as glycol. Hence the name...electrolytic. No confusion here. NOT used for run caps.

So the issue with single phase is there is no rotation. We just have North and South magnetic poles swapping places. But if the pole energizes with the rotor at an angle since the rotor has an induced current it will pull the rotor around again. During voltage bulls the rotor coasts past the “dead spot”. But when the motor starts there is nothing induced out of phase. So you can “pull start” a motor with a bad start circuit but it won’t start on its own.

We then add an auxiliary coil 90 degrees offset from the main coil. If it’s smaller we could just wire it up. This is called permanent split pole coils (PSC). They work but since one coil opposes the other all the time efficiency is rotten and torque is not great.

We could just switch off the starting coil. We just need to know when. The off signal can be a timer, a mechanical centrifugal switch, or a voltage relay that triggers when the main coil voltage drop changes as the motor comes up to speed. Modern starters lean towards the potential relay because it’s more reliable.

Thing is it’s a highly inductive load so we can offset some of this with a power factor correction capacitor. This one is energized continuously so it is typically oil filled and sized to match the motor power factor, The motor can run without it but you lose some torque and efficiency. These often look like a big bulge on the side of the motor,

The second issue is starting coil starting works but torque is limited. On motors not designed to start this way it won’t even start. It would be nice to get plenty of torque. Enter the starting capacitor. It is about 10 times bigger but only energizes for a few seconds so it isn’t as big as it would be. Voltage is greatly increased by 2-3 times normal line voltage as seen at the motor. If the switch that disconnects it fails they explode. If they dry out they arc and explode. So they don’t last very long.

There are dual caps that contain both capacitors in one can.

Personally I hate single phase motors. They are poorly labeled. You spend half the time just figuring out what everything is and whether the last guy just put in the wrong parts or wires it up wrong. They are always on the verge of not working. Every manufacturer tries to make the sizes nonstandard to charge you more for very cheap parts. Everything you need to see happens in about 2 seconds. And everything costs $20 except the motor. Three phase motors are just so much higher torque, smoother running, higher efficiency, and very easy to work on. It’s so cheap often the best way to “fix” one is just test the motor itself and the contactor, then just replace both capacitors and the potential relay (or change to one) and call it a day. My shop doesn’t even stock the parts because there’s no money in it. I have to go to the competitors to buy repair parts.
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Old 06-27-2020, 02:21 PM   #20
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Quote:
Originally Posted by MorganCustard View Post
That was my first post here, I obviously left out a bunch of the details. Both of these buckets work fine with other motors. Both were tested and ran no problem. I switched the bucket not the contactor simply because it is much faster and they needed the plant up. The motor megs out just fine. No damage in the peckerhead and in Ohms good. The only common denominator that is broken is the gearbox, which makes zero sense.

Ask me more questions please, things to try or troubleshoot. I still think its impossible, but I don't know what else to say is the issue. When on another motor everything is electrically fine in the buckets. Will be interesting to see what happens when they change the gearbox.
If the starters work fine elsewhere, then it’s in the control circuit that is telling the starter to turn on. That circuit remains the same when you change the starter, so there’s another clue.

The motor and gearbox don’t affect the starter, it’s the other way around. Chattering the contactor is going to destroy the gearbox and motor. It’s also going to burn the contacts out in the starter. Chattering ALWAYS has to do with the control circuit, not the power circuit. The bad things you see in the power circuit are always the RESULT of chattering.
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