Buzzing starter

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  #1  
Old 08-08-04, 07:16 PM
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Buzzing starter

Now that the shop has power I'm working on my compressor. It's a big industrial grade job with a 3 hp 220v/16 amp motor and a magnetic starter. I got the electric fired up today and the motor works but the starter has a buzzing sound. I cleaned the contacts but it still does it. Is this normal? I also noticed that when the power is turned off the motor winds down and when it reaches a certain rpm it makes a "down shift" sound and slows down further. It's not a sound like something's wrong It just sounds like some motors do when the power is first switched on...
It's a big Baldor with a thermal protection switch on it.
Just wondering if anyone has any experience with industrial motors and controls.
 
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Old 08-09-04, 02:23 AM
Light4u2
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What voltage is on the coil of the contactor to make it chatter ? Is it sufficient. Unless the coil has full voltage it requires than you will get a chatter because it's not strong enough to keep the contacts in, thus giving you a noise from the contactor. It could have a control power transformer in side the enclosure which will hum. You might check the voltage first.
 
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Old 08-09-04, 06:03 AM
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It has 220 v on 10 ga wire. It does have places for low voltage switching and a pilot light so it must have a transformer in there somewhere. I'm gonna clean up the coil and contacts again today. It doesn't sound like a transformer hum it's a pretty noisy chatter. Thanks for the help.
 
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Old 08-09-04, 08:03 AM
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I've corrected "chattering" starters by connecting a capacitor across the starter-coil. The capacitor will "charge" to the peak-voltage, and then discharge this voltage across the coil during the period when the line-voltage declines to Zero.

Capacitors are used extensively for starting single-phase motors, and are available at HVAC supply-houses.

Good Luck & Enjoy the Experience!!!!!!
 
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Old 08-09-04, 05:52 PM
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What are spec. Cap should I use. They're in picofarads right?
Do I just connect it to the lugs where the power goes into the coil?
I have it on a 20 amp circuit and the motor is a 16 amp/220 volt. It's an old Cutler Hammer NEMA size 1 starter with a big box so there should be room for a cap. if it's not too big.
I cleaned the contacts really good and they still have plenty of silver surface. If I put light pressure on the bar that the coil pulls down it quiets down. It seems to be a positional thing if the bar pulls down on a "sweet spot" it's pretty quiet. If it pulls down to a slightly different position it chatters.
Thanks a million for the help.
 
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Old 08-09-04, 07:40 PM
mgb
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The "buzzing" sound is probably just the coil itself and not the contacts.
 
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Old 08-10-04, 07:35 AM
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What you describe suggests a possible mechanical problem, but a capacitor may be a solution because it tends to maintain a "contant" voltage across the magnetic coil which results in a more contant magnetic pull.
A Cap for this application would be rated in micro-farads.It would be connected directly across the coil.

Visit an HVAC supply-house to determine what size Cap is available. Explain your need to the S-H personell-- they are familiar with capacitor current and voltage requirements. You certainly wouldn't need one used in a starting a 2-HP single-phase motor.
 
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