humming contactor 250v ac

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kimani Active Contributor Join Date: Dec 2008 Posts: 13	humming contactor 250v ac 12/13/2008 5:06 AM
	i replaced a burnt out contactor that operated a 1.5 kw single phase pump ,this is the third the contactor is being replaced,the contactor i replaced with is rated 250v though when i measured voltage across the coil it reads 214v could this drop be the reason the contactors keep humming then burning?
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#4 "Re: humming contactor 250v ac" by Roman on 12/14/2008 1:39 AM (score 2)

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#10 "Re: humming contactor 250v ac" by Emjay4119 on 12/15/2008 11:24 PM (score 1)

harry potter

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Join Date: Nov 2008

Location: India

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Re: humming contactor 250v ac

12/13/2008 6:57 AM

DEAR READER,

GENERALLY HUMMING OCCURES BECAUSE OF DIRTY MAGNET. CLEAN THE MAGNET OF THE CONTACTOR BY CRC 2 26 / EUIVALANT CLEANER / RUB THE MAGNET CORE CONTACT SURFACES GENTLY BY EMERY PAPER. 99% YOUR PROBLEM WOULD BE SOLVED. THEN COIL SHALL NOT BURN ALSO.

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Hendrik Guru Join Date: Jan 2007 Location: Centurion, South Africa Posts: 3921 Good Answers: 97	#2 In reply to #1 Re: humming contactor 250v ac 12/13/2008 1:05 PM
	Harry please use your wand and turn CAPS LOCK off. __________________ Never do today what you can put of until tomorrow - Student motto
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Dave M. Associate Join Date: Jan 2008 Posts: 34	#3 Re: humming contactor 250v ac 12/13/2008 11:42 PM
	I'd like a little more information. What exactly is burning up -- is it the coil, the points, or are the arc shields melting?
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Roman Power-User Join Date: Jun 2006 Location: Manila Philippines Posts: 171 Good Answers: 8	#4 Re: humming contactor 250v ac 12/14/2008 1:39 AM
	Same with harry potter comments, dirty coil could caused the humming sound, can you also check the frequency if you are fitting correct one either 50 hz or 60 hz it should correspond on your supply frequency, consider also the magnetic contactor rating if it is rated equivalent to your 1.5 kW motor. what about the voltage drop during certain period of time? maybe the time you take across the line read 214v what about when the time the contactor burnt? could be 180 volts who knows. to summaries the following has to take into accounts; dirty contactor, frequency, rating of the magnetic contactor and voltage drop. if all of this are in order, then you should haven't problem. Kind regards Roman
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noshorts Power-User Join Date: Jun 2008 Location: Olive Branch, Ms. USA Posts: 124	#5 Re: humming contactor 250v ac 12/14/2008 8:46 AM
	Past experiences lead me to suggest a capacitor across the coil terminals. This will eliminate the A.C sine wave and allow for constsat voltage to pull the coil in. __________________ Tell 'em what they need to hear; not what they want to hear!
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wareagle Guru Join Date: Jun 2008 Location: Alabama Posts: 1604 Good Answers: 63	#6 In reply to #5 Re: humming contactor 250v ac 12/14/2008 6:10 PM
	How does placing a capacitor across the coil terminals eliminate the AC sine wave?
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ca1ic0cat Guru Join Date: Jun 2006 Location: Rochester, NY Posts: 867 Good Answers: 11	#8 In reply to #6 Re: humming contactor 250v ac 12/15/2008 8:47 AM
	>>How does placing a capacitor across the coil terminals eliminate the AC sine wave? By absorbing some of the energy in the sine wave as it charges and then discharges. Not perfect but it will help. Of course the one thing missing from this whole thread is "what is the current draw?" It's good that the contactor is rated for 250v but if the circuit is drawing too much current the contactor isn't going to last too long. Going to have to know this to size a capacitor properly as well. __________________ Eric
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Leonf Power-User Join Date: Nov 2008 Location: Windhoek, Namibia, South west africa Posts: 410 Good Answers: 23	#7 Re: humming contactor 250v ac 12/15/2008 4:00 AM
	Good day, can you supply contactor specs? make, rating, incoming 'fuse' or breaker size & how you connected it? __________________ tHe days of good inglisH haz wented.
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DRFREON Power-User Join Date: Nov 2008 Posts: 158 Good Answers: 1	#9 Re: humming contactor 250v ac 12/15/2008 4:43 PM
	Let's start with the knowns, which are very little. If your coil rated voltage is 250, its one I never heard of in 30 years! The COIL voltage, as with 99% of applications, needs to be + or - 10 % of the rated voltage. Need to know the AMPERAGE & HORSEPOWER ratings of the switching poles of the contactor as well as its rated voltage. Then I can help you. Also, need to know the environmental conditions and the ACTUAL measured amperage of the pump under max. load.
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Emjay4119 Guru Join Date: Dec 2005 Location: Queensland Coalfields Australia. Posts: 697 Good Answers: 11	#10 Re: humming contactor 250v ac 12/15/2008 11:24 PM
	Yep, sure can. If the coil is rated at 50hz and you have 60hz that will make it even worse. A 240v 50hz coil requires 277 at 60hz. If your voltage is bad the motor won't like it too much either. AC contactors have a shading ring that holds the pole faces together as the field decays at zero crossing with low voltage the average poleface gap increases which increases the reluctance of the magnetic circuit. This in turn increases the average current in the coil, also the average contact pressure is reduced. So as you can see low control voltage leads to failure of both coil and contacts. Find the cause of low voltage and fix it. In large installations with large contactors it is often caused by a daisy chained neutral. In a stand alone 1.5kw application long runs of too small wire is the usual culprit, but check all joints and control devices. I could give you work arounds to protect the contactor but it is futile if the result is only to burn out the motor.
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Leonf Power-User Join Date: Nov 2008 Location: Windhoek, Namibia, South west africa Posts: 410 Good Answers: 23	#11 In reply to #10 Re: humming contactor 250v ac 12/16/2008 1:59 AM
	Hi 4119, I would seriously appreciate if you could spend the time to explain how you worked out the 50/60hz & voltage thing. kind regards, leon. __________________ tHe days of good inglisH haz wented.
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