Contactor/relay repair question

Put a full wave rectifier in the circuit to the coil. But you might also need a series inductor or power resistor to limit the coil current to a reasonable level.

HTH,

Jeff

It didn't do this until the last couple years and the machine was old when we got it 10 years ago. What causes the relay to buzz anyway?

JohnF

Disassemble and clean the laminated iron pole pieces in the coil assembly. They have accumulated dirt or rust on the faces that come together when the contactor is energized, preventing intimate contact.

Also check the shading coil( a little copper loop inset in one face) to make sure it is not broken or missing. That will also cause buzzing.

Randy

The buzz is either something loose in the assembly (core, wires, frame, etc) that is interacting with the AC, low voltage to the windings so it does not pull in hard, or a partially shorted winding that is not pulling the armature in hard enough. I'd run a voltmeter on the terminals and see what voltage you are getting. I'd also check the current and see how it stacks up against the coil ratings.

For a $3000 unit (??), it should be fully serviceable. I'd change out the coil.

JohnF wrote:

I started making my own contacts many years ago. I buy fine silver plate from a jewelry hobby store and solder new blocks on the contact bars using jeweler's silver solder sheets. Works great, lasts longer and WAY cheaper than buying a contact set. You should splurge on a new coil and find any other problem. Contactors should be seen but not heard.

AC relays and solenoids often have a "shading coil" to reduce buzz. Look for something like a D made of heavy copper that surrounds only part of the core. Sometimes it's heavy copper wire that goes thru a hole or slot in the core. If that is missing or open (cracked), the unit will buzz loudly. It's usually found near the "business" end of the coil, near the armature that it moves.

How it works: the current in the coil is primarily inductive, so about 90 out of phase with applied voltage. The current in the shading coil is determined by transformer action from part of the flux (since it doesn't encircle the whole core) and its (low) resistance, so it's more in phase with applied voltage. The result is "two phase" local magnetic flux which may fluctuate but never goes thru zero.

If you go with DC excitation as Jeff suggests, first measure the resistance of the coil with an ohmmeter and look at the rated AC coil current The right average DC voltage will be the rated current times the resistance reading. You'll probably find that it's much lower than the rated AC voltage, so you'll probably need a dropping transformer before your bridge rectifier.

In

In the past I have made a new shading coil from 14 or 12 ga. copper wire silver soldered together and forced back into the slot on the face of the solenoid. If yours dosen't have a slot you may still be able to put Cu wire through the holes and with a micro torch silver solder the ends. I don't think regular solder would hold up.

Chuck P.

The copper goodies are in there but broken. I remember something about them helping to stop relays from buzzing and was thinking about making some replacements from copper wire just as you suggest. does it have to be a continuous loop or can it be open and just crimped in the slot of the armature?

JohnF

It has to be a closed electrical circuit, and the joint has to be low-resistance -- welded or silversoldered. As another poster noted, soft solder may not hold up well in that location.

Start with cleaning it all up thoroughly and lubricating per the instructions, it may be nothing more than rust or crap keeping the pole pieces from seating properly. Look for bent guides that are not letting the pole pieces mate squarely against each other. Or you have a series/parallel multi-tap coil that has one open winding.

Agreed that you can make your own - but if you sit down and honestly figure in the labor hours needed to track down the supplies and retread your old contact sets, that usually makes the current production ones on the shelf cheaper. Might be time to find another supplier with a markup more to your liking.

And I can't do it for a paying customer, because if "something goes terribly wrong" the liability lawyers would have a field day.

If the replacement parts are totally discontinued, or they're so old that the supplier is hand-building the replacement parts they sell making them über-expensive, /that's/ the time to roll your own.

And when the money situation is better, buy a replacement contactor. Preferably current production, and a bit oversized for longer life.

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Hey John,

More details about this contactor would help. Make, size, poles, coil voltage, number and purpose/how many/NO/NC of "aux contacts".

Some shading coils on older contactors are made with "U" type threaded rod with nuts. You just have to clean the thing up and it will kill the noise. I had one a while ago that was on a big motor gen set with the big mercury vapor tubes, for a 150 hp vertical boring mill . The noise from the contactor could be heard through the whole plant. The local maintenance guy couldn't believe that what I told him to do would fix the noise but after he did it, the thing was completely quiet. I couldn't do anything for the motor gen noise though.

John

I inspected the guts of the thing today and found that it has been "rattling" for so long the surfaces of the laminate parts are worn and out of parallel. It appears that part of the cover that holds the assembly together had vibrated loose some time back and let the whole thing float around to a degree. I am going to make new shading coils from 12ga copper wire and resurface the laminates so they will sit flat together. I still have to get some new aux contacts/switches but those are only about $400.00.

There is no ID except for the #'s relative to the Reliance drive part so, at this point, I'm stuck with parts from the drive manufacturer rather than the component manufacturer. I can find no specs in any drawings or literature I have except that the motor is a 40HP 240vdc and 108/150 amp listed at 850/2550 rpm.

Cover me! I'm goin' in!

JohnF

The buzz is usually caused by dirt, rust, or grease on the solenoid faces. Cleanliness is next to godliness with these units. A contactor that expensive should have replacement parts available from the mfr. Bugs

I've had smaller contactors, that over years of use, vibrated the "assembly screws" loose that held the two halves together, with the coil between. When the screws became loose, the coil was no longer clamped in position and it would buzz/vibrate. Simply tightening up the assembly screws on the contactor solved the problem. Years ago, they used to use wooden wedges on transformer coils to keep them from buzzing. Possibly some cardboard shims, or maybe even hot melt glue would solve your problem. HTH Ken.

According to JohnF :

It has to be a continuous loop. It has to be a very *low* resistance shorted turn. It shifts the phase of *part* of the pole in the solenoid, so when the main part drops to zero magnetic field during the cycles, there is some pull from the phase-shifted part to keep it from starting to release.

Enjoy, DoN.

OK, 1st off THANKS for all the help. I took the contactor apart, resurfaced the nasty, vibrated to death, mating areas, made up new copper goodies and had them silver soldered. Thing is quiet as a church mouse (whatever that means) now. Machine is working again for less than 400 bucks rather than the OG $3000.00 it was going to cost for a new contactor and aux's.

Thanks again for the help

JohnF