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Author Topic: Buzzing relays  (Read 3616 times)
gumpy
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« on: July 21, 2008, 08:25:30 PM »

I've been rewiring my electrical system. I got the batteries, inverter and shore input back together tonight, and was testing it. I plugged in the shore line and one of the relays in my transfer switch was buzzing. I've never heard it buzz before. Checked all the connections, and they're correct. Had proper voltage.

I started messing with it, and found that if I put some pressure on it, it would stop buzzing, but would start up as soon as I let up.

So, I played with it awhile, activating and deactivating it manually. This relay controls a couple others in the transfer switch. After cycling it several times in rapid succession, one of the other relays started chattering (like buzzing on steroids). Note that there was no load on the system, so no current draw through the contacts.

Has anyone ever run into buzzing and chattering 120 volt relays?   

I'm expecting I'll probably have to replace them, but I'm really wondering what's causing it.
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Craig Shepard
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« Reply #1 on: July 21, 2008, 09:44:57 PM »

Gumpy, is it possible that You have a rectifier that has gone west causing ac voltage to be applied to the relay coils.  My transfer unit has a small bridge rectifier that failed and caused a hell of a loud buzzing.  I do not know if that is Your problem but it is a possible cause.  Hope this might help.  Regards,John
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« Reply #2 on: July 22, 2008, 05:48:12 AM »

They are 120vac coils on the relays.  Now, it's possible they do something internal that I'm not aware of, but the coil control is 120vac.



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Craig Shepard
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« Reply #3 on: July 22, 2008, 06:21:40 AM »

Craig,

I know you said they 120v relays, what is the actual voltage they are getting? Are these the cube type with spades or pins? I know from experience in our industry we have received bad lots at times and the bases do not fit the spades or pins properly. Have you tried switching them around?

Paul
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« Reply #4 on: July 22, 2008, 06:34:24 AM »

Yep, check for low voltage to the coil.
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« Reply #5 on: July 22, 2008, 06:47:14 AM »

They are Omron MGN2C-AC120 Power Relays (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=Z267-ND).

Measured 120v on the coil with meter. Connected to 50A shore power. Good voltage.

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Craig Shepard
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« Reply #6 on: July 22, 2008, 06:57:44 AM »

Craig, After looking at the type you have, I don't know what could be causing it other than age, maybe. Somewhere something does not like the voltage. Sorry wish I could have been more help. Good Luck.

Paul
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« Reply #7 on: July 22, 2008, 07:04:26 AM »

Since the voltage tests good, I'd replace it with a new one. They sometimes do go bad .  .  .  .  Cry

You do have a spare, don't you?  Grin
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« Reply #8 on: July 22, 2008, 07:39:34 AM »

The buzzing or hum at 60 cycles is probably loose laminations and not much you can do except replace it.  The chattering on an ac coil is almost always a low voltage problem.

Len
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« Reply #9 on: July 22, 2008, 08:57:44 AM »

So, I found this.....

Quote
While relays are usually taught and more easily understood as DC devices, in
practice AC relays are commonly used. These relays typically employ shaded
poles, similar to the shaded pole induction motor. A shaded pole is a coil loop
which is not separately excited by the relay source; it is excited by the flux on
the main relay coil. This coil then produces an opposing current, flux and
voltage (Faraday’s and Lenz’s law) which holds the contact during zero voltage
intervals on the main coil. Failure of the shaded pole leads to “relay
chatter”— a 120 Hz clicking that occurs every time the main relay voltage
crosses the zero point.


Sounds a lot like my problem.  Maybe I blew out the shaded pole leads on the second relay.
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Craig Shepard
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« Reply #10 on: July 22, 2008, 09:26:04 AM »

Thanks Craig!
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« Reply #11 on: July 22, 2008, 09:30:08 AM »

Ditto!

Always good to hear WHY!

Paul
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« Reply #12 on: July 22, 2008, 12:22:40 PM »

Stick a 4 amp diode in one of the relay coil lines.
that will probably stop the noise. I have done that on industrial stuff
and it solved the problem.

Relay coils get weak over time and use. Most are made with very cheap
lamination sheeves ( iron wafers ). If you could determine that the core
laminations are loose, You could apply a thin shellac to them.

We used a vacuum kettle filled with a shellac mixture, loaded the cores
onto a tray and lowered them into the shallac, closed the lid and pulled
a vacuum for 20 minutes to get all the air out and help the shellac soak
fully into the laminations. ( That's how transformers and relay coils are made!)*
(qualified: Not all are done that way these days. )

Dave....
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« Reply #13 on: July 22, 2008, 12:53:29 PM »

Interesting. So a diode on an AC control line might have an affect? 

I would think that would make it worst, as only half the waveform would be controlling the coil, and it would basically be zero voltage for half the period. Maybe I'm not understanding some (many) things about this.

So, what's a 4 amp diode look like?  Any particular part number I should try? I'm not familiar with ratings. I've used 1N4004 diodes on my DC relay coils, and some larger stud diodes on the headlights, but I don't really know the ratings any more on these. I would think the 1N4004 might be about right considering the coils draw something like 320 mA.

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Craig Shepard
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« Reply #14 on: July 22, 2008, 06:33:21 PM »

Interesting. So a diode on an AC control line might have an affect? 

I would think that would make it worst, as only half the waveform would be controlling the coil, and it would basically be zero voltage for half the period. Maybe I'm not understanding some (many) things about this.

So, what's a 4 amp diode look like?  Any particular part number I should try? I'm not familiar with ratings. I've used 1N4004 diodes on my DC relay coils, and some larger stud diodes on the headlights, but I don't really know the ratings any more on these. I would think the 1N4004 might be about right considering the coils draw something like 320 mA.



Sorry to be confusing.. Yes a single diode would make it 1/2 wave (30hz) and yes it could make it louder. But the d.c. component will create a stronger attraction on the magnetic part and may be silent. If not the a full wave bridge rectifier could be employed.

The trick with diodes and relay coils is to make sure the PIV rating is very high.
(Peak Inverse Voltage) That is the spike that feeds back when a magnetic field collapses.

The diode must survive that feedback... ie: A Diode with a forward voltage rating of 200 volts might have a PIV rating of 1000 volts. ( They are all different. ) The higher the PIV rating means that it will withstand more voltage surging back towards it.

I don't have my handy dandy diode manual so would have to locate a source and data on which would be the right one to try.  1N4001 series might work, all you would do is fry a cheap diode if it doesn't work.

Well so much for long shots....

Dave...
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« Reply #15 on: July 22, 2008, 06:43:31 PM »

It is my recollection that inserting a diode in the 120 volt feed to an AC relay is that it will drop the voltage to somewhere in the 65 volt range.

I used to do this in some of the equipment I manufactured. I would use the full 120 volts to energize the relay or solenoid and then insert a diode in the circuit to hold the relay energized. This significantly increased the life span of the unit. After the units were up to speed I also transferred all the operational control voltage from the dirty utility power to the clean output power of the power conditioner.

Richard
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« Reply #16 on: July 23, 2008, 04:51:18 AM »

Well, I tried the diode trick. I put one of the 1N4004 diodes in the ground side of the coil control line. It seemed to just make the clatter louder. The diode did not burn out, but it didn't help the clatter any, so I removed it. After I took it out, the relay stopped chattering and seemed to work ok. The first relay is still buzzing, but it's a very low buzz. If I smack the enclosure it's mounted in with my hand, it will change pitch, sometimes for the better. It's not any louder than the inverter humm. I purchased new relays to replace them, but for now, I'm going to leave the old ones in place since it's going to be a pain in the rear to get them out (operator installation error) and I'm kind of pressed for time right now.

I got most of my electrical back in place. Still have to hook up the A/C and Aquahot lines. Now I can start on getting the generator installed (which is what prompted this whole mess). I'll have to redo a few things after the summer trip, as I'm just trying to get it functional now, and it's not necessarily pretty.

craig
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Craig Shepard
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« Reply #17 on: July 23, 2008, 09:02:26 AM »

use four 1N4007's hooked in a bridge configuration; 1000 volt rated, radio shack fodder, if not there, Digikey...cheap...
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« Reply #18 on: July 23, 2008, 10:23:28 AM »

Ok, so effectively, with this setup, you're just supplying a continuous DC current to the coil?  Correct?

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Craig Shepard
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« Reply #19 on: July 23, 2008, 04:21:46 PM »

Sometimes these types of relays can get some rust between the pole piece and the armature. A cleaning with a scotch brite pad can clear up the buzzing. It is also possible for the pole piece or armature to get a groove wore into it after it has been energized for extended periods of time. In this case a piece of 220 grit sand paper folded over might get the hump smoothed down, if it is to serious, it has to be replaced.
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« Reply #20 on: July 23, 2008, 08:27:16 PM »

So, tonight I tried the bridge rectifier. I didn't have the 1N4007 diodes, but I had used the 1N4004s the other day and they survived, so I twisted some of them together and attached with alligator (galliator?) clips. The results were very promising. The
second relay was clattering away before I put the bridge on. Afterward, it was silent and completely stable. Very impressive.

Now I need to find the specified diodes, and figure out how to mount them so I can attach them to the relays. I'm thinking I can attach ring terminals to them, and attach them to a piece or plastic board along with the control lines to the relays. I can then mount it on the inside of my transfer switch box.

Since I'm running out of time, I may just mount the 1N4004s for the time being. Looks like I may have to redo some of this work after our vacation this summer, as I'm still not satisfied with the layout and access to the electrical box and transfer switch. The generator is just not playing fair and it's placement is becoming a problem. I may end up cutting one of my underfloor ribs to get it installed. It's blocking access to the exhaust and maintenance door. Not my preference, but it may have to be done.

craig
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Craig Shepard
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« Reply #21 on: July 23, 2008, 11:42:31 PM »

Craig, you might prefer a more sanitary setup than a bunch of diodes on a board. Just use a bridge from Radio Shack. They're small and completely sealed except for the connections!

For what it's worth.

Tom Caffrey
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gumpy
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« Reply #22 on: July 24, 2008, 04:43:41 AM »

Craig, you might prefer a more sanitary setup than a bunch of diodes on a board. Just use a bridge from Radio Shack. They're small and completely sealed except for the connections!

For what it's worth.

Tom Caffrey

Yeah, I was thinking about that. I saw a photo of one when I was looking up what a bridge diode structure was. If I can find some of the IC units, I can probably just solder my lines to it, and mount it on a board somehow. Will have to see what they look like. I think I have some edge connectrors so I might be able to mount it on a PC board, and attach a few wire connectors to it, and mount it with some standoffs inside the panel box.

I have 4 relays in the box, although only 2 are buzzing currently ( heh heh, currently. Get it? Ok, so it wasn't that good. Still, I got a chuckle out of it. So little things amuse little minds.)  I should probably mount 4 bridges in there. I might be able to do it with less, though, since some of my control lines feed multiple relays. Will have to go over my schematic in more detail.

This is great. I'm learning some new stuff here. One more thing to postpone the alzheimer's.

So, here's a question.  If these relays have a tendency to degrade and start chattering, and the simple fix is to put a bridge on the control lines, why don't the manufactures simply include the bridge in the original design to begin with rather than the shaded pole configuration?  Or, why isn't there a simple bridge component already made that can easily be added to the relay when it starts chattering.

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« Reply #23 on: July 24, 2008, 07:17:13 AM »

I believe buzzing relays is something that very seldom happens, and cleaning the rust or dirt off the armature generally solves the problem. Also, the relays are designed to have a certain impedance with 60 hertz applied. By applying DC you very easily may exceed the current rating of the unit causing them to overheat and quickly destroy themselves.

Richard
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« Reply #24 on: July 24, 2008, 09:04:48 AM »

Hi Gumpy,
I can't help wondering why you have four relays in your transfer switch. Is your transfer switch a manufactured one or something you home brewed? Why would there be more than two triple pole relays for a 50 amp, 120/240 volt transfer switch? Are you using it to transfer something other than shore and generator power? What functions you are using your transfer switch for?

Thanks, Sam 4106

"Two are buzzing currently"! Is that "pun in cheek" humor?
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« Reply #25 on: July 24, 2008, 09:28:23 AM »

Hi Gumpy,
I can't help wondering why you have four relays in your transfer switch. Is your transfer switch a manufactured one or something you home brewed? Why would there be more than two triple pole relays for a 50 amp, 120/240 volt transfer switch? Are you using it to transfer something other than shore and generator power? What functions you are using your transfer switch for?
Hi Sam,

How'd your procedure go the other day?  Did you get to see the barn raising?


It's a home brew. It also includes neutral/ground bonding for my electrical system, as well as L1-L2 crossover when not on 240V shore line so both busbars in the distribution panel are powered. This is normally done by the dogbone adapter when plugged in, but my system also crosses L1-L2 when on inverter power. Also, I used DPDT relays, not tripple pole, because that's what I could find and afford at the time.

Quote
"Two are buzzing currently"! Is that "pun in cheek" humor?

Yeah, I got a chuckle out of it after I wrote it. Wasn't sure anyone else would find it funny.
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Craig Shepard
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« Reply #26 on: July 24, 2008, 10:22:04 PM »

Yeah, Craig. I thought it was funny.

I see that I forgot that the bridge might apply too much power to the relay coil because of lack of impedance. If you do use the bridge, it might require some resistance in series with the coil to hold the current to no more than the current when using AC.

I brought it up mainly to reduce the strong vibrations caused by the 60 Hz power. I expect that eddy currents in the armature contribute to the buzzing.

For what it's worth.

Tom Caffrey
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« Reply #27 on: July 25, 2008, 03:57:36 AM »

So, how does one go about figuring out how much and what size resistance to put inline? 

I suspect it requires some tools more sophisticated than my $3 harbor freight digital multimeter.


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Craig Shepard
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« Reply #28 on: July 25, 2008, 05:44:35 AM »

Don't you think it would be far simpler to just replace the relays? Or, replace them with DC coils and use a bridge rectifier for each one.
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« Reply #29 on: July 25, 2008, 05:48:27 AM »

Don't you think it would be far simpler to just replace the relays? Or, replace them with DC coils and use a bridge rectifier for each one.

Oh come on. Now you're just trying to be logical! That's not what we do. What fun would that be? What would I learn by just replacing them? I already know how to turn a screwdriver.

This isn't about practicallity. If it were, I probably shouldn't even own a bus   Roll Eyes

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Craig Shepard
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« Reply #30 on: July 25, 2008, 05:50:49 AM »

Just a thought.  Impedance does not mean a hill of beans when it comes to dc being applied to a relay coil.  With ac yes dc no.  The resistance of the coil does however.  A bridge rectifier does not increase the power applied to the coil.  If you look at the output of a bridge rectifier You will not see pure dc, You will see pulsating dc.  In short some relays will not care and some will.  The transfer relay in My coach, a commerical unit uses a bridge rectifier to power the relays.  The relays are a common heavy duty relay seen in many pieces of commerical equipment.  The reason for this is to reduce the hum being heard during normal operation.  All relays produce magnetic fields and by using dc metal panels,read ferrous panels will not resonate at the applied ac frequency.  Try it it might work.  Do not put a capacitor on the output side of the bridge in this application.  My 2 cnts.  John
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« Reply #31 on: July 25, 2008, 06:18:29 AM »

Thanks John,

That was kind of where I was headed. Try it. See what happens. I figure the worst thing that could happen is the relay coil burns out, and I have to replace it. At this point, I'm there already, and the bridge may just allow me to salvage the relay and keep it going for "awhile longer". That "awhile longer" might be a day, or a week, or it might be 20 years. Regardless, it's an improvement over declaring the relay dead today and replacing it. I figure I'm only out a few bucks and a little time to try, and I might actually learn something new here.

I was not planning on putting in a capacitor. If I were to replace the relay with a DC coil relay, then I'd probably add the capacitor and resistor to make a cleaner DC trace.  But that does lead me to wonder why the bridge output does not produce the same buzzing as the AC does. It's waveform also drops to zero between each rectified half-cycle, so shouldn't the coil begin  dropping out on each of the low voltage dips in the wave?

It sure seems to work, though. The test I ran with the 4 1N4004 diodes was very impressive with how quiet the relay became.

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Craig Shepard
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« Reply #32 on: July 28, 2008, 06:03:27 AM »

Just thought I'd post an update to my buzzing relay problem.

When we returned home yesterday from our mini-rally at Devin's (awesome time, by the way), the bridge rectifiers I ordered from DigiKey were waiting for me. I soldered on some leads, and spent a bit of time connecting them into the coil wires on the two relays that were buzzing and chattering. Plugged in the coach and voila, no buzzing or chattering.

5 minutes later, I heard a relay click, and thought, "Hmmm, that's not supposed to happen."  I opened my transfer switch cover, and smoke rolled out.

The upshot of it is one relay coil fried itself and the other was just seconds away from doing the  same.

So, as usual, Richard was correct, and the relays ate themselves on DC in a very short time.

What really gets me is that after replacing the two bad relays, I plugged in the repaired box a couple times, and on the second plug-in, one of the remaining 2 original relays started chattering!!  So, I'll probably be replacing them all before long. I'm going to dissect one of the two I replaced and see if there are any indications of why it failed.

Also, one of my bus friends wrote and said he might have some 60amp relays that he had salvaged. I like to install them in place of these 30 amp relays. I don't think that has anything to do with the current problems, but I'd feel better if I didn't have to have my contacts tied together to get adequate amp throughput.

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Craig Shepard
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