Noisey MEM switch

[AJWParticipant @ajw]

[AJWParticipant @ajw]

I have a MEM NVR switch that supplies my ML7 with power which when it is operated it buzzes, most annoying!
I have had it apart and the noise seems to come from the meeting of the laminated cores.
I have cleaned where they meet and even applied a lubricant to help but it invariably buzzes.
Give the case a whack and it might sort it for a while – or make it worse!
Any ideas, other than replace it!

Alan

[Anonymous]

Even the slightest piece of dirt will stop the poles of an open frame contactor from mating properly, with resultant buzzing. Take it apart again and wipe the faces, clean them again and then wipe with a no residue solvent like acetone. Don't apply lubricant, the faces should be bone dry.

In terms of the magnetic circuit even a few thou gap is very significant.

Andrew

[AJWParticipant @ajw]

Thanks for your reply, I must admit to not dismantling it but I did draw a sliver of paper between the cores where they meet and didn’t find any real dirt there but I will pull it apart for a proper clean.
It can only be the cores vibrating but it can be so annoying!

Alan

[EmgeeParticipant @emgee]

If the starer is not fixed to a flat surface the case can be distorted and prevent complete closing of the poles.

Emgee

[Mike PooleParticipant @mikepoole82104]

You may have some copper inserts in the poles, check they are not broken.

Mike

[AJWParticipant @ajw]

Thanks guys, I think this will get a close examination tomorrow – will report back my findings.

Alan

[Brian Sweeting 2Participant @briansweeting2]

It could also be the operating coil beginning to weaken, depending on age of course.

Edited By Brian Sweeting on 08/11/2018 14:15:25

[John HaineParticipant @johnhaine32865]

? How does that work?

[SillyOldDufferModerator @sillyoldduffer]

I like Andrew's suggestion as being more likely, but loose laminations are a possibility. Worth a look at how they are held together in your switch.

Dave

[Howard LewisParticipant @howardlewis46836]

To me it sounds like the laminations are vibrating because of the alternating magnetic field. Maybe a copious coating of varnish or paint would "glue" them together again, and solve the problem.

Howard

[john fletcher 1Participant @johnfletcher1]

The pole faces should dry and free from even the smallest particles to avoid that annoying bussing sound. All the starters and contactors I've seen have had ground pole faces. I remember taking some noisy one apart and having the faces ground a second time hoping to improve things, but that was when labour was cheap.Years ago MEN and other motor starter manufactures offered a resistor and rectifier kit so that to coil was operating on DC, that eliminate the buzz completely. John

[Phil WhitleyParticipant @philwhitley94135]

check the screws that hold the contact box to the armature are tight, they cause noise! look also at the screws/tabs that hold the lower armature to the base, and generally (with the power off of course!!) tighten everything up. Hope this helps.

Phil.

[AJWParticipant @ajw]

Dismantled the switch tonight which wasn’t ‘dirty’ as such just a haziness to the insides, quite good since it’s been there since the early 50’s. Cleaned contacts with a fibreglass pen which were ok. Nothing was loose.
Removed laminated cores and found they had six rivets through each, didn’t feel or look loose in any way but made sure they were riveted tightly by giving an extra session with hammer and punch. The ground faces of the cores were wiped on a flat surface and cloth.
Put it all back together and it was exactly the same! Sometimes quiet and others it would buzz away like a goodun.
The bottom fixed core is secured by spring clips and carefully prodding this around would affect the rattle.
So I have now incorporated pieces of rubber (inner tube) between the core and the switch chassis and it is now the quietest it’s ever been! A gentle hum.
Going to delclare it fixed!
Thanks for all you pointers.

Alan

[AJWParticipant @ajw]

Well, my ‘gentle hum’ turned into a really annoying rattle, very waring, tapping the case changed it for a while but didn’t eliminate it.
My bench drill has the same (similar) switch so I thought I would do a swap.
All changed over, only took an hour! and this one is even worse.
Had enough now, ordered a replacement so I can get on with a quiet turning session!

Alan

[Phil WhitleyParticipant @philwhitley94135]

Is the starter mounted on the machine? check that the contacts for the overloads are clean, and also the little holding in contacts on the top, next to the three main ones. If the machine has even a very small amount of vibration, this can cause the overload contact to arc, and cause buzzing and random noise. Better off mounting them on the wall and using a remote stop/start on the machine. If you look at the bar which bears on the end of the overload heaters and push the bar against the spring you open the overload contacts, and can inspect them.

[AJWParticipant @ajw]

Thanks Phil, yes that switch is mounted on the lathe cabinet, but it has been for the last 60 years!
I have had it all apart and cleaned all contacts, which are not burnt.
It is coming from the lower fixed core, this is spring clip mounted on the lower chassis and designed to allow a small amount of floating movement so when the top core is pulled down it allows the cores faces to meet fully.This is where the noise comes from.
I have tried all sorts of packing pieces (rubber) which appears to help for a while but I have decided I have put enough time and effort into the problem and will settle for a new switch!

Alan

[DalboyParticipant @dalboy]

Reading one of your posts you say you changed the switch from you drill and that one made the same noise when you fitted it to the lathe, so is there another electrical fault that is causing the problem loose contact elsewhere in the system start from the plug and work through the electrics buying a new switch may just be spending money that need not be spent.

I hope I did not read that post wrong

[AJWParticipant @ajw]

Derek, no you didn’t read it wrong!
I think the problem has been masked as my lathe used to be fitted with a 1/3 horse single phase motor, I didn’t realise it at the time but it had quite a ‘throb’ to it which I believe masked the noise from the switch.
A few months ago I fitted the lathe (ML7) with a new 1/2 horse Brooks 3 phase motor supplied from a new Bosch VFD.
This new setup has transformed lathe operations and is near silent at normal turning speeds and as a result the switch noise has become very obvious!
Sort of tolerable for a quick bush but on longer jobs it’s becomes really annoying!
And yes the drill switch also makes a noise but I am aware of turning it off then on again in the hope that it would come back on quieter but as it was on the drill it wasn’t actually in for that long.

Alan

[Phil WhitleyParticipant @philwhitley94135]

Yes, the lower clip os usually the culprit, but we must allow for the fact that it is old, and it has been, as you say, on the lathe for 60 years! they do get noisy, and there are things you can do to quiten them, but after a time it becomes a hiding to nothing. The problem is, what do you replace it with? British and European are fairly expensive, and the alternatives are either Indian or Chinese. Last new one I fitted came from a local electrical wholesaler, was indian, and cost about £45-00. It was ok, fitted to a v twin 2 stage 3 phase compressor, bit small internally, but generally ok. Looked it up on Alibaba, to find that they cost $4-50 per unit if you buy 100! The MEM starters are well made, and just about bullet proof, but can be noisy………………………………

Good luck with it!

Phil

[Phil WhitleyParticipant @philwhitley94135]

Just read the last post again, if you have a VFD, it mat be interacting with the coil to cause the noise, something to do with the squarish waveform vfd's produce, why not take the starter off and start the motor from the vfd, and also fit a remote stop to the VFD so you have an emergency stop?

[Philip RoweParticipant @philiprowe13116]

Definitely not to be recommended but 55 years ago when I was an apprentice this was a common fault in the factory where I worked, cured albeit short term by sticking a layer of insulating tape to one side of the laminations. Instant result and happy workers who had been plagued by the noise. I never did find out how long this bodge would last and the factory is now a supermarket so never will know.

Phil

Edited By Philip Rowe on 11/11/2018 16:58:32

[AJWParticipant @ajw]

My MEM switch is used as a supply (and emergency stop) for my lathe with its powered milling attachment.
The supply comes to the MEM switch which then supplies mains to a double switched socket, one for the lathe, one for the mill. Each motor has its own VFD.
My switch makes the vibrating noise regardless of whether any ‘load’ is switched on or not!

Alan

[John Doe 2Participant @johndoe2]

I know this is an old thread but readers might find this interesting.

In a former career we had technical vehicles with electronic transmission equipment running on standard single phase 240VAC mains, (from a trailer generator). There was a 36V DC battery back-up system to maintain the equipment in the event of a mains failure.

The 36V back-up supply had a relay so that if the mains disappeared, the relay would switch on the 36V and keep the electronics alive. On one particular van this relay always buzzed and frankly was a pain. By tapping the relay, you could sometimes quieten it.

About 5 years later myself and a colleague were stripping out and refitting the electronics in this particular van. When we came to the 240VAC power board, we discovered that the line conductor feeding the 240VAC from the tailboard connector into the van electrics had cracked completely through just above the soldered joint, but the wire was just touching together.

So, all those hours putting up with a buzzing relay ! The cracked line conductor obviously sometimes made a good contact, other times a poor contact, or a diode effect, causing the relay to try to switch on every cycle of the mains, and this caused the 50Hz buzz !! Oddly, the cracked wire passed line voltage and current very well – we would have noticed a drop in mains voltage or current limiting.

So, as someone in the thread did suggest, faults like these might point to a problem in the mains supply rather than the buzzing item itself.

Worth checking all connectors and switches in the mains path. Both the internal wire joints and the external plug and socket pins

Edited By John Doe 2 on 13/01/2022 10:20:32

Edited By John Doe 2 on 13/01/2022 10:23:23

[Howard LewisParticipant @howardlewis46836]

As ever, coming in late, My NVR switch started to buzz.

Removal /strepping disclosed no problem. Refitting with the screws TIGHT cured the problem!

Possibly, if the problem is loose laminations, MAYBE painting the laminations with varnish (But not over the pole faces ) will help matters.

Howard.

[Author]

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