Contactor rattle ?

[KD0CAC John]

Helping a friend with a old deep fryer , the thing started rattling - contactor magnetic opening / closing .
Seems like it is rattling to 60 cycle power ?
It has 2 contactors 1 smaller unit supplies power to controller panel --- this just a switch & thermostat - then the 2nd larger contactor controls the heating element .
1st repair attempt - took out both contactors and files the points , worked for a short time - now rattling again .
The owner wants to replace 1st / smaller contactor , I think that it is seems to be reacting to the 60 cycle Hz ?

[timeandfrequency]

Hello KD0CAC John,

It could be interesting to check the waveform of the control signals that energize the coils of the relays.
So an oscilloscope is required.

Are the control signals 24VDC ? 24VAC ? Or mains voltage ?
If mains, using a truly isolated scope is quite compulsory and it would keep you on the safe side.
Alternatively, a high voltage differential probe plus a vanilla oscilloscope would do it too.

[Xena E]

Assuming AC coil. And mains frequency buzzing/rattling...

magnetic path of the contactor armature is either not being fully pulled together, due to being stuck or dirty... or

The stationary part of the core is loose... or

The shading ring is broken or loose.

X

[timeandfrequency]

Or one single turn of the coil makes a short

[KD0CAC John]

I do have a Rigol scope & differential probe - not typical tools I would bring to this restrant  , but thought about doing .

The  heating elements are 240 ac , the control coils are operated by one leg 120 ac .
When looking into some of this gear & cleaning and looking on internet for info , I did see some reference to " SHADING RING " but that was a first I've heard of .
Noticed when working on larger controller , it would only go back together one way - I think that was the reason - shading ring .
Have to take the smaller one apart to look for shading ring .

More info on shading ring ?

Thanks

Will be back after looking at .

[Xena E]

Shading ring ...
Usually a copper or alloy loop formed int part of the stator section of the manetic core to cause a partial phase shift and maintain magnetic attraction through the zero crossing of the mains cycle.

Edit: only for line frequency relays and contactors.

X

[timeandfrequency]

More info on shading ring ?

Yes here : https://en.wikipedia.org/wiki/Shading_coil  (*)
The same principle is used in appliance fan motor (shaded pole motor) : https://en.wikipedia.org/wiki/Shaded-pole_motor


(*) Actually, I discovered just yesterday that shading rings were also used for relays. It was mentionned in the wikipedia page indicated above. Was looking for some information on the Internet while trying to provide some help on that topic (small single coil ECM motor).

[KD0CAC John]

Started shopping around , new $150-190 , reconditioned $110-140 .
Sighs of use - $45 .

Then thought more [ played with this a while back , a few times ] and it was working & then started the rattling - off / on - so at that time I took out both the smaller & larger unit & sanded the contacts .
Get called back and they said it worked for a very short time & then same rattle .
So seems like something else .

Guess I will just replace - but waiting for friend to get back to let him choose  ---- I do not feel [ with these unknowns ] i want to use the cheapest - ebay used ??

[Xena E]

So. Rattling on off on?

Do you mean completely dropping out, not just buzzing wholst pulled in?

X

[floobydust]

If the contactors are subjected to high heat (it's a deep fryer) as others have mentioned, the coils can fail and have shorted turns. Sometimes intermittent as well, and can overcurrent whatever is driving the coil.
I would check that is not the problem- one contactor coil going low impedance and overloading the control power if it's say 24VAC, which drops and causes trouble for the other contactors due to them being undervolted.

Not sure what size these are, but bigger ones you can replace just the coil. Otherwise, the cheap chinese ones are prolific.

[microwhat]

Surely new contactors from, say, Automation Direct, are cheaper than your time spend fiddling. You're switching resistive loads, so an IEC contactor applied within its AC-1 rating would suffice.

I don't work for them or supply them, but I have bought things from them on multiple occasions.