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Old 14th Jun 2014, 3:10 pm   #7
QQVO6/40
Hexode
 
Join Date: May 2009
Location: Newcastle, Australia
Posts: 316
Default Re: FT107 sticky relays

Hello all.

I have had a bit to do with relays and their larger brothers, contactors.
We are dealing with an electronic device here that is a few years old. Most things these days use plastics of may breeds for structure and insulation within them. Over a period of time with elevated temperatures the plastisizer tends to evaporate out of the plastic materials. Mostly it is an oily, sticky residue and it can condense on other components within the machine. A classic example of this is the interior surface of a car windscreen where the car is left out in the sun for a number of days during the hotter part of summer. Result is an oily film on the inside of the windscreen that is damnably hard to remove. Iso Propyl Alcohol (IPA) to the rescue.

The same oily residue can end up on relay contacts and for a relay that is slow to release, on the face of the pole piece and inside face of the armature.

As has been said above, suitable strips of good quality printer paper doubled over or single strips of Manila paper. (The type of stiffer paper found in Manila paper office folders.) Really, any type of good quality very fine fibre paper. Do not use news print as the fibres are too coarse and can end up lodging between the contacts.
My favourite is pure hemp fibre paper. The fibres are very long and very strong.
I put a few drops of IPA on the paper strip. Place the paper strip between the contacts and gently press the contacts together. I usually use finger pressure on the relay armature to accomplish this. Stroke the paper strip to and fro a number of times. I dampen the paper strip with IPA for the first few passes until I get no further colour from the contact or armature I am cleaning. Clean strip of paper for each pass.
Once I get to the point that I am not getting anymore dirt on the paper. I start to burnish the contact with just clean dry paper strips.
The wood used to make paper has within it's structure small amounts of silica.
This silica acts as a very fine abrasive and this feature can be used to burnish relay contacts without fear of removing much metal from them.
This abrasive action I learnt at an early age from my Aunt when I used her good dress making shears to cut some paper for something I was doing. My error was brought home quite swiftly!
If the piece of paper strip is difficult to draw through the contacts then I would start to suspect that the contacts may be burned. Further investigation would be needed to see how bad they are. There are special contact burnishing files available. The good ones have very fine powdered diamond dust on them and the tips are flexible. I have my own but would not know where to buy them these days.
Again I make the comment that a relay that is slow to release, quite often, has some of this oily scunge on the mating surfaces of the pole piece and armature.

I hope this has helped.

Cheers, Robert.
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