PI and the Art of Coil Repair

[whiskey]

Another search coil causing problems. Oxidation, anyone?

http://www.youtube.com/watch?v=0OwrkEOpPiQ

How much paid for that coil? ...and it has masking tape holding the wire on.

Oxidation can form in as little as four hours and the tape may have accelerated the process. Should have been a better connection there to begin with.

One thing that can't be seen is the oxidation that is forming on the soldered connections that may one day cause a reduction and breakage...unless the soldered joints were properly sealed.

I would think that all search coils are not this easy to take apart; let alone, fix.

[Reg]

Hi Whiskey,

My experience with the Coiltek coils that failed was that normally they were very noisy and would really sound off if the bottom of the coil were flexed. What I found to be true was the paper coated with a carbon based paint (used for shielding) was no longer glued firmly to the bottom of the coil form. Instead, the paper had warped, maybe stretched so it could flex, thus creating the noise when the plastic used for the bottom of the coil moved with respect to the windings. Gluing the paper down again eliminated the problem. I also recommended some form of extra foam to take up the extra space, thus not allowing the bottom to flex or at least, not as much.

Now, on the down side, I had to sacrifice one larger coil before I could figure out just what was happening since there appeared to be nothing obviously wrong physically when I first checked the coil. It was only after playing around with the paper did I figure out the problem since the windings and connections all appeared to be just fine.

BTW, once this info was posted, one guy simply drilled a small hole and filled the bottom of the coil with insulating foam commonly used around the house to seal air leaks. This foam took up all extra space and wouldn't let the shielding paper move.

Reg

[whiskey]

Hey Reg.

You got me to thinking about that insulating foam. I ripped into a defective Garrett coil and what a nice mess it was...insulation foam everywhere.

One thing I noticed is that the cured foam distorted the plastic skeletal frame that the coils are supported on and I'm not sure if there would be any concern there as the distortion was slight.

Another issue if someone is to use the foam would be of injecting too much foam. There needs to be an exit hole or riser as such to vent escaping air and excess foam before it cures. I foresee a problem should the foam cure too fast and become trapped and expand the panels outward cracking them. The added foam will add some weight too.

A better idea that the Garrett coil used in concern to the shielding was to paint the inside of the panels and use two stranded leads soldered to two strips that looked something like lead. I can not say as to how the strips were adhered, but they did peel off easily.

My poorest suggestion would be to tear the paper off and spray the inside of the coil covers and attach the leads. A possible problem after doing such is the expansion and contraction of the panels in relation to the painted carbon. This expansion I believe is expressed as a thermal coefficient. A good visual example of this problem is vehicles that are covered with a two stage paint. The clear coat expands at a different rate than the base and the adhesion separates and also cracks. A solution would be to remove the carbon paint from the spray can add a flex agent and reducer/thinner and use a paint sprayer.

Another possible solution and perhaps the best to consider after tearing off the carbon paper may be to use 3M Scotch #24 around the coils instead.

Being that the coil was an expensive one this rebuilding becomes a ding against Coiltek.

whiskey

[Reg]

Hi Whiskey,

I use a rigid two part foam to fill my coil forms once the windings are positioned and I usually end up with too much foam inside which results in distortion to the coil housing itself.

Since I use a shielding that wraps around the windings and not the carbon paper, I don't worry about the distortion hurting anything. To be honest, I can't see where it causes any problems at all. As such, I am not sure it would cause problems even on a coil using the conductive paper.

I prefer filling the form with foam because it makes it waterproof and quite rigid, thus there will be no flexing or excessive movement of windings.

Reg