Chemically cleaning a corroded electrical connection

[Theo]

One of the relay bases in my car's fusebox has turned blue. This appears to be causing an intermittent electrical connection.

I have some conductive zinc gloop[*] to put in it to improve the connection, but how to clean it beforehand? I can't really mechanically clean it since it's embedded in the plastic of the fusebox and the fusebox is part of the wiring loom of the car.

So I was wondering the best way to remove the oxidation before I smother it in gloop. I've sprayed it with neat IPA (which can be relabelled 'contact cleaner') to no avail.

I've heard one suggestion being an acid (vinegar?) to reduce the oxidation, followed by an alkali (baking soda?) to neutralise the acid... but then how to get rid of the alkali (water/IPA?) without causing further corrosion?

Is there a better way to do this?

Thanks Theo

[*]

[RJH]

I'm not sure if it'd work in your situation, but I've used this (Soudal contact cleaner) to clean up electrical connections, then plug/uplug/make/break a few times before wiping.

[Brian Gaff]

I think it depends on the material. What about the other side of the contact? If it takes a decent current it could also be pitted and hence it may never really be reliable. Is there some way that another relay can be piggy backed across it with suitable rating? Back in the old days when I was young, I remember my Father doing something like this to avoid a great expense on replacing a moulded bank of relays What is this relay switching that takes enough current to cause this, oh and if you are piggy backing, be very very sure the TO off points are very well connected and protected from gunge and cannot short to anything. Brian

[Brian Gaff]

Yes but I feel the real problem is the connection itself,and hence unless you can get underneath directly, to tighten the grip, it will all be in vain. As I say whether its base or contacts, the piggy back relay usually works but is not of course very pretty!

Brian

[nothanks]

you have access to apply the zinc "gloop" then can't you make a suitable widget and stick some fine emery paper on the end of it, or a cut-down nail board, or use a small diamond file?

[Theo]

Not easily. The connector has pressed contacts which are designed to engage with the spade terminals on the bottom of the relay, ie like this:

Trying to abrade them internally risks opening up the pressed contacts and making the connection worse, not better.

Normally I'd just replace the contact, but here they're not removable.

Theo

[Theo]

Highly Refined Base Oil 1-20% Kerosine, unspecified >25% Butane >25% Propane >25%

so I think it's just mineral spirit, rather than anything with oxidation removal properties. It might keep connections clean, but not clean old ones.

Theo

[nothanks]

If they're like the ones shown in that link you can remove them by sliding a small flat gizzmo down the shaft of the contact to depress the spring tab, then pull the contact out using the wire. With care they should be reusable but replacement is easy if you know the brand of connector

[alan_m]

I once had a Vauxhall Nova where the plastic holders were so soft that contact designed to accept the spade pushed out when a connection was made. This resulted in some intermittent connections, especially behind the dash and radio slot.

[Paul]

I don't know if this is going to work, but some people have fixed electrical problems they had with it. I don't really know whether material like this is intended for ampere-level problems.

Stabilant 22A Kit

The only sure solution, when mating contacts corrode, is to replace both the male and female parts. Replacing just one of them, will only result in the same impaired function later on.

Typically (but not always), surfaces in electronics are built upon a plating stack. Maybe the base metal is copper, you put nickel plate on next. Then a more precious metal over top of that. Only a metallurgist knows the proper order of assembly.

When corrosion occurs, it can be pinholes in the precious top layer, allowing solvent chemistry with the metals below. Neither chemical attack nor abrasion, really makes the damaged plate-up stack perform any better.

Soldering the items together, works in limited circumstances. Most of the time, there's no way to get a soldering iron close to the working-bits. You could use solder paste and a hot air gun, but then, the insulation is probably too poor to take hot air gun temperatures.

Soldering should not be used in high-current applications. Because the joint will be too ohmic for the level of current, the joint will heat, the solder will run, the joint will become really ohmic. You would not repair a kitchen toaster oven with solder, as an example of a bad thing to do. This is why modern toaster ovens can be almost completely spot-welded together at the factory.

Paul

[RJH]

Ah gotcha, OK. It was actually this ('I knew it began with S'), which I think is much the same:

Used the same can over the past 20 years on errant volume pots in the main. Certainly helped with that, and never seemed to have done any harm elsewhere.

[Theo]

Pretty much:

Hydrocarbons,C3-4-rich, petroleum distillate Petroleumgas (1,3-butadiene < 0.1%) 30-60%

Alkanes (C9-12, iso) 30-60%

It sounds like it's useful as a lubricant (it's just oil, after all) and to exclude air from things. But not for cleaning up already corroded things unless you can agitate them enough to expose fresh metal. It might actually make things worse if there's not enough friction to expose the fresh metal (as oil is an insulator)

I looked at various 'dielectric grease' products, which seem to be roughly the same idea, but you have to use them somewhere you have a means to apply mechanical pressure to stop them forming an insulating layer.

Theo

[Theo]

Thanks, that does look interesting. It sounds like it solves the problem of putting 'something' conductive between the connections, so that if there's any conductive surface remaining the current will flow through that, bypassing the corroded contact surface.

I bought some replacement relays, but they are from a scrap vehicle so still have some wear. However I can access the terminals to abrade them, and being from a different vehicle perhaps the wear points will be in slightly different places.

(that will also rule out the problem being the relay contacts themselves, rather than the socket)

The Stabilant looks like it's designed to cope with plating failures, so it sounds useful in that respect. I suspect the reason for my terminals being blue instead of green is it's the nickel plate on top of a copper terminal which has corroded.

Maybe I should just try what mechanical abrasion that I can manage (via a micro screwdriver) and then try the zinc gloop. It's not quite the same as Stabilant but maybe will do roughly the same job.

Thanks Theo

[Animal]

Conductive gloop is the wrong material. Gloop can help prevent further corrosion if it's silicone or petroleum - don't use other greases. Conductivity only adds problems. Very fine sandpaper can clean things up, but won't leave the surfaces smooth or adequately plated so use gloop. If the problem recurs, sometimes it does, often due to lost springiness, then I'd solder wired to the socket & to the relay, the latter then sitting otuside of the usual box. That's if you can't identify which wires go to that socket, snip em & mount the relay on a new base outside the box, or move it to an unused slot.

[Thomas Prufer]

Perhaps those very small round dental brushes, "interdental brushes"?

Toothpicks spun in the round bits that go around the spade?

Thomas Prufer