The Arch Enemy of Electrical Connections.... What do you suggest? 1

[vonsteimel]

Greetings,

I work for a small firm making unique recreational vehicles. Our engines were originally designed for snowmobiles and later converted to also be used in aircraft.

Some of our vehicles operate in salt-water. We are having an increasing number of problems with engine performance in salt-water, particularly with the Electronic Fuel Injection (EFI) engines.

The engines are not designed for direct salt-water exposure but have performed satisfactory until recent times. The EFI systems have a number of "water-tight" plugs that have generally been bad-new for us. We've been caking them inside & out with dielectric grease to help stem the problems.

However just recently we've gotten a good look at a vehicle that has had heavy saltwater exposure for about 100 hours of operation (stretched over probably 6-mo) and the pins inside the plugs are badly corroded!

The plugs are running parallel with the floor/ground and are not at a low point where all the water will run... Water seem to be able to penetrate virtually everything with time. The capillary action is quite an amazing phenomenon... And if that water contains salt, watch out...

How/why would the dielectric fail like this? Can the dielectric mix with saltwater? Perhaps its becoming a mini gel-battery?

What do you use/suggest to use as an insulating grease? Any alternative suggestions to help seal the plugs & keep salt out?

Someone has suggested Silicon Grease..? I thought dielectric grease was silicon? And I know some Silicon Products can produce acetic acid which is as much bad news as salt-water....
So many problems... So little time.

Any comments or suggestions will be greatly appreciated.
Thanks,
VS

 

[EdStainless]

Sounds like you need to change the connectors. They should be sealed to the wires, and have heat seal tubing over the outside of them. Look into the ones that are designed for use in marine applications. The water could be wicking down the wire under the insulation.
If you are going to use grease it should be a synthetic, I prefer Krytox. And it should have a corrosion inhibitor in it.

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Plymouth Tube

 

[MikeHalloran]

I worked on an analytical instrument that contained salt water with a wetting agent. The only grease resistant to that stuff was Dow Corning High Vacuum Grease, silicone- based and very stiff. Our electrolyte would dissolve any other grease, including generic silicone types, in mere minutes.

There's a separate issue. All wire insulation has pinholes, even if it's visually undamaged. Salt water can enter the pinholes and travel the length of the wire. ... unless the wire has 'anti wicking' applied. It's some kind of icky goop applied to the copper before the insulation is extruded over it. I think some auto companies use it underhood. Definitely not all. Talk to Belden about your hookup wire.



Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

Take a look at Jet skis and see what they do.
B.E.

You are judged not by what you know, but by what you can do.

 

[vonsteimel]

BTW, these plugs are exposed to direct salt spray, and sometimes complete saturation, but not submersion while operating.

 

[vonsteimel]

It looking like we're going to start potting all the plugs now.
The need to disconnect is rare.

It seems no matter what you do, aside from complete enclosure (i.e. potting), any terminal connection that is exposed to direct salt spray/saturation will corrode. If you grease it, it will corrode under the grease.
The only other option I see is to have it thoroughly cleaned with a salt-flusher & coated with a corrosion inhibitor after every single operation --- which is not feasible....

Hopefully potting will solve the problem.

Any comments will be appreciated.
Thanks,

VS

 

[EdStainless]

Look at what you are using for wire, make sure that it is rated for continuous water exposure.
I have seen water wick down thousands of feet of cable to penetrate a connector.

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Plymouth Tube

 

[MikeHalloran]

I hate hearing the word 'hopefully' in any engineering context. I used to work with a highly productive idiot who used it all the time; now I wince at hearing or reading the word.

Test your proposed potting product and process before you get all lathered up about it. Then test it again.

Buy yourself a grit-edge hacksaw blade or two for destructive evaluation of potting. The round ones with fine grit will section an optical assembly, including lenses, without cracking the glass.


One thing you may not have tried is Dow Corning Flowable RTV. It comes in a few colors and clear. You pour it over your assembled connection, rotate the assembly a little to keep the thickness even, breathe on it to make it form a skin, and let it cure undisturbed for a while. It comes out shiny and water resistant, and (just barely, with a fight) removable. Not perfect, but better than any potting IMHO.

Also, again, as has been mentioned, check that the wire itself has anti-wicking defense of some kind, or sealing the connectors won't matter.



Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

"If you grease it, it will corrode under the grease." Just change the word grease to potting compound.
Both types of material can fail if not selected correctly. My preference would be for a proper grease so the connector can still be disconnected. A silicone grease should be capable of preferentially wetting the contact surfaces and displacing water.

 

[jsscott]

IMO all of the above may help (hopefully ) but if you want to completely dis-allow entry of water into your electical path you might take a look at Impulse and/or Seacon underwater penetrators
Impulse
Seacon
I've deployed hundreds of surface and subsurface applications using their products. When used properly (per their specification) they provide long-term secure protection and reliability. I've had some of these out for over 2-3 years without a failure. They are not cheap solutions. You get what you pay for

I've also done many field splices with excellent reliability. I'll typically cover the soldered joint with heat shrink tubing (the one that uses adhesive that melts under heat gun) then coat this with 3m ScotchCoat. Layer of Scotch33 extending WELL BEYOND either end of the splice, then another layer of ScotchCoat. Lastly another heat shrink tubing (again w/ the internal adhesive)and extending well beyond the splice. (The extra length also gives a nice bit of strain relief to the joint)

Lastly, the comment "We've been caking them inside & out with dielectric grease to help stem the problems" could be part of your problem. Typically we use a very light coat of the Dow Vacuum Grease Mike H mentioned above. This stuff works really well and keeps the mating surfaces from weathering. BUT if you use too much of it you might be preventing a proper seal of the mates which can allow entry of water. (I've seen this occur many times when people get overly excited applying grease to o-ring face seals.) You might try using a lighter silicon based spray lube on the mating surfaces: spray as much as you like on both surfaces then give them a shake to disperse the excess, then mate the connection. Should provide years of happy service life
-s