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When / where to use dielectric grease?

 
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blues750



Joined: 06 Jun 2015
Posts: 46

PostPosted: Tue Jan 01, 2019 9:49 am    Post subject: When / where to use dielectric grease? Reply with quote

Recently, while inspecting the engine compartment after some routine maintenance, I noted a section of "browned and crispy" wire insulation. This particular wire was one of the 3 phase wires which come from the 30A PMA associated with the engine. The brown and crispy portion was at the back of a plastic 6 blade connector half where crimped 1/4 female spade connectors are inserted to mate with the Regulator/Rectifier. The crimps are good, all spades firmly seated into the shell, though the spade (associated with the browned wire) location on the shell also show sign of getting too hot. But only at the one spade connection. Overheating due to high resistance is the only thing that comes to mind. I did apply dielectric grease to these particular spades to help them fully mate and as a corrosion/moisture preventative. I do this routinely on older cars up here in the Northeast with no issues. Could this be a problem? I typically draw 18-22 amps load while flying but when topping off the batteries will draw closer to 30 amps for 10-15 minutes of flying if the batteries have been drawn down for extended times during non flight activity. Note that the output from the R/R looked fine but they are a larger gauge wire. (12ga versus 14ga of the 3 phase wires into the R/R) Rather lengthy problem description for what appear to be an overheated wire, open for all thoughts or ideas. The only one I can come up with is poor connection / high resistance, though not sure of the mechanism. Thanks, Happy New Year to all!!

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gilles.thesee(at)free.fr
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PostPosted: Tue Jan 01, 2019 10:34 am    Post subject: When / where to use dielectric grease? Reply with quote

Le 01/01/2019 à 18:49, blues750 a écrit :
Quote:
I did apply dielectric grease to these particular spades to help them fully mate and as a corrosion/moisture preventative. I do this routinely on older cars up here in the Northeast with no issues. Could this be a problem? I routinely draw 18-22 amps while flying but when topp!

Hello,

Just to mention that "dielectric" means "insulating".
Don't know if this is a problem, but gas tight metal to metal is key.
Quote:
Rather lengthy problem description for what appear to be an overheated wire, open for all thoughts or ideas. The only one I can come up with is poor connection, though not sure of the mechanism.


We have had the same issue with some wires off the voltage regulator
connector. We replaced the wires and spade terminal, paying attention to
the quality of the crimp.

Happy New Year !
--
Best regards,
Gilles
http://contrails.free.fr
http://lapierre.skunkworks.free.fr


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blues750



Joined: 06 Jun 2015
Posts: 46

PostPosted: Tue Jan 01, 2019 12:54 pm    Post subject: Re: When / where to use dielectric grease? Reply with quote

Gilles, I think you may be on to something! I likely "gobbed" on too much dielectric grease and prevented a good electrical connection as the grease heated up and spread over the metal to metal connections. My plan is to clean up and replace the connections, reassemble with no dielectric grease! Thanks for the reply. Cheers! Dave

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user9253



Joined: 28 Mar 2008
Posts: 1350
Location: Riley TWP Michigan

PostPosted: Tue Jan 01, 2019 5:45 pm    Post subject: Re: When / where to use dielectric grease? Reply with quote

Most common grease is dielectric. Its use should not cause a problem. A properly crimped joint forces all grease out from between the metals. I have coated automotive battery terminals with grease and the vehicle still starts fine. The problem is due to a bad crimp.

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Joe Gores
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BARRY CHECK 6



Joined: 15 Mar 2011
Posts: 739

PostPosted: Tue Jan 01, 2019 6:42 pm    Post subject: When / where to use dielectric grease? Reply with quote

Joe & Gaggle:
Dielectric Grease is Silicon based all 100% synthetic.  Automotive greases, and oils for that matter which are NOT 100% synthetic, and there should not be any 100% synthetics.  [Yes, I know they advertise 100% synthetic but unless something has changed no, engine oil is 100% synthetic.]  Petroleum Oils & Greases will trap moisture!  Just like the water that is found in your engine oil.  The axle grease on the battery terminals will work for a long, long time.  It is just not the best way to attack the issue.  Do you really need to go the route of the Ultimate Silicon Dielectric Grease path?  Well, not for a automotive battery terminal.  BUT!  For the whole $1.00 for a Permatex packet - YES - That is the way to go.  And when using the dielectric grease on terminals of different metals:- copper, silver, gold, tin, solder and mixtures of them, why take a chance of corrosion.  After all, we know automotive oils do become acidic!
The posted question on WHY use dielectric grease especially since the term dielectric means Non-Conductive.  GREAT QUESTION!
Slop on the dielectric grease to the point of just becoming sloppy.
THEN complete the connection...  Fast-On connectors just slide them together.  As they push together the CONTACT POINTS will make both a mechanical and an electrical contact pushing the dielectric grease out of the way.  YET!  The grease will be in enough places to create a oxygen and moisture barrier.  DON'T think you solved the problem for ALL time.  The dielectric grease will migrate and become washed off, by YOU - When you wash the plane or use engine de-greasers or fly through rain.  Use it...  Then re-use it when you cannot see the nice coating you original put on.  
Joe - You said it!  BAD CRIMP!  Yup, I agree 1,000 %.  Wrong size terminal.  Wrong size wire for the terminal. Wrong type wire used.  Wrong TOOL used for the crimp.  
Little Trick:  One job that I worked on where the terminals were in a particularly difficult location to get at for inspection or repair AND the piece of equipment was was on the deck of an Aircraft Carrier for extended periods of time.  The requirement was to:
1 - Put Dielectric Grease - IN - the terminal BEFORE CRIMPING.
2 - Dip the wire into Dielectric Grease.
3 - Assemble and then CRIMP.
There were no issues of a resistive connection.
Yes, I do believe in dielectric grease.
And, it's great for keeping your hair in place on dry staticky days.


Barry
On Tue, Jan 1, 2019 at 8:50 PM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

Most common grease is dielectric.  Its use should not cause a problem.  A properly crimped joint forces all grease out from between the metals.  I have coated automotive battery terminals with grease and the vehicle still starts fine.  The problem is due to a bad crimp.

--------
Joe Gores




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blues750



Joined: 06 Jun 2015
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PostPosted: Wed Jan 02, 2019 4:38 am    Post subject: Re: When / where to use dielectric grease? Reply with quote

Here are a few pics of the connector in case anything can be determined by the pic. Will post pics of crimps when I remove wires and assess. Thanks for the input all. Dave

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blues750



Joined: 06 Jun 2015
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PostPosted: Wed Jan 02, 2019 4:36 pm    Post subject: Re: When / where to use dielectric grease? Reply with quote

OK, had a chance to remove the wires from the connector shell. I would like to think all my crimps looked like the "good looking crimp and wire" I cannot imagine I would have proceeded without having them otherwise. But... the other wires look pretty p*ss poor! The bare wire had hardened insulation which I peeled off to inspect wire condition. Seems like a lot of corrosion for such a "young" connection! In reading Bob's related reply, I can easily be lead to believe that those (my) crimps are in the "neophyte" category for these particular terminals. I cannot recall the crimp tool name I used, but it is oe I purchased from SteinAir expressedly for doing open barrel crimps. Thoughts, insights, and opinions??

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