Dielectric grease on cable lugs? Lets test!

[Vigo]

I think an analogous comparison would be RTV and especially anaerobic sealants. As an auto tech i fasten some pretty large and rigid flanges to each other like engine and transmission housings. . There is basically no concern of 'trapping' a liquid sealant between two flanges and having it hold them apart. Even in the case of engine 'girdles' which contain the lower main bearing caps and where a flange sealant COULD change bearing clearances (typically ~0.002") to an unacceptable degree IF it were to become trapped, it's still not an issue. The excess (which there technically shouldnt be unless you apply too much) just finds its way out as the assembly is torqued. A less rigid flange surface would be even less of a concern because it would simply distort to allow an exit path for any excess sealant or in this case dielectric grease.

I cant think of many bolted terminals/lugs where the fastener size vs the lug size was such that the fastener couldnt clamp the two contact surfaces together hard enough to conform them to each other, ie flex/distort the surfaces enough to create an exit path for any grease getting pressurized between them. I would think the only way you get grease 'trapped' holding two contact surfaces apart from each other is if you have some really distorted surfaces AND insufficient torque on the fasteners. You can certainly get some non-compressible stuff in a 'blind' bolt hole and cause problems, but i dont think that's very analogous to cable lugs.

 

[Skypower]

(Please read the attached attachment link at bottom) I have personally tested clean and greased contact surfaces and found no statistically significant differences in conductivity…. Initially.
In time the unprotected surface will degrade. Then it’s the all too common “the battery was working so good for so many months and now it won’t balance”.
I tested using an internal resistance meter across the junction and then again using a very sensitive voltage meter across the junction with a steady load. By far the biggest variable is oxidation, particularly on the aluminum cell post or aluminum busses. Just a light buffing of the terminal with 3M scotch bright is all that’s needed, no power tools! The other problem was contacting surface parallelism. Some common nickel plated busses were concave or convex depending upon what side is in contact and also distorted by the slotted punched holes. In most cases the loss was measurable but not functional issues unless the current was near the upper operating range for the cell. Some cable lugs are also not flat which would not be a problem if the higher torque normally associated with these could be used, but not so with the cell terminals. Now along comes the two hole terminals. Well the fastener can be have much longer thread engagement but you are still limited by the torque of the whole terminal post of the cell not rotating causing serious damage or leaking.
So a friend gets some two hole terminal
cells with a “billet” busses (3/8” thick nickel plated copper) and he’s got hot terminals. I take one off and see that they are .010 concave on both sides so when installed they were only contacting the two hole terminals with a couple of knife edges. We switched to the flexible buss bars like I was using and the problem went away.

Conductive Greases vs. Corrosion - Practical Sailor

Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.

www.practical-sailor.com

 

[Skypower]

I do want to mention that the article shows that “Green grease” was superior in THIER test. I have not tried it on our cells. I have however used No-Ox-Id and it’s been unproblematic for several years.

 

[Hedges]

Now along comes the two hole terminals. Well the fastener can be have much longer thread engagement but you are still limited by the torque of the whole terminal post of the cell not rotating causing serious damage or leaking.

If torquing against the cell.
If you instead restrained with a tool on the terminal, you could torque to your heart's delight.

 

[Skypower]

If torquing against the cell.
If you instead restrained with a tool on the terminal, you could torque to your heart's delight.

True.
Just got to have a good feel of balance or squeeze the two tools with one hand. Just wrap em up so nothing shorts. Too early for the forth.

 

[Boron]

Going with the theory that it fills "voids", lets assume one of your connectors has a concave surface. You now trap an insulator in that void and as you try to tighten the terminal the hydraulic force of the "insulator" prevents you from getting it to flatten out more as you tighten. Yes, an exaggerated example, but I'm not buying that it will all just "squeeze out" and be as good of a connection that did not have remnants of an insulator trapped in there. As I noted earlier, sealing up the outside of the connection is fine, but I will never (nor have I ever) put it on the actual contact surfaces. But hey, people can do whatever they want.

Yup I resemble that, Yeehaa dont mess with Texas - they might secede from the Union - Bubba - gotta love a Whataburger served by strong Matrons on roller blades wearing cheerleader gear - dont ever forget that $ tip Tx

 

[Boron]

True.
Just got to have a good feel of balance or squeeze the two tools with one hand. Just wrap em up so nothing shorts. Too early for the forth.

I have resorted to using SS shakeproof washers on M6 M8 studs, they easily bite thru any oxide for ring terminals etc, then finish the joint with an outside coating of Si grease - works for me - but I dont go above 100A. Bigger stuff is a new ball game. Making high current joints is a special skill.

 

[Skypower]

I have resorted to using SS shakeproof washers on M6 M8 studs, they easily bite thru any oxide for ring terminals etc, then finish the joint with an outside coating of Si grease - works for me - but I dont go above 100A. Bigger stuff is a new ball game. Making high current joints is a special skill.

I hope you don’t mean between the cell post and the lug/busses?