Anywhere there’s resistance in a connection, has a voltage standing across it and that introduces loss. Grease does not conduct well, much like rust. That’s why we clean our connections when they’ve corroded. Why would we goop non-conductive grease all over it?
Dielectric grease can be applied but only on already electrically mated connections. It keeps moisture and gunk out but that’s it.
Note that on low current connections* it won’t matter much. That loss is in direct proportion to the current going through it and since the current is low, the loss across the connection is low as well.
On high current components (starters, batteries, alternators) one would want to minimize that voltage drop or loss so you’d want to minimize the resistance and only goop after the connection has been mated.
*(connectors with signal wires, thin stuff - like 18 gauge wire)
I guess some just don’t get the point. Di electric grease MUST be non conductive, otherwise it could short out at the connections. In place as a thin film, like all grease, it helps cut down corrosion by cutting off the O2. Corrosion is a much greater factor in non conductivity between the connections. In this use, it AIDS conductivity by cutting down on the corrosion formation ! The current loss is negligible when grease applied according to directions. It is not when corrosion begins to form over time. Slapping grease on the outside is not guaranteed to make an air tight seal especially when O2 is already present at the connections. The directions for using this stuff infer , that if the connection is interfered with by too thick an application, redu it. You don’t have that option when the battery fails to turn over at the worse possible time due to corrosion.
In Keith’s words…I guess all the electrical engineers are wrong.
RemcoW, nobody is defeating Ohms law. We used to use dielectric grease on the connections of the magnetrons used in our radar systems in the Navy, tell me that is not a high current application. They draw about 1.5 megawatts. Very high voltage, but very high current as well.
As for putting grease on after making the connection, that is counter productive. That is why I prefer to just leave the connection dry. One of the services, Army I believe did a study on this for motor pool maintenance and discovered that a coating of grease (GP grease was used in those days) allowed moisture to wick up into the connection from beneath and would be trapped by the grease. They had less corrosion when they left the connection dry. This study was done some 40 years ago. They did not coat the connections before assembly in that study because no one did that then.
The dielectric grease sold for this purpose today are a different story. While I still leave my battery connections dry because that has worked for me for over 40 years and I don’t see a reason to change, if I were to use it, I would coat the connection first.
Let me throw a little more in here. The reason for the conductivity in thin film applications has to do with the way the grease will ionize in the presence of an E-field. I have seen papers on this phenomena, but I don’t remember the details. It was a bit complicated.
I will also add this, in every application where I’ve seen dielectric grease used on the mating surfaces of the connectors, it was a sliding connection. That insures that the grease is a thin film, very thin film. I have seen a lot of multi-pin connectors used in modern cars that were packed in grease, which I assume is a dielectric grease or it would short out the pins.
The battery connection is a clamping connection. In the power industry, clamping connections, which are live front connections use a grease that is embedded with zinc oxide to make it conductive, though I have seen some applications where dielectric grease is used instead. In a live front connection, insulation is not a consideration at the connection. Interesting that it is called a live front connection, but if you touch it, your dead, where in a dead front connection (insulated), in theory you could touch it and live. But since most of those connections involve voltages of at least 7200 volts, no one wants to touch them with any less than a 10 ft (min) fiberglass pole.
If you’re greasing the components before assembly, it works because you’re squeezing the grease out where it makes contact. It would have to. Grease does not conduct well, even when it is a mil thick.
I suspect that those 1M5W tubes had connections you really sock down - not a mere lead lug connection, am I right? Those connections no doubt were MIL grade, very likely gold plated, not on par with the average car battery connection. They are meant to make absolute positive contact, maximizing contact area.
My battery connections are dry as well because you can’t sock a battery connection down too much for fear of the lead breaking or stretching. In other words, that grease will introduce somewhat of resistance, even if it is just a bit of film. Maybe it gets hot because of the higher resistance and it boils off but that’s not ideal. A connection like that should be dry, as we both agree.
Once socked down properly, I personally don’t use dielectric grease there but Fluid Film to keep the weather out. Never had a corrosion problem.
Edit: one more thought:
It could be that the breakdown voltage of that grease you used on radar applications was lower than the voltage applied. Basically, every material has a breakdown voltage, even the insulation of wires. If you buy wire, you can only apply a certain voltage to it. Well, grease has a dielectric constant that does the same thing. if the potential is high enough, it will start to conduct to some extent, if not completely.
Of course, car batteries are much lower in voltage than those used in radar applications so that principle does not apply.
A typical metal surface looks like a mountain range on a microscopic scale.
When two surfaces are pressed together they only touch at the peaks.
With a dry metal there is air where the metal doesn’t touch.
If the metal is coated with grease the grease is pushed away at the peaks if the pressure is high enough, so there’s still electrical connection.
The grease fills in where there would be air and that improves thermal conductivity; commonly done on heatsunk electronic components.
There are high voltage switches that make the contact while immersed in non-conductive oil.