On Wednesday, April 6, 2016 at 7:43:17 PM UTC-4, Phil Hobbs wrote:
On 04/06/2016 08:42 AM, Tim R wrote:
On Tuesday, April 5, 2016 at 10:41:13 PM UTC-4, Ralph Mowery wrote:
"Rheilly Phoull" wrote in message
...

Have you got some dirt or oil/grease on the battery posts? That's what it
sounds like to me.

So when is grease on the terminals bad ??

When it gets between the battery post and the clamp.

If it is on the outside it is fine.

Conventional wisdom says when you tighten it down the grease gets squeezed out and there is direct metal to metal contact.

Whether that's based on data or not I don't know. But that's the way mechanics do it successfully.


Of course air is a better insulator than grease.

The actual metal-to-metal contact area is surprisingly small--it's
roughly equal to the total preload divided by the yield strength of the
weaker material. As long as the grease can get out of the way of the
high spots that actually do the conducting, it won't hurt the conductance..

What it will do is keep acid out of the joint, which is a win.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

I have always put a coating of low viscosity grease on the battery and terminal, then wiped it out. The small of amount of lubricant left will be displaced at the actual contact points over the surface of both by the clamping force and left to fill the tiny pockets of what otherwise be air and moisture. I have never had a car battery contact problem ever.