Heavy amp car DC connection probs

[Oznog]

I keep running into problems with the high amp DC wiring under my hood going to the deep cycle battery.
I have seen substantial voltage drops even between the stranded wire and a screw-down clamp, like 100's of mv even under low charging currents. The charger sees a higher voltage and it falsely concludes it is fully charged. The battery voltage itself is good, but the under-the-hood side of the interconnects are so bad it's definitely ruining the charger's functionality and it doesn't discharge high current loads well at all.

In fact, there is a noticible voltage drop across the stainless steel screw post itself, measured between the post and the rest of the lead terminal. I see 0.06v or so under mild currents. This is sucking horribly and I'm coming to the conclusion that the screw post is just a terrible way to connect stuff due to the high internal resistance of stainless.

Is there anything I can do for the oxidized copper stranded wire? It's an expensive 2ga cable run and would be difficult to replace. I made the mistake of not leaving enough slack in there to cut back if the termination were damaged. I don't know how deep the oxidation is inside that cable end either.

Should "battery terminal grease" be used here? I don't really get the point of that stuff, it's an insulator, right? I've thought it was mostly for keeping the battery acid from creeping in, but this particular junction is off the battery terminal. There will be no way to clean out the terminal grease from the fine stranded wire if it doesn't work. I'm not sure if there's any hope of being able to get solder into it.

Is there a chemical which could remove the wire's oxidation so I can maybe solder it? At least this will take care of the wire-to-terminal bond.

 

[David Bridgen]

Try vinegar. If there isn't enough slack to dip the end of the cable in a small vessel of it you can apply it with a paint brush.

Wash well with warm clean water afterwards and dry with a hair dryer.

The usual recommendation for battery terminals is Vaseline. Trouble is, the damned stuff is affected by heat and most of it runs away. I use a very light application of silicon grease which stays put.
(And to clean corrosion from battery acid use a solution of baking soda.)

 

[zevon8]

I highly recommend the use of a proper dielectric grease on all connections on vehicles after the connection has been made. I install high current draw equipment on heavy vehicles, and always use dielectric grease. Connections covered with the grease have seen 2 or 3 years of service in a road salt enviornment and still look like new.

You could also try conductive grease, often a light grease filled with copper powder. It used to be available commonly as a anti-sieze compound for high heat applications like brake and exhaust fasteners, but has been replaced by synthetic compounds.

One other cheap thing that helps is to solder the lugs onto the wire, and cover the joint with adhesive lined heat-shink tubing. This keeps any corrosion from entering the wire-terminal joint. Then use "internal-external" lockwashers. These are the ones with small teeth on the inner and outer circumfrences, looking like a gear. Also, try to isolate the connection from vibration by tying off the cable close to the termination. This is important on vehicles, to help stop the vibrations loosening the connection fasteners.

As a last resort, I have had some luck cleaning oxidized wire with acid flux, used in plumbing. Dip the wire in the flux, then heat to the point where the acid flux does its job. Then clean the wire with plenty of water that has baking soda mixed in, to neutralize the acid. This often turns the copper a reddish colour, but atleast it is clean.

 

[spuffock]

For cleaning copper there is nothing to beat dilute nitric acid, or a mix of battery acid and nitrate fertiliser. Be good and sure to wash off all the acid when clean, or there will be corrosion problems.
Another one that works really well if heat is not a problem, heat the copper with a blowlamp until it glows, and quench in methylated spirit.
It is a very good idea to move the blowlamp well away before quenching.

 

[Dialtone]

Here is a link to some anti-oxident material that has been in use by US telcoms since the dawn of time. It is one of the best electric connector anti-corrosives I have ever seen. Check out the section for NO-OX-ID A Special
https://www.sanchem.com/ox.html

Some of the older non electronics formulations were known in military circles as cosmoline.

We used it in all DC power applications in building Telecom Switching and power plants in the US for AT&T and the Bell System operating companies, and to my knowledge, it is still in use. I have seen battery strings installed 25+ years ago and the intercell connectors look as good now as when they were first installed. Practice was to coat the conductor ends with it before lugs were crimped on the cables, then also coat the bolt down connection points.

Dialtone