Negative/Ground wire

Wot? Why would anyone be worried about corrosion?? :R

Here's what the mini-breaker in our A-frame looked like after a year. I don't see any corrosion, lol!

The 2nd photo is what the ground lug in the A-frame looked like after a year. I replaced it with two new larger lugs with more surface area and the connections are soldered and wrapped with heat shrink tubing. I made it a redundant ground setup and attached the lugs on opposite sides of the A-frame with stainless steel self-tappers. While I didn't use it, a little dielectric grease might help too. The ground lugs they use aren't approved for wet locations but they all seem to use them.

The converter will also be grounded with a bare and insulated ground wire to the frame (probably near the converter). We had a a couple of similar ground lugs like the above one attached to the frame. Think of all the water thrown up by the tires. The green wire was being hit by the tire all the time and would have worn through at some point. I replaced the original lugs with a brass grounding split type stud intended for wet locations. One of these studs would be a good choice for the grounding in the A-frame.

I went a step further and relocated all the splices and breakers in our (typical) 4x4 metal box into a watertight PVC box. Some of the marrettes were upside down and filled with water. Some of the wires were tarnished and I dipped the ends in acid before soldering the splices.

Thanks for the replies. I know what I'm going to do, but it is a secret to avoid flaming.

I used a long length of copper water pipe as a second negative path in parallel with the frame in the 5er we had. Had short wire connection each end to battery neg and DC panel neg lug. It worked great to increase amps from converter to battery.

You don't need to have equal R for neg and pos paths since it is a circuit and the total R is what counts. Reducing R anywhere helps.

The was no "loop effect". Got some "loop effect" in another set-up though where there were several grounds in play, but that was with an inverter that had an internal fault where it was "looping" inside itself. Just paralleling your converter-battery paths to reduce R is ok. (do fuse the second pos path)

theoldwizard1 wrote:

lenr wrote:
2) Is there anything wrong with adding a negative wire, but leaving the frame connections?

Yes, you will create a "ground loop", which could potentially depleat the battery.

I see no reason that a battery would be depleted, a ground loop is just a concern for electronic equipment interference.

lenr wrote:
On the next two trailers, there was no negative wire. Negative was grounded to the frame at the converter and at the batteries with a fairly small self-tapping hex head screw. My concern is long term corrosion at the frame grounding point. 1) Am I being overly concerned?

No !

lenr wrote:
2) Is there anything wrong with adding a negative wire, but leaving the frame connections?

Yes, you will create a "ground loop", which could potentially depleat the battery.

Without getting too technical, connect a multimeter to the battery post and then touch connection of the converter (or other grounds) with the other probe. You could be reading over 100 mV ! Not good.

Go one way or the other. Copper wire to all negative load connections OR connect to the chassis. If you are using the chassis for ground, inspect those connections at least once a year. At the first sign of corrosion, remove the screw, clean the chassis to bare metal, re-install with a stainless screw and put a good "gob" of dielectric grease on top.

Not something I would worry about. Not at all a commonly reported problem. Mine still works fine after 12 years, never touched.

You can add a wire running from battery neg to the neg battery lug on the DC fuse panel. This will make a neg path in parallel with the existing path via the frame. That will lower the R of the neg path and thus for the whole circuit. You will likely see more amps to the battery from the converter when you are charging the battery bank.

Only thing is to make sure the new wire path is fat enough gauge to handle all the amps in case one day you lose the original path (as you are worried about) and it has to carry all the weight.

nothing wrong with adding the appropriatge wire size for the ground as long as you keep the existing frame grounding. I'd recomend updating the frame ground with a 1/4 self tapping or threaded bolt & star washer.

In reality the extra run isn't going to do much for you.

The frame is a lower resistance path than any reasonable sized wire is, and more than likely all or most of the 12V fused runs ground to the frame as well so you still need the frame ground. All the extra wire will do is give a ground path from the battery to the converter, yes, it is in parallel with the frame ground but the frame ground is much lower resistance.

lenr wrote:
Our first trailer had both the positive and negative 12 volt wires running from the battery to the combination distribution/converter panel. The negative wire was also grounded to the frame. On the next two trailers, there was no negative wire. Negative was grounded to the frame at the converter and at the batteries with a fairly small self-tapping hex head screw. My concern is long term corrosion at the frame grounding point. 1) Am I being overly concerned? 2) Is there anything wrong with adding a negative wire, but leaving the frame connections? It seems to me that the wire will increase the odds of a good solid connection for years to come.

I would be very concerned. Automotive struggles with grounding issues, and they actually know how to design for less than favorable conditions. I would be looking to add dielectric grease for corrosion protection.

My battery is grounded to the frame with a self tapping bolt. I removed it, cleaned the contact surfaces with a wire brush, installed the screw then painted it to maintain a corrosion free connection. Has worked fine since 2013.