Trying to understand 12 volt electrical system

[Trailer traveler]

I have a 2019 Salem Hemisphere travel trailer. When we got to the campground, I lowered the tongue jack and disconnected the trailer. After the trailer was unhooked, the tongue jack and all internal 12 volt did not work. The stabilizer jacks, slides and awning all worked. They even work when the battery disconnect is in the off position. I moved the truck so that I could plug the 7 pin in ( the hitch was not connected). Still no power to the interior or tongue jack. I connected to shore power and everything worked. When we returned home, the tongue jack worked until I unhitched. So I started looking for a grounding issue.

The two 30 amp circuit breakers on the frame are the automatic type so no ability to reset. Tests with a volt meter indicated they were passing current. They are pretty corroded so ordered replacements to have on hand. Previous experience with these has also resulted in some strange 12 volt cases of what works and what doesn't.

When I moved on to the buss bar, it seemed the connection to the frame was not so good. Moving it and tightening the screw to the frame restored power to the tongue jack and interior 12 volt.

My purpose in posting this is to share my experience and see if others have encountered a similar wiring setup?

[TheWolfPaq82]

Not unheard of for a Ground to get enough corrosion or rust for it to lose contact. I try to check mine periodically looking for lose or corroded connections.

[mwdilday]

Sounds like you have a battery issue.

[woo10-210]

Originally Posted by Trailer traveler

My purpose in posting this is to share my experience and see if others have encountered a similar wiring setup?

Certainly not uncommon as mentioned, especially is wetter areas of the country. Be thankful you have the knowledge to trace the problem and fix it. Most would probably just tug it back to the dealer and file a warranty claim or pay $$$$ to fix a simple problem.

[Larry-NC]

Originally Posted by mwdilday

Sounds like you have a battery issue.

Michael, did you read the original post carefully? The OP described the symptoms AND THEN DESCRIBED THE SOLUTION, a bad ground connection. It was a great post, informative for the rest of us, but it was NOT a battery issue.

Larry
Just down the road from you in Ivor, VA, right now

[boondocking]

[TitanMike]

Originally Posted by TheWolfPaq82

Not unheard of for a Ground to get enough corrosion or rust for it to lose contact. I try to check mine periodically looking for lose or corroded connections.

One of the first "upgrades" on my TT was to replace all chassis ground connections with #4 awg wire, grind paint off frame where connection was made, and install lug type connectors secured to the frame with self tapping BOLTS instead of screws. Also put some oxide prevention grease under lug at frame that is designed for electrical connections and switch gear.

One connection near junction box at front of frame and another right under the converter at the frame with a third right behind the battery disconnect.. This upgrade made a big difference in voltage drop when charging even with old Converter.

[Trailer traveler]

Originally Posted by mwdilday

Sounds like you have a battery issue.

The fact that the slides, landing gear and awning (all higher draw than the interior LED lights) worked normally lead me to think otherwise. I neglected to mention in the original post that when I checked the battery voltage it was above 12.6 volts. I also neglected to mention in the original post that when I was hooked to shore power, I was getting 13.2 volts or more at the battery terminals indicating that the charger was working. Sorry for those omissions.

Thanks for the responses. I hope this discussion might help someone else in the future.

[Trailer traveler]

Originally Posted by TitanMike

One of the first "upgrades" on my TT was to replace all chassis ground connections with #4 awg wire, grind paint off frame where connection was made, and install lug type connectors secured to the frame with self tapping BOLTS instead of screws. Also put some oxide prevention grease under lug at frame that is designed for electrical connections and switch gear.

One connection near junction box at front of frame and another right under the converter at the frame with a third right behind the battery disconnect.. This upgrade made a big difference in voltage drop when charging even with old Converter.

Did you have a plastic underbelly cover that had to be removed or cut through to access the grounds by the converter and the battery disconnect? My battery disconnect is in the front compartment pretty close to directly above the chassis ground that I worked on. I'll have to take a closer look, but I don't think there are any other wires below the underbelly cover.

Do you know what is on each of the three separate grounds on your RV? I was really surprised that the slides and landing gear worked when the battery disconnect was off.

[Chuck_S]

My tongue jack positive pole is connected directly to the battery. The jack is bolted to the trailer chassis which is the trailer's ground connection. My battery disconnect severs the Negative connection at the battery and kills everything dependent on power from the trailer -- but everything truck connection regardless of the battery disconnect switch position.

Truck can't charge the trailer battery, though, when switched off. Nor will the brakes active ate if the trailer disconnects. Gotta be sure to switch On before towing.

-- Chuck

[Trailer traveler]

Originally Posted by Chuck_S

My tongue jack positive pole is connected directly to the battery. The jack is bolted to the trailer chassis which is the trailer's ground connection. My battery disconnect severs the Negative connection at the battery and kills everything dependent on power from the trailer -- but everything truck connection regardless of the battery disconnect switch position.

Truck can't charge the trailer battery, though, when switched off. Nor will the brakes active ate if the trailer disconnects. Gotta be sure to switch On before towing.

-- Chuck

Interesting. On my trailer, the tongue jack positive goes to one of the two 30 amp circuit breakers mounted on the frame. The battery disconnect is on the positive side. There is another large gauge positive that by passes the battery disconnect. This is probably what is feeding the slides and landing gear since they work when the battery disconnect is in the off position.

[Chuck_S]

I have no idea why trailer manufacturers are breaking the positive side of the circuit. Can't be safety as the first thing to do when working under the hood of your "other 12v system" (AKA your car or truck) is to disconnect the Negative cable (not the positive).

Only one (1) cable is needed on the Negative side as the trailer frame is the ground connection. Just like there is one negative connection at the fuse box, that buss bar. Severing the Negative connection eliminates all power.

There are half a dozen wired connected to the positive side of my battery. Can't switch 'em all, nor is there a need to.

-- Chuck

[Larry-NC]

Originally Posted by Chuck_S

I have no idea why trailer manufacturers are breaking the positive side of the circuit. Can't be safety as the first thing to do when working under the hood of your "other 12v system" (AKA your car or truck) is to disconnect the Negative cable (not the positive).

-- Chuck

Chuck, the only reason for this safety precaution on automobiles is that if someone leaves the negative terminal connected to ground and begins to disconnect the positive terminal, he could swing the wrench so that it contacts some ground (chassis metal, core support, battery hold-down, etc.) and make a spark. This is especially likely with side-terminal automotive batteries.

Lead-acid batteries emit hydrogen while charging. If the spark ignites the hydrogen, the mini-explosion can blow sulfuric acid into the person's face. This is a real risk. It happened to my neighbor's husband and he has a glass eye as a result.

Travel trailer batteries are generally wide open. Perfectly safe to remove either terminal first.

(Conjecture: the hold-down clamps for batteries these days are at the battery base, not over the top. I wonder if that was concurrent with the change to side terminals, to reduce the spark exposure.)

Larry

[Trailer traveler]

Originally Posted by Chuck_S

There are half a dozen wired connected to the positive side of my battery. Can't switch 'em all, nor is there a need to.

-- Chuck

My trailer has one positive wire and one negative wire connected to the batteries. The negative goes to the buss bar that I worked on. The positive goes to a 30 amp automatic reset circuit breaker and feeds other positive connections including the battery disconnect from there.

Beginning to seem no two trailers are wired alike.

[mwdilday]

Originally Posted by Larry-NC

Michael, did you read the original post carefully? The OP described the symptoms AND THEN DESCRIBED THE SOLUTION, a bad ground connection. It was a great post, informative for the rest of us, but it was NOT a battery issue.

Larry
Just down the road from you in Ivor, VA, right now

Sorry Larry. I guess I missed it. Ivor is a one stop light town. If you blink you missed it.