diy solar

diy solar

12V Power to RV

An RV trailer aways uses the house battery for the emergency breakaway braking system as installed at the factory.
etrailer sells a kit for utility and horse trailers etc with a small battery for this purpose because there is no other battery installed.
 
Isn't the chassis the 12V ground?
Chassis is the ground of all systems. Both 12v ground and 120vac ground. If a 24v system is installed it is also the 24v ground and can serve as 48v too.
Just more to keep straight. Black as the 120v hot gets confused with 12v negative often enough. 12v negative is usually a white wire in an RV with a black wire to the positive battery terminal.
 
This is where I say I’m no electrician.

i use a chassis ground for small things, not for large items. I hook into chassis ground for one or two amps, like a light bulb. That’s just the way I learned.

There’s some up to amperage limit that it does get hooked to the chassis, but when the 12 volts is flowing at 70 amps, I want it going through an insulated wire. I don’t have access to NEC code to see a limit if they put it in there. An older ABYCC code is available for free download, perhaps its in there.

I’ve also gone through and verified my negative busbar is attached to chassis ground, and it iS.
In automotive and tractor applications loads in excess of 500 amps using chassis ground of some sort are commonly used. Except for little tinfoil cars the problem isn’t the ability of the chassis to carry the current but the difficulty in keeping a good connection at the grounding points on the chassis. Never bury a grounding connection or locate it close to something that has a low flash point.
 
This is where I say I’m no electrician.

i use a chassis ground for small things, not for large items. I hook into chassis ground for one or two amps, like a light bulb. That’s just the way I learned.

There’s some up to amperage limit that it does get hooked to the chassis, but when the 12 volts is flowing at 70 amps, I want it going through an insulated wire. I don’t have access to NEC code to see a limit if they put it in there. An older ABYCC code is available for free download, perhaps its in there.

I’ve also gone through and verified my negative busbar is attached to chassis ground, and it iS.
So you ran a wire directly to the 12V battery negative terminal?
 
So you ran a wire directly to the 12V battery negative terminal?
Yes;

negative 12 volt converter —> Negative 12 volt battery cable
Positive 12 volt converter —> Positive 12 volt battery cable.

I enclosed the connections in a plastic box to keep it trouching anything. The 12 volt battery is now removed. my battery connectors were lugs, so they were easy to connect to lugs i put on the 12 volt side of the converter..
 
I would like to point out 3 advantages to using the chassis (frame) of an rv as the negative conductor for dc power.

1. Wire size. The frame of even the lightest duty trailer is a better conductor than the wire normally used to power devices. This means that if you are using the frame as your negative power you only need to calculate the one conductor for your wire size otherwise you must double the wire length in your calculations to get the total conductor length. I suspect this is the reason most rvs use the Chassis as the conductor for the negative side of the house battery as well as at least reference for the running lights and brakes.
2. Since it is necessary that the running light circuit be grounded to the chassis all chassis connections should be maintained regardless of if you are intentionally using it as a conductor or not.
3. Using the chassis as a conductor simplifies trouble shooting as it is impossible for a safe trailer frame to not conduct electricity.

The main problem with using the chassis as a conductor is keeping a good connection to the frame itself. This method of power has been used for over 100 years in the automotive world and works very well.
I would like to point out that I am not suggesting using the Chassis as a conductor for any form of ac current.
 
RVs tend to have a negative ground bus for lighting and other small items with a negative return wire to the bus.
Bus goes to the frame, battery negative is also on the frame.
 
RVs tend to have a negative ground bus for lighting and other small items with a negative return wire to the bus.
Bus goes to the frame, battery negative is also on the frame.
My present rv has a variation of that with battery ground connected to the tongue of the trailer and 30 feet from the battery a 1 foot ish wire running to a buss where all the small loads connect. The largest draw device (slide out motor) is connected directly to the frame.
 
I can't think of any 12 volt device in my trailer that doesn't have two wires running to it from the main distribution panel.

The tongue battery had a short negative cable that attached to the trailer frame, but another cable was stacked on the same bolt/screw taking the negative side of the circuit directly up to the main distribution panel. In other words, my trailer doesn't rely on the chassis.
 
I can't think of any 12 volt device in my trailer that doesn't have two wires running to it from the main distribution panel.

The tongue battery had a short negative cable that attached to the trailer frame, but another cable was stacked on the same bolt/screw taking the negative side of the circuit directly up to the main distribution panel. In other words, my trailer doesn't rely on the chassis.
All of the “small” loads to lights and devices usually use 2 wires because their is no good place to use the chassis in a typical travel trailer. If your distribution panel is close to the battery it makes sense to use wire rather than the frame to avoid more connections than are necessary. In my case a home run with the negative cable would have required 38’ of additional wire and possibly moving up one gauge. In my opinion the manufacturers priorities are speed of manufacture first cost second and quality third and somewhere in there is making everything as light weight as possible.
 
Most of the automotive industry, has moved away from using the chassis for power flow. Due to connection issues and efficiency losses.
With the exception of engine mounted equipment.
 
Most of the automotive industry, has moved away from using the chassis for power flow. Due to connection issues and efficiency losses.
With the exception of engine mounted equipment.
I think In the case of Engine mounted equipment a bad connection is les likely than mechanical damage to extra wires.
 
A lot of sensors and solenoid valves use the engine as return path, for simple one wire connection.
And of course, the connection between alternator battery and starter.
 
A lot of sensors and solenoid valves use the engine as return path, for simple one wire connection.
And of course, the connection between alternator battery and starter.
Due to the use of floating grounds used by PCM's in vehicles, Your statement is not correct about sensors.
 
Due to the use of floating grounds used by PCM's in vehicles, Your statement is not correct about sensors.
To clarify
Aftermarket, not OEM.
All of the computer systems are isolated.
And to clarify further, not completely isolated. But, individually circuited.
 
I can't think of any 12 volt device in my trailer that doesn't have two wires running to it from the main distribution panel.
I can’t find any chassis grounded device in my fifth wheel. Every 12 volt device has two wires that disappear into the wall and either run to a negative distribution bar or a chassis ground. Which, I‘m not sire I can t see it. I do have a chassis ground from the battery, so they probably exit’s.

I don’t know anything I would add in the Rv that would use chassis ground.
 
The only place where my chassis is used to carry current is the main battery negative to the main negative in the distribution panel through the ground bus connected to the frame.
 
The only place where my chassis is used to carry current is the main battery negative to the main negative in the distribution panel through the ground bus connected to the frame.
That is generally the case with an rv occasional exceptions like in the case of my large slide motor. Devices in the cabin are generally not feasible to connect to the chassis.
 
I can't think of any 12 volt device in my trailer that doesn't have two wires running to it from the main distribution panel.

The tongue battery had a short negative cable that attached to the trailer frame, but another cable was stacked on the same bolt/screw taking the negative side of the circuit directly up to the main distribution panel. In other words, my trailer doesn't rely on the chassis.
In many trailers (including my personal travel trailer), running lights, turn signals, and brake lights use the frame, in order to reach the 7-pin grounding wire back to the Tow Vehicle. But, exactly as in your trailer, my 12-VDC appliances all run cables back to a "grounding bus" behind the distribution panel.

IIRC, some ancient Parallax panels actually brought the grounding wires into a small bus bar INSIDE the unit - but that was a terrible idea, and AFAIK no one does that anymore. PD for example, provides a grounding bus bar on the back side of many "distribution panel" products. One small grounding wire typically leads to the 12v fuse panel, for the purpose of supporting blown fuse indicator lights.
 
IIRC, some ancient Parallax panels actually brought the grounding wires into a small bus bar INSIDE the unit - but that was a terrible idea, and AFAIK no one does that anymore. PD for example, provides a grounding bus bar on the back side of many "distribution panel" products. One small grounding wire typically leads to the 12v fuse panel, for the purpose of supporting blown fuse indicator lights.

This is how my WFCO main distribution panel is wired. The negative/ground bus bar is "floating" outside the panel. I say floating because the factory never attached it to a surface, it's just hanging out in the compartment. One of these days I'll secure it.

I don't think any of my running lights use the chassis. It's been a while since I fiddled with them, but clearance lights all had two wires that ran all the way to the panel.
 
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