12 Volt ground question

[RedPillRover]

Hi.  Working through my cargo trailer build and have more than a few uncertainties about the the electrical wiring.  At this point, all i really have is easy questions, but they are sure to get harder  :s

The batteries, charge controllers, inverters etc will be physically located in the rear of the trailer (18 feet).  My intention is to have a 12 volt fuse distribution box at the front of the trailer that will provide electricity to some LED lights, MaxxAir fan and 12 volt phone charging station.

So do I need to run both positive and negative wires from front to back of the trailer to power my fuse panel?  Or is it that I can just run the positive wire, and ground the fuse panel directly to the frame of the trailer from there?

Seems like it would be fine, but I still have uncertainties about electricity flow.  I get the concept of an electrical "circuit", but when the ground leads to the chassis, it throws me off (certainly that is a dead end and not a circuit right?).

 

[highdesertranger]

just think of the chassis as a wire. one big ole honkin wire. LOL

it's best to locate the fuse box as physically close to the battery bank as possible.

highdesertranger

 

[wayne49]

"The batteries, charge controllers, inverters etc will be physically located in the rear of the trailer (18 feet). "

Putting some weight far behind the axle(s). You may want to move that weight forward. Reducing the length of the wiring runs as well.

 

[tx2sturgis]

You can use the frame of the trailer as your ground return, but you have to be EXTRA careful to fuse everything, and isolate, insulate, and protect every hot wire as it travels next to or passes thru openings in metal edges and surfaces, because road vibrations can and will cause the wires to chaffe and possibly short. You have to secure the wires and cables well, AND fuse them.

Also it is usually better to have the mass of your batteries ahead of, or directly over, the axle, but if you plan to offset the weight of the batteries with heavy items such as water storage tanks, then you should be OK there as well.

 

[Ticklebellly]

My Campervan has bonded panels. Using the body/chassis as earth return is consistent with the design of the vehicle.

If doing a trailer build from scratch, a circular earth buss of serious copper is what I would do. Trailer chassis parts and panels are often steel and electrical connections to steel are prone to problems. For me, it's a confidence thing. I can be really confident of soldered, heat shrunk connections over any kind of copper to steel connection. A serious connection to a distributed buss from the Battery also allows for options for the placement of the battery bank.

 

[tx2sturgis]

This brings up a good point, and for simplicity and staying on topic, I did not elaborate the situations where I WOULD used a dedicated negative cable or wire. 

The OP was going to install a small remote-mounted fuse panel for some LED lights, a maxxair fan and a charger for a phone. 

This type of load is fine with a vehicle frame ground. There is not much current being supplied, so the load carrying ability is not being pushed to any limits.

But, maybe someone will read this and figure, well if he says that will work for those loads, then my 3000 watt inverter will too. 

WRONG.

I would absolutely recommend for that type of load (and any load over about 50 amps or so) to run heavy copper cables with positive AND negative supplies for something like a large capacity inverter, but also, that inverter needs to be fairly close to the batteries so those heavy cables will not be very long.

Just a clarification.

 

[sneaks]

I agree with what is being said. I would put the fuse panel close to the batteries as well. for the reasons already mentioned, but primarily economic, considering most of your loads are light. Good OFC wire gets more expensive the larger the gauge. So, if you only need to support a few amps for LEDs & USB, you can get away with your long runs being 12-18ga and keep your bigger wire short. There's a HUGE difference in price between, say, 25' (yes, your trailer is only 18' but you aren't going to be running wire "as the crow flies" and instead, probably around the perimeter) of 4/6ga and 25' of 12ga. This is coming from someone who has both the batteries and the engine in the back of the vehicle. I have three fuse panels: one about 5' from the house battery which has most of the heavy loads with 6ga, one under the dash for house battery (13' as direct line, 18' in actual wire length) which supports small stuff and has a 10ga hot lead, and one under the dash (OEM) for the vehicle system which from the factory is 10ga (and known to be problematic as it goes through the ignition switch unfused, I'm going to change that soon). I need to run 2ga from the back to the front - both hot and earth - to my winch on the bumper. That gets expensive really fast. I earth most of my circuits to the chassis near the load, except for my ham radio, inverter, and winch. Those go back to the battery earth.

 

[highdesertranger]

what is OFC wire? abbreviations people, define your abbreviations. highdesertranger

 

[sneaks]

what is OFC wire?  abbreviations people,  define your abbreviations.  highdesertranger

Sorry, Oxygen Free Copper, compared to CCA - Copper Clad Aluminum. The latter is cheaper but not as flexible and has higher resistance (and will run hotter because of it). I only use OFC when running wire over long runs, in enclosed spaces, or under carpet\wood\plastic. OFC costs more by about 30%, but much cheaper than an insurance claim.

 

[highdesertranger]

there is also just plain old copper wire. I wouldn't run copper clad aluminum for anything under any circumstances. highdesertranger

 

[Weight]

Most any USA rated fine strand wire uses oxygen free copper. I would not trust the china stuff at the auto parts store.

 

[RedPillRover]

"The batteries, charge controllers, inverters etc will be physically located in the rear of the trailer (18 feet). "

Putting some weight far behind the axle(s). You may want to move that weight forward. Reducing the length of the wiring runs as well.

Yes, I was using the term "rear" in a general sense. The battery weight will be right near the axles.

 

[RedPillRover]

This brings up a good point, and for simplicity and staying on topic, I did not elaborate the situations where I WOULD used a dedicated negative cable or wire. 

The OP was going to install a small remote-mounted fuse panel for some LED lights, a maxxair fan and a charger for a phone. 

This type of load is fine with a vehicle frame ground. There is not much current being supplied, so the load carrying ability is not being pushed to any limits.

But, maybe someone will read this and figure, well if he says that will work for those loads, then my 3000 watt inverter will too. 

WRONG.

I would absolutely recommend for that type of load (and any load over about 50 amps or so) to run heavy copper cables with positive AND negative supplies for something like a large capacity inverter, but also, that inverter needs to be fairly close to the batteries so those heavy cables will not be very long.

Just a clarification.

This exactly. I didn't really make it clear in my question, but most of my loads will connect near the inverter. I just didn't want to run alot of smaller wires towards the back when I could get away with running a single heavier gauge wire to the front.

 

[RedPillRover]

I agree with what is being said. I would put the fuse panel close to the batteries as well. for the reasons already mentioned, but primarily economic, considering most of your loads are light.

Yeah, because I was came into this project with pretty much zero electrical expertise, I built a prototype of the electrical system in my basement 6 months ago.  I have a 25 foot length of 8 gauge wire I used for that that I can salvage, so no new expense.

 

[RedPillRover]

Thanks all for the advice!  I think I finally got this forum reply quoting thing figured out now too, so bonus knowledge!