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I have an RV travel trailer that I use a 2000W generator to supply power to the 30A incoming power socket. I have also added 2 × 100W solar with battery minder, a 3000W sine wave corrected inverter for electrical devices and replaced the original single 12V deep cycle with a pair of 6V golf cart batteries in series. The trailer has conventional (for an RV) electrical/propane fridge and is fitted with multiple 110V outlets for use when connected to the generator or municipal power. I've added a couple of (completely isolated) 110V outlets that are supplied by the battery bank through the inverter.

During sunny days, the solar is more than enough to keep everything happy; in fact, there is potential power being 'left on the table'. I want to add to my battery bank so as to take advantage of this but weight distribution (and trailer tongue weight) would dictate that I mount any new batteries to the rear luggage rack.

During my previous additions to the electrical system I have noticed that all 12V seems to be wired directly; i.e. one positive and one negative; the frame is not used as a common ground like an automobile. I was planning on paralleling additional batteries to the originals with 4 or 6 gauge AWS which can start getting expensive running the length of a 28ft trailer.

Is there any reason not to use the frame as the ground and only pass a single wire the length of the trailer?

Addendum:

The 3000W inverter was intentional overkill. The 3000W model had dual cooling fans, wattage and voltage metering, remote shut-off and two 12V ± inputs (two +, two -) on a bus bar. Smaller wattage models did not have all of these. While the parasitic power is slightly more than the smaller models it is a trade-off I can live with. I typically run 30-40W (ecostar TV and a tablet PC for a movie) although I have run an 8 amp (110V) wet/dry vacuum with no problem from an outlet powered by the inverter.

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The main thing you'll need to worry about is the very large currents flowing. A 3000W inverter on a 12V battery will draw up to 250A. That means you need very low resistance wiring, and really good connections on all wire joins.

Bolting a lug onto a steel chassis may not be good enough in the long run, especially if the steel starts to rust around the join.

You'll want to keep the distance between the batteries and the inverter as short as possible, since the very large currents noted above will require very thick wires.

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  • \$\begingroup\$ Thanks for your input; your advice is sound and will be heeded. I've added an addendum to my question (too long for a comment) to address one of your concerns. \$\endgroup\$
    – user158568
    Aug 1, 2017 at 18:56
  • \$\begingroup\$ Running high currents through a steel chassis will always end up causing nasty galvanic corrosion on every microscopic crack on the path of the current flow. It's not feasible unless it's a very high quality stainless steel chassis, with very tight weld process quality control. \$\endgroup\$ Aug 21, 2022 at 23:29
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What in the world do you want a 3000W inverter for? Are you trying to run AC on battery/solar?

I agree with previous about beware of large currents in the chassis. For ultimate safety all load current should return to battery via wires, not chassis, even for 12V. I.e. follow the same wiring safety rules as for AC. Earth ground (green wires) on AC carries NO current unless theres a hot short to the chassis somewhere. Earth grounds provide low R path to the earth (lower R than your body soyou wont fry). A real earth ground is essentially an infinite capacity current sink, which your frame (and yourself) is not.

12 or 24 V is small enough you wont get electrocuted by it. So unfortunately some rv manufacturers avoid running more wires by using chassis as a return path. It will work but is not "correct".

Also if you want to monitor load current to see how much power your 12V is delivering, you need all returns in one path, e.g. at the battery terminal. If you have muliple batts in different locations (my situation) that can be another wiring mess.

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  • \$\begingroup\$ Why is it not correct to use the chassis as a return path for low-voltage DC? This is absolutely standard practice for low-voltage. The chassis has lower resistance than any wire. For AC it makes sense to run a copper GND wire for reliability... I would hate to get electrocuted because one of my chassis bonds was corroded and became high resistance. \$\endgroup\$
    – user57037
    Aug 21, 2022 at 22:18

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