How does your tow vehicle handle a second battery (which you need for solar)?

[THene1713]

Originally Posted by David Tilston

It is a good idea to isolate your vehicle starting battery from becoming drained by accessories. Adding an isolating relay between the starting battery and your accessory battery makes sense. When the vehicle is running the relay senses the additional charging voltage and connects the accessory battery so it charges as well. When the vehicle is shut off, the lower voltage causes the relay to open, preventing accessories from draining the starting battery:
https://www.amazon.com/Dual-Battery-.../dp/B08JYQHTRZ

Most all 7-pin tow harnesses are wired thru vehcile relay that disocnnects when TV IGN=OFF to prevent draining. Just also make sure properly fused on BOTH ends of any wires?

[ThomasC]

Originally Posted by Raspy

It seems to me that a lot of current running through 20 feet or more of steel parts, connected with steel bolts, will have a lot more resistance than fine stranded copper wire. There also seems to be some concern about welding on the frame, not only because of affecting the temper of the steel, but just running a lot of current through it that can affect the computer. Am I wrong? Is running that current through the frame better?

While I was at that Victron seminar I noticed a wiring diagram that ran two wires instead of using a chassis ground to a B to B charger so I questioned the instructor on it. This was a VERY knowledgeable boat guy from St. Pete FL. Boats don't have or use chassis grounds and in land vehicles he was in favor of running two wires. When I asked if I should run a second wire in my truck he said no both methods are correct.

If I do one again I will run two wires......Tom

[Raspy]

Thanks for that post Tom.

I wish someone with more knowledge than me would make a comparison of the two methods as far as resistance goes, or any other issue with running high amperage through the frame in a modern truck.

[ThomasC]

Originally Posted by Raspy

Thanks for that post Tom.

I wish someone with more knowledge than me would make a comparison of the two methods as far as resistance goes, or any other issue with running high amperage through the frame in a modern truck.

I actually have one of those crazy twin lead ohm meters that can measure the resistance in a wire. I can think of a way to use it to measure the resistance in my chassis. Unfortunately all of my stuff is packed in boxes and under plastic to keep the Barn Swallow poop off while I wait for my building to be finished. So don't hold your breath it will be a while but it would be interesting.

[Defenestrator]

My biggest concern would probably be corrosion at the connections. Partly because the chassis tends to be exposed to the elements and using it as an electrical connection requires removing paint from that area, and partly because you're passing current through a connection between dissimilar metals.

[Raspy]

I see using the frame as simply a cost saving measure, but I can't imagine an advantage in performance. I don't see how the frame could be better than high quality and correctly sized wire. The cost and labor associated with one more wire seems like a small price to pay for the better design of two known conductors. But again, I just don't know how the frame will perform.