Camper Battery Under Truck Hood

[teambeeson]

Hoping you all can help me work through this...

I have my house/camper/aux battery under my pickup hood in the spare bay wired to my starter battery through an isolator. Works awesome. I then run 12 gauge back under the truck and hook into my 12v camper system.

The battery is not connected to the camper's internal converter at all since my truck is in charge of... charging, but all my internal camper 12v- is connected to the negative of the battery directly with a wire spinner. All my 12v+ internals are wire spun together also. It works, but...

What I'm seeing is massive voltage drop when using my water pump/furnace. Furnace sail switch won't even trip. Voltmeter shows down to ~9v when the water pump is finalizing it's pressurization. Yoikes. I have a couple theories...

1. 30yr old wiring/massive resistance internally in the camper? Sure looks okay to me, but I'm not seeing the guts.

2. Too many grounds?? I have the ground/- wire from the battery mixed in with camper frame ground wires... is that bad? I can't see why really, but there is that.

Can't I just get a negative bus bar fuse block mounted in the camper and connect the aux battery from under the hood right to that and then right into my 12v circuits? Would I then even need a camper ground at all?

3. 12 gauge too small for the 16' run from under the hood to the back of the camper? I've pumped a lot of amps through that kinda distance before so I don't think that's it, but maybe.

Thoughts? Those are the only three things I can think of. Gonna start testing stuff. I NEED my furnace sail switch to throw or the main burner doesn't ignite and we've been camping to 20 degrees at night already... in July haha.

[KD4UPL]

8 amps going 16' on #12 is over 3% voltage drop. Honestly not as bad as I thought it would be but still pretty high.
I would think you'd want at least #8 for that run.

[JoeChiOhki]

You need #8 at minimum for good service. With low voltages, you need large sized cables to serve without major voltage drop. You also need that on both sides, going back to the battery, don't use the truck frame.

http://www.powerstream.com/Wire_Size.htm

[teambeeson]

jimh425 wrote:
I think 12 gauge is too small. There are a lot of charts that show what size wire to use for the amps.

I was suspect of this being the problem because my max amp draw is the 7.5a water pump... furnace is only 2.9a... and 16 feet isn't that long, but I'll check into it. All my fuses are 15a and none of them has ever blown. That's why I think it's mis-wire issue, but I'll go to 8-10 gauge anyway probably... as long as it's flexible since I'm running along the truck frame. Thanks for the reply!

[jimh406]

I think 12 gauge is too small. There are a lot of charts that show what size wire to use for the amps.

[teambeeson]

PS - Brand new deep cycle Napa battery...