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.

[d3500ram]

teambeeson wrote:
...
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.

I do not think that too many grounds is a bad thing... as long as they are good and proper grounds. Relying solely on any frame IMHO is not a proper ground.

If as you say the grounds are "mixed in." Perhaps one of those components of the mix has failed and it is relying on the remaining grounds to complete the circuit. The whole might have worked at one time, but the remaining grounds may be comprised as another fails and it is happening piece meal.

Use KISS principle. In my opinion establish and confirm that you have a good ground in your voltage drop experiments.

[teambeeson]

ticki2 wrote:
How is the 12v wiring set up ? Do you have 1 wire or 2 wires going to lights and pump/furnace

The whole thing is janky.. wires everywhere.. the previous owner looks to have tried re-wiring the whole thing. I'm re-doing most of it. As is the pump and furnace each have their own wire, but not into a block or anything... just spun together in a heap. I'm looking to buy a negative bus bar block and put each thing on it's own. If anything it'll clean it all up.

ticki2 wrote:
BTW , most group 24 deep cycle batteries are 80 to 85 AH . Is yours really 50AH ?

It's a Napa 8240 with "Battery Reserve Capacity" of 120 minutes... no one seems to rate in amp hours anymore I guess. I figure since that's 2hrs @ 25amps it's the equivalent of 50ah.

[teambeeson]

DWeikert wrote:
Do you have an non contact IR thermometer?

I do and that's a good idea thanks!

[ticki2]

mkirsch wrote:
Just FYI, 12.3V is 30 percent, which is more than you generally want to discharge a lead acid battery.

I'm confused , is that 30 percent SOC , or 30 percent used . All my charts say 12.3v @ 70 degrees would be 75 percent SOC .

[ticki2]

How is the 12v wiring set up ? Do you have 1 wire or 2 wires going to lights and pump/furnace . The older campers usually had 1 wire feed and grounded to aluminum skin back to battery . After years the connections corrode and have poor contact . Just a thought . Also , has the problem always existed or is it new ?


BTW , most group 24 deep cycle batteries are 80 to 85 AH . Is yours really 50AH ?

[DWeikert]

Do you have an non contact IR thermometer? One thing to try is turn on the load and check the temperature of your connections. Any that are adding resistance to the circuit will show a temperature increase. Could save some time...

[mkirsch]

Just FYI, 12.3V is 30 percent, which is more than you generally want to discharge a lead acid battery.

[teambeeson]

teambeeson wrote:
I brought a battery into the camper, hooked into the 12v directly and still see voltage drop to as low as ~9v at the end of a water pump cycle so I think that rules out wire gauge/distance since I eliminated that variable.

Last night I hooked the water pump up directly to my 12.6v 3s50p lithium test battery (old ebike battery re-purposed) and the water pump only dipped it to 12.38v full bore (as opposed to ~9v when connected to the internal camper 12v system) so now I know for certain my problem is a wiring issue. Going to hook up each 12v device one at a time and see what's what via process of elimination. Progress!

[teambeeson]

bodacious wrote:
Your converter is also a battery charger. If your battery is being charged ONLY when the truck is running(charging), your battery may not be getting fully charged. You might check the true state of charge of the battery or maybe charge it fully with a portable charger.

Hi. Thanks for the reply. The converter is not hooked into charging the battery, just the truck. I disable the truck's RVC system during camping trips so the camper battery gets the full 14v+ from the alternator and comes off hot at 12.8-12.9v when we camp. It's a 50ah Group 24, which is plenty for our purposes. Even after days of boondocking I've yet to see it go below 12.3v resting.

[bodacious]

Your converter is also a battery charger. If your battery is being charged ONLY when the truck is running(charging), your battery may not be getting fully charged. You might check the true state of charge of the battery or maybe charge it fully with a portable charger.

[teambeeson]

I brought a battery into the camper, hooked into the 12v directly and still see voltage drop to as low as ~9v at the end of a water pump cycle so I think that rules out wire gauge/distance since I eliminated that variable.

On to testing for bad/crushed/corroded wiring one device at a time. This is actually kind of fun because I'm learning a lot more about what's wired to what and how. Always good to know your camper systems better I suppose. Thanks all for the brainstorming! Great community here!

[wcjeep]

Technically your 12ga wire can handle the amperage. You may have further voltage drop from okd splices and maybe partially crushed wiring. Do you have a Flir to monitor the wiring? Can you add a second camper battery inside the camper?

What happens if you temporarily move the camper battery to the camper? Loss of distance should clear up your problems.

[WNYBob]

I have a similar system, with my 2nd battery connected to an inverter. I bought a 10' kit from Samlex, that came with #2.

[Artum_Snowbird]

Most likely the cause of your problems is a weak connection somewhere. Normally #12 would handle the load with no problem, but if you have a weak connection it's like putting on a hidden load that will get worse and worse as it weakens and causes the amps in the circuit to climb and the voltage to drop.

The best way to check this is putting in an ammeter, and turning stuff on to see if the meter reading really matches the load. Chances are, it's where the loads come together, and it's often the negative return wire because that carries all the load back to the battery.

It's an easy test to use your long jumper cables, and bring a good solid connection on both the negative and positive lines back to where you connect in the camper. You might find that one or the other really helps and then that will lead to the problem wire.