My Dual Battery Setup (with Diagram)

[ausbran]

I'm putting an auxiliary battery in my engine compartment purely for camping pleasures.
I'm just looking for general feedback on my setup and what people think. It is simple, but should be all that I need.

I will be running 4AWG wire from the AUX battery in the engine compartment to the fusebox (safetyhub 150) in the truck bed. Is 4 AWG wire sufficient for my setup? I'll be running a 400w inverter from my fusebox as well as a couple small accessories (fan, LED bar, water pump.) All of the details are within the diagram. The 400w inverter will be hooked up to one of the safetyhub 150's high amp AMI fuse ports which are rated for up to 200 amps. I'll fuse it with a 35amp fuse (or should I go higher?)

I'm just unsure of how the Safetyhub 150 works. Why is it able to work without having to run a negative cable from a port on it to the chassis of the truck? How does this work?

Diagram attached here.

 

[ausbran]

We dont know total continious loads you are planning to carry.
Anyway, For chassis wiring, 4AWG will handle about 100A.
Inverter fuse at 35A Is right on the cusp of its theoretic maximum. I suggest at least 50A, and size its conductors accordingly.

The mystery of ”without having to run a negative” is no mystery. The negative bussbar on the hub is an optional thing. If you are going to utilise, it should be connected to battery negative, but can connect to chassis with a theoretic small loss of performance.
The negative conductor of your loads can be connected to that bussbar or directly to chassis if desired.
Both good and ’less good’ arguments can be made for negatives connecting to either chassis or bussbar.
Thats an engineering decision suited only for the Gods or whoever is actually doing the work.

The AUX battery is isolated and will only be used on average 2-3 hours per night. What I will be using it for is below.

These three electronics will be hard wired to the safetyhub 150:
2 led lights bars
1 caframo 757 fan - .3amp-.5amp
water pump - 3 amp

These devices will be charged using the AC and USB ports on the 400w inverter:
(the 400w inverter has a continuous load of 400w with surge up to 800w)
laptop charger - macbook pro 15"
two iphones charging

It will be very rare for me to be running all of these simultaneously. The waterpump will only be used in short intervals (less than 60 seconds at a time) every now and then as well as the lights. The fan will be on for extended periods of time.

Ok, isn't it strange that the safety hub has less negative ports than it does positive for grounding? Can you ground more than one device to one of the larger ports on the bus bar of the safetyhub?
Also if I run a short ground from the safetyhub to the chassis, should it be the same gauge wire as the positive feed wire coming from the battery?

 

[nutcracker]

Charge the phones with 12 volts, don't use inverterpower for that.

 

[ausbran]

Charge the phones with 12 volts, don't use inverterpower for that.

I'm honestly not in need of power most nights road tripping, this is just luxury. I'll try and charge them in the truck while driving, but sometimes I will need to plug into the inverter to charge at night. the inverter has a switch that allows just the USB ports to be powered while not sending any power to the AC outlets. Says that they are rated at 2.1 amps. Seems fine for charging phones every now and then no? Will it drain the battery a good bit?

 

[dwh]

Yea, if you use the ground bus on the safetyhub, then it will need to be grounded with the same size wire as the positive - #4 in your diagram. Best practice would be to run a matched set of #4 +/- from the safetyhub to the aux battery.

I have a similar 400w inverter. I used to run a 100ah aux battery and had #10 feeding the inverter (the leads it came with). The voltage drop when running my big HP 17" laptop would cause the inverter to shutdown early. I.e., the battery would be at like 11.5v, but the inverter would see 10.5v and shutdown. Which was fine with me.

Be aware that #12 will have the same problem, only worse. But it's only a problem if you run the battery down that far.

Had the inverter on a 30a fuse then. Never loaded the inverter enough to blow the fuse. When I redid my setup and went to 400ah of AGM, I rigged the inverter with #8 and a 40a fuse. I haven't drawn the battery down far enough for the inverter to shutdown, so dunno how much the #8 helped over the #10, but I think it runs cooler - I notice the fan coming on less than it did with the old setup.

 

[Trestle]

Bluesea makes electrical fuse boxes, battery isolators, and other items for boats, and vehicles. I like their stuff. Here is a link to their wire size calculator: http://circuitwizard.bluesea.com/#

You will have to click thru a warning, but it will take you to a wire size calculator that can be used to determine the size of wire. It comes down to load, distance, and how much voltage drop you can allow by percent.

Use that tool to determine the correct wire size for your situation. Maybe the load is your water pump and a phone charging plus 10%. This way you won't blow a fuse every time you forget to unplug everything before using the water pump. You get the idea.

Then use a fuse that is sized to protect the wire. The point of the fuse is to keep the wire from overheating and causing a short by burning through its insulation and finding ground.

If you want to put a smaller fuse on the wire so as to protect the devices at the end of the wire, go for it. Never exceed the wire rating though. Most devices will have some sort of protection for them built into the 12v plug or other, so you have to do a bit of research on each item.

Final thought - you never know if you want to scale up a bit. What is fine now, may need to be slightly more robust later when someone gets a fancy new toy that is added to the list of things pulling energy. Never a bad idea to go up one wire size, since a big part of what you are doing cost wise involves your time which is worth something.